APPENDIX 1
June 1993
ENGINEERING AND ENVIRONMENTAL
ASPECTS OF RECYCLED MATERIALS FOR
HIGHWAY CONSTRUCTION
Final Report
Environmental Protection Agency
Office of Health and Environmental Assessment
U. S. EPA, ECAO-CIN
26 W. MLK
Cincinnati, Ohio 45268
US. Department of Transportation
Federal Highway Administration
Research and Development
Turner-Fairbank Highway Research Center
6300 Georgetown Pike
McLean, Virginia 22101-2296
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Foreword
The information provided in this report constitutes a condensation of a literature search and a
survey of highway agencies. The report gives a basic overview and assessment of different
technologies, processes, and methods for the recycling of different types of materials into
various highway components and for highway construction.
Byron Lord, Acting Director
Office of Engineering and Highway
Operations Research and Development
Notice
This document is disseminated under the sponsorship of the Department of Transportation
and the Environmental Protection Agency in the interest of information exchange. The
United States Government assumes no liability for its contents or the use thereof. This
report does not constitute a standard, specification, or regulation.
The United States Government does not endorse products or manufacturers.. Trade and
manufacturers' names appear herein only because they are considered essential to the object
of this document.
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Technical Report Documentation Page
1. Report No.
FHWA-RD-93-088
2. Government Accession No.
3. Recipient's Catalog No.
4.11(16 and Subtitle
ENGINEERING AND ENVIRONMENTAL ASPECTS OF
RECYCLED MATERIALS FOR HIGHWAY CONSTRUCTION
5. Report Date
July 1993
6. Performing Organization Code
7. Author(s)
D. Bloomquist, G. Diamond, M. Oden, B. Ruth, M. Tia
8. Performing Organization Report No.
9. Performing Organization Name and Address
Western Research Institute
Laramie, Wyoming 82071
10. Work Unit No. (XRAIS)
NCP 3C2A
11. Contract or Grant No.
DTFH61-93-C-00060
12. Sponsoring Agency Name and Address
U.S. Department of Transportation
Federal Highway Administration, McLean, VA 22101-2296
U.S. Environmental Protection Agency, Cincinnati, OH 45268
13. Type of Report and Period Covered
Final Report
September 1992 - June 1993
14. Sponsoring Agency Code
15. Supplementary Notes
Contracting Officer's Technical Representative (COTR) - Michael R. Smith, HNR-20
16. Abstract
This report presents an assessment of environmental aspects and engineering factors related to the
utilization of recycled materials in highway construction. A basic overview and assessment of different
technologies, processes, and methods for recycling of various material into highway appurtenances and
for highway construction are presented with consideration of environmental/health risks.
17. Keywords
Recycled materials, highway construction,
environmental, engineering, health, scrap
tires, crumb rubber modifier.
IS. Distribution Statement
No restrictions. This document is available to the
public from the National Technical Information
Service, Springfield, Virginia 22161.
19. Security Classif. (of this report)
Unclassified
20. Security Classif. (of this page)
Unclassified
21. No. of Pages
220
22. Price
Form DOT !•'1766.7
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APPROXIMATE CONVERSIONS TO SI UNITS
Multiply By To Find
LENGTH
25.4
0.305
0.914
1.61
AREA
millimeters
meters
meters
kilometers
square millimeters
square meters
square meters
hectares
square kilometers
milliliters
filers
cubic meters
cubic meters
NOTE: Volumes greater than 10001 shal be shown in m».
square inches
square (eel
square yards
acres
square miles
fluid ounces
gallons
cubic (eel
cubic yards
645.2
0.093
0.836
0.405
2.59
VOLUME
29.57
3.785
0.028
0.765
MASS
oz
Ib
T
ounces 28.35
pounds 0.454
short tons (2000 Ib) 0.907
TEMPERATURE (exact)
grams
kilograms
megagrams
Fahrenheit 5
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TABLE OF CONTENTS
Chapter
Page
1. INTRODUCTION . • . • 1
ENVIRONMENTAL CONSIDERATIONS 1
ENGINEERING CONSIDERATIONS " 2
FORMULATION AND RESPONSE TO SURVEYS OF
HIGHWAY AGENCIES 5
TECHNICAL APPROACH FOR SEARCH AND
EVALUATION OF LITERATURE ON HUMAN
HEALTH AND ENVIRONMENTAL RISKS 7
REPORT ORGANIZATION .- 10
2. ENVIRONMENTAL ASSESSMENT . . . . . . 13
RISK ASSESSMENT OF ASPHALT PAVING
MATERIALS AND MODIFIED ASPHALT
PAVING MATERIALS . . 13
HAZARD IDENTBFICATION/DOSE-RESPONSE
ASSESSMENT 17
EXPOSURE ASSESSMENT 23
RISK CHARACTERIZATION 62
SUMMARY 66
3. ENGINEERING ASSESSMENT . . . - 73
CRUMB RUBBER MODIFIER 73
RECYCLING OF ASPHALT PAVEMENTS USING
AT LEAST 80 PERCENT RECYCLED ASPHALT
PAVEMENT (RAP) 96
CRUSHED GLASS APPLICATIONS 106
RECYCLED PLASTIC APPLICATIONS 113
OTHER MATERIALS 117-
DISPOSAL, REUSE, AND RECYCLING OF HIGHWAY
MATERIALS 138
4. SUMMARY OF FINDINGS • 161
ENVIRONMENTAL ASSESSMENT . . . 161
ENGINEERING ASSESSMENT 163
in
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TABLE OF CONTENTS (Continued)
APPENDIX A. LETTER OF TRANSMITTAL AND SURVEY FORM
N0- ! 171
APPENDIX B. LETTER OF TRANSMITTAL, SURVEY FORM NOS
1 AND 2, AND ONE-PAGE QUESTIONNAIRES 173
BIBLIOGRAPHY 1??
GENERAL
CARBON BLACK '
COAL ASH
CRUMB RUBBER MODIFIER . .
CRUSHED GLASS
INCINERATOR ASH \\\\
PAPER/CELLULOSE IN STONE MATRIX ASPHALT (SMA) 200
PLASTICS AND POLYMERS 201
RECYCLED ASPHALT PAVEMENT 202
RECYCLED PORTLAND CEMENT CONCRETE 204
RECYCLING OF ASPHALT - COLD MIX 204
RECYCLING OF ASPHALT - HOT MIX . 208
RECYCLING OF ASPHALT - SURFACE . 209
ROOFING MATERIALS . . 9no
SLAGS .' 210
TIRE CHIP AND WHOLE TIRE APPLICATIONS . . . . .' .' .' .' .' .' \\\\ 211
IV
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LIST OF FIGURES
Figure No.
1. Elements of risk assessment /. . . . 13
2. Some of the types of chemicals used in rubber manufacture 24
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LIST OF TABLES
Table No.
I.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
Provincial .and State use of wastes and byproducts
in transportation construction 4
Summary of responses to surveys 5
Some commonly found chemicals in asphalt 19
Rubber chemicals with significant production volumes 25
Emission factors (mg/Mg) from the Thamesville (Ontario) study .... 29
Emission factors (mg/Mg) from the Haldimand-Norfolk (Ontario) study 34
Emission factors (mg/Mg) from the Farmer County (Texas) study .... 39
Emission factors (mg/Mg) from the San Antonio (Texas) study 42
Emission factors (mg/Mg) for conventional and modified HMA 45
PAH in tank headspace samples Owg/m3) 59
Worker exposure to conventional asphalt fumes—particulates 63
Worker exposure to conventional asphalt fumes—PAH 64
Summary of responses to the surveys on CRM pavements 86
Summary of the survey on pavements using more than
80 percent RAP 99
Uses of coal ash _ 120
States with guidelines for use of ash 121
Summary of disposal/utilization survey 139
Summary of recycling specifications of 50 States
and the District of Columbia 150
Disposal/utilization of materials removed from highways 172
VI
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ACRONYMS
AI Asphalt Institute
ARAM Asphalt-rubber and aggregate membrane
ARHM Asphalt-rubber hot mix
ARPG Asphalt Rubber Producers Group
ATSDR Agency for Toxic Substances and Disease Registry
CRAVE Carcinogen Risk Assessment Verification Endeavor
CRM Crumb rubber modifier
DNA Deoxyribonucleic acid
DGHMA Dense Graded Hot-Mix Asphalt
EPA Environmental Protection Agency
FHWA Federal Highway Administration
HMA Hot-mix asphalt
IARC International Agency for Research on Cancer
IRIS Integrated Risk Information System
MffiK Methyl isobutyl ketone (4-methyl-2-pentanone)
NAPA National Asphalt Paving Association
NAS National Academy of Sciences
NCAT National Center for Asphalt Technology
NIOSH National Institute for Occupational Safety and Health
NMR Nuclear magnetic resonance
OGFC Open Graded Friction Course
OSHA Occupational Safety and Health Administration
PAH Polycyclic aromatic hydrocarbons
PCB Polychlorinated biphenyls
PCDD Polychlorinated dibenzo-p-dioxins
PCDF Polychlorinated dibenzofurans
PEL Permissible exposure level
RAP Recycled asphalt pavement
RfD Reference dose
RUMAC Rubber modified hot-mix asphalt concrete
TACB Texas Air Control Board
VOST Volatile Organics Sampling Train
WRI Western Research Institute
Vll
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CHAPTER 1. INTRODUCTION
ENVIRONMENTAL CONSIDERATIONS
Environmental health issues related to the production, use, recycling, and disposal of
asphalt paving mixtures modified with waste materials, such as scrap tire rubber, plastic, and
glass, can be viewed as having two major dimensions:
• The production of new complex mixtures of hazardous materials.
• The redistribution of hazardous components of the modifying agents in the environment.
Both derive from the fact that asphalt cement, rubber, plastic, and glass are complex
mixtures that contain hazardous constituent chemicals.
New mixtures will be produced when the components of rubber, plastic, or glass are
added to asphalt paving mixtures. The toxicological properties of these modified asphalt
pavements may be different from conventional asphalt pavements. Components of the
modifying agent and asphalt cement may interact physically or chemically to produce
synergistic or antagonistic effects on biological systems. In addition, the fate of the
components in the environment may be altered, resulting in changes in exposure profiles.
The significance of these potential interactions is that characterization of risks associated with
modified asphalt paving mixtures may not be accurately predicted from assessments of
conventional asphalt paving mixtures or the modifying agents as separate entities.
Rubber tires, plastic, and glass are currently being disposed of, stored, and recycled to
varying degrees. These processes result in the destruction, dilution, or concentration of the
hazardous components of these materials in various environmental media and give rise to a
continuum of exposure profiles and related risks. Production, application, recycling, and
disposal of asphalt pavements modified with rubber, plastic, or glass will result in the
removal of some quantity of these materials from the current waste stream and will alter the
distribution of the constituent materials in the environment. Exposure patterns will change as
a result.
Predicting the change in human and environmental exposures resulting from incorporat-
ing modifying agents into asphalt paving mixtures is an enormous challenge. The complexity
of the problem can be understood by considering the pathways of human exposure to rubber-
derived chemicals during the production, application, and use of asphalt paving mixtures
containing crumb rubber modifier (CRM). Similar pathways will be associated with other
types of modified asphalt pavements. During storage and processing of scrap tires for the
production of CRM for use in asphalt paving mixtures, constituents of rubber will enter and
exit intermediate pools that have varying mobilities in certain environmental media. For
example, 40-mesh CRM can more easily become airborne than rubber in a stored tire. Some
rubber constituents may volatilize during heating of the asphalt-rubber paving mixture.
Although stored tires are generally considered to represent a relatively immobile waste pool
for rubber, occasionally a tire storage facility ignites and large amounts of hazardous material
1
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are rapidly transported into the air. As a result of use of CRM in asphalt pavements, rubber
constituents will be transferred from a highly concentrated and relatively immobile waste
pool at a tire storage facility to a highly diluted matrix of paved road surfaces If certain
components of rubber are more mobile and more readily transported to water from the
asphalt pavement matrix, environmental exposures to these chemicals may be greater near a
road surface made of asphalt pavement modified with CRM than near a tire storage facility
On the other hand, release of rubber-derived chemicals from asphalt pavement made with
CRM may be no greater than releases that result from tire wear.
^ The challenge for risk characterization is to analyze both the "new mixtures" and the
redistribution" dimensions to the problem and arrive at quantitative estimates of the net
change in risk that will result from production, application, recycling, and disposal of
modified asphalt pavements. A complete risk characterization should also consider the
relative risk of net producing modified asphalt pavements. For example, the risks associated
with altering the existing waste stream via production, use, disposal, and recycling of asphalt
pavements modified with CRM should be compared to the risks associated with other tire
waste options such as storage or combustion. The overall strategy for developing a risk
characterization of this scope is contained in the National Academy of Sciences (NAS)
paradigm (described in chapter 2). The major limitation is the availability of high quality
data to support dose-response and exposure assessment. In chapter 2 of this report the
available data relevant to risk characterization of modified asphalt pavements are profiled
and select data are analyzed in an attempt to estimate the upper bounds on relative risk of
asphalt paving mixtures modified with CRM vs. conventional asphalt paving mixtures.
ENGINEERING CONSIDERATIONS
Background
Over the years, the population growth, changing life styles, new technologies, and the
resultant flood of low-cost disposable products have greatly increased domestic waste
generation to the point that sanitary landfill sites can no longer accommodate demand
Landfills are quickly reaching capacity and it is becoming more difficult to find new landfill
sites due to societal concerns and environmental criteria. Consequently, many areas of the
country have developed or attempted to develop recycling programs for the purpose of
resource recovery and to reduce the demand for landfill space.
There is, at this time, considerable emphasis on the use of recycled materials for
highway Construction. Many States have initiated legislation to direct their highway agencies
to investigate the possibility of recycling different waste byproducts into highway pavements
and/or appurtenances. Section 1038 of public law 102-240, the "Intermodal Surface
Transportation Efficiency Act" enacted by Congress on December 18, 1991 directs the US
Environmental Protection Agency and the U.S. Department of Transportation, in cooperation
with the States, to conduct studies on the use of recycled materials in highway construction
It is hoped that this effort will provide sufficiently detailed information to establish the
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benefits, disadvantages, and overall feasibility of recycling materials into highway applica-
tions. ,
Technical Problems Associated with Disposal and
Recycling of Materials for Highway Applications
The recent status of recycled material utilization in transportation construction has been
summarized by Emery and MacKay as shown in table 1.® The ranking, number of users,
and number of agencies with specifications covering the material's use provide an indication
of the material's availability, cost, and feasibility for use in construction. The first four
ranked materials (asphalt pavement, concrete, blast furnace slag, and fly ash) are materials
that have been commonly recycled or reused in highway construction. Steel slag (ranked
fifth) must be carefully evaluated and controlled because of potential problems with expan-
sion due to chemical composition and age. Silica fume is an example of a low quantity
material that is being used frequently to produce high strength concrete. Similarly, waste
foundry sand and glass are generated in relatively low quantities, which relegates their use to
applications near the supply source.
The belief that hot-mix asphalt (HMA) modified by plastics, crumb rubber, or other
material will automatically improve pavement properties such as resistance to rutting or
durability neglects many other factors involved in long-term performance. Major factors
contributing to pavement performance are: (1) subsurface moisture and drainage conditions
relative to subgrade soil and granular base characteristics, (2) thickness and quality of
granular base materials, (3) asphalt mixture quality and rate of aging of asphalt binders,
(4) climatic exposure conditions (freeze-thaw, rapid cooling, high temperature), and
(5) characteristics of heavy trucks with different wheel and load configurations.
The concept of using recycled materials as an additive to conventional pavements is more
difficult than if the recycled materials were used to fabricate specific appurtenances (e.g.,
plastic fencepost) on highways due to the complex and variable nature of HMA. Basically,
all highways utilize gravels, sands, crushed stone, or synthetic aggregates for the construc-
tion of pavements (both asphalt and concrete). The availability, engineering properties, and
costs for these aggregates vary from one locality to the next. The specifications, especially
for the particle size distribution for asphalt mixtures, concrete mixtures, or base and subbase
courses, vary between States. Consequently, the addition of any particulate type recycled
material (crushed glass, crumb rubber, fly ash, etc.) often requires modification of aggregate
gradation specifications to accommodate the recycled material without adversely affecting
quality.
Current HMA specifications, among other criteria, specify the selection of crushed
aggregate that has a desired gradation (particle size distribution). Although two or more
different aggregates may be blended to meet specifications (e.g., for asphalt paving mixture),
the addition of recycled materials may necessitate changing the aggregate producer's
operations and/or State specifications. It is not always possible to add other materials (e.g.,
recycled materials) to conventional asphalt paving mixtures, portland cement concrete, or
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Table 1. Provincial and State use of wastes and byproducts
in transportation construction.1
Rank2
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Material
Old Asphalt
Old Concrete
Blast Furnace Slag
Air-Cooled
Pelletized
Granulated
Fly Ash
Steel Slag
Silica Fume
Nickel and Copper Slags
Bottom Ash
Mine Waste Rock
Waste Tires
Kiln Dusts
Lime
Cement
Waste Foundry Sand
Waste Glass
Waste Shingles
Users
p3
10
4
2
1
1
4
4
4
2
2
4
2
1
1
1
1
S4
42
29
18
1
15
46
18
15
2
6
10
19
6
3
2
2
1
Specifications
P
3
1
1
1
1
1
1
1
1
1
S
19
8
12
2
12
4
2
1
1
5
2
Summarized from a survey of transportation departments completed during the first
quarter of 1991. Also includes specific city and demonstration uses. Survey response
achieved was 100 percent.
Rank is based on an overall evaluation of current and potential uses in terms of material
availability, technical suitability, favorable economics and positive environmental impact.
P - Provinces. Number out of 10 Provinces, plus the Yukon and Northwest Territories.
4 S - States. Number out of 50 States, plus the District of Columbia.
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granular base courses without reducing strength, durability, overall performance, and/or cost-
effectiveness.
Another important aspect of using recycled materials such as crumb rubber from
discarded tires is the recyclability of asphalt pavements containing crumb rubber. Currently,
there is very little experience with recycling asphalt pavements containing crumb rubber. A
significant consideration in the use of recycled materials in asphalt or concrete pavement is
whether or not it has subsequent or cascading effects upon recycling of pavement or reuse of
the pavement materials. If the capability of recycling pavements is lost, then the magnitude
of the disposal problem has been escalated with the end result being that the recycling of
waste byproducts has been greatly diminished.
FORMULATION AND RESPONSE TO SURVEYS OF HIGHWAY AGENCIES
The initial research effort was concentrated on the documentation of literature pertaining
to the use of recycled materials in highway construction and the formulation of detailed
spreadsheets for each major topic area (material type) as given in the following list:
• A1A Hot-Mix Asphalt Containing Crumb Rubber Modifier (15 pages).
• A IB Asphalt Rubber Spray Applications (11 pages).
• A1C Recycling of Hot-Mix Asphalt: Pavements Containing Crumb Rubber (18 pages).
• B1A Recycling of Pavements Using Over 80 Percent RAP (14 pages).
• BIB Plastics in Highway Construction (11 pages).
• B1C Crushed Glass in Highway Construction (7 pages).
• BID Reuse, Recycling, and Disposal of Other Recycled Materials Used in Highway
Construction (13 pages).
The first survey forms (SUR-1) titled "Disposal/Utilization of Materials Removed from
Highways" were mailed to highway agencies' construction engineers (appendix A), The
second mailing included the second and third one-page survey forms (SUR-2 and SUR-3),
entitled "Information Urgently Needed and Critical to Our Survey of Hot-Mix Asphalt
Containing Crumb Rubber Modifier (CRM)," and "Information That is Needed and Critical
to Our Survey on Recycling of Hot-Mix Asphalt Pavements Containing Crumb Rubber
Modifier," respectively. These two survey forms, cover letter, and a shortened version of
the detailed spreadsheets may be found, in appendix B.
The response to these questionnaires are summarized by State, Province, or municipality
in table 2. Those agencies that responded may have indicated some form of activity in the
recycling of a given material or they may have excluded the material from use. In some
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Table 2. Summary of responses to surveys.
STATE
Alabama
Alaska
Arizona
Hawaii
Massachusetts
Michigan
Minnesota
Missouri
Mississippi
CANADA
Province
Alberta
Nova Scotia
Surl
*
~TT
+
+
+
+
+
Sur2
*
+
+
Sur3
+
+
~T~T
+
A1A
*
~T~
__
+
A1B
*
*
~T~[
A1C
+
+
TT
+
B1A
..
^
~TT
+
+
BIB
-
-
— TT
BIG
-
-
~^~r
+
j Bin
+
No. Sta
+
STATE
New
Hampshire
Nevada
North Carolina
North Dakota
Ohio
Oregon
Pennsylvania
South Carolina
South Dakota
Tennessee
Texas
Utah
Virginia
Washington
W. Virginia
Wisconsin
Wyoming
tes Responding
Surl
*
42
Sur2
_.,,+
39
Sur3
,+
23
A1A
*
29
A1B
*
22
A1C
*
19
B1A
•f
30
BIB
-
19
BIG
-
23
BID
-
18
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cases, the highway agency submitted detailed research reports that have been reviewed and
suitable information documented on the survey forms and/or the spreadsheet questionnaires.
TECHNICAL APPROACH FOR SEARCH AND EVALUATION OF LITERATURE
ON HUMAN HEALTH AND ENVIRONMENTAL RISKS
The initial focus was to identify existing scientific literature and data that might be
relevant to characterizing relative human health and environmental risks associated with the
manufacture, application, and recycling of conventional vs. modified asphalt pavements. A
literature search was conducted with the objective of profiling the types of information that
are currently available to support an assessment of relative risk and to identify information
gaps. The results of this search were captured in an annotated bibliography.
As it became apparent that existing data were inadequate to support a complete character-
ization of relative risk, effort was redirected towards evaluating the few available studies in
which hazardous emissions from conventional and modified asphalt paving mixtures were
compared. The rationale was that it might be possible to use the results of these studies to
project exposures to humans and the environment, and thereby establish upper and lower
bounds on the magnitude of relative risk.
Production of Annotated Bibliography3
The annotated bibliography includes studies related to the following topics:
• Composition, environmental chemistry, environmental effects, and health effects of
conventional asphalt paving mixtures and asphalt paving mixtures modified by the
addition of crumb rubber, plastic, or glass.
• Chemicals released to the environment from rubber, plastic, and glass.
•-• Chemical hazards associated with alternative means of tire disposal and recycling.
• Environmental chemistry, environmental effects, and health effects of chemicals released
into the environment from asphalt paving mixtures.
The bibliography was assembled by identifying relevant studies; indexing these studies
with keywords that characterize the content of each study and provide a mechanism for
sorting the bibliography by subject; and entering brief comments regarding the methods,
results, or content of each study.
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Identification of Relevant Studies
^ Relevant studies were identified by computer literature searches, tree-searches of review
arfacles discussions with scientists and engineers at the Federal Highway Administration
(FHWA), Environmental Protection Agency (EPA), Western Research Institute (WRI) and
the University of Florida, and phone queries to selected manufacturing and regulatory'
organizations involved in highway construction or materials manufacture, including the
National Asphalt Paving Association (NAPA), Asphalt Institute (AT), National Center for
Asphalt Technology (NCAT), and Asphalt Rubber Producers Group (ARPG).
Computer searches of on-line bibliographic data bases were initially conducted to identify
reports on asphalt"; separate search strategies were used to capture information on composi-
tion and environmental chemistry, environmental effects, or health effects. Each strategy
was applied to several electronic data bases, including:
• CAS on-line (primarily chemistry information).
• TOXLINE (primarily toxicity information).
• NTIS (government publications).
• APILIT (petroleum industry data base).
• COMPENDEX (engineering and technology data base).
• CIN (chemical industry information).
Searches by CAS number were also conducted, including searches of the following data
bases: "
• EFDB (environmental fate information).
• TSCATS (unpublished environmental fate, exposure, environmental effects, and health
effects information).
Literature searches were screened by environmental chemists and toxicologists to identify
pertinent studies. Reports that contained information on environmental emissions were
retrieved and the data were reviewed to identify the chemicals that had been shown to be
released[intojfae^environment. Available emissions studies are limited to asphalt and asphalt
modified with CRM, and generally limited to measurements of priority toxics (e g air and
water toxics). The latter limitation reflects the focus of these studies on detecting potential
noncompliance with State and Federal pollution laws. As a result, many chemicals in crumb
rubber and other asphalt modifiers have not been monitored. In order to identify chemicals
ttat have the potential for release into the environment, computer searches were conducted
for sources of information on leaching and volatilization from tires, rubber, plastic and
glass, and information regarding composition, disposal, and recycling of tires These reports
were reviewed to identify potential emissions.
8
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Searches were conducted to identify authoritative reviews, including those prepared by
the EPA, Agency for Toxic Substances and Disease Registry (ATSDR), National Institute for
Occupational Safety and Health (NIOSH), and Occupational Safety and Health Administra-
tion (OSHA), on the environmental chemistry and health and environmental effects of
chemicals reported to be emitted from conventional or modified asphalt pavements. For
some emitted chemicals, reviews were not located and it was necessary to conduct additional
computer literature searches to identify primary sources of information on the environmental
fate and toxicity of the chemical.
Assignment of Index Keywords and Comments
Reports were indexed using a standardized scheme. The keywords allow the user to
quickly determine the subject of any study in the bibliography, including for example, such
details as the test material, the endpoints examined, the species tested, and the route of
exposure for a toxicity study. The keywords also allow sorting of the bibliography for
selected review of entries on a specific subject (e.g., all human epidemiology studies on
asphalt). Comments were recorded as needed to summarize important study details that
could not be accommodated in the keyword index, as well as results.
Literature Survey and Review
The identified literature was surveyed for information pertinent to performing an
assessment of the relative health risks of conventional asphalt pavements vs. asphalt
pavements modified by the addition of CRM, plastic, or glass. Health effects data were
available only for conventional asphalt paving mixtures. Therefore, it was not possible to do
a comparative risk assessment using traditional methods. However, several studies were
located that compared air emissions from conventional asphalt paving mixtures to asphalt
paving mixtures modified by the addition of CRM. These studies were reviewed in detail in
the hope that it might be possible to use the results of these studies to project exposures to
humans and the environment, and thereby establish upper and lower bounds on the magnitude
of relative risk.
The studies that were reviewed fall into three groups: studies of environmental emissions
from asphalt hot-mix plants during virgin operation, studies of environmental emissions from
asphalt hot-mix plants using recycled asphalt pavement (RAP), and studies of worker
exposure from asphalt mixing plant operations and road-paving operations. For each
pertinent study, emissions profiles for conventional and rubber-modified asphalt paving
mixtures were compared. Studies within each of the three groups were also compared to
each other and to additional, similarly-designed studies of conventional asphalt pavement
emissions in an attempt to identify patterns that could point to differences in relative risk
between conventional and rubber-modified asphalt paving mixtures;
None of the available studies that contained comparisons,of emissions from conventional
and modified asphalt pavements included a sampling regimen adequate to support statistical
testing for differences in emissions between conventional and modified asphalt pavements.
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Therefore, comparisons were based on mean values and offer only rough indications of
trends in the data. Comparisons of results between different studies were based on means, or
even ranges, and were useful only for indicating broad patterns in the data.
REPORT ORGANIZATION
This report has been formulated to provide a synthesis of available information relating
to environmental/health aspects, physical characteristics, and the engineering considerations
involved in the use of recycled materials in highway construction. Considerable emphasis
has been placed upon recycled material utilization in pavements since this has considerably
more impact on the quality and longevity of our highway system than the use of recycled
materials for highway appurtenances (e.g., signs, guardrail posts, fence posts, etc.).
Information on the use of recycled materials and their environmental/health consideration
has been derived from an extensive literature search. The intent of the report is to provide a
fairly concise, but comprehensive, overview of the most important aspects regarding use of
recycled materials in highway construction. The references and bibliography are documented
to allow the reader to investigate any subject area in more detail. It is not intended that the
report be all-inclusive and reiterate all aspects and detail provided in the literature. Rather,
it is the intent that the reader gain a good perspective or overview of the status of current '
technology, potential or actual benefits, problems or disadvantages, and the need for further
research.
Another source of key information was obtained from survey forms and questionnaires
sent to the different State (Provincial) highway agencies. A one-page questionnaire on each
of the following topics and a letter of transmittal was sent to different highway agencies:
• Hot-Mix Asphalt Containing Crumb Rubber Modifier.
• Recycling of Hot-Mix Asphalt Containing Crumb Rubber Modifier.
• Disposal/Utilization of Materials Removed from Highways.
Additional detailed spreadsheet questionnaires were included in the mailing. The requested
information pertained to the following subjects:
• Hot-Mix Asphalt Containing Crumb Rubber Modifier.
• Asphalt-Rubber Spray Applications.
• Recycling of Pavements Using Over 80 Percent RAP.
• Plastics in Highway Construction.
• Crushed Glass in Highway Construction.
10
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• Reuse, Recycling, and Disposal of Other Recycled Materials Used in Highway Construc-
tion.
The data derived from these survey forms were analyzed to evaluate the current level of
activity of the different agencies in their utilization of recycled materials in highway
construction. Also, information regarding performance or problems with pavements and
appurtenances containing or made from recycled materials was evaluated and summarized
according to each type of recycled material.
References
1. National Academy of Sciences, Risk Assessment in the Federal Government: Managing
the Process, Washington, DC: National Academy Press (1983).
2. John Emery and Michael MacKay, Use of Waste and By-Products as Pavement Construc-
tion Materials, presented at the 1991 TAG Annual Conference, Winnipeg, Manitoba,
Canada (paper available from John Emery Geotechnical Engineering Limited,
Downsview, Ontario).
3. Unpublished Report, Annotated Bibliography: Human Health and Ecological Risks
Associated with the Manufacture, Application, and Recycling of Asphalt Paving
Materials Containing Crumb Rubber, and Other Materials Reclaimed from
Commercial and Municipal Waste Streams, U.S. Federal (Highway Administration,
Washington, DC (1993).
11
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CHAPTER 2. ENVIRONMENTAL ASSESSMENT
RISK ASSESSMENT OF ASPHALT PAVING MATERIALS AND MODIFIED
ASPHALT PAVING MATERIALS
Risk Assessment—Definitions and Basic Concepts
Risk assessment is defined for the purpose of this study as the qualitative or quantitative
characterization of the potential adverse effects of a chemical on human health or the
environment. Risk assessment can be thought of as an integration of four processes
(figure 1):(1)
• Hazard identification.
• Dose-response assessment.
• Exposure assessment.
• Risk characterization.
Hazard Identification
Does the chemical produce ad-
verse effects?
Dose-Response Assessment What is the relationship between
dose and adverse effect?
Exposure Assessment
Risk Characterization
What exposures occur or are
anticipated?
What is the estimated incidence of
adverse effect at a given exposure?
Figure 1. Elements of risk assessment.
Hazard Identification
The objective of the hazard identification is to identify chemical properties or character-
istics that may initiate or contribute to adverse ecological or human health effects. Hazard
identification is usually the initial step hi a risk assessment. Hazard identification results in
information used for dose-response and exposure assessments, which are integrated in risk
characterization to estimate the incidence of adverse effects associated with a given exposure
scenario.
13
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Hazard identification consists of data collection and analysis, with a focus on the
following issues:
• The validity and meaning of experimental and monitoring data.
• The weight-of-evidence that a substance causes a given toxic effect or will persist in the
environment.
• The likelihood that the effect observed in a given population (e.g., experimental animals)
will occur in other populations (e.g., humans).
Hazard identification is not limited to specific exposure scenarios; this is deferred to the
exposure assessment and risk characterization phases of risk assessment. The risk character-
ization phase determines if the conclusions of hazard identification are relevant to a specific
exposure scenario. For example, hazard identification considers whether or not a chemical
can potentially cause cancer in humans, not whether cancer is likely to occur within a given
population living near an emission source.
Hazard identification encompasses a review of all data relevant to evaluating or predict-
ing the environmental fate and toxicity potential of a chemical. This includes the analysis of
structure-activity relationships that provide additional insight regarding the fate or toxicity
potential of the chemical.
Dose-Response Assessment
The objective of dose-response assessment is to characterize the relationship between the
dose of the chemical and incidence or severity of adverse effect. Dose-response functions
are usually established in experimental studies in which the dose can be rigorously controlled
and the response rigorously evaluated. It is usually feasible to examine only the high dose
region of the dose-response relationship in experimental studies; therefore, dose-response
assessment often involves extrapolating response rates from high to low doses. This is
usually accomplished through the use of probabilistic models. Epidemiological studies can
provide information about response rates at doses associated with environmental or occupa-
tional exposure levels, although causal relationships between exposure and response are often
obscured by exposures to other hazards. Experimentally derived dose-response functions can
sometimes be validated with epidemiological studies. Dose-response assessment considers
and attempts to quantify uncertainties related to extrapolating dose-response functions across
species, age, sex, and subpopulations.
Exposure Assessment
The objective of exposure assessment is to quantify the magnitude, frequency, and
duration of exposure to humans or other organisms that might be adversely affected by
exposure to a chemical. Exposure can occur through various environmental media such as
air, food, water, and soil. The exposure medium determines the physiological routes through
14
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which exposure is translated into dose, for example, inhalation; ingestion; or absorption
across skin, gills, or roots. Exposure assessment also considers indirect routes of exposure,
for example, bioconcentration in food or prey organisms.
Exposure assessment considers the fate of chemicals released from the source and
estimates the levels that would be expected to occur in relevant environmental media as a
function of time, direction, and distance from the source. This information can be used to
estimate dose to an organism at a specific location over a specific length of time. Numerous
variables can affect transport and persistence of a chemical in the environment. These
include rates of abiotic and biodegradation, water solubility, adsorption to soil, volatility, and
dispersion and diffusion in air and water. These variables are, in turn, dependent on the
physical and chemical properties of the chemical, characteristics and location of the source,
and numerous environmental variables such as wind velocity, precipitation, soil character-
istics, topography, and ground and surface water characteristics. Exposure assessment often
relies on a combination of environmental monitoring and theoretical models of fate processes
to simulate exposure gradients.
Risk Characterization
The objective of risk characterization is to predict the incidence of adverse effects that
will result from a given exposure scenario. Risk characterization integrates dose-response
assessment with exposure assessment. Risk characterization may assign quantitative
contributions to sources of risk that are relevant to managing risk, for example, the contribu-
tion of various exposure pathways to total risk (e.g., inhalation of air vs. ingestion of food
vs. dermal contact with water). Other dimensions of risk may also be considered in a risk
characterization, such as risk gradients across species, age, sex, geographic location, or
socioeconomic status. Assigning values to various dimensions of risk allows the risk
manager to weigh mitigation or remediation options relative to the magnitude each will have
on total risk.
Risk characterization considers uncertainties in the hazard identification, dose-response
assessment, and exposure assessment. Sources of uncertainties are identified and quantified,
if possible, in absolute or relative terms in order to assess the confidence in the risk
estimates. Examples of sources of uncertainty include: interspecies extrapolations, extrapo-
lations of risks from less-than-chronic exposure to lifetime exposure, extrapolations across
routes of exposure, extrapolation from one subpopulation to another (e.g., adults to chil-
dren), and inadequate information about exposure or dose-response relationships.
Risk Assessment of Complex Mixtures
Risk characterizations of complex mixtures such as asphalt present a unique set of
problems and uncertainties.0 The U.S. Environmental Protection Agency (EPA)
15
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recommends three approaches to risk assessment of complex mixtures that should be selected
based on the availability and quality of data on the:®
• Mixture of concern.
• Similar mixtures.
• Components of the mixture.
The ideal risk characterization would be based primarily on data on the incidence of
adverse effects in populations or organisms exposed to the exact "mixture of concern"-
however, such data are difficult to obtain and are usually not available. It is important to
emphasize that the "mixture of concern" is a dynamic concept. A plant producing asphalt-
rubber hot mix (ARHM) will produce a continuum of mixtures of varying composition in the
environment as a result of environmental fate processes acting on each chemical in the
emissions mixture. Thus, the "mixture of concern" will change across time and space; for
example, it will be different for a worker at an asphalt production facility than for a person
residing several miles upwind from the plant or several miles downwind from the plant. It
win also be different for different target populations at a given location or time; for example,
the "mixture of concern" for a human will be different from that for soil invertebrates or
aquatic species.
^ Experimental and epidemiological approaches can be used to assess risks associated with
a given mixture of concern. For example, an array of soil samples can be collected from
specific locations in the vicinity of an asphalt plant and subjected to toxicity bioassays. Such
studies may identify hazards and establish dose-response relationships for the mixtures at
those locations; however, greater uncertainty will be associated with extrapolation to other
locations. Epidemiologic studies can capture more realistic profiles of environmental
exposures (at least as it applies to the target population studied). However, subjects are
usually exposed to other hazards in addition to the mixture of concern, making it more
difficult to establish causal relationships and dose-response relationships that can be extrapo-
lated to different exposure scenarios.
Studies of "similar" or "surrogate" mixtures can be used to support a risk characteriza-
tion of the mixture of concern. For example, if the objective is to characterize the health
risks in a population residing several miles upwind from an asphalt plant producing ARHM
the mixture of concern would be the exposure mixture at that location. A laboratory study in
which mice are exposed to the ARHM, or an epidemiology study of workers at the asphalt
plant producing ARHM, are studies of "similar mixtures" because the study mixture may not
have the same composition as the "mixture of concern"; the change in the composition of the
emissions across time, distance, and direction from the source is not simulated in these
studies. Studies of "similar mixtures" can provide information about hazard identification or
dose-response functions. However, greater uncertainty is associated with applying this
information to assessments of risk associated with the "mixture of concern."
Risk assessments of complex mixtures can also be based on a "component" approach. In
this approach, exposure and dose-response assessments of the hazardous components of the
16
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mixture are integrated into an estimate of combined risk. This approach relies on the
availability of high quality data on the composition of the mixture, dose-response relation-
ships and environmental fate of the various components, environmental monitoring of the
mixture components, and certain critical assumptions about the interactions, or lack of
interactions, between components. If it is assumed that the components do not interact
toxicologically, then combined risk may be estimated as the sum of risks associated with the
individual mixture components. This approach may underestimate or overestimate combined
risk if synergistic or antagonist interactions occur.
Risk Assessment—Major Issues Related to Modified Asphalts
In the context of the National Academy Sciences (NAS) paradigm, the major issues that
must be addressed in order to assess the relative risks of manufacture, application, recycling,
and disposal of asphalt paving mixtures modified with rubber, plastic, or glass can be
summarized as follows :a)
• Are the chemical compositions of conventional and modified asphalt paving mixtures,
and emissions from production, application, and recycling of these mixtures, adequately
characterized to support hazard identification?
• Are environmental monitoring data adequate to support assessments of exposure to
humans or other organisms in the environment?
• Is the information on the environmental fate and toxicity of the major hazardous consti-
tuents of asphalt pavements and modifying agents adequate to support exposure models?
• Is there adequate information on dose-response relationships for components of conven-
tional and modified asphalt paving mixtures, and/or for the "mixtures of concern" or
"similar mixtures"?
• Are the toxicologic interactions that occur between the chemical constituents of modified
asphalt pavements adequately characterized?
HAZARD IDENTIFICATION/DOSE-RESPONSE ASSESSMENT
In this section, information on the composition and health effects of conventional asphalt
paving mixtures are summarized. A brief discussion is presented on the possible components
of asphalt pavements modified by the addition of CRM. No information on the human health
effects or environmental effects of asphalt pavements modified with CRM was located.
Furthermore, no information on the composition or human health and environmental effects
of asphalt pavements modified with other types of waste materials or on recycled asphalt
paving material modified with CRM was located.
17
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Conventional Asphalt Pavement
Composition
Asphalt cement is a complex mixture of aromatic and paraffinic compounds with a
molecular weight range of 500 to at least 2,500.<3>4> The components present in a particular
asphalt cement are dependant on the source of the crude oil from which the asphalt cement
was obtained, as well as the exact processing conditions used to manufacture and process the
asphalt cement. Thus, a complete chemical analysis of an asphalt cement would necessarily
apply only to that specific asphalt cement and could not reasonably be applied to other
asphalt cements with different origins and processing methods. Asphalt cements are not
manufactured to a specific composition, rather they are manufactured and sold to comply
with performance-based specifications. Nonetheless, polycyclic aromatic hydrocarbons
(PAH) such as naphthalene, fluorene, anthracene, fluoranthene, and benzopyrenes, and long
chained hydrocarbons (e.g., nonane, decane, and dodecane) have been consistently detected
in asphalt cements from diverse sources and manufacturing conditions. (See references 5
through 9.) table 3 shows some of the chemicals commonly found in asphalt cement.
Aged or weathered asphalt pavement is chemically different than new asphalt pavement.
No data were found in the available literature concerning the chemical composition of aged
asphalt pavement. Some information, however, is available concerning the types of chemical
changes that accompany the aging process.00' In general, aging is accompanied by an
increase in the asphaltene content of the asphalt cement (asphaltenes are large, complex
nonpolar molecules) by condensation of oils and resins (polar materials) to asphaltenes.
Asphaltenes, however, undergo oxidation to produce lower molecular weight materials with
increased oxygen content.
Health Effects of Asphalt
The discussion herein is restricted to an overview of potential health effects of asphalt
and PAH, a class of compounds that are thought to be responsible, at least in part, for the
carcmogenicity of certain fossil fuels and their products. The PAH are an example of
hazardous components of asphalt. Other hazardous chemicals are present in asphalt and may
contribute to the toxicity of asphalt (e.g., benzene). The association between certain fossil
fuel products and their constituents (e.g., mineral oils and certain monocyclic aromatic
hydrocarbons and PAH, such as benzene and benzo[a]pyrene) and skin cancer in humans and
laboratory animals has focused research on the ability of petroleum products, including
asphalts, to produce cancer. The EPA currently has no guidelines regarding the carcinogenic
or noncarcinogenic health hazards presented by asphalt, and ATSDR has not prepared a
lexicological profile on asphalt.(1U2)
Some of the studies available on the health effects of asphalt involved exposure specifi-
cally to paving asphalt, but others were based on exposure to roofing asphalt or mastic
asphalt. Although there may be some differences in composition between the various types
18
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Table 3. Some commonly found chemicals in asphalt.(6>7>28)
CAS Number
Chemical Name
50-32-8
53-70-3
53-70-3
56-49-5
56-55-3
71-43-2
83-32-9
85-01-8
86-73-7
86-74-8
91-20-3
92-24-0
98-86-2
100-52-7
108-88-3
111-65-9
111-84-2
112-40-3
112-95-8
120-12-7
124-18-5
129-00-0
142-82-5
191-07-1
191-97-2
192-97-2
193-39-5
198-55-0
206-44-0
207-08-9
208-96-8
217-59-4 .
218-01-9
544-76-3
593-45-3
629-50-5
629-59-4
629-62-9
629-78-7
629-92-5
629-94-7
629-97-0
Benzo[a]pyrene
Dibenz[a,h]anthracene
1,2,5,6-Dibenzanthracene
3-Memylcholanthrene
Benz[a]anthracene
Benzene ,
1 ,2-Dihydroacenaphthylene
Phenanthrene
Fluorene '
9H-Carbazole
Naphthalene
Tetracene
Acetophenone
Benzaldehyde , • .
Toluene ;
Octane
Nonane
Dodecane
Eicosane
Anthracene
Decane
Pyrene
Heptane
Coronene
Benzo[g,h,i]perylene
Benzo[e]pyrene
Indeno[l,2,3-cd]pyrene
Perylene
Fluoranthene
Benzo[k]fluoranthene
Acenaphthylene
Triphenylene
Chrysene
n-Hexadecane
Octadecane
Tridecane
Tetradecane
Pentadecane
Heptadecane
Nonadecane
Heneicosane
Docosane
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Table 3. Some commonly found chemicals in asphalt (Continued).(6>7>28)
CAS Number
Chemical Name
629-99-2
630-01-3
630-02-4
630-03-5
632-51-9
638-67-5
638-68-6
646-31-1
1120-21-4
1330-20-7
25551-13-7
26140-60-3
28804-88-8
Pentacosane
Hexacosane
Octacosane
Nonacosane
1,1',1",1" '-(1,2-Ethenediylidene)tetrakisbenzene
Tricosane
Triacontane
Tetracosane
Undecane
Xylene
Trimethylbenzene
Terphenyl
Dimethylnaphthalene
-
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of asphalts, there are also many similarities. Because the data base on paving asphalt itself is
not complete, studies of the toxicity of all types of asphalts were included in the discussion,
so as not to exclude potentially relevant information.
Several epidemiology studies have investigated the relationship between exposure to
asphalt and health effects in humans. Hammond et al. demonstrated a statistically significant
association between long-term occupation in the roofing industry (> 20 years) and elevated
mortality from cancer of the lung.(13) A significantly increased risk of lung cancer among
roofers was also reported by Menck and Henderson.(14) Additional supporting data were
obtained by Milham, who reported elevated proportional mortality ratios for lung and
laryngeal cancer among roofers.(15) Interpretation of these studies with respect to the ability
of asphalt to cause cancer is complicated because roofers in these studies may have been
exposed to fumes of petroleum-based asphalt and/or fumes of coal-tar pitch, a material that is
more enriched in benzo[a]pyrene and other PAH than is asphalt, and adjustments for
confounding exposure to other carcinogens (e.g., tobacco smoke) were not made.(16)
A series of studies were recently conducted by Hansen.(rM9) Hansen found that mortality
due to cancer was significantly higher among older, unskilled workers in the Danish asphalt
industry than among older, unskilled workers from other Danish industries.(17) Nonsignifi-
cant increases in mortality were seen for respiratory, digestive, and bladder cancers, while a
significant increase was found for brain cancer. However, this study was compromised by
classification of exposure category based only on employment on the date of the census. In
another study, Hansen studied a historical cohort of heavily exposed mastic asphalt workers
and found that cancer mortality was significantly increased compared to the total Danish male
population.(18>19) Tumor sites with significantly increased mortality were the lung, mouth,
esophagus, and rectum. Confounding variables, such as smoking, urbanization, and potential
exposure to coal-tar pitch were controlled. Mortality due to liver cirrhosis and respiratory
diseases (bronchitis, emphysema, and asthma) were also elevated in the mastic asphalt
workers. The Occupational Safety and Health Administration (OSHA) has proposed a
permissible exposure level (PEL) derived from the study by Hansen showing significantly
increased risk of lung cancer in Danish mastic asphalt workers.m
Studies of the health effects of asphalt in animals consist mostly of skin painting and
injection studies. The results of these studies were mixed. Hueper and Payne found that
four paving asphalt cements of differing manufacture produced mild-to-moderate carcinogenic
responses in mice, rabbits, and rats exposed for up to 2 years by dermal application or
intramuscular injection.C1) Simmers et al. reported that a pooled sample of six petroleum
asphalts (including some that were air-blown) produced a high incidence of malignant tumors
at the site of treatment in mice tested by skin painting and subcutaneous injection.^
Bingham and Barkely found malignant skin tumors in 9 of 17 mice treated with twice weekly
dermal applications of a "raw petroleum pitch" dissolved in toluene.C3) On the other hand,
negative results were obtained in studies of eight paving grade asphalt cements, a penetration
grade 150-200 asphalt cement, and a roofing asphalt.(9>24>25)
The International Agency for Research on Cancer (IARC) concluded that there was
sufficient evidence for the carcinogenicity of extracts of steam-refined bitumens and air-
refined bitumens in experimental animals, limited evidence for the carcinogenicity of
21
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undiluted steam-refined bitumens and cracking residue bitumens, and inadequate evidence
that undiluted air-refined bitumens are carcinogenic to animals or that bitumens are carcino-
genic to humans.<26>27> Bingham et al. concluded from their review of the animal experiments
that the "potential for inducing cancer by petroleum-derived asphalts, which in certain
instances is clearly less than that of coal tar products, is dependent in a complex way upon
their source and is influenced by refining history and the processing of the final mixtures. "<16)
In a study completed after lARC's review, Niemeier et al. observed statistically signifi-
cant elevations of skin tumor incidence in two different strains of mice treated with
cyclohexane/acetone solutions of fume condensates from heated type I or type HI roofing
asphalts; the fumes were generated at approximately 200 °C or 300 °C.™ This study also
examined the carcinogenicity of fume condensates from type I or type HI coal-tar pitch and
found carcinogenic responses to these materials as well. PAH, including naphthalene
benzo[a]pyrene, and benzofluoranthenes, were detected in condensed fumes from asphalt and
coal-tar pitch, but the PAH concentrations were approximately 10-fold to 100-fold higher in
coal-tar pitch fume condensates than in fume condensates from roofing asphalts. The
investigators noted that the magnitude of the differences in PAH concentrations (particularly
benzo[a]pyrene) between asphalt and coal-tar pitch fume condensates was not in scale with
the carcinogenic response to the two types of materials and speculated that compounds other
than PAH (e.g., aliphatic hydrocarbons) may have enhanced the carcinogenic activity of the
low amounts of PAH in the asphalt materials. Nuclear magnetic resonance (NMR) analysis
of the fume indicated that less than 1 percent of the asphalt fume material used in this
experiment was aromatic, and greater than 99 percent was aliphatic, whereas the coal-tar
pitch fume contained more than 90 percent aromatic compounds.
Studies have shown that extracts of bitumen and bitumen fumes were not mutagenic in
Salmonella and did not produce deoxyribonucleic acid (DNA) unwinding in rat liver
in vivo.3a> Application of a "black bitumen paint" to human skin (in vitro) or mouse skin
(in vivo) produced damage to skin DNA (i.e., DNA adducts detected by
P-postiabeling).<31'32> The test material was not chemically characterized by the investi-
gators, but was described as a commercial preparation containing 57 percent (v/v) bitumen- it
is not clear whether the material was derived from coal-tar or petroleum distillation residue
Health Effects of Polycyclic Aromatic Hydrocarbons (PAH)
Uof)' EPA reviewed the available research literature on 15 PAH found in the environ-
ment. PAH are, in general, well-studied as mutagenic agents in short-term tests and as
carcinogens in animals. U.S. EPA presented evidence for cancer weight-of-evidence
classifications of group B2, probable human carcinogens, for seven PAH's (benzo[a]anthra-
cene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, chrysene, dibenzo[a hl-
anthracene, and indeno[l,2,3-cd]pyrene) based on inadequate evidence of carcinogenicity in
humans and adequate evidence in animals. ^ These classifications were verified by the
Carcinogen Risk Assessment Verification Endeavor (CRAVE>Work Group and are listed on
the U.S. EPA Integrated Risk Information System (IRIS)/11) Data were considered sufficient
to derive a quantitative risk estimate for oral exposure for only one of the seven PAH —
benzo[a]pyrene. Evidence for classifications of group D, not classifiable as to human
22
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carcinogenicity, were presented for eight PAH (acenaphthylene, anthracene, benzo[g,h,i]-
perylenej fluoranthene, fluorene, naphthalene, phenanthrene, and pyrene) based on inade-
quate evidence for carcinogenicity in humans or animals.
Little information is available concerning noncarcinogenic health effects produced by
PAH. Nevertheless, data from animal studies are suitable for the derivation of reference
doses (RfD's) for several PAH including naphthalene, acenaphthene, anthracene,
fluoranthene, fluorene, and pyrene.(33)
Asphalt Pavement Modified with CRM
Composition
' The addition of modifying agents to asphalt paving mixtures will change the chemical
composition of the mixtures and, potentially, the composition of manufacturing and applica-
tion emissions. As with conventional asphalt pavements, the composition of modified asphalt
pavements will vary with feed materials and manufacturing processes, but for modified
asphalt pavements this includes variation in the composition or availability of components of
the CRM; which may vary depending on such factors as the type of rubber, production
methods, and particle size. Studies of the composition of asphalt pavements modified with
CRM were not located. However, the potential complexity of the composition of modified
asphalt pavements is apparent from a survey of the types of chemicals in rubber. Figure 2
shows a partial listing of the types of chemicals used in the manufacture of rubber. A list of
high production volume constituents of rubber that might be anticipated to occur in asphalt
pavements modified with CRM is presented in table 4. It is not known which of these
chemicals may be present in aged waste tires, asphalt pavements modified with CRM, or tire
dust generated from tire wear.
EXPOSURE ASSESSMENT
This section summarizes the available data on environmental emissions and worker
exposure due to production, application, and recycling of asphalt paying mixtures modified
with CRM. For studies that included monitoring of emissions from conventional asphalt
paving mixtures, the results regarding conventional asphalt pavement are discussed as well.
In addition, the results of studies that investigated only emissions from conventional asphalt
pavements are presented, where possible, for comparative purposes, although it was beyond
the scope of this document to discuss the results of these studies in detail. No information
was located on emissions from the production, application, recycling, or Disposal of paving
asphalts modified with materials other than CRM.
23
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Redalnwd
material
Crumb Rubber
Modifier
(Scrap Tire Rubber)
Constituents
(Functional groups)
-elastomers (natural/synthetic polymers)
-antldegradants
-accelerators
-activators
-retarders
-ptastlelzers
-processing aids
-ralnfofcing agents, fillers and diluents
-bonding agents
-solvents
- miscellaneous agents
Constituents
(Chemical classes)
Constituents
(Individual chemicals)
Processing
Products
Fate
Products
•sulfur
—dlthlocarbamates
—guanldlnes
—thlazoles
r-2-mercaptobenzothlazole (MBT)
—thloureas |-2£'-dltnlobls[benzothlazolel (MBTS)
—thluramsulfldes L-o-morphollnyM-benzothlazolyl
-sulfenamldes dlsulflde (MDTBT)
—aldehyde/amines
—xanthates
—ttilophospnates
MBT-
inzothlazola
-MBT (persistent)
-MBTS
Figure 2. Some of the types of chemicals used in rubber manufacture.
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Table 4. Rubber chemicals with significant production volumes.
Rubber Accelerators
— Thiazoles
N-tert-Butyl-2-benzothiazolesulfenamide
2,2'-Ditbiobis[benzothiazole]
Antioxidants
— para-Phenylenediamines
000101-54-2 4-Aminodiphenylamiiie
000101-72-4 N-Isopropyl-N'-phenyl-p-phenylenediamine
000793-24-8 N(l,3-Dimethylbutyl)-N'-phenyl-l,4-benzenediamine
001047-16-1 Cinquasia Red
015233-47-3 N-(l-Methylheptyl)-N'-phenyl-l ,4-benzenediamine
— Phosphites
000140-08-9 Tris(2-chloroethyl)phospMte
026523-78-4 Nonylphenol phosphite
031570-04-4 2,4-Di-tert-Butylphenol, phosphite (3:1)
:— Phenolics
000088-60-8
000090-00-6
000095-48-7
000095-65-8
000095-87-4
000096-69-5
000104-43-8
000105-67-9
000106-44-5
000108-39-4
000108-68-9
000118-82-1
000119-47-1
000123-07-9
000128-37-0
000526-75-0
000527-60-6
000576-26-1
Phenol, 2-(l,l-dimethylethyl)-5-methyl-
Phenol, 2-ethyl-
Phenol, 2-methyl-
Phenol, 3,4-dimethyl-
Phenol, 2,5-dimethyl-
Phenol, 4,4'-thiobis 2-(l,l-dimethylethyl)-5-methyl-
Phenol, 4-dodecyl-
Phenol, 2,4-dimethyl-
Phenol, 4-methyl-
Phenol, 3-methyl-
Phenol, 3,5-dimethyl-
Phenol, 4,4'-methylenebis 2,6-bis(l,l-dimethylethyl)-
Phenol, 2,2'-methylenebis 6-(l,l-dimethylethyl)-4-methyl-
Phenol, 4-ethyl-
Phenol, 2,6-bis(l, l-dimethylethyl)-4-methyl-
Phenol, 2,3-dimethyl-
Phenol, 2,4,6-trimethyl-
Phenol, 2,6-dimethyl-methyl-
25
-------
Table 4. Rubber chemicals with significant production volumes (Continued).
000620-17-7 Phenol, 3-ethyl-
001300-71-6 Phenol, dimethyl-
001319-77-3 Phenol, methyl-
001323-65-5 Phenol, dinonyl-
001806-26-4 Phenol, 4-octyl-
002409-55-4 Phenol, 2-(l,l-dimethylethyl)-4-methyl-
002416-94-6 Phenol, 2,3,6-trimethyl-
007786-17-6 Phenol, 2,2'-methylenebis 4-methyl-6-nonyl-
025154-52-3 Phenol, nonyl-
027193-86-8 Phenol, dodecyl-
068815-67-8 Phenol, thiobis\tetrapropylene-
084852-15-3 Branched Nonylphenol
Acyclic Compounds
Accelerators
— Dithiocarbamic acid derivatives
000128-04-1 Carbamodithioic acid, dimethyl-, sodium salt
000136-23-2 Zinc, bis(dibutylcarbamodithioato-S,S')-, (T-4)-
000513-74-6 Carbamodithioic acid, monoammonium salt
013927-77-0 Nickel, bis(dibutylcarbamodithioato-S,S')-, (SP-4-1)-
015890-25-2 Antimony, tris(dipentylcarbamodithioato-S,S')-, (OC-6-11)-
— Mercaptans
000111-88-6 n-Octyl mercaptan
— Miscellaneous
000097-77-8 Disulfiram
000090-30-2 N-Phenylnaphthalamine
000091-53-2 Quinoline, 6-ethoxy-l,2-dihydro-2,2,4-trimethyl-
000103-34-4 Morpholine, 4,4'-dithiobis-
000793-24-8 1,4-Benzenediamine, N-(l,3-dimethylbutyl)-N'-phenyl-
000836-30-6 Benzenamine, 4-nitro-N-phenyl-
26
-------
Sampling strategies in all of the comparative studies discussed below involved a total of
three or four short sampling periods for determination of emissions. In some cases, the three
or four sampling periods for a given type of asphalt pavement were all performed consecu-
tively on a single day. Hot-mix asphalt production is, by nature, a highly variable process,
dependent on parameters such as fueling rate of the dryer, mix temperature, asphalt through-
put rate, and asphalt binder content, which are all themselves subject to variation. ^
Extensive sampling would be required to determine emission rates with the degree of
precision necessary to differentiate between emissions from conventional and modified
asphalt pavements. The limited sampling performed in the available studies was inadequate
to assess emissions from mixing of asphalt pavements with satisfactory precision, as
demonstrated by the erratic nature of the sampling results for many chemicals and the
resultant large standard errors. The data base was insufficient to support statistical testing of
differences in emission rates between conventional and modified asphalt pavements.
Therefore, comparisons of emissions from conventional and modified asphalt paving mixtures
were, of necessity, based only on mean emission rates for the various constituents. Howev-
er, standard errors are shown with their associated means in the tables of emission rates so
that the reader may judge the variability of the specific comparisons made in the text. Due
to the highly variable nature of the available emissions data, comparisons based only on
mean values, as made in the text below, can offer only rough indications of trends in the data
and do not necessarily imply the existence of meaningful differences. Variation within a set
of samples for a particular contaminant from a particular type of asphalt pavement frequently
spanned several orders of magnitude. Therefore, in the following discussion, emission rate
differences between conventional and modified asphalt pavements of less than one order of
magnitude (tenfold increase or 90 percent decrease) were not generally considered to indicate
meaningful differences.
Studies of Environmental Emissions From Asphalt Mixing Plants
(Virgin Operation)
Thamesville (Ontario) Study
This study was conducted jointly by the Ministries of Transportation and the Environ-
ment of the Province of Ontario. Results are available only in preliminary form.05'3"5 The
study consisted of field trials conducted at.a drum-mix plant in Thamesville, Ontario. Stack
emissions were monitored during mixing of conventional hot-mix asphalt pavement (HMA)
and rubber-modified hot-mix asphalt concrete (RUMAC).
The drum-mix plant was a Boeing Model 200 equipped with a Venturi scrubber. The
Genco burner on the plant was fueled by No. 2 stove oil during the trials. Coarse and fine
aggregates entered the drum at the burner end. CRM, constituting 2 percent by weight of
the aggregate, was added directly to the drum (dry process) 3.5 m from the nonburner end.
Asphalt cement (Petro-Canada 85-100 penetration grade), making up 5.3 percent of the HMA
formula and 6.1 percent of the RUMAC formula, was added to the drum 4.1 m from the
nonburner end. These discharge points were roughly two-thirds of the way up the drum
towards the burner end; mixing time in the drum was approximately 1 min. The burner
27
-------
flame was encased in a pyrocone to prevent pyrolysis of the asphalt binder and CRM. A
dense-graded mix (HL 4) was used as the base for both the HMA and RUMAC. CRM
added to the RUMAC was #4 mesh size. The mixing plant operated at a production rate of
140 to 162 Mg/h during the emissions testing. Mix temperature averaged 154 °C at
discharge from the drum.
Emissions were monitored in the main exhaust stack of the plant using the Metals
Sampling Train, Trace Organics Sampling Train, Volatile Organics Sampling Train (VOST),
Fluorides Sampling Train, and Continuous Emissions Monitoring for combustion gases.
Four trials were conducted for the standard mix and three trials were conducted for the
asphalt-rubber mix (except that there were four trials for VOST testing of the asphalt-rubber
mix). Emission rates (mg/Mg asphalt concrete produced) were calculated from measured
stack concentrations by taking into account stack conditions, such as percent moisture in
stack gas, stack pressure, and stack velocity, at the time of monitoring.
The results of the emissions tests at the Thamesville plant are shown in table 5.
Emission rates for elements during mixing of conventional asphalt ranged from
< 0.01 mg/Mg for silver to > 2,000 mg/Mg for calcium. For most elements, emission
rates were lower during mixing of RUMAC than during mixing of HMA. The largest
difference was a 70-percent lower emission rate for boron from RUMAC than from HMA.
Silver and tellurium were the only elements that were detected only during mixing of HMA
and not during mixing of RUMAC. However, both of these elements were found in minute
concentrations close to apparent detection limits; thus, only a slightly lower emission
concentration from RUMAC would have resulted in nondetection of the two elements.
Emission rates were slightly (less than twofold) higher for a few elements (antimony,
selenium, and vanadium) emitted at relatively low concentrations during mixing of RUMAC
(< 5 mg/Mg). Bismuth was the only element released during mixing of RUMAC, but not
HMA; however, only small amounts of bismuth were emitted during mixing of RUMAC
(< 0.5 mg/Mg). Although emission rates of most elements (including those with the highest
emission rates such as calcium, magnesium, and iron) were lower during mixing of RUMAC
than mixing of HMA, total particulate emissions were higher (34 g/Mg, HMA; 62 g/Mg,
RUMAC). The difference in the mean particulate emissions was less than twofold, but
noteworthy because of the relatively large amounts involved. Among gaseous inorganic
compounds, there were slightly (less than 30 percent) lower emission rates for hydrogen
chloride and fluorides and slightly (less than twofold) higher emissions for nitric acid and
sulfuric acid during mixing of RUMAC than during mixing of HMA.
For PAH, which constitute the bulk of the semivolatile compounds monitored, emission
rates during mixing of HMA ranged from < 0.01 mg/Mg for acenaphthene and m-terphenyl
to 271 mg/Mg for 9,10-dimethylanthracene. Emission rates of PAH were higher during
mixing of RUMAC than during mixing of HMA. Total semivolatile emission rates were
3.5-fold higher (555 mg/Mg, HMA; 1,932 mg/Mg, RUMAC) and there was a remarkably
consistent pattern of threefold to ninefold higher emission rates for most individual PAH.
The most notable exception to this pattern was 7,12-dimethylbenzo[a]anthracene, which was
emitted in relatively small quantities (1 mg/Mg) during mixing of HMA, but was not
28
-------
Table 5. Emission factors (mg/Mg) from the Thamesville (Ontario) study.
Conventional HMA
Contaminant
Inorganics
Aluminum
Antimony
Arsenic
Barium
Beryllium
Bismuth
Boron
Cadmium
Calcium
Chromium
Cobalt
Copper
Iron
Lead
Lithium
Magnesium
Manganese
Mercury
Molybdenum
Nickel
Phosphorus
Potassium
Selenium
Silicon
Silver
Sodium
Strontium
Tellurium
Tin
Titanium
Vanadium
Zinc
Total cations +anions
Total paiticulates
Hydrogen chloride
Nitric acid
Sulfuric acid
Fluorides
Mean
442
0.0802
0.632
5.56
0.0365
BDL
12.5
0.0537
2347
2.43
1.07
3.1
903
1.77
0.68
1806
36.7
0.682
0.842
65.7
13
242
0.0537
162
0.00575
97.5
3.57
0.0115
2.85
5.35
2.03
8.91
10,482
33,735
109
233
3930
42.3
/Standard \
I Error /
(79)
(0.0136)
(0.228)
(0.2)
(0.0069)
—
(5.4)
(0.0137)
(516)
(0.57)
(0.19)
(0.5)
(181)
(0.11)
(0.12)
(1,201)
(5.9)
(0.201)
(0.130)
(5.3)
(3)
(38)
(0.0212)
(36)
(0.00575)
(28.8)
(0.75)
(0.0115)
(1.01)
(0.96)
(0.26)
(1.47)
— •
(3,880)
(26)
(23)
(236)
(8.2)
Modified HMA
Mean
331
0.143
0.401
4-68
0.0155
0.418
3.47
0.0316
2193
1.21
0.512
1.73
607
1.44
0.552
585
21.5
0.46
0.51
37.4
8.4
181
0.0916
117
BDL
53.2
3.07
BDL
3.33
5.46
2.93
6.2
10,999
62,038
94.1
409
6314
30.4
/Standard \
\ Error /
(64.5)
(0.012)
(0.204)
(1.16)
(0.007)
(0.418)
(2.08)
(0.0069)
(494)
(0.08)
(0.030)
(0.24)
(105)
(0.27)
(0.099)
(111)
(3.2)
(0.11)
(0.13)
(12.7)
(1.7)
(43)
(0.0561)
(14)
—
(4.3)
(0.74)
—
(1.85)
(0.57)
(0.12)
(1.4)
— •
(29,012)
(15.2)
(52)
(182)
(5.6)
Modified:
Conventional HMA
0.75
1.78
0.63
0.84
0.42
' —
0.28
0.59
0.93
0,50
0.48
0.56
0.67
0.81
0.81
0.32
0.59
0.67
0.61
0.57
0.65
0.75
1.71
0.72
0.00
0.55
0.86
0.00
1.17
1.02
1.44
0.70
1.05
1.84
0.86
1.76
1.61
0.72
29
-------
Table 5. Emission factors (mg/Mg) from the Thamesville (Ontario) study (Continued).
Conventional HMA
Contaminant
Semivolatiles
Accnaphthene
Acenaphthylene
Anthracene
Benzo[a]anthracene
Benzo[b]fluoranthene
Benzo[k]fluoranthene
Benzo[a]fluorene
Benzo[b]fluorene
Bcnzo[ghi]perylene
Benzo[a]pyrene
Benzo[e]pyrene
Biphenyl
9, 10-Dimethylanthracene
7,12-Dimethylbenzo[a]-
anthraccne
Fluoranthene
Fluorene
Indeno[123cd]pyrene
2-McJhylanthracene
l-Methylnaphthalene
2-Mcthylnaphthalene
1-Methylphenanthrene
9-Methylphenanthrene
Naphthalene
Perylene
Phenanthrene
Pyrene
m-Terphenyl
o-Teiphenyl
Triphenylene/chrysene
Chlorinated dibenzodioxins
Chlorinated dibenzofurans
Chlorobenzenes
Chlorophenols
Polychlorinated biphenyls
Total scmivolatile organics
Mean
0.00731
1.797
3.475
0.473
0.576
0.861
2.158
0.829
0.119
0.117
0.101
7.628
270.973
0.969
0.59
8.748
BDL
3.795
24.797
35.093
16.124
5.245
153.846
0.736
12.043
1.575
0.00859
0.151
2.208
0.000195
0.0026
0.00349
0.0142
0.0597
555.121
/Standard \
\ Error /
(0.00731)
(0.791)
(0.973)
(0.128)
(0.121)
(0.577)
(0.291)
(0.162)
(0.050)
(0.038)
(0.038)
(2.746)
(96.195)
(0.969)
(0.19)
(3.193)
—
(1.385)
(17.606)
(25.618)
(4.676)
(1.705)
(62.308)
(0.217)
(4.336)
(0.433)
(0.00515)
(0.082)
(0.607)
(0.000122)
(0.0022)
(0.00033)
(0.0048)
(0.0224)
Modified HMA
Mean
3.996
6.3
11.143
1.718
1.827
0.931
5.972
2.22
0.566
0.462
0.489
32.653
858.744
BDL
4.074
30.335
0.0257
13.436
110.267
138.79
53.72
17.618
568.269
2.822
45.845
9.156
0.0797
0.68
8.004
0.000273
0.000092
0.755
0.659
0.095
1931.66
/Standard \
I Error /
(3.991)
(2.6)
(4.825)
(0.694)
(0.707)
(0.387)
(2.689)
(0.95)
(0.186)
(0.120)
(0.223)
(16.024)
(421.427)
(1.741)
(13.135)
(0.0257)
(6.516)
(55.386)
(68.91)
(24.19)
(8.137)
(252.630)
(1.140)
(21.969)
(4.229)
(0.0796)
(0.42)
(3.512)
(0.000273)
(0.000060)
(0.296)
(0.365)
(0.056)
Modified:
Conventional HMA
546.65
3.51
3.21
3.63
3.17
1.08
2.77
2.68
4.76
3.95
4.84
4.28
3.17
0.00
6.91
3.47
3.54
4.45
3.95
3.33
3.36
3.69
3.83
3.81
5.81
9.28
4.50
3.63
1.40
0.04
216.33
46.41
1.59
3.48
30
-------
Table 5. Emission factors (mg/Mg) from the Thamesville (Ontario) study (Continued).
Conventional HMA
Contaminant
Volatiles
Acetone
Benzene
Bromomethane
2-Butanone
Carbon disulfide
Chlorobenzene
Chloro ethane
Chloromethane
Ethylbenzene
Methylene Chloride
4-Methyl-2-pentanone
Styrene
Tetrachloroethene
Toluene
1,1, 1-Trichloroethane
Trichloroethene
Trichlorofluoromethane
Vinyl chloride
Xylenes (total)
Total volatile organics
Mean
1.54
234
0.0534
16.8
40.4
0.0259
0.111
617
172
1.72
BDL
127
BDL
312
0.0693
BDL
0.115
1.13
895
2419
/Standard \
I Error /
(0.32)
(52)
(0.0315)
(10.8)
(5.7)
(0.0259)
(0.067)
(528)
(80)
(1.46)
—
(46)
—
(122)
(0.0398)
—
(0.092)
(0.66)
(510)
Modified HMA
Mean
4.2
206
0.0142
8.97
84.2
BDL
0.0183
175
48.8
2.74
130
89
0.0201
252
0.947
0.957
0.0136
0.193
319
1,322
/Standard \
\ Error /
(2.2)
(42)
(0.0142)
(1.62)
(5.0)
. —
(0.0183)
(11)
(6.8)
(2.68)
(51)
(32)
(0.0201)
(49)
(0.554)
(0.933)
(0.0136)
(0.193)
(83)
—
Modified:
Conventional HMA
2.73
0.88
0.27
0.53
2.08
0.00
0.16
0.28
0.28
1.59
—
0.70
— ,
0.81
13.67
—
0.12
0.17
0.36
0.55
BDL = below detection limit
31
-------
detected during mixing of RUMAC. Indeno[l,2,3-cd]pyrene was detected only during
mixing of RUMAC, but at very low levels (0.03 mg/Mg) close to the apparent detection
limit.
Emission rates among chlorinated semivolatiles during mixing of HMA were very low,
ranging roughly from 0.0002 mg/Mg for polychlorinated dibenzodioxins to 0.06 mg/Mg for
polychlorinated biphenyls. Emissions of most of these compounds were higher during
mixing of RUMAC. For chlorobenzenes and chlorophenols, the differences were large
(46-fold to 216-fold), while for polychlorinated dibenzo-^-diodns (PCDD), and
polychlorinated biphenyls (PCB) the differences were small (less than twofold). In contrast
to these results, emission rates for polychlorinated dibenzofurans (PCDF) were 96 percent
lower during mixing of RUMAC than during mixing of HMA.
Emission rates for volatile organic chemicals during mixing of HMA ranged from
0.03 mg/Mg for chlorobenzene to 895 mg/Mg for mixed xylenes. Emission rates of most
volatile organic compounds were lower during mixing of RUMAC than during mixing of
HMA. The difference was close to 70 percent for those chemicals having the greatest
emission rates (xylenes, chloromethane). Emissions of total volatile organics were lower by
roughly 45 percent during mixing of RUMAC (2,400 mg/Mg, HMA; 1,300 mg/Mg,
RUMAC). Although most volatile organic compounds were emitted at lower rates during
mixing of RUMAC than during mixing of HMA, there were several exceptions. Acetone
and methylene chloride were emitted at higher rates from RUMAC, but the results for these
chemicals are suspect because both of them are potential laboratory-introduced contaminants.
Carbon disulfide was also emitted at a higher rate from RUMAC, although the difference
was only twofold. 1,1,1-Trichloroethane was emitted at a tenfold higher rate from RUMAC
than HMA; however, the emission rate from RUMAC was still relatively low (1 mg/Mg).
The most striking finding among volatile organics was the emission of relatively large
quantities (130 mg/Mg) of 4-methyl-2-pentanone (methyl isobutyl ketone) during mixing of
RUMAC. This compound was not detected during mixing of HMA. The emission rate of
130 mg/Mg for 4-methyl-2-pentanone means that during mixing of RUMAC this compound
had the fourth highest emission rate among volatile organics, after xylenes (319 mg/Mg),
toluene (252 mg/Mg), and benzene (206 mg/Mg), and accounted for 10 percent of all volatile
emissions. Two other chemicals, trichloroethene and tetrachloroethene, were also detected
only during mixing of RUMAC, but emission rates for these chemicals were relatively low
(1 and 0.02 mg/Mg, respectively).
Haldimand-Norfolk (Ontario) Study
Contained in one of the reports on the Thamesville, Ontario study were the results of a
study of emissions from a batch plant during mixing of conventional HMA and HMA
modified with CRM.^ This study was conducted by the Regional Municipality of
Haldimand-Norfolk within the Province of Ontario. Details regarding the mixing process
and the addition of CRM at this plant were not located. Sampling methods appear to have
been similar to those used in the Thamesville study; except for the absence of the fluorides
sampling train, the lists of chemicals monitored in the two studies are almost identical.(34>36)
In the Haldimand-Norfolk study, three trials were conducted for the CRM asphalt mix and
32
-------
for VOST testing of the standard mix. Emission rates (mg/Mg asphalt concrete produced)
were calculated from measured stack concentrations by taking into account stack conditions
at the time of monitoring.
The results of the emissions tests are shown in table 6. Emission rates for inorganic
elements during batch mixing of conventional HMA ranged from 0.07 mg/Mg for tellurium
to 155 g/Mg for calcium. For most inorganics, emission rates were lower during batch
mixing of modified HMA than during mixing of conventional HMA. Differences came close
to 90 percent for a few elements (chromium, selenium). Tin was detected only during
mixing of conventional HMA. The emission rate for tin from conventional HMA was
relatively low (11 mg/Mg), but still larger than those of several other elements. The
emission rate of copper was sixfold higher during mixing of modified HMA, but was still
relatively low (less than 10 mg/Mg). Slightly (less than twofold) higher emission rates from
modified HMA occurred for several elements (i.e., barium, lithium, magnesium, mercury,
silicon, sodium, strontium). Bismuth was emitted at a rate of 13 mg/Mg during mixing of
modified HMA, but was not detected during mixing of conventional HMA. Total particulate
emissions from the batch plant were very high (approaching 1 kg/Mg) for both conventional
and modified HMA; emissions were slightly higher during mixing of modified HMA
(910 g/Mg) than during mixing of conventional HMA (710 g/Mg).
Emission rates for PAH ranged from 0.001 mg/Mg for /Herphenyl to 65 mg/Mg for
naphthalene during mixing of conventional HMA. Emissions of most PAH were higher
during mixing of modified HMA. The differences were mostly between twofold and
fourfold, although emission rates.of m- and ^-terphenyls from modified HMA were more
than tenfold higher than from conventional HMA. The most notable finding among
semivolatile chemicals was the emission of 7.4 mg/Mg of tetralin during mixing of modified
HMA. This was the fourth highest emission rate among semivolatiles emitted from the batch
plant during mixing of modified HMA, after naphthalene (22 mg/Mg), 2-methylnaphthalene
(8.5 mg/Mg), and 9,10-dimethylanthracene (7.5 mg/Mg), and it accounted for 12 percent of
total semivolatile emissions. Tetralin was not detected during mixing of conventional HMA.
Although emissions were higher for most PAH during mixing of modified HMA, total
semivolatile emissions were lower (95 mg/Mg, conventional HMA; 59 mg/Mg, modified
HMA). This reflects the fact that the emission rate of naphthalene, the PAH with the highest
rate of emission, was lower by 65 percent. Lower emission rates were also seen for
1-methylnaphthalene and 2-methylnaphthalene, two of the other PAH emitted at high rates.
Acenaphthene and 7,12-dimethylbenzo[a]anthracene were detected only during mixing of
conventional HMA. Although emission rates for these chemicals were relatively low (0.6
and 0.2 mg/Mg, respectively), they were higher than emission rates for many other PAH.
Emission rates of chlorinated semivolatiles ranged from 0.0001 mg/Mg for PCDD to
0.02 mg/Mg for PCB during mixing of conventional HMA. Mixing of modified HMA
produced small amounts of PCDF (0.0003 mg/Mg) and chlorophenols (0.02 mg/Mg), which
were not emitted during mixing of conventional HMA. Emission rates of chlorobenzenes
and PCB were slightly (less than twofold) higher during mixing of modified HMA, while
emissions of PCDD were 80 percent lower.
33
-------
Table 6. Emission factors (mg/Mg) from the Haldimand-Norfolk (Ontario) study.
Contaminant
HMA
Inorganics
Aluminum
Antimony
Arsenic
Barium
Beryllium
Bismuth
Boron
Cadmium
Calcium
Chromium
Cobalt
Copper
Iron
Lead
Lithium
Magnesium
Manganese
Mercury
Molybdenum
Nickel
Phosphorus
Potassium
Selenium
Silicon
Sodium
Strontium
Tellurium
Tin
Titanium
Vanadium
Zino
Total cations +anions
Total particulates
Hydrogen chloride
Conventional HMA
/Standard \
Mean \ Error /
2,531 —
1.15 -
2.92 —
122 —
0.432 —
BDL —
36.7 —
0.252 —
15,5351 -
36.1 —
3.74 -
1.19 —
5,660 —
5.29 —
2.3
80,758 —
237 —
1.26 —
12.7 —
21 —
128 —
1,265 -
0.864 —
638 —
222 —
4,074 —
0.072 —
10.7 -
69.4 -
8.14 -
32.8 —
251,371 -
714,481 -
139 —
Modified HMA
Mean
1,899
0.492
2.09
160
0.228
13.4
17.1
0.156
145,722
4.63
2.71
6.67
3,776
5.11
2.75
88,526
210
1.57
2.36
8.32
86.6
1,136
0.12
857
445
6,022
0.036
BDL
61.8
5.11
21.1
249,096
908,445
102
/Standard \
I Error /
(603)
(0.335)
(0.95)
(391)
(0.043)
(8.9)
(2.0)
(0.012)
(22,714)
(2.06)
(0.60)
(2.234)
(1,657)
(1.39)
(0.27)
(4089)
(18)
(0.06)
(0.42)
(2.02)
(33.5)
(164)
(0.09)
(317)
(54)
(1,286)
(0.036)
(26.0)
(1.95)
(7.1)
(62,939)
(25)
Modified:
Conventional
0.75
0.43
0.72
1.31
0.53
0.47
0.62
0.94
0.13
0.72
5.61
0.67
0.97
1.20
1.10
0.89
1.25
0.19
0.40
0.68
0.90
0.14
1.34
2.00
1.48
0.50
0.00
0.89
0.63
0.64
0.99
1.27
0.73
34
-------
Table 6. Emission factors (mg/Mg) from the Haldimand-Norfolk (Ontario) study (Continued).
Contaminant
HMA
Semivolatiles
Acenaphthene
Aoenaphthylene
Anthracene
Benzo[a]anthracene
Benzo [b] fluoranthene
Benzo[k]fluoranthene
Benzo[a]fluorene
Benzo [b]fluorene
Benzo[ghi]perylene
Benzo[a]pyrene
Benzo[e]pyrene
Biphenyl
Coronene
9,10-Dimethylanthracene
7,12-Dimethylbenzo[a]-
anthracene
Fluoranthene
Fluorene
Indeno[123cd]pyrene
2-Methylanthracene
1-MNethylnaphthalene
2-Methylnaphthalene
1-Methylphenanthrene
9-Methylphenanthrene
Naphthalene
Perylene
Phenanthrene
Pyrene
m-Terphenyl
o-Terphenyl
/7-Terphenyl
Tetralin
Triphenylene/Chrysene
Chlorinated dibenzodioxins
Chlorinated dibenzofurans
Chlorobenzenes
Conventional HMA
/Standard \
Mean V Error /
0.638 —
1.007 —
0.0159 —
0.007990 —
0.0489 —
0.0218 —
0.0282 -
0.0224 -
0.0969 —
0.004930 —
0.0172 —
1.277 —
0.0351 —
4.681 —
0.223 —
0.279 . -
0.502 —
0.007270 —
0.0245 —
7.58 —
11.106 —
0.431 —
0.141 —
65 —
0.003670 —
0.894 —
0.367 —
0.0036 —
0.0312 —
0.001010 —
BDL —
0.0888 —
0.000122 —
BDL —
0.007690 —
Modified HMA
Mean
BDL
0.499
0.0245
0.0246
0.124
0.099
0.122
0.0486
0.111
0.0418
0.0757
1.9
0.0364
7.538
BDL
0.218
0.612
0.0281
0.0239
5.942
8.477
0.876
0.276
22.343
0.004
1.181
0.295
0.162
0.124
0.0823
7.365
0.238
0.000025
0.000342
0.009140
/Standard \
\ Error /
—
(0.124)
(0.0190)
(0.0124)
(0.067)
(0.055)
(0.013)
(0.0306)
(0.047)
(0.0389)
(0.0586)
(0.1)
(0.0090)
(2.829)
—
(0.059)
(0.057)
(0.0201)
(0.0239)
(0.103)
(0.294)
(0.142)
(0.033)
(3.354)
(0.005)
(0.416)
(0.003)
(0.004)
(0.009)
(0.0043)
(0.723)
(0.036)
(0.000025)
(0.000130)
(0.001003)
Modified:
Conventional
0.00
0.50
1.54
3.08
2.54
4.54
4.33
2.17
1.15
8.48
4.40
1.49
1.04
' 1.61
0.00
0.78
1.22
3.87
0.98
0.78
0.76
2.03
1.96
0.34
1.09
1.32
0.80
45.00
3.97
81.49
—
2.68
0.21
—
1.19
35
-------
Table 6. Emission factors (mg/Mg) from the Haldimand-Norfolk (Ontario) study (Continued).
Conventional HMA Modified HMA
Contaminant
HMA
Semivolatilcs (continued)
Chlorophenols
Polychlorinated biphenyls
Total semivolatile organics
Volatiles
Acetone
Benzene
Bromodichloromethane
Bromomethane
2-Butanone
Carbon Disulfide
Chlorocthane
Chloromethane
1,1-Dichloroethane
1 ,2-Diohloro ethane
1 , 1-Dichloroethene
Ethylbcnzene
2-hexanone
Mcthylene chloride
4-methyl-2-pentanone
Styrcne
Tetrachlorocthene
Toluene
1,1, 1-Trichloroethane
Trichloroethene
Trichlorofluoromethane
Vinyl acetate
Vinyl chloride
Xylencs (total)
Total volatile organics
Mean
BDL
0.0243
94.619
BDL
42.2
0.0409
BDL
0.243
49.7
0.121
4.05
16.7
2.34
0.255
10.9
BDL
21.3
BDL
5.87
BDL
30.6
7.51
BDL
0.212
BDL
0.0459
57.4
249
/Standard \
\ Error / Mean
— 0.0203
— 0.0406
— 58.964
— 27.2
— 29
— BDL
— 0.0229
— 5.33
— 36.7
— 0.316
— 15.1
— 17.7
— 0.558
— 0.683
— 16
— 2.18
— 28.7
— 15.8
- 7.5
— 0.526
— 36.1
— 16.9
- 0.42
— 0.415
- 3.7
— 0.0571
— 65.9
— 327
/Standard \
\ Error /
(0.0056)
(0.0159)
(15.1)
(3)
(0.0229)
(2.95)
(5.3)
(0.073)
(1.8)
(3.1)
(0.303)
(0.682)
(4)
(2.18)
(6.0)
(4.4)
(2.6)
(0.209)
(7.1)
(7.4)
(0.15)
(0.057)
(2.0)
(0.0570)
(15.2)
Modified:
Conventional
1.67
0.62
0.69
0.00
_
21.93
0.74
2.61
3.73
1.06
0.24
2.68
1.47
1.35
,L
1.28
1.18
2.25
_
1.96
1.24
1.15
1.31
BDL — below detection limit
36
-------
During mixing of conventional HMA, emission rates for volatile organic chemicals
ranged from 0.04 mg/Mg for bromodichloromethane to 57 mg/Mg for mixed xylenes; the
rate for total volatile organics was 250 mg/Mg. During mixing of modified HMA, emissions
of total volatile organic compounds were slightly higher (330 mg/Mg). Emissions of most
individual volatiles were higher as well during mixing of modified HMA, although most of
the observed differences were less than twofold. The most notable exception was
2-butanone, which had an emission rate from modified HMA that was more than tenfold
higher than that from conventional HMA (0.24 mg/Mg, conventional HMA; 5.3 mg/Mg,
modified HMA). Several volatile organic compounds were detected only during mixing of
modified HMA. These included chemicals emitted in small amounts (< 1 mg/Mg:
bromomethane, trichloroethene, and tetrachloroethene), moderate amounts (2 to 4 mg/Mg:
2-hexanone and vinyl acetate), and relatively large amounts (> 15 mg/Mg:
4-methyl-2-pentanone and acetone). The emission rate of 16 mg/Mg for 4-methyl-
2-pentanone made up 5 percent of total volatile emissions during mixing of modified HMA.
The results regarding acetone are suspect because acetone is a potential laboratory contami-
nant during VOST analysis. Bromodichloromethane was the only volatile organic compound
that was emitted during the mixing of conventional HMA, but not during mixing of modified
HMA. However, it was emitted in very small quantities (0.04 mg/Mg).
Farmer County (Texas) Study
A joint study by the Texas Department of Transportation and Texas Air Control Board
included monitoring of stack emissions during mixing of HMA and ARHM at a drum-mix
plant in Farmer County, Texas.(37) The drum-mix plant was a Barber-Greene plant equipped
with a Venturi scrubber. CRM was added to the mix by the wet process (i.e., it was added
to the asphalt binder before the binder was mixed with the aggregates in the drum). CRM
was added to the mix at 18 percent by weight of the binder. The percent of binder used in
the mix was not reported. The mixing plant operated at a production rate of 287 to
302 mg/h during the emissions testing. Mix temperature was 171 °C (340 °F) during
mixing of HMA. ARHM was mixed at 171 °C (340 °F) and 150 °C (302 °F) in separate
trials. Other production details were not available.
Emissions were monitored in the exhaust stack of the plant for total particulates (EPA
method 5 and TACB method 23), total hydrocarbons (EPA method 25A), formaldehyde
(EPA method 0011), semivolatile organic chemicals (EPA modified method 5), and selected
volatile organic chemicals (VOST). Three trials were conducted for each test condition
[HMA, ARHM at 171 °C (340 °F), and ARHM at 150 °C (302 °F)]. The duration of the
trials for total particulate, formaldehyde, and semivolatile was 62.5 min, while that for
VOST chemicals was 20 min. All testing was conducted over a 3-d period. Emission rates
were calculated as pounds per hour from measured stack concentrations by taking into
account stack conditions at the time of monitoring. For this report, emission rates were
converted to units of mg/Mg asphalt pavement produced by dividing the emission rate (Ib/h)
by the plant production rate (ton/h) and converting to metric units. This adjustment was
made so that the data could be directly compared with the data from the Thamesville
(Ontario) and Haldimand-Ndrfolk (Ontario) studies.
37
-------
Emission rates at the Farmer County drum-mix plant are shown in table 7. Emissions of
total particulates were approximately 27 g/Mg for HMA. Particulate emissions were slightly
higher (less than a twofold difference) during mixing of ARHM at 171 °C (340 °F).
Particulate emissions during mixing of ARHM at 150 °C (302 °F) were 50 percent lower
compared to ARHM at 171 °C (340 °F).
Emission rates for semivolatile organic compounds during mixing of HMA ranged from
approximately 3 mg/Mg for 2-methylphenol and n-nitrosodiphenylamine to approximately
800 mg/Mg for formaldehyde. Differences between HMA and ARHM at 171 °C (340 °F)
were not substantial. The largest difference was a fourfold higher emission rate for acenaph-
thene from ARHM. Emission rates of other chemicals were either less than twofold higher
(e.g., 2-methylnaphthalene, anthracene, n-nitrosodiphenylamine, and butyl benzyl phthalate)
or less than 50 percent lower (e.g., formaldehyde, fluorene, naphthalene, phenanthrene, and
phenol). Emissions during mixing of ARHM at 150 °C (302 °F) were generally lower
compared to ARHM at 171 °C (340 °F). Although the differences were small (< 50
percent) in most cases, they approached 90 percent lower for a few chemicals (phenanthrene
and butyl benzyl phthalate). Formaldehyde and naphthalene both had slightly higher
emissions from 150 °C (302 °F) ARHM compared to 171 °C (340 °F) ARHM. Several
semivolatile chemicals were emitted only during mixing of ARHM. Pyrene (6 mg/Mg) and
4-methylphenol (25 mg/Mg) were detected only during mixing of ARHM at 171 °C
(340 °F). Dibenzofurans (30 mg/Mg) and bis(2-ethylhexyl)phthalate (5 mg/Mg) were
detected during mixing of ARHM at both temperatures, with emission rates at 150 °C
(302 °F) lower by more than 50 percent compared to 171 °C (340 °F). Isophorone was
detected only during mixing of ARHM at 150 °C (302 °F). 2-Methylphenol was the only
semivolatile chemical that was detected only during the mixing of HMA. However, the
emission rate for this chemical (3 mg/Mg) was the lowest among the semivolatile chemicals ~.
monitored.
Monitoring of volatile organic chemicals at the Farmer County drum-mix plant was
limited to benzene, styrene, and 1,3-butadiene. During mixing of HMA, styrene emissions
were roughly 80 mg/Mg and benzene emissions were roughly 1,100 mg/Mg. During mixing
of ARHM at 171 °C (340 °F), emissions of each of these chemicals were slightly
(< 10 percent) lower. Compared to emissions from CRM mixing at 171 °C (340 °F),
emissions of these chemicals during CRM mixing at 150 °C (302 °F) were higher, although
only slightly (less than twofold). 1,3-Butadiene (224 mg/Mg) was detected only during
mixing of ARHM at 150 °C (302 °F). Emission rates for total nonmethane hydrocarbons
showed a pattern similar to benzene and styrene; the rate was slightly lower during the
mixing of ARHM at 171 °C (340 °F) and slightly higher during the mixing of ARHM at
150 °C (302 °F) [94 g/Mg, conventional; 85 g/Mg, ARHM at 171 °C (340 °F); 113 g/Mg
ARHM at 150 °C (302 °F)].
San Antonio (Texas) Study
A second study, jointly sponsored by the Texas Department of Transportation and Texas
Air Control Board, was conducted at a drum-mix plant in San Antonio, Texas.(38) CRM was
added to the asphalt using the wet process. CRM made up 18 percent by weight of the
38
-------
Table 7. Emission factors (mg/Mg) from the Farmer County (Texas) study.
MD
Conventional HMA
/Standard \
Contaminant Mean \ Error /
Inorganics
Total particulate (EPA)
Total particulate (TACB)
Semivolatiles
Formaldehyde
Acenaphthene
Anthracene
Fluorene
2-Methylnaphthalene
Naphthalene
Phenanthrene
Pyrene
Bis(2-ethylhexyl)phthalate
Butyl benzyl phthalate
Dibenzofurans
Isophorone
2-Methylphenol
4-Methylphenol
n-Nitrosodiphenylamine
26,779.2
38,068.3
790.361
7.88784
20.5084
55.2148
697.285
421.21
39.4392
BDL
BDL
6.31027
BDL
BDL
3.15513
BDL
3.15513
(2,219.6)
(4,220.0)
(69.413)
(7.88784)
(20.5084)
(17.3532)
(94.654)
(48.90)
(9.4654)
—
—
(0.03155)
—
—
(3.15513)
(3.15513)
Reduced Temperature
Modified HMA Modified HMA
/Standard \ /Standard \ Modified:
Mean \ Error / Mean I Error / Conventional HMA
44791.2
71916
403.244
29.5816
31.1385
26.4677
751.995
266.234
24.9108
6.2277
4.67078
14.0123
29.5816
BDL
BDL
24.9108
6.2277
(18926)
(20402)
(160.363)
(29.5816)
(15.5693)
(26.4677)
(151.022)
(45.151)
(24.9108)
(3.1138)
(3.11385)
(0.4671)
(29.5816)
—
—
(24.9108) "
(6.2277)
26349.2
44370.8
551.887
15.3729
52.2679
19.9848
559.574
333.592
3.07458
BDL
1.53729
1.53729
12.2983
7.68645
BDL
BDL
BDL
(1532.7)
(630.3)
(210.609)
(7.6864)
(4.6119)
(10.7610)
(33.820)
(76.865)
(3.07458)
—
(1.53729)
(1.53729)
(12.2983)
(7.68645)
—
—
1.67
1.89
0.51
3.75
1.52
0.48
1.08
0.63
0.63
—
—
2.22
~~
—
0.00
1.97
Reduced
Temperature
Modified:
Conventional HMA
0.98
1.17
/\ nr\
V. I\J
1.95
2.55
0.36
0.80
OTrt
.79
0.08
_
0.24
~~
—
0.00
0.00
-------
Table 7. Emission factors (mg/Mg) from the Farmer County (Texas) study (Continued).
Conventional HMA
Contaminant
Volatiles
Phenol
Benzene
Styrene
1,3-Butadiene
Total hydrocarbons
Mean
44.1719
1075.9
82.0335
BDL
93638.1
/Standard \
\ Error /
- "
(22.0859)
(208.2)
(41.0167)
(7583.4)
Modified
Mean
20.24
949.725
77.8463
BDL
84657.9
HMA
/Standard \
1 Error /
(15.57)
(457.736)
(29.5816)
(18488.5)
Reduced Temperature
Modified HMA
Mean
16.9102
1680.26
155.266
224.444
11318
/Standard \
1 Error I
(16.9102)
(132.21)
(59.954)
(224.444)
(778)
Modified:
Conventional HMA
0.46
0.88
0.95
0.9
Reduced
Temperature
Modified:
Conventional HMA
0.38
1.56"
1.89
1.21
BDL = below detection limit
-------
binder, and the binder made up 7.5 to 9.0 percent of the asphalt pavement produced. The
plant was equipped with a baghouse rather than a scrubber and operated at a production rate
of 340 to 363 mg/h during the emissions testing. Mix temperature was 163 °C (325 F) for
HMA. ARHM was mixed at 163 °C (325 °F) and 149 °C (300 °F) in separate trials.
Other production details were not reported.
Emissions were monitored in the baghouse exhaust stack of the plant for total particulates
(EPA method 5 and TACB method 23), total hydrocarbons (EPA method 25A), semivolatile
organic chemicals (EPA modified method 5), volatile organic chemicals (VOST), and
1 3-butadiene (EPA method 18). Three trials were conducted for each test condition [HMA,
ARHM at 163 °C (325 °F), and ARHM at 149 °C (300 °F)]. Trials for total particulate,
semivolatile organics, and 1,3-butadiene lasted 60 min, while trials for VOST chemicals
lasted 20 min. All testing was conducted over a 6-d period. Emission rates were calculated
as pounds per hour from measured stack concentrations by taking into account stack
conditions at the time of monitoring. For this report, emission rates were converted to units
of mg/Mg asphalt pavement produced.
Emission rates at the San Antonio drum-mix plant are shown in table 8. Total particulate
emissions were 51 g/Mg for HMA and 10 g/Mg for ARHM at 163 °C (325 °F) Particulate
emissions for ARHM at 149 °C (300 °F) were similar to ARHM at 163 C (325 F). All
trials for emissions from HMA were conducted on the same day, and it was suggested in the
study report that baghouse failure may have inflated the numbers for particulate emissions
from HMA in this study.
The only semivolatile organic chemicals detected during mixing of HMA were 2-methyl-
naphthalene (1,600 mg/Mg), naphthalene (350 mg/Mg), and phenanthrene (120 mg/Mg).
The emission rate for total PAH during mixing of HMA was 2,100 mg/Mg. The phenan-
threne emission rate was roughly twofold higher during mixing of ARHM at 163 °C
(325 °F), but there was very little difference between emission rates of the other PAH during
HMA and ARHM mixing. Phenanthrene was not detected during mixing of ARHM at
149 °C (300 °F). For naphthalene, 2-methylnaphthalene, and total PAH, lower ARHM
temperature resulted in only slightly lower emission rates.
Emissions of VOST compounds during mixing of HMA ranged from 1 mg/Mg for
methvlene chloride to 400 mg/Mg for acrolein. Emissions of VOST compounds generally
were higher during mixing of ARHM at 163 °C (325 °F). Total VOST emissions were
threefold higher during mixing of ARHM than during mixing of HMA (1,300 mg/Mg,
HMA- 3 700 mg/Mg, ARHM at 163 °C (325 °F)). Emission rates of xylenes, ethylbenzene,
and toluene were similarly higher during mixing of ARHM at 163 °C (325 °F); these were
among the individual VOST compounds emitted at the highest rates. Emission rates for
styrene, carbon disulfide, and methylene chloride (considered to be a possible laboratory
contaminant) were 10-fold to 100-fold higher during mixing of ARHM at 163 C (325 F);
all were emitted at relatively low rates (< 10 mg/Mg) from HMA. Acrolein and acryloni-
trile which were emitted at relatively high rates from HMA, were emitted at substantially
(approximately 90 percent) lower rates from ARHM at 163 °C (325 °F). Emission rates of
volatile compounds during mixing of AEJ3M generally were lower under reduced tempera-
41
-------
Table 8. Emission factors (mg/Mg) from the San Antonio (Texas) study.
Conventional HMA
Contaminant
Inorganics
Total participate (EPA)
Total participate (TACB)
Semivolatiles
2-Methylnaphthalene
Naphthalene
Phenanthrene
Total PAH (MM5)
Volatiles
Acetone
Acrolein
Acrylonitrile
Benzene
2-Butanone
Carbon disulfide
Chlorobenzene
Ethylbenzene
Methylene chloride
4-Methyl-2-pentanone
Mean
51060.7
53085.6
1617.33
350.809
119.946
2088.08
116.076
406.525
111.82
96.9883
23.8601
7.48048
BDL
198.233
1.03179
BDL
/Standard \
\ Error /
(11465.8)
(11633.4)
(201.20)
(54.169)
(59.328)
(314.61)
(18.443)
(19.088)
(8.38)
(9.6730)
(0.5159)
(3.99819)
(10.447)
(1.03179)
Modified HMA
Mean
9737.52
12845.8
1840.46
381.762
211.517
2432.44
99.5677
52.7503
17.0245
63.842
25.2789
106.79
1.54768
560.391
96.0854
1189.52
/Standard \
\ Error /
(1134.97)
(515.9)
(130.26)
(42.561)
(10.318)
(180.56)
(31.4696)
(52.7503)
(8.5123)
(7.351)
(10.4469)
(44.37)
(1.54768)
(420.712)
(34.6939)
(1189.52)
Reduced Temperature
Modified HMA
Mean
10343.7
12936.1
1577.35
305.668
BDL
1883.02
31.2116
93.506
29.0191
81.7694
17.1535
BDL
BDL
49.3969
10.5758
BDL
/Standard \
\ Error /
(2979.3)
(2656.9)
(88.99)
(21.925)
(110.921)
—
Modified:
Conventional HMA
0.19
0.24
1.14
1.09
1.76
1.16
0.86
0.13
0.15
0.66
1.06
14.28
2.83
93.12
—
Reduced
Temperature
Modified:
Conventional HMA
0.20
0.24
0.98
0.87
0.00
0.90
0.27
0.23
0.26
0.84
0.72
0.00
0.25
10.25
-------
Table 8. Emission factors (mg/Mg) from the San Antonio (Texas) study (Continued).
Conventional HMA
Contaminant
Styrene
Toluene
Xylenes (total)
Total VOC (VOST)
1,3-Butadiene
Total speciated organics
Total hydrocarbons
Mean
5.67484
93.6349
264.396
1325.72
488.81
3902.62
34745.5
/Standard \
\ Error /
(2.83742)
(5.2879)
(9.415)
(488.81)
(2321.5)
Modified HMA
Mean
109.757
376.474
989.229
3688.26
BDL
6122
107925
/Standard \
\ Error /
(85.381)
(300.380)
(694.911)
(53756)
Reduced Temperature
Modified HMA
/Standard \
Mean \ Error /
2.57947 -
54.8138 -
63.4551 -
433.481 —
BDL -
2316.5 —
££'''71 1 /OC1A< <£N
3OO/1.1 vyjJLVW.u/
Modified:
Conventional HMA
19.34
4.02
3.74
2.78
0.00
1.57
3.11
Reduced
Temperature
Modified:
Conventional HMA
0.45
0.59
0.24
0.33
0.00
0.59
1.63
BDL = below detection limit
-------
ture conditions. These differences exceeded 90 percent for some chemicals (e.g. styrene
etnylbenzene, and xylenes) and brought emission levels for ARHM at 149 °C (300 °F) lower
than emission levels for HMA for most chemicals. Exceptions were acrolein and acryloni-
tnle, which were emitted at twofold higher rates from ARHM at 149 °C (300 °F) compared
to ARHM at 163 °C (325 °F). A striking result was the emission of large amounts of
4-methyl-2-pentanone (1,190 mg/Mg) during mixing of ARHM at 163 °C (325 °F) This
was the highest emission rate for any volatile organic during mixing of ARHM at 163 °C
(325 _ F) and made up 32 percent of total VOST emissions under these conditions This
chemical was not detected during mixing of HMA or ARHM at 149 °C (300 °F) The same
pattern was seen for chlorobenzene, but this chemical was emitted only in small amounts
(1.5 mg/Mg) during mixing of ARHM. The opposite pattern was found for 1,3-butadiene
which was emitted at a rate of 500 mg/Mg during mixing of HMA, but was not detected '
during mixing of ARHM at either temperature. Total nonmethane hydrocarbon emissions
were 35 g/Mg during mixing of HMA, 108 g/Mg during mixing of ARHM at 163 °C
(325 °F), and 57 g/Mg during mixing of ARHM at 149 °C (300 °F).
Discussion, Including Studies of Environmental Emissions From Conventional HMA
^ Emission rates of chemicals released during mixing of conventional and modified HMA
in the Thamesville (Ontario), Haldimand-Norfolk (Ontario), Farmer County (Texas) and San
Antonio (Texas) studies are presented in table 9, along with the results of other studies that
monitored stack emissions during mixing of conventional HMA without RAP ^^ Examina-
tion of table 9 shows that interstudy variance is large. For most chemicals, the interstudy
range of emission rates is similar to, or exceeds, the intrastudy differences between conven-
tional and modified HMA paving mixtures. The interstudy ranges exceed a factor of 10 for
many chemicals and a factor of 1,000 for some chemicals. Potential sources of this variation
are numerous and include type of plant, type of burner fuel, type of emission control, source
or asphalt, mix specifications, mix temperature, process by which rubber is added to the mix
and CRM particulate size and gradation, among other factors.
For most chemicals, the interstudy range of emission rates for conventional and modified
HMA overlap and exceed the differences between conventional and modified HMA emissions
observed within each study. For example, the magnitude of the higher emission rate of PAH
from RUMAC in the Thamesville (Ontario) study is relatively small compared to the
interstudy range of emission rates for PAH. This does not preclude the possibility that for a
given plant, there may be a pattern of higher PAH emissions from mixing modified as
compared to conventional HMA. However, the magnitude of the difference that derives
from the addition of CRM to the mix may be insignificant compared to differences in PAH
emissions that result from other variables (e.g., type of mixing plant). In light of the high
interstudy variability of emissions for both conventional and modified HMA it can be
argued that for most chemicals, the effect of CRM on emissions may be relatively small
compared to the effects of other variables.
Of all the potentially meaningful differences between conventional and modified HMA
emissions identified in the individual study descriptions above, only one consistent finding
44
-------
Table 9. Emission factors (mg/Mg) for conventional and modified HMA.
Conventional HMA
Contaminant
Inorganics
Aluminum
Antimony
Arsenic
Barium
Beryllium
Bismuth
Boron
Cadmium
Calcium
Chromium
Cobalt
Copper
Iron
Mean
442
2,531
40.93
0.0802
1.15
0.632
2.92
5.56
122
0.0365
0.432
0.20
BDL
BDL
12.50
36.70
0.0537
0.252
3.04
2,347
15,5351
3,140.66
2.43
36.10
1.42
1.07
3.74
3.10
1.19
903
5,660
52.78
/Standard \
I Error /
(80)
(0.0136)
(0.227)
(0.92)
(0.0069)
—
(5.37)
(0.0137)
(516)
(0.57)
(0.19) .
(0.46)
(181)
Modified HMA
Mean
331
1,899
BDL
0.143
0.492
0.401
2.09
4.68
160
0.0155
0.228
BDL
0.418
13.40
3.47
17.10
0.0316
0.156
BDL
2193
145,722
BDL
1.21
4.63
BDL
0.512
2.71
1.73
6.67
607
3,776
BDL
/Standard \
\ Error /
(65)
(603)
(0.012)
(0.335)
(0.204)
(0.953)
(1.16)
(40)
(0.0078)
(0.043)
(0.417)
(8.90)
(2.08)
(1.97)
(0.0069)
(0.012)
(494)
(22,716)
(0.08)
(2.06)
(0.030)
(0.59)
(0.24)
(2.23)
(105)
(1,657)
Reference
1
. 2
3
1
2
1
2
1
2
1
2
3
1
2
1
2
1
2
3
. 1
2
3
1
2
3
1
2
1
2
1
2
3
45
-------
Table 9. Emission factors (mg/Mg) for conventional and modified HMA (Continued).
Conventional HMA
Contaminant
Lead
Lithium
Magnesium
Manganese
Mercury
Molybdenum
Nickel
Phosphorus
Potassium
Selenium
Silicon
Silver
Sodium
Strontium
Mean
1.77
5 on
.29
OO A
.34
0.68
2.30
1,806
80,758
108.40
36.70
OOT
237
3CC
.55
0.682
1f\/r
.26
10.84
0.842
12.70
65.70
1 1
21
1OO
.22
13
128
242
1,265
0.0537
0.864
162
638
0.005750
97.50
222
3.57
4,074
/Standard \
I Error /
(0.11)
~~~
™~ ~"
(0.12)
"*~
(1201)
(5.87)
—
~~
(0.201)
—
(0.130)
(5.26)
—
~
(3)
—
(36)
(0.0212)
(37)
_
(0.005750)
—
(28.76)
BDL
(0.75)
Modified HMA
Mean
1.44
5.11
BDL
0.552
2.75
585
88,526
BDL
21.50
210
BDL
0.46
1.57
BDL
0.51
2.36
37.40
8.32
BDL
8.40
86.60
181
1,136
0.0916
0.12
117
857
BDL
BDL
53.20
445
3.07
6,022
/Standard \
\ Error /
(0.27)
(1.39)
—
(0.099)
(0.27)
(HI)
(4,089)
(3.23)
(18)
—
(0.11)
(0.06)
(0.13)
(0.42)
(12.74)
(2.02)
—
(1.70)
(33.50)
(43)
(164)
(0.0561)
(0.09)
(13)
(317)
_
—
(4.30)
(54)
(0.74)
(1,286)
Reference
1
2
3
1
2
1
2
3
1
2
3
1
2
3
1
2
1
2
3
1
2
1
2
1
2
1
2
1
2
1
2
1
2
46
-------
Table 9. Emission factors (mg/Mg) for conventional and modified HMA (Continued).
Conventional HMA
Contaminant
Tellurium
Tin
Titanium
Vanadium
Zinc
Total cations +anions
Total particulate
Semivolatiles
Formaldehyde
Acenaphthene
Acenaphthylene
Mean
0.0115
0.072
2.85
10.70
5.35
69.40
2.03
8.14
16.92
8.91
32.80
3.85
10,482
251,371
33,735
714,481
51,060.70
BDL
26,779.20
BDL
137,000
BDL
3,384.15
790.361
BDL
77
0.007310
0.638
7.887840
BDL
1.797
1.007
/Standard \
1 Error )
(0.0115)
—
(1.01)
—
(0.96)
—
(0.26)
—
—
(1.47)
—
—
—
(3,879)
—
(11,465.80)
—
(2,219.64)
—
—
—
—
(69.413)
—
—
(0.007310)
—
(7.887840)
—
(0.791) ..
_.
Modified HMA
Mean
BDL
0.036
3.33
BDL
5.46
61.80
2.93
5.11
BDL
6.20
21.10
BDL
10,999
249,096
62,038
908,445
9,737.52
10,343.70
44,791.20
26,349.20
BDL
6,934.40
BDL
403.244
551.887
BDL
3.996
BDL
29.5816
15.3729
6.30
0.499
/Standard \
\ Error ./
(0.036)
(1.85)
—
(0.57)
(26.05)
(0.12)
(1.95)
—
(1.36)
(7.07)
—
—
(104,985)
(29,012)
(62,938)
(1,134.97)
(2,979.29)
(18,926)
1,532.68
—
—
—
(160.363)
(210.609)
—
(3.991)
—
(29.5816)
(7.6864)
(2.58)
(0.124)
Reference
1
2
1
2
1
2
1
2
3
1
2
3
1
2
1
2
4
4*
5
5*
6
7
3
5
5*
6
1
2
5
5*
1
2
47
-------
Table 9. Emission factors (mg/Mg) for conventional and modified HMA (Continued).
Conventional HMA
Contaminant
Anthracene
Bcnzo[a]anthracene
Bcnzo[a]fluorene
Bcnzo[a]pyrene
Benzo[b]fluoranthene
Benzofl>]fluorene
Benzo[e]pyrenc
Bcnzo[ghi]perylene
Benzo[k]fluoranthene
Biphcnyl
Bis(2-ethylhexyl)phthalate
Butyl benzyl phthalate
Mean
3.475
0.0159
20.5084
BDL
0.71
0.473
0.007990
0.02
2.158
0.0282
0.117
0.004930
BDL
BDL
BDL
0.576
0.0489
0.40
0.05
0.829
0.0224
0.101
0.0172
0.02
0.119
0.0969
0.861
0.0218
0.05
7.628
1.277
BDL
BDL
6.310270
BDL
/Standard \
\ Error /
(0.973)
(20.5084)
—
—
(0.127710)
—
—
(0.291)
—
(0.038)
—
—
—
—
(0.120)
—
—
—
(0.162)
—
(0.038)
—
—
(0.050)
— _
(0.577)
(2.746)
(0.031551)
—
Modified HMA
Mean
11.143
0.0245
31.1385
52.2679
BDL
1.718
0.0246
BDL
5.972
0.122
0.462
0.0418
BDL
BDL
BDL
1.827
0.124
BDL
BDL
2.22
0.0486
0.489
0.0757
BDL
0.566
0.111
0.931
0.099
BDL
32.653
1.90
4.670780
1.537290
14.0123
1.537290
/Standard \
1 Error /
(4.825)
(0.0189)
(15.5693)
(4.6118)
—
(0.694)
(0.0123)
—
(2.689)
(0.013)
(0.120)
(0.0388)
—
(0.707)
(0.067)
—
(0.95)
(0.0306)
(0.223)
(0.0586)
—
(0.186)
(0.047)
(0.387)
(0.055)
—
(16.024)
(0.12)
(3.113850)
(1.537290)
(0.4671)
(1.537290)
Reference
1
2
5
5*
3
1 ,
2
3
1
2
1
2
5
5*
3
1
2
6
3
1
2
1
2
3
1
2
1
2
3
1
2
5
5*
5
5*
48
-------
Table 9. Emission factors (mg/Mg) for conventional and modified HMA (Continued).
Conventional HMA
Contaminant
Chlorobenzenes
Chlorophenols
Coronene
Dibenzodioxins
(chlorinated)
Dibenzofurans
(chlorinated)
Dibenzofurans
9 , 10-Dimethylanthracene
7,12-Dimethylbenzo[a]-
anthracene
Fluoranthene
Fluorene
Indeno[123cd]pyrene
Isophorone
2-Methylanthracene
1-Methylnaphthalene
Mean
0.003490
0.007690
0.0142
BDL
BDL
0.0351
0.000195
0.000122
0.0026
BDL
BDL
BDL
270.973
4.681
0.969
0.223
0.30
0.59
0.279
0.70
0.29
8.748
0.502
55.2148
BDL
BDL
0.007270
0.30
0.01
BDL
BDL
3.795
0.0245
24.797
7.58
/Standard \
\ Error /
(0.000332)
(0.0048)
(0.000122)
(0.002171)
—
(96.195)
(0.969)
(0.19)
(3.193)
(17.3532)
— '
—
(1.385)
(17.606)
Modified
Mean
0.755
0.009140
0.659
0.0203
BDL
0.0364
0.000273
0.000025
0.000092
0.000342
29.5816
12.2983
858.744
7.538
BDL
BDL
BDL
4.074
0.218
BDL
BDL
30.335
0.612
26.4677
19.9848
0.0257
0.0281
BDL
BDL
BDL
7.686450
13.436
0.0239
110.267
5.942
HMA
/Standard \
\ Error /
(0.296)
(0.001003)
(0.365)
(0.0056)
(0.0090)
(0.000273)
(0.000025)
(0.000060)
(0.000130)
(29.5816)
(12.2983)
(421.427)
(2.829)
E
(1.741)
(0.059)
(13.1354)
(0.056)
(26.4677)
(10.7610)
(0.0257)
(0.0201)
(7.686450)
(6.516)
(0.0239)
(55.386)
(0.103)
Reference
1
2
1
2
1
2
1
2
1
2
5
5*
1
2
1
2
6
1
2
6
3
1
2
5
5*
1
2
6
3
5
5*
1
2
1
2
49
-------
Table 9. Emission factors (mg/Mg) for conventional and modified HMA (Continued).
Conventional HMA
Contaminant
2-MethylnaphthaIene
1-Methylphenanthrene
9-McthyIphenanthrene
2-Methy]phenol
4-Methylphenol
Naphthalene
N-Nitrosodiphenylamine
Perylene
Phenanthrene
Phenol
Polychlorinated Biphenyls
Mean
1,617.33
BDL
35.093
11.106
697.285
BDL
16.124
0.431
5.245
0.141
3.155130
BDL
BDL
BDL
350.809
BDL
153.846
65
421.21
BDL
3.155130
BDL
0.736
0.003670
0.02
119.946
BDL
12.043
0.894
39.4392
BDL
10.20
44.1719
BDL
0.0597
0.0243
/Standard \
\ Error /
(201.20)
—
(25.618)
—
(94.654)
—
(4.68)
—
(1.705)
—
(3.155130)
—
—
—
(54.169)
—
(62.308)
—
(48.90)
—
(3.155130)
—
(0.217)
—
—
(59.33)
—
(4.335)
—
(9.4654).
—
—
(22.0859)
—
(0.0223)
—
Modified HMA
Mean
1,840.46
1.577.35
138.79
8.477
751.995
559.574
53.72
0.876
17.618
0.276
BDL
BDL
24.9108
BDL
381.762
305.668
568.269
22.343
266.234
333.592
6.2277
BDL
2.822
0.004
BDL
211.517
BDL
45.845
1.181
24.9108
3.074580
BDL
20.24
16.9102
0.095
0.0406
/Standard \
\ Error /
(130.26)
(88.99)
(68.91)
(0.294)
(151.022)
(33.820)
(24.19)
(0.142)
(8.137)
(0.033)
—
(24.9108)
—
(42.561)
(21.925)
(252.630)
(3.354)
(45.151)
(76.864)
(6.2277)
—
(1.140)
(0.005)
—
(10.318)
—
(21.969)
(0.416)
(24.9108)
(3.074580)
—
(15.57)
(16.9102)
(0.056)
(0.0159)
Reference
4
4*
1
2
5
5*
1
2
1
2
5
5*
5
5*
4
4*
1
2
5
5*
5
5*
1
2
3
4
4*
1
2
5
5*
3
5
5*
1
2
50
-------
Table 9. Emission factors (mg/Mg) for conventional and modified HMA (Continued).
Conventional HMA
Contaminant
Pyrene
m-Terphenyl
o-Terphenyl
p-Terphenyl
Tetralin
Triphenylene/Chrysene
Chrysene
Total PAH
Total VOC (MM5)
Total Semivolatile Organ
Volatiles
Acetone
Acrolein
Acrylonitrile
Mean
1.575
0.367
BDL
BDL
0.80
0.77
0.008590
0.0036
0.151
0.0312
BDL
0.001010
BDL
BDL
2.208
0.0888
0.12
2088.08
BDL
19.70
12.26
6816.30
555.121
94.619
116.076
BDL
1.54
BDL
406.525
BDL
111.82
BDL
/Standard \
I Error /
(0.433)
—
—
—
—
—
(0.005154)
—
(0.081)
—
—
—
—
—
(0.607)
—
—
(314.70)
—
—
—
—
—
—
(18.443)
— '
(0.32)
— .
(19.088)
—
(8.38)
—
Modified HMA
Mean
9.156
0.295
6.2277
BDL
BDL
BDL
0.0797
0.162
0.68
0.124
BDL
0.0823
BDL
7.365
8.004
0.238
BDL
2,432.44
1,883.02
BDL
BDL
BDL
1931.66
58.964
99.5677
31.2116
4.20
27.20
52.7503
93.506
17.0245
29.0191
/Standard \
\ Error /
(4.229)
(0.003)
(3.1138)
—
—
—
(0.0796)
(0.004)
(0.42)
(0.009)
—
(0.0043)
—
(0.723)
(3.512)
(0.036)
—
(180.563)
(110.917)
—
—
—
—
—
(31.4696)
—
(2.20)
(15.08)
(52.7503)
—
(8.5123)
—
Reference
1
2
5
5*
6
3
1
2
1
. 2
1
2
1
2
1
2
3
4
4*
6
3
8
1
2
4
4*
1
2
4
4*
4
4*
51
-------
Table 9. Emission factors (mg/Mg) for conventional and modified HMA (Continued).
Conventional HMA
Contaminant
Benzene
Bromodichloromethane
Bromomethane
1,3-Butadiene
2-Butanone
Carbon Bisulfide
Chlorobenzene
Chloro ethane
Chloromethane
1,1-Dichloroethane
1 ,2-Dichloroethane
1,1-Dichloroethene
Mean
96.9883
BDL
234
42.20
1075.90
BDL
BDL
0.0409
0.0534
BDL
488.81
BDL
BDL
BDL
23.8601
BDL
16.80
0.243
7.480480
BDL
40.40
49.70
BDL
BDL
0.0259
BDL
0.111
0.121
617
4.05
BDL
16.70
BDL '
2.34
BDL
0.255
/Standard \
\ Error /
(9.6730)
—
(51)
—
(208.24)
—
—
—
(0.0315)
—
(488.81)
—
—
—
(0.5159)
—
(10.84)
—
(3.998190)
—
(5.66)
—
—
—
(0.0259)
—
(0.067)
—
(527)
—
—
—
—
—
—
Modified HMA
Mean
63.842
81.7694
206
29
949.725
1,680.26
BDL
BDL
0.0142
0.0229
BDL
BDL
BDL
224.444
25.2789
17.1535
8.97
5.33
106.79
BDL
84.20
36.70
1.547680
BDL
BDL
BDL
0.0183
0.316
175
15.10
BDL
17.70
BDL
0.558
BDL
0.683
/Standard \
\ Error /
(7.3515)
—
(42)
(3)
(457.736)
(132.207)
_
—
(0.0142)
(0.0229)
_
_
(224.444)
(10.4469)
—
(1.60)
(2.95)
(44.37)
—
(5.05)
(5.30)
(1.547680)
—
—
—
(0.0183)
(0.073)
(11)
(1.83)
_
(3.07)
(0.303)
_
(0.682)
Reference
4
4*
1
2
5
5*
1
2
1
2
4
4*
5
5*
4
4*
1
2
4
4*
1
2
4
4*
1
2
1
2
1
2
1
2
1
2
1
2
52
-------
Table 9. Emission factors (mg/Mg) for conventional and modified HMA (Continued).
Conventional HMA
Contaminant
Ethylbenzene
2-Hexanone
4-Methyl-2-pentanone
Methylene Chloride
Styrene
Tetrachloroethene
Toluene
1 , 1 ,1-Trichloroethane
Trichloroethene
Trichlorofluoromethane
Vinyl Acetate
Vinyl Chloride
Mean
198.233
BDL
172
10.90
BDL
BDL
BDL
BDL
BDL
BDL
1.031790
BDL
1.72
21.30
5.674840
BDL
127
5.87
82.0335
BDL
BDL
BDL
93.6349
BDL
312
30.60
0.0693
7.51
BDL
BDL
0.115
0.212
BDL
BDL
1.1-3
0.0459
/Standard \
\ Error /
(10.447)
—
(80)
— '
—
—
—
—
—
—
(1.031790)
—
(1.46)
—
(2.837420)
—
(46)
—
(41.0167)
—
—
—
(5.2879)
—
(122)
—
(0.0398)
—
—
(0.092)
—
—
—
(0.65)
—
Modified HMA
Mean
560.391
49.3969
48.80
16
BDL
2.18
1,189.52
BDL
130
15.80
96.0854
10.5758
2.74
28.70
109.757
2.579470
89
7.50
77.8463
155.266
0.0201
0.526
376.474
54.8138
252
36.10
0.947
16.90
0.957
0.42
0.0136
0.415
BDL
3.70
01193
0.0571
/Standard \
\ Error /
(420.712)
—
(6.83)
(4.06)
-
(2.18)
(1,189.52)
—
(51)
(4.38)
(34.6939)
—
(2.68)
(5.96)
(85.381)
—
(32)
(2.64)
(29.5816)
(59.954)
(0.0200)
(0.209)
(300.380)
—
(49)
(7.09)
(0.554)
(7.41)
(0.933)
(0.15)
(0.0136)
(0.057)
(2.01)
(0.193)
(0.0570)
Reference
4
4*
1
2
1
2
4
4*
1
2
4
4*
1
2
4
4*
1
2
5
5*
1
2
4
4*
1
2
1
2
1
2
1
2
1
2
1
2
53
-------
Table 9. Emission factors (mg/Mg) for conventional and modified HMA (Continued).
Conventional HMA
Contaminant
Xylenes (Total)
Total VOC (VOST)
Total Hydrocarbons
Mean
895
57.40
264.396
BDL
1,325.72
BDL
2,419
249
11,635.50
149,932
93,638.10
BDL
34,745.50
BDL
14,000
/Standard \
I Error /
(510)
—
(9.415)
—
—
—
—
—
—
—
(7,583.36)
—
(2,321.53)
—
Modified
Mean
319
65.90
989.229
63.4551
3,688.26
433.481
1,322
327
BDL
BDL
84,657.90
113,180
107,925
56,671.10
BDL
HMA
/Standard \
\ Error /
(83)
(15.22)
(694.911)
—
_
—
(18,488.50)
(778)
(53,756)
(35106.60)
—
Reference
1
2
4
4*
4
4*
1
2
8
9
5
5*
4
4*
6 .
'Thamesville, Ontario study (U.S. FHWA, 1992)<3®
2Haldimand-Norfolk, Ontario study (U.S. FHWA, 1992)<39
3U.S. EPA, 1985'44*
4San Antonio, Texas study (Southwestern Laboratories, 1992)(38)
5Parmcr County, Texas study (WEST, 1992)07)
'Khan et al., 1977;<«> Khan and Hughes, 1977<42>
'AirNova, 1992P?>
*Gunkel and Bowles, 1985<4I)
'Bcggs, 1981^
* ~ reduced temperature; BDL = below detection limit
54
-------
emerged from comparison of all the studies together. 4-Methyl-2-pentanone (methyl isobutyl
ketone or MIBK) was detected only during mixing of modified HMA in three out of the four
comparative studies: Thamesville (Ontario), Haldimand-Norfolk (Ontario), and San Antonio
(Texas).(3S'38) It was not monitored in the Farmer County (Texas) study.(37) Furthermore,
although the levels detected during mixing of modified HMA varied over a factor of 100
between the three studies, these levels were among the highest for volatiles in each of the .
three studies, constituting 5 to 32 percent of the total volatile emissions.
The source of the MIBK emitted during mixing of modified HMA is not known for
certain. MIBK itself is not expected to be present in high concentrations in tire rubber.
However, it is plausible that MIBK is a thermal degradation product of isoprene (2-methyl-
1,3-butadiene), which is an important chemical used in the manufacture of butyl rubber.
This is consistent with the observation that the rate of emission of MIBK was higher during
mixing of ARHM at high temperatures than during mixing of ARHM at lower temperatures
in the San Antonio (Texas) study.P8)
In view of the results of monitoring studies that suggest that MIBK (108-10-1) is emitted
during mixing of HMA modified by the addition of CRM, a brief review of the environmen-
tal fate and toxicity of MIBK is presented here, based on more detailed reviews by U.S. EPA
and Krasavage et al.(45>46)
MIBK in the atmosphere reacts with photochemically generated hydroxyl radicals so that
the half-life in air is estimated to be < 1 day. This chemical has relatively high water
solubility and a low soil adsorption coefficient, suggesting that it should be highly mobile in
soil. MIBK has been identified in leachates from landfills and is a potential groundwater
contaminant.
MIBK is absorbed from the respiratoiy tract following inhalation exposure, and from the
digestive tract following oral exposure. The compound is metabolized by o>-l oxidation to
the corresponding hydroxy ketone, and carbonyl reduction to the secondary alcohol, in
guinea pigs. Excretion is predominantly in the urine.
MIBK vapor is an irritant. Acute inhalation exposure to MIBK (> 100 ppm) may
produce weakness, loss of appetite, headache, eye and throat irritation, nausea, vomiting,
and diarrhea. MIBK is also a central nervous system depressant. Acute inhalation of high
concentrations (> 1,000 ppm) can produce ataxia, unconsciousness, and death in animals,
and possibly humans as well. Following longer-term exposure by either the oral or inhala-
tion route, target organs are the kidney (increased organ weight and general nephropathy in
rats of both sexes, hyaline droplet nephropathy in male rats) and liver (increased organ
weight and hepatomegaly, without accompanying histopathological changes, in rats and mice
of both sexes). Several studies looked for, but failed to find, convincing evidence for
physical damage to the nervous system in animals exposed to MIBK for prolonged periods.
Inhalation exposure to MIBK produced fetotoxic effects (developmental delay) at an exposure
concentration (3,000 ppm) that also produced overt maternal toxicity (hypoactivity, ataxia,
partial paralysis). Studies regarding carcinogenicity of MIBK were not located, but
genotoxicity studies were mostly negative.
55
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Studies of Environmental Emissions From Asphalt Mixing Plants (RAP Operation)
New Jersey Study
, Only one study was located that investigated emissions from recycling of RAP already
containing crumb rubber. In this study, sponsored by the New Jersey Department of
Transportation, asphalt pavement containing 3 percent crumb rubber was milled and added as
RAP to an 1-5 surface course being mixed in a drum plant using a 20 percent RAP addition
rate.(47-49) The milled pavement had been applied 1 year earlier as RUMAC containing 3
percent crumb rubber added by the dry process (PlusRide* mixture #12), but had failed
prematurely due to excessive raveling. Emissions testing was limited to monitoring of
carbon monoxide, total hydrocarbon, and total particulate emissions from the stack of the
drum plant during mixing of 1-5 with 20 percent rubber-modified and conventional RAP.
Two monitoring tests, each 1 hour in duration, were conducted for both types of RAP. Both
testing sessions for rubber-modified RAP were conducted on the same day; one of the tests
for conventional RAP was also conducted on this day, while the other was conducted several
days earlier. The particulate emission rates were very similar for both types of
RAP—0.59 kg/h (1.30 Ib/h) during mixing of HMA containing conventional RAP and
0.60 kg/h (1.32 Ib/h) during mixing of HMA containing rubber RAP. The stack concentra-
tions of total hydrocarbons (dry volume of methane equivalents corrected to 7 percent O2)
were also very similar—33 ppm for conventional RAP and 29 ppm for rubber RAP.
However, there were higher stack concentrations of carbon monoxide (dry volume corrected
to 7 percent O^) during mixing of HMA containing rubber RAP (448 ppm) than during
mixing of HMA containing conventional RAP (306 ppm). Carbon monoxide emissions may
be affected by any number of variables, including humidity and temperature, and erratic
variations in carbon monoxide emissions were noted throughout this study.(48) Therefore, the
apparent finding of slightly higher carbon monoxide emissions during use of rubber-modified
RAP may not have been due to the presence of rubber in the RAP. This study, although far
from conclusive, found no clear evidence to suggest that emissions from the mixing of HMA
containing rubber RAP differed meaningfully from emissions from the mixing of HMA
containing conventional RAP.
Studies of Worker Exposure From Asphalt Mixing Plant
Operations and Road-Paving Operations
NAPA Study
A pilot study of occupational exposure to asphalt rubber fumes was recently released by
NAPA.(50) Personal and area air samples were collected during road-paving operations on
2 consecutive days in August 1992. During this study, ARHM that was prepared using the
wet process at a batch-mixing plant in Canyon County, California, was used to repave over
existing asphalt roadbase at two paving sites (one each day) in Valencia, California. The
ground rubber, a mixture of three parts tire rubber (20 to 30 mesh) to one part natural rubber
(50 mesh), was fed continuously into a mixing chamber [204 to 218 °C (400 to 425 °F)]
where it was blended with AR 4,000 standard paving-grade asphalt cement containing
56
-------
extender oil to produce an asphalt-rubber binder consisting of 20 percent ground rubber.
The binder was then transported to the asphalt-rubber reaction tank, where it was circulated
continuously for 30 to 45 min at 204 °C (400 °F). In the mixing plant, the asphalt-rubber
binder was added to aggregate to produce an open-graded ARHM surface course consisting
of asphalt-rubber binder (10 percent), crushed stone (74 percent), sand (15 percent), and
mineral filler (1 percent). At the paving sites, the ARHM material was applied to the road
surface using conventional paving equipment and techniques at temperatures ranging from
132 to 177 °C (270 to 350 °F).
Two sampling schemes were used to collect personal air samples from workers at the
paving sites. According to the primary scheme, a worker had to carry four independent
sampling trains: one to evaluate exposure to total particulate (Modified NIOSH 0500),
benzene-soluble fraction of total particulate (NIOSH 5023), PAH (NIOSH 5506), and sulfur
heterocyclics (Heritage Research Group method), and others to evaluate exposure to volatile
aromatic compounds (NIOSH 1500), 1,3-butadiene (OSHA 56), and nitrosamines (OSHA
27). Because carrying this apparatus was a burden to workers, a secondary sampling scheme
that included only the first sampling train was also used. Only a limited number of personal
air samples were actually collected. The primary sampling scheme was carried out on a
single worker, who was employed as a screedman (observes and adjusts thickness and width
of asphalt layer). The secondary sampling scheme was carried out on two additional
workers, one laborer (dumps asphalt load from trucks, observes advancement of paver,
directs trucks delivering asphalt) and one paver operator (operates/drives the paver). In
addition to personal air samples, some area air samples were also collected. Area air
samples were collected, using the primary sampling scheme, from the rear of the paving
machine and from the headspace of the liquid asphalt storage tank and the asphalt-rubber
reaction tank at the hot-mix plant. All samples were collected on both days of the study,
although two personal air samples (laborer and paver operator on day 1) were damaged in
such a way that total particulate and benzene-soluble fraction could not be determined for
these samples. Analysis of field blanks showed that background contamination with
1,3-butadiene was unacceptably
high, indicating that no meaningful interpretation of the 1,3-butadiene data was possible.
Therefore, results regarding 1,3-butadiene are not discussed further below.
Levels of total particulate in the personal air samples ranged from 0.71 to 2.16 mg/m3,
with the benzene-soluble fractions ranging from 0.29 to 1.54 mg/m3. The percent of total
particulate that was soluble in benzene ranged from 41 to 87 percent in the different samples.
Eight of the seventeen PAH that were sampled for (fluorene, phenanthrene, anthracene,
fluoranthene, pyrene, chrysene, benzo[b]fluoranthene, and benzo[e]pyrene), were detected in
at least one personal air sample and four of these (phenanthrene, anthracene, fluoranthene,
and pyrene) were detected in all six personal air samples collected. Detected concentrations
ranged from 0.67 to 9.48 /xg/m3 for fluorene, 0.80 to 9.48 j«g/m3 for phenanthrene, 0.23 to
3.79 jLtg/m3 for anthracene, 0.45 to 5.97 jug/m3 for fluoranthene, 0.11 to 2.18 jug/m3 for
pyrene, 0.11 to 0.95 ^g/m3 for chrysene, 0.08 to 0.10 /ng/m3 for benzo[b]fluoranthene, and
0.06 to 0.57 jwg/m3 for benzo[e]pyrene. None of the three sulfur heterocyclics that were
sampled for (thianthrene, dibenzothiophene, thianaphthene), were detected in any of the
personal air samples, but low molecular weight sulfur heterocyclics were detected at concen-
trations ranging from 45 to 455 /*g/m3 in all six samples. Two peaks were seen in the low-
57
-------
molecular weight region of five of the six samples. However, it was noted that
quantification of low molecular weight sulfur heterocyclics by the Heritage Research Group
method is crude and subject to error. None of the seven nitrosamines
(n-nitrosodibutylamine, n-nitrosodiethylamine, n-nitrosodimethylamine,
n-nitrosodipropylamine, n-nitrosomorpholine, n-nitrosopiperidine, and n-nitrosopyrrolidine)
or five volatile aromatic compounds (benzene, toluene, ethylbenzene, xylenes, and styrene)
sampled for, were detected in the personal air samples from the screedman who participated
in the primary sampling scheme. Comparison of the results among the different members of
the paving crew suggests that the laborer received lower exposure than the paving operator
or screedman. Total particulate, benzene-soluble fraction of total particulate and percent of
total particulate soluble in benzene were all lowest in the laborer. The laborer also had the
lowest PAH exposure and the lowest exposure to low molecular weight sulfur heterocyclics.
The screedman generally had the highest levels of exposure.
Results from area air samples collected at the rear of the paver suggest that paving crew
workers could be exposed to higher contaminant levels than revealed by personal air samples
in this study. Total particulate levels in these area samples averaged 5.54 mg/m3; the
benzene soluble fraction averaged 4.86 mg/m3 and accounted for approximately 88 percent of
the total particulate. The eight PAH detected in the personal air samples were detected in
the area air samples at concentrations similar to the highest of the personal air samples. An
additional three PAH, not found in any of the personal air samples, were detected as well:
naphthalene (10.21 /ig/m3), benzo[k]fluoranthene (0.37 ^g/m3), and dibenz[a,h]anthracene
(0.10 /tg/m3). In contrast to the results of the personal air samples, one of the sulfur
heterocyclics (dibenzothiophene) was detected in the area air samples (12.11 ywg/m3). Low
molecular weight sulfur heterocyclics were detected at concentrations of 127 to 720 /*g/m3,
and two peaks were observed. Benzene was present at the detection limit (0.07 mg/m3) in
one of the area air samples; the other volatile aromatics were not detected. Nitrosamines
were not detected, although results were available only for 1 day.
Both paving sites were located on relatively busy highways. Workers were exposed to
gasoline and diesel exhaust in addition to asphalt fumes, but this was not thought to have
significantly influenced the results. Worker smoking was limited to an occasional cigarette
by the laborer; tobacco smoke was not thought to have biased the results. Winds were light
to moderate the first day and higher on the second day, but wind direction and speed were
not thought to have influenced the sampling results; no windblown dust was observed.
At the mixing plant, area samples were collected from the headspace of the liquid asphalt
storage tank and the asphalt-rubber reaction tank. Noteworthy differences between the tanks,
other than rubber content, were higher temperature of the liquid asphalt tank [210 to 218 °C
(410jo 425 °F)] compared to the asphalt-rubber reaction tank [195 to 198 °C (383 to
386 °F)] and more stable product levels in the liquid asphalt storage tank. The same 10
PAH's were detected in the headspace of the liquid asphalt storage tank and the asphalt-
rubber reaction tank; however levels of individual PAH were higher in the former tank by as
much as fivefold (see table 10). The PAH detected were the same as those found in the area
58
-------
Table 10. PAH in tank headspace samples (>g/m3).(53)
Polyaromatic
Hydrocarbon
Naphthalene
Acenaphthylene
Fluorene
Phenanthrene
Anthracene
Fluoranthene
Pyrene
Chrysene
Benzo[b]fluoranthene
Benzo[e]pyrene
Liquid Asphalt
Storage Tank
795
6,515
1,366
2,706
398
1,102
261
1,025
471
949
Asphalt/Rubber
Reaction Tank
333
5,066
512
1,229
282
488
227
209
92
188
59
-------
sample at the paving site, with the exception of the absence of benzo[k]fluoranthene and
dibenz[a,h]anthracene and the addition of acenaphthylene. The absence of benzopc]-
fluoranthene and dibenz[a,h]anthracene is understandable because these PAH were detected at
very low limits in the paving site area sample and detection limits were thirtyfold higher in
the tank area samples due to the complex nature of the headspace fume matrix. Among the
sulfur heterocyclic compounds, both dibenzothiophene and thianaphthene were detected in
both tanks. Levels of dibenzothiophene were higher in the liquid asphalt storage tank
(5,698 ftg/m ) than the asphalt-rubber reaction tank (1,261 /xg/m3 in one sample; undetected
in the other). Levels of thianaphthene were slightly higher in the reaction tank (1,612 ^g/m3
vs. 1,226 /ig/m ). Very high concentrations of low- and high-molecular weight sulfur hetero-
cychcs were detected in both tanks, with the higher levels occurring in the liquid asphalt
storage tank. Concentrations were 323,257 ^g/m3 (88 to 94 peaks) and 151,292 ^g/m3 (28
to 30 peaks) for low- and high-molecular weight sulfur heterocyclics, respectively in the
liquid asphalt tank, compared to 161,092 ^g/m3 (77 to 78 peaks) and 73,104 jug/m3 (23 to 27
peaks), respectively, in the asphalt-rubber reaction tank. All of the volatile aromatic
compounds sampled for, were detected in area samples from both tanks. Levels of benzene
toluene, xylenes, and styrene were several-fold higher in the rubber-asphalt reaction tank '
24o^4'i?2;89' 158'24' and 9'91 mg/m3' resPectively) *an the liquid asphalt storage tank
(4.96, 11.4, 39.92, and 2.6 mg/m3, respectively). However, levels of ethylbenzene were
similar in both tanks (11.10 vs. 10.15 mg/m3). Four of the seven nitrosamines sampled for
were detected in headspace samples from the asphalt-rubber reaction tank (n-nitrosodiethyl- '
amme at 1.12 jig/m3, n-nitrosodimethylamine at 11.66 jug/m3, n-nitrosodipropylamine at
10.09 /tg/m , and n-nitrosomorpholine at 9.43 Atg/m3). Two of these were also detected at
lower concentrations in the headspace samples from the liquid asphalt storage tank (n-nitroso-
dimethylamine at 1.25 jug/m3 and n-nitrosomorpholine at 6.20
Comparison of the headspace results for the liquid asphalt storage tank and the asphalt-
rubber reaction tank might suggest that the addition of rubber leads to higher levels of
volatile aromatic compounds and nitrosamines, and lower levels of PAH and sulfur
heterocyclics. However, this is not really a valid comparison to make, due to the presence
of several confounding factors. For example, reduced levels of PAH and sulfur heterocyclics
could be due to a lower temperature in the reaction tank or depletion of these substances
from the liquid asphalt in the storage tank prior to mixing with rubber in the reaction tank.
ARPG Study
A previous study of worker exposure to asphalt emissions when using rubber-asphalt
mixes was published by ARPG.<5» In this study, workers from various mixing plants and
paving sites in southern California were monitored for exposure to total particulates (OSHA
method), total aromatic hydrocarbons (NIOSH 1500), benzene (NIOSH 1501) coal-tar pitch
volatiles (NIOSH 5023), and PAH (NIOSH 5506) using personal air sampling. The specific
PAH monitored for, were phenanthrene, anthracene, pyrene, chrysene, and benzo[a]pyrene.
A total of nine separate tests were conducted over a 2.5-year period. Four of the tests
involved the mixing or laying of ARHM, four involved the spraying of asphalt-rubber and
aggregate membrane (ARAM), and one involved the monitoring of exposure during non-
asphalt-rubber applications. The asphalt-rubber binder used in this study was a mixture of
paving-grade liquid asphalt, 15 to 17 percent automotive tire rubber, 5 percent natural
60
-------
rubber, and 2 percent extender oil (added to enhance the reaction process). Temperature
during mixing was 204 to 218 °C (400 to 425 °F). For ARHM application, the asphalt-
rubber binder was added to aggregate in the mixing chamber of the hot-mix plant, transport-
ed to the job site, and laid down using conventional paving equipment and procedures at
temperatures of 196 to 204 °C (385 to 400 °F). For ARAM application, the asphalt-rubber
binder was sprayed on the road [2.49 to 3.17 L/m2 (0.55 to 0.70 gal/yd2)] and then covered
with heated aggregate [127 to 162 °C (260 to 325 °F)] precoated with paving-grade liquid
asphalt (0.70 to 1.0 percent by weight of aggregate).
The initial test was conducted during an ARAM application in Costa Mesa on
September 8, 1988. Total aromatic hydrocarbons were monitored in an aggregate control
operator (0.62 mg/m3) and blender operator (0.95 mg/m3) at the mixing plant and a bootman
(1,63 mg/m3) at the paving site. Total particulates were monitored in a laborer/rubber feeder
(26.4 mg/m3) at the mixing plant and a raker (23.0 mg/m3) at the paving site. The second
test, conducted during an ARAM application in Whittier on December 28, 1989, involved
monitoring of two workers at the mixing plant and two workers at the paving site for
exposure to benzene. Detectable levels of benzene were not found in the personal air
samples of any of these workers. In the third test, six mixing plant workers were monitored
for exposure to benzene (n=3) or coal-tar pitch volatiles (n=3) during mixing of ARHM in
Irwindale on January 8, 1990. Neither contaminant was detected in any of the samples
collected.
Subsequent tests involved monitoring for coal-tar pitch volatiles and PAH. In test
number 4, an ARAM application in Palm Springs on March 22 and 23, 1990, monitoring
was conducted on three workers at the mixing plant (1 day only) and five workers at the
paving site (three on both days). PAH were not detected in personal air samples from any of
these workers. Coal-tar pitch volatiles ranged from undetected up to 3.0 mg/m3 in the
mixing plant workers and undetected to 0.96 mg/m3 in the paving site workers. Test number
5 was an ARHM application in the Rosemead/Whittier area on May 23 through 31, 1990.
Two workers at the mixing plant were monitored on 2 days and three or four workers at the
paving site were monitored on 3 days. PAH were not above detectable limits in any of the
samples collected. In contrast, coal-tar pitch volatiles were found in almost all samples.
Concentrations ranged from 1.0 to 4.6 mg/m3 in samples from mixing plant workers and
undetected to 7.8 mg/m3 in samples from paving site workers. Because test number 5 was
conducted in a heavily congested area, additional tests (numbers 6 and 7) of ARHM
application were conducted in low-traffic areas. Test number 6 involved monitoring of four
workers at the paving site in the residential area of Rosemead on September 17, 1990. PAH
were detected in samples from the paver operator (0.002 mg/m3), raker (0.003 mg/m3), and
one of the screedmen (0.005 mg/m3). The specific PAH identified was pyrene. Coal-tar
pitch volatiles were detected only in the sample collected from the other screedman
(0.69 mg/m3). Test number 7, conducted in residential Monterey Park on February 14 and
15, 1991, involved monitoring two workers at the mix plant on 1 day and two or three
workers at the paving site on both days. PAH were not detected in personal air samples
from mixing plant workers, but four paving worker air samples contained phenanthrene
(0.002 to 0.02 mg/m3), one contained pyrene (0.006 mg/m3), and one contained
benzo[a]pyrene (0.004 mg/m3). Coal-tar pitch volatiles were not found in samples from
mixing plant workers, but ranged from undetected up to 3.5 mg/m3 in paving-site workers.
61
-------
Test number 8 involved monitoring three paving-site workers during ARAM application
in Pasadena on September 26 and 27, 1990. Pyrene (0.003 to 0.01 mg/m3) was detected in
four personal air samples and phenanthrene (0.002 mg/m3) was detected in one. Coal-tar
pitch volatiles were detected in samples from the bootman (1.8 to 2.9 mg/m3) and the
spreader operator (0.44 to 0.90 mg/m3), but not the beltman. The final test, number 9,
involved monitoring for coal-tar pitch volatiles during manhole adjusting activities that did
not involve asphalt-rubber application. Coal-tar pitch volatiles were detected at 1.5. mg/m3 in
one sample and were undetected in the other three samples collected.
Discussion, Including Studies of Worker Exposure to Conventional Asphalt
Several studies have been conducted to monitor worker exposure to conventional asphalt
fumes. The results of these studies are summarized in tables 11 and 12. Because of
differences between the studies, only general comparisons can be made between the studies
of worker exposure to asphalt pavements modified with CRM and studies of worker exposure
to conventional asphalt pavements. The range of particulate exposure in the NAPA study
(0.71 to 2.16 mg/m3) was within the range of values reported in studies of worker exposure
to conventional asphalt pavement (0.02 to 15.1 mg/m3). Particulate levels in the ARPG
study (23 to 26 mg/m3) were somewhat higher, however. Worker exposure to PAH
appeared to be somewhat higher in the NAPA and ARPG studies than in studies of worker
exposure to conventional asphalt. Specific PAH found at higher concentrations in workers
exposed to modified asphalt pavement included anthracene, benzo[a]pyrene, fiuoranthene,
fluorene, phenanthrene, and pyrene. These results are suggestive of relationships that may
exist between occupational exposure to modified asphalt pavements and breathing air
concentrations of particulates and PAH, but do not provide any real evidence for the
existence of such relationships.
RISK CHARACTERIZATION
The available data are inadequate to develop a quantitative characterization of absolute or
relative risk associated with the production, application, recycling, or disposal of asphalt
paving mixtures modified with CRM, plastic, or glass. Numerous gaps exist in the data
needed to support hazard identification, dose-response assessment, and exposure assessment
of these mixtures. The most critical data that are lacking are environmental monitoring data
that can be used to define the "mixtures of concern" or "similar mixtures" for the purpose of
dose-response and exposure assessment. The monitoring data on modified asphalts are
limited to a few studies on air emissions during mixing of HMA modified with CRM and
two preliminary studies of worker exposure. These data are not adequate to estimate
exposure levels to humans or other organisms near or distant from these mixing facilities.
Nevertheless, the stack emission studies provide some information regarding the relative
magnitude of differences in exposure levels that might be anticipated to result from mixing of
62
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Table 11. Worker exposure to conventional asphalt fumes—particulates.
Worker Location
Mixing plant
Paving crew
Paving crew
Paving crew
Paving crew
Paving crew
Paving crew
Mixing plant
Paving crew
Total Particulate
(mg/m3)
0.1-15
0.11-0.86
0.143-1.079
0.15-5.61
0.4-15.1
0.58-0.83
0.02-1.29
0.069-4.06
0.16-0.80
Benzene-Soluble Fraction
of Total Particulate
(mg/m3)
0.011-1.7
0.03-4.4
BDL-0.756
ND
0.1-0.3
0.16-0.171
ND
0.017-0.152
0.14-0.71
Reference
AI, 1991(52)
AI, 1991(52)
NAPA, 1989(53>
Puzinauskas, 1980(54)
Brandt et al., 1985(5)
Monarca et al., 1987®
Norseth et al., 1991(5S)
Braszczynska et al.,
1987(S6)
Braszczynska et al. ,
1987(S6)
1 Cyclohexane-soluble fraction of total particulate
BDL = below detection limit; ND = not determined
63
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Table 12. Worker exposure to conventional asphalt fumes—PAH.
Worker exposure (jig/m3)
Contaminant
Acenaphthene
Acenaphthylene
Anthracene
Benzo[a]anthracene
Benzo[b] fluoranthene
Benzo[k]fluoranthene
Benzo[g,h,i]perylene
Benzo[a]pyrene
Benzo[e]pyrene
Chrysene
Dibenzo[a,h]anthracene
7, 12-Dimethylbenzo[a]anthracene
Fluoranthene
Fluorene
Indeno[l,2,3-cd]pyrene
Naphthalene
Perylene
Phenanthrene
Pyrene
Total PAH
Mixing
Plant1 <51>
BDL-4
BDL
BDL
BDL
BDL
BDL
BDL
BDL
BDL
BDL
BDL-0.38
ND
BDL-0.61
BDL-1.7
BDL-0.5
BDL-6.3
ND
BDL-0.76
BDL
ND
Paving
Crew1 <52>
BDL-6.9
BDL-8.1
BDL-0.11
BDL
BDL
BDL
BDL
BDL
BDL-0.27
BDL-0.2
BDL
ND
BDL-0.37
BDL-0.98
BDL
1.3-15
ND
BDL-1.3
BDL-0.31
ND
Paving
Crew1 <53>
BDL
BDL-8.52
BDL-0.65
BDL-0.19
BDL-0.09
BDL
BDL
BDL-0.07
BDL
BDL
BDL-0.19
ND
BDL-1.52
BDL-2.36
BDL-10.42
BDL-9.48
ND
BDL-6.29
BDL-1.55
3.10-28.41
Paving
Crew1 <"
ND
ND
ND
2.25-8.78
ND
0.01-0.05
0.03-0.10
BDL-0.02
ND
0.19-2.49
BDL-0.01
0.02-0.14
0.78-0.92
ND
0.01-0.04
ND
BDL-0.06
ND
0.33-2.14
4.32-12.99
Paving
Crew2 <">
1.26
BDL
0.13
3.50
1.03
0.67
0.19
0.61
ND
0.20
0.98
ND
1.13
0.08
0.05
0.24
ND
0.22
0.54
9.70
1 Range
2 Mean values (range not provided)
BDL = below detection limit; ND = not determined
64
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conventional vs. modified HMA. If certain very simplistic assumptions are accepted, some
conclusions can be made regarding the upper bounds on relative risk associated with
production of conventional and modified HMA. These assumptions are as follows:
• The processing methods used in the Thamesville (Ontario), Haldimand-Norfolk (Ontar-
io), Farmer County (Texas), and San Antonio (Texas) studies are representative of
methods that would be used in other plants.
• Emission rates of the chemicals monitored in these studies are good indices of exposure
levels in the immediate vicinity of the plant.
• Exposures that might result from these emissions, in the near vicinity of the plant,
represent the major determinants of the upper bound on risk that would apply to popula-
tions of all species at all locations.
The first assumption regarding processing methods is probably not valid, given that the
technology for production of asphalt pavements modified with CRM is currently evolving and
is likely to continue to evolve based on the results of performance studies. The second
assumption regarding indexing of exposure to emission rates is probably reasonable at
locations very near the asphalt plant and during the mixing process, however, it becomes
progressively less valid at other times and as the distance from the plant increases. Over this
distance, fate process will become an increasingly more important factor in defining the
exposure "mixture of concern."
The third assumption, that exposure (indexed to emission rate) is the major determinant
of risk, is extremely tenuous for the following reasons. Small differences in the level of
exposure to highly toxic chemicals, or small differences in exposure levels that persist for
long durations, can substantially impact risk. Furthermore, all of the hazardous chemicals
that are emitted from asphalt paving mixtures (conventional and modified) may not have been
monitored in the Texas and Ontario studies; some chemicals may have escaped observation
because they were not in the monitoring protocol.
If the above caveats are set aside for the sake of speculation, and the three assumptions
are accepted, it is possible to draw some limited conclusions regarding relative risk of
conventional asphalt paving mixtures vs. asphalt paving mixtures modified by the addition of
CRM. Although some differences in the emission patterns between conventional and
modified asphalt pavements were detected in studies that compared mixing of both pavements
at the same facility, for most chemicals, the magnitude of these differences were small
compared to differences between studies. This suggests that for most chemicals, differences
in emission rates resulting from the addition of CRM to the mix are smaller (or at least no
larger than) the differences produced by other factors. If the above three assumptions hold,
then it can be concluded that the risks associated with release of these chemicals from asphalt
paving mixtures modified with CRM may be no greater than the risks associated with
conventional asphalt paving mixtures (i.e., the relative risk due to release of these chemicals
may not be different from the relative risk of 1). This conclusion may not apply to
4-methyl-2-pentanone (methyl isobutyl ketone or MIBK), which was consistently observed to
be emitted from modified asphalt paving mixtures, but not conventional asphalt paving
65
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mixtures. Here again, with of the exception of the previous three assumptions, this would
suggest the possibility that the relative risk associated with release of MIBK is greater than
the relative risk of 1 (i.e., the risk associated with the release of MIBK from modified
asphalt pavement is greater than that from conventional asphalt pavement). The magnitude
of the relative risk cannot be quantified with the existing data.
SUMMARY
Although there are considerable amounts of data on individual components of asphalt
paving mixtures, rubber, plastic, and glass that are relevant to risk assessment, high quality
data on the composition, emissions, exposures, and dose-response relationships for asphalt
pavements modified with these materials are lacking. This precludes deriving estimates of
absolute or relative risk associated with production, application, recycling, or disposal of
modified vs. conventional asphalt pavements.
Studies of emissions during production of conventional and modified asphalt pavements
were analyzed to determine if the results would lead to any insight regarding relative risk
Intrastudy differences in emission rates between conventional and modified asphalt paving"
mixtures were generally smaller than interstudy differences by factors of 10 to 100 This
suggests that variables other than CRM may be more important determinants of emission
rates for most chemicals. Risks associated with the release of most chemicals from conven-
tional and modified asphalt pavements may not be significantly different. The one exception
is methyl isobutyl ketone, which was consistently observed to be emitted during mixing of
asphalt pavement modified with CRM, but not during mixing of conventional asphalt These
conclusions must be highly caveated with assumptions regarding the relationship between the
emission rates observed in these studies, and human health and environmental risks.
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Fumes," Scand. J. Work Environ. Health 15:101-105 (1989a).
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Occupational Cohort," Br. J. Ind. Med. 46:582-585 (1989b).
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20. Occupational Safety and Health Administration, "Air Contaminants: Proposed Rule "
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Roofing Materials," Am. J. Ind. Med. 2:59-64 (1981).
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the Carcinogenic Risk of Chemicals to Humans — Polynuclear Aromatic Compounds
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the Carcinogenic Risk of Chemicals to Humans — Overall Updating of IARC Mono-
graphs, Volumes 1 through 42, Lyon, France: World Health Organization (1987).
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"A Comparison of the Skin Carcinogenicity of Condensed Roofing Asphalt and Coal tar'
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bons: A Decade of Progress, pp. 609-647, Richland, VA: Battelle Press (1988).
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ment of the Mutagenicity of Road Coating Asphalt," Bull. Environ. Contam Toxicol
47(4)617-622 (1991).
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30. Pasquini, R., Monarca, S., Scassellati. Sforzolini, G., Savino, A., Bauleo, F.A., and
G. Angeli, "Urinary Excretion of Mutagens, Thioethers and D-Glucaric Acid in Workers
Exposed to Bitumen Fumes," Int. Arch. Occup. Environ. Health 61(5):335-340 (1989).
31..Schoket, B., Hewer, A.H., Grover, P.L., and D.H. Phillips, "Formation of DNA
Adducts in Human Skin Maintained in Short-Term Organ Culture and Treated With
Coal-Tar, Creosote or Bitumen," Int. J. Cancer 42:622-626 (1988a).
32. Schoket, B., Hewer, A.H., Grover, P.L., and D.H. Phillips, "Covalent Binding of
Components of Coal-Tar, Creosote and Bitumen to the DNA of the Skin and Lungs of
Mice Following Topical Application,11 Carcinogenesis 9:1253-1258 (1988b).
33. U.S. Environmental Protection Agency, Drinking Water Criteria Document for Polycy-
clic Aromatic Hydrocarbons (PAH's), ECAO-CIN-D010, Office of Health and Environ-
mental Assessment, Environmental Criteria and Assessment Office, Cincinnati, OH for
the Office of Drinking Water (1993).
34. Chapman, Q.R., The Environmental Impact of Rubberized Asphalt, Environmental
Criteria and Assessment Office, U.S. Environmental Protection Agency, Cincinnati, OH
(1993).
35. Lawrence, C.E., Killackey, B.J., and D.F. Lynch, Experimental Hot Mix Pavement with
Scrap Tire Rubber at Thamesville, Ontario: Report #1, Huron Construction Co., Ltd.,
Chatham, Ontario/Ontario Ministry of the Environment/Ministry of Transportation,
Ontario, Canada (N.D.).
36. U.S. Federal Highway Administration, "Canada's Experiences with Crumb Rubber," In
Crumb Rubber Modifier — Round Table Discussions, April 6r 1992, sponsored by the
U.S. Federal Highway Administration and the U.S. Environmental Protection Agency
(1992).
37. WEST, Inc., Stack Emissions Survey, Duinick Brothers, Inc., Farmer County, TK,
Western Environmental Services and Testing, Inc., Austin, TX, 40 pp. (1992).
38. Southwestern Laboratories, Air Pollutant Emissions Testing at Asphalt Plant Baghouse
Stack, San Antonio, Texas Facility, Southwestern Laboratories, Houston, TX (1992).
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Facility, AirNova, Inc., Pennsauken, NJ (1992).
40. Beggs, T.W., Emissions of Volatile Organic Compounds From Drum Mix Asphalt Plants,
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41. Gunkel, K.O'C. and A.L. Bowles, "Drum Mix Asphalt Plants — Maryland's Experi-
ence," In Proc. 78th Air Pollution Control Association Annual Meeting, Detroit MI
June 16-21, 1985, Paper 85-61.7, 20 pp. (1985).
42. Khan, Z.S. and T.W. Hughes, Source Assessment: Asphalt Hot Mix, Industrial Environ-
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43. Khan, A.S., Buttler, G.W., and T.H. Hughes, "Polycyclic Organic Material Emissions
From Asphalt," In Proc. 70th Air Pollution Control Association Annual Meeting,
Toronto, Ontario, Canada, June 20-24, 1977, 13 pp. (1977).
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(1985).
45. U.S. EPA Environmental Protection Agency, Health Effects Assessment for Methyl
Isobutyl Ketone, EPA 600/8-88/045, Office of Health and Environmental Assessment,
Environmental Criteria and Assessment Office, Cincinnati, OH for the Office of
Emergency and Remedial Response, Washington, DC, 24 pp. (1987).
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Clayton, and RE. Clayton (eds.), Patty's Industrial Hygiene and Toxicology, Vol. 2C
3rd ed., pp. 4747-4752, New York, NY: John Wiley & Sons (1982).
47. New Jersey Department of Transportation, Rubberized RAP Recycling: Ferry Street,
Ne\vark, New Jersey, Trenton, NJ (1992).
48. New Jersey Department of Transportation, Recycling PlusRide® Paving Mixtures: Ferry
Street, Newark, New Jersey, Trenton, NJ (1992).
49. Air Recon, Stack Sampling Report for the Asphalt Plant Stack Outlet at Mount Hope
Rock Products, Wharton, NJ, Raritan, NJ: Recon Systems, Inc. (1992).
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Corporation, Sacramento, CA for the National Asphalt Pavement Association, Lanham
MD (1993).
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Phoenix, AZ: Asphalt Rubber Producers Group (1991).
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Report. Radian Corporation, Sacramento, CA for the Asphalt Institute, College Park
MD(1991).
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(1989).
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54. Puzinauskas, N.P., Exposures of Paving Workers to Asphalt Emissions, Research Report
80-1, College Park, MD: Asphalt Institute (1980).
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pounds in Road Maintenance Workers Exposed to Asphalt," Am. J. Ind. Med. 20:737-
744 (1991).
56. Braszczynska, Z., Osinska, R., Linscneid, D., and E. Smolik, ["Polycyclic aromatic
hydrocarbons at tar- and asphalt-concrete preparation and road asphalting"], Medycyna
Pracy 38(4):359-367 (1987) (Polish).
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CHAPTER 3. ENGINEERING ASSESSMENT
CRUMB RUBBER MODIFIER
Overview
Approximately 242 million tires that are comprised of over 1.8 million megagrams (Mg)
(2 million tons) of rubber are discarded annually.(1>2) Currently, about 11 percent of these
scrap tires are used as a tire-derived fuel (TDF) source for heat or power generation. About
5 percent are exported and less than 7 percent are recycled or processed for other products.
Of this 7 percent, about 2 percent is used in tire manufacturing, 3 percent is turned into
rubber products (e.g., floor mats, mudguards, carpet padding, etc.), and 2 percent is used as
crumb rubber in asphalt pavements. This leaves 77 percent to be placed into stockpiles,
landfills, or to be illegally dumped. However, about 49 States have enacted legislation
regulating the disposal of scrap tires. At least 18 States have developed market incentive
programs for recycling or use as TDF.(1)
The disposal of scrap tires into landfills is an expensive process since tires occupy a
large space and present both a fire hazard and a health hazard.^ Landfilling fees in the U.S.
range between $31.80 and $98.00/Mg ($35 and $108/ton) for whole scrap tires.(1) Often
whole tires are not allowed in the landfill and shredding is necessary prior to disposal. With
shredding costs of about $22.70/Mg ($25/ton), the landfill fees range between $11.80 and
$40.90/Mg ($13 and $45/ton). This results in approximate savings of $0 to $34.50/Mg ($0
to $38/ton) when shredded tire rubber is used in place of whole scrap tires.
An alternative is to use shredded tires as a TDF source in power plants, tire manufac-
turing plants, cement kilns, and pulp and paper production/1-4' The high heat value of scrap
tire rubber 37.9 MJ/kg (16,000 Btu/lb) vs. 27.5 MJ/kg (12,000 Btu/lb) for most coal) makes
it a viable fuel although it is often used in combination with other fuels (composite fuel) and
burned in a fluidized bed to facilitate efficient combustion and minimize handling problems.
Alternative uses for whole tires, including erosion control, retaining walls, highway
crash barriers, reefs, and breakwaters, playground equipment, etc., do not have much
potential for significant scrap tire utilization and in some cases may be considered as
aesthetically undesirable/0
Another major approach is to process the scrap tires for use in the manufacturing of
rubber products, pavements, sludge composting, split tire products, playground gravel
substitute, pyrolosis, etc.® The generation of used tires has been drastically reduced by new
tires having greater life and the used tires being upgraded by retreading. The National Tire
Dealers and Retreaders Association claims that properly inspected retreaded tires have
lifetimes and failure rates comparable to new tires.(1) Currently, it is estimated that about 50
percent of the usable tires are being scrapped.(1) This is due to the user frequently replacing
all tires on the vehicle when only one or two are worn out.
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The following segments of this chapter of the report contain an overview of crumb
rubber modifier (CRM), processes for blending or mixing, and available methods and
applications that range from a stress-absorbing membrane (SAM) to hot-mix asphalt (HMA)
paving mixtures. Also, since there are numerous terms used in CRM technology a list of
more commonly used words and their definitions are presented in the following section.
Definitions of Terminology1
This document uses the terminology as defined below.
• Ambient Ground CRM — Crumb rubber that is produced by processing scrap tire rubber
at ordinary room temperature.
• ARM-R-SHIELD" — A trade name of the Arizona Refining Company for an asphalt
rubber produced by a wet process using about 20 percent crumb rubber (20 to 40 percent
devulcamzed and 60 to 80 percent ambient ground vulcanized, all passing through the
no. 40 sieve), 2 to 4 percent extender oil, and 76 to 78 percent asphalt cement. Blending
is usually performed for about 15 s at 190 to 220 °C (originally patented by the Union
Oil Company).
• Asphalt Rubber (AR) — Asphalt cement modified by the addition of a crumb rubber
modifier. (Also a general term used as an adjective and referring to a specific use or
application of asphalt rubber, e.g., asphalt rubber binder, asphalt rubber hot-mix asphalt
rubber pavement, etc.)
• Beugnet Method — A wet processing method developed in France that is marketed under
the trade name Flexochape using crumb rubber, an extender oil, and a catalyst that is
mixed directly with asphalt cement at elevated temperature (180 °C). The formulation
for this storable asphalt rubber binder is:
80/ioo
CRM (100 percent passing through the no. 20 sieve) ...... 10 0 percent
^ ' ''"
. ... 6.0 percent
Catalyst (synthetic elastomer, storage at 160 °C) ............... 2.5 percent
JBitumar Method — A wet process method originating in Montreal, Canada that is
claimed to completely dissolve 10 percent of the crumb rubber modifier (passing through
the no. 5 sieve) into the asphalt cement. (Trade name: EcoFlex™ )
'Definitions based upon those provided in State of the Practice—Design and Construction
of Asphalt Paving Materials with Crumb Rubber Modifier, Publication No FHWA-SA-92-
022, Federal Highway Administration, May 1992. Modifications, additions, and deletions of
portions or entire definitions as listed in this publication were done to enhance clarity
74
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Buffing Waste — A high quality scrap tire rubber that is a byproduct from the
conditioning of tire carcasses in preparation for retreading.
Continuous Blending Method — A wet processing method using a continuous production
mode to produce various asphalt rubber paving materials.
Crackermill — A CRM production process that tears apart tire rubber by passing the
material between rotating corrugated steel drums, reducing the size of the rubber to a
crumb particle (generally 4.75 mm to 425 jim (no. 4 to no. 40) sieve).
Crumb Rubber — Scrap tire rubber that has been processed to particle sizes usually less
than 9.5 mm (sometimes referred to as ground tire rubber GTR or CRM).
Crumb Rubber Modifier (CRM) — A. general term for scrap tire rubber that is re-
duced in size and is used as a modifier in asphalt paving materials.
Cryogenic — A CRM production process that freezes the scrap tire rubber and crushes
the rubber to the desired particle size.
Devulcanized Rubber — Tire rubber treated by heat, pressure, and the addition of
softening agents to alter the properties of the rubber.
Diluent — A light petroleum product (typically kerosene) added to an asphalt rubber
binder just before the binder is spray-applied to the pavement surface.
Dry Process — Any method that mixes the crumb rubber modifier with the aggregate
either before or after the mixture is charged with asphalt binder. This process only
applies to hot-mix asphalt production.
Extender Oil — An aromatic oil used to supplement the asphalt/crumb rubber modifier
reaction (often provides oil to reduce viscosity and to replace oils adsorbed by the crumb
rubber modifier).
Generic Dry Method — A dry processing method using a crumb rubber modifier with
particle sizes generally less than 2 mm that is mixed with either dense-graded, open-
graded, or gap-graded aggregates to modify the asphalt binder and/or provide rubber
aggregate.
Granulated CRM — Cubical, uniformly shaped, cut crumb rubber particles that are
generally produced by a granulator.
Granulator — An ambient CRM production process that shears the scrap tire rubber,
cutting the rubber with revolving steel plates that pass at close tolerance, reducing the
size of the rubber to a crumb rubber particle (generally 9.5 mm to 2.00 mm (3/8 in to no.
10 sieve)).
75
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Ground CRM — Irregularly shaped torn crumb rubber particles with a large surface area
that are generally produced by a crackermill.
McDonald Method — A wet batch processing method used in the production of various
asphalt rubber paving materials generally formulated using the following:
Temperature 190 °C to 205 °C
CRM particle size 2.00 mm (No. 10 sieve) and finer
Amount of CRM (by weight of total binder) 15 to 25 percent
Process time . -45 minuteg
This method incorporates the developments of ARCO and Suhuaro.
Micro-Mill — A CRM production process that further reduces the particle size of the
crumb rubber below a 425 /tm (no. 40) sieve.
Qverflex" — A trade name of the Sahuaro Petroleum and Asphalt Company for an
asphalt rubber produced by the wet process using about 20 percent crumb rubber by
weight, generally without extender oil or other additives.
PlusRide' Method — A patented dry processing method using about 2 to 3 percent (by
weight of mix) coarse rubber particles (e.g., 1 to 7 mm) that are added to a gap-graded
aggregate.
Pressure Reaction Method — A wet processing method that involves a preblending of
CRM in the hot-asphalt cement followed by a pressure reaction system to achieve
reaction times considerably less than 15 min. The processing equipment will be
available through Modified Asphalt Systems, Inc. (MASI).
Reaction — The interaction between asphalt cement and crumb rubber modifier when
blended together. The reaction, more appropriately defined as polymer swell, is due to
the absorption of aromatic oils from the asphalt cement into the polymer chains of the
crumb rubber. It is not considered to be a "chemical reaction."
Rubber Aggregate — Crumb rubber modifier added to hot-mix asphalt mixture using the
dry process that retains its physical shape and rigidity.
Rubber-Modified Hot Mix Asohalt fRTJMAr.^ — Hot-mix asphalt mixtures that
incorporate crumb rubber modifier primarily as rubber aggregate.
Shredding — Scrap tire recycling process that reduces scrap tires to pieces 0.15 m2
(6 in2) and smaller.
Stress-Absorbing Membrane (SAM) — A surface treatment (chip seal) using an asphalt
rubber spray application and cover aggregate.
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• Stress-Absorbing Membrane Interlaver (SAMP — A membrane beneath an overlay
designed to resist the stress/strain of reflective cracks and delay the propagation of the
crack through the new overlay. The membrane is a spray application of asphalt rubber
binder and cover aggregate.
• Wet Process — Any method that blends a crumb rubber modifier with the asphalt cement
prior to incorporating the binder in the asphalt mixture.
Crumb Rubber Modifier Production and CRM Paving Processes/Products
The use of crumb rubber in highway pavement construction may be considered as
experimental or operational depending upon the type of application and the past experience
within a given State. Crumb rubber may be blended with an asphalt cement (wet process)
prior to mixing with aggregates or it may be added (dry process) directly to the aggregates
prior to mixing with asphalt or directly to the asphalt mixture during the mixing process.
The characteristics of the crumb rubber and the equipment systems used to produce CRM are
often dependent upon the applications that are to be used on the paving project.
Generally, scrap tires are converted to crumb rubber by first shredding and then
processing in a granulator, crackermill, cryogenic system, or micro-mill to produce the
desired particle size and surface texture. In the process, steel and fiber, which constitute
about 30 percent by weight of the tire, are removed. Generally, whole tires contain 20 to 26
percent synthetic rubber and 21 to 33 percent natural rubber.(5) The granulator produces
particle sizes in the range of 2.00 to 9.5 mm, which are often used in RUMAC.(6)
Crumb rubber from a crackermill or micro-mill (particles < 2.0 mm (< 0.08 in)) may
be used in the dry or wet process to produce dense-graded, open-graded, or gap-graded
mixtures. The smaller the crumb rubber particles, the greater the flexibility in its use for
hot-mix applications. Florida has followed this approach by using micro-mill CRM that
minimizes the influence of CRM particle size on the VMA and improves binder homogene-
ity, which facilitates the testing of the CRM binder. Gap-graded mixtures should be
deficient in aggregate sizes to accommodate the rubber particles that swell due to their
absorption of malthenes (oils) from the asphalt cement (a size/time/temperature-dependent
reaction). Consequently, the properties of dense-graded asphalt rubber mixtures may be
affected depending upon particle size and amount of CRM. The dense-graded aggregate
blend must be able to accommodate the rubber particle sizes without excess expansion or
dilation of the compacted mixtures. Similarly, the amount of rubber used in the mix, if
excessive, will produce swelling or prevent adequate compaction due to the high viscosity of
the asphalt-rubber binder regardless of whether the dry or wet process is used.
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Overview of CRM Construction Methods
PlusRide*
The PlusRide* method is a patented RUMAC mixture marketed under the trade name of
PlusRide . This method is a dry process using a blend of ground and granulated rubber
added to a gap-graded aggregate with the addition of an asphalt cement binder. The coarse
rubber particles act as compressible elastic aggregate that flex under traffic.ro This flexing
has the advantage of breaking up ice and providing better skid resistance during pavement
icing conditions than conventional HMA mixtures.® The experience of different States
ranges from poor mix design and construction, to no difference between PlusRide* and
conventional pavement, to improved skid resistance with slightly more rutting than the
control section.
Chunk Rubber
The Cold Regions Research and Engineering Laboratory (CRREL) experimented with the
use of chunk rubber in hot mix asphalt to improve ice debonding.(5) This laboratory
evaluation involved the use of RUMAC mixture, including PlusRide*, where chunk rubber is
added as part of the aggregate component.® The CRREL concept was to produce a gap-
graded CRM/aggregate asphalt mix using various amounts of rubber (3 to 100 percent) to
replace aggregate while maintaining the desired CRM/aggregate gradation. The CRM
gradation was modified to provide a particle size range from 4.75 mm (no. 4 sieve) up to a
12.5-mm (¥2-in) sieve.
Generic Dry
The Generic Dry method differs from the other dry processing methods because the
CRM can be added to conventional open-graded, gap-graded, or dense-graded asphalt
concrete mixtures with only slight modification of the aggregate gradation. Consequently,
variations in aggregate blend gradations between various localities does not require signifi-
cant adjustments in gradation to accommodate the CRM. The amount and particle size of
CRM used in an asphalt mix is dependent upon whether or not the aggregate gradation has
sufficient void space for the CRM without creating excessive expansion or dilation of the
mix. Therefore, certain gap-graded aggregate blends are much more adaptable to this
process than dense-graded mixtures.
McDonald
The most widely used wet processing method is probably the McDonald method that has
been used throughout the Southwestern U.S. to produce asphalt-rubber membranes (SAM),
asphalt-rubber membrane interlayers (SAMI), and asphalt-rubber hot-mix.(5>9) This is a wet
batch process where the CRM is added to hot asphalt cement (~ 185 °C to 200 °C) in a low
78
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agitation mixer and is then pumped into a holding tank where the CRM/asphalt is circulated
for 45 min at about 190 °C to complete the reaction prior to metering into the mix at the
asphalt hot-mix plant.(5>10) The time required to achieve satisfactory reaction is usually
determined using a rotational viscometer by evaluating when a uniform viscosity has been
attained.
Continuous Blending
The Continuous Blending wet processing method relies on using finely ground rubber,
e.g., 425 or 180 ftm (no. 40 and 80 sieve, respectively), to facilitate short blending times
(< 15 min) at temperatures ranging between 150 °C and 177 °C.(11'12) The underlying •
concept is to provide continuous production of AR binder without "batch" blending and
reacting the asphalt cement and CRM. This concept may be extended to the asphalt terminal
where blending immediately prior to transport to the construction project could be achieved.
Although storage time is extended up to 4 days or more using a finely ground CRM, there
are questions relating to storage and the potential for separation over long time periods.(11)
Some form of continuous agitation may be necessary.
Beugnet
Development work on the Beugnet method began in 1981. In 1985 it was found that a
catalyst added to the process produced an improved AR binder.(13) Experimentation with this
wet process indicated that 10 percent CRM produced the greatest viscosity without separation
or the need for agitation. Subsequently, the formulation given below, which goes under the
trade name Flexochape™, was selected as generally being the most desirable for AR paving
applications.03' The key advantage of this method is that viscosity and ring and ball (R&B)
softening point remained fairly constant over 6-day storage in a hermetically sealed vessel
without agitation with the exception that R&B softening increased within the first 2 days.
Bitumar
Bitumar, Inc., has developed a patented wet process method that is marketed under the
trade name Ecoflex™. According to their promotional literature, Ecofiex™ contains 10 percent
CRM of 4- to 10-mesh size that can be blended at refineries or at liquid bulk asphalt
terminals, transported, and used at asphalt hot-mix plants without any modifications to
existing plants or construction equipment. The unique aspect is that Bitumar claims that their
method produces complete dissolution of the CRM to ensure permanent and irreversible
homogeneity. They state "it guarantees extended storage stability and allows for the eventual
recycling of the pavement itself."
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Applications/Performance
Arizona started evaluating CRM materials in the mid-1960's and California has been
evaluating CRM on State highways since the mid 1970's. In most States, experimentation
with CRM in HMA has occurred within the last 5 years. The ensuing discussion on
applications and performance is based upon research reports and survey data.
Spray Applications
• Stress-Absorbing Membrane (SAM)
The SAM or asphalt-rubber chip seals have been used commonly in the Southwest and
even in South Africa.(14>15) Some improvements noted on well-designed and constructed
SAM's are improved adhesion to chips, which reduce chip loss under traffic, increased
resistance to reflection cracking due to improved flexibility, and increased durability and
weatherability.<15) In California, CALTRAN's experience with SAM construction has been
generally very good.(16) Damage claims for broken windshields were minimal or nonexistent
except in a few cases that were attributed to poor traffic control during construction.
CALTRAN's overall appraisal of SAM constructibility and performance was excellent and
the service record history showed good life-cycle costs and maintenance-free performance.
Similarly, in Arizona the application of SAM's on U.S. Routes and State Routes
extended the service life of the pavements about 8 and 10 years, respectively.(17) In the case
of the U.S. Routes, about 40 percent of the pavements were older than 23 years at the time
of the SAM treatment. Interstate pavements averaged about 11 years when a SAM was
applied mat extended the life on the average of 5 years (50 percent).
In colder climates, the SAM's appear to give more variable performance. Two SAM test
sections were constructed in Minnesota that gave diverse performance/18) The section that
gave good performance had high quality aggregate that was precoated with 0.5 percent of a
120/150 pen AC. The SAM project that failed included similar AR application rates, but
excessive rock dust on the chips and high moisture content, due to rain, were attributed to
the extensive loss of aggregate. In their opinion, there was a place for SAM's somewhere
between a hot-mix overlay and an emulsion chip seal.
Two SAM experimental sections were constructed with the addition of an emulsion sand
seal in Connecticut/19) After 9 years, cracks were almost nonexistent, but the control section
was so extensively cracked that it was not meaningful to make crack length measurements.
Several other SAM sections were placed and after 4 or 5 years, one was chip sealed and the
other 'overlaid with 50 mm of asphalt concrete, which is essentially a SAMI. The amount of
cracking in the control sections was two to three times that on the SAM sections. SAM's are
more effective in reducing chip loss when properly constructed under favorable weather
conditions.
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• Stress-Absorbing Membrane Interlayers (SAMI)
Arizona placed approximately 528 km (330 mi) of SAMI's between 1975 and 1980. The
age of pavements prior to application of a SAMI ranged from 8 to 44 years. The mean life
of the SAMI's on Interstate, State Routes, and U.S. Routes was 9, 9.5, and 7.8 years,
respectively, although individual projects extended up to 15 years. (17) Slightly better
performance was achieved on Interstate pavement even though they received 10 times the
load repetitions than the State or U.S. Routes. This was attributed to either the better
condition of the Interstate pavements or the greater thickness of overlay [1,000 mm vs.
500 mm (39.4 in vs. 19.7 in)] used on the Interstate. Comparisons of SAMI to control
sections indicated very little difference in distress, however, one project had an overlay
thickness of 110 mm (4.5 in) on the control vs. 60 mm (2.4 in) for the SAMI. Typically,
other forms of distress, such as roughness and bleeding, had a greater effect on service life
than cracking.
The primary findings from eight SAMI test sections on three construction projects in
Minnesota indicated a reduction in cracking on two projects, but reflective cracking, was not
totally eliminated. (18) The third SAMI project provided little or no reduction in reflective
cracking over the conventional overlays. Some aggregate loss and pickup of the AR was
experienced from construction traffic. Also, a short segment of a SAMI had an excessively
heavy spray application of AR, resulting in instability requiring replacement. Construction
of the SAMI's were performed without much difficulty, but their ability to extend an
overlay's life span was not established.
Similarly, in Connecticut, the SAMI's did not perform better than conventional overlays
and in several cases, even worse.(19) However, this poor performance may have been
attributable to the use of crushed stone hot-mix overlay resulting in the stone being forced
into the SAMI during overlay compaction.
FHWA demonstration projects in 8 States indicated that 7 of the 10 SAMI projects
provided the same relative performance as conventional overlay. a0) Only two projects were
considered to be better than the control sections. Similarly, New Mexico concluded SAMI's
do retard the rate of reflective cracking or necessarily prevent reflective cracking.01" Florida
found that open-graded mixtures should not be placed over SAMI's and that SAMI's
performed better over old pavement than freshly placed leveling courses because aggregate
embedment and flushing of AR was prevented. a2) The evaluation of two SAMI projects in
Pennsylvania indicated an insignificant increase in service life, but the use of SAMI was not
economically justified. a3) Vermont found that a 50-mm-thick overlay was more effective in
preventing reflection cracking than the
The cost of a SAM or SAMI is somewhere in the range of $1.55 to $2.15 /m2 ($1.30 to
$1.80/yd2) or approximately twice the cost of a conventional chip seal.(16"18) However, if the
cost for the SAMI is combined with the cost of a 30- to 50-mm (1.2-in to 2.0-in) thick
overlay, the total rehabilitation cost is only 30 to 40 percent greater than using only the
overlay. .
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Dense-Graded Mixtures
The performance of dense-graded AR mixtures is highly dependent upon the gradation of
the CRM, aggregate gradation, volume of voids in the mineral aggregate, characteristics of
the asphalt cement or asphalt rubber, climatic and traffic conditions, and the type and degree
of pavement distress (e.g., amount of cracking) existing prior to placement of the overlay.
Eighteen test sections constructed with 38 mm (1.5 in) of dense-graded RUMAC mixtures
containing 1 and 2 percent (by weight of mix) CRM (30 mesh) in Connecticut using the
generic dry process were compared to the control section after 9 years of service.(19) One
percent CRM reduced the amount and rate of longitudinal cracking as compared to the
control except in those sections that were originally highly distressed. The use of 2 percent
CRM apparently affected the hardness of the binder resulting in twice the amount of
longitudinal cracking that was produced on control sections.
Section 403, Hot-Mix Asphalt Concrete Pavement Specifications for New York that were
adopted in 1992, provides the option for the use of 18 percent by weight of binder of a 3.2-
mm (0.125-in) maximum size CRM in the generic dry process for asphalt concrete
mixtures.*25*
Recently (1992), test road sections in Iowa with CRM contents ranging between 5 and 20
percent (by weight of asphalt) were constructed using the Continuous Blending and
McDonald wet process methods to pave AR test sections on five different projects. (See
references 26 through 30.) Although it is too soon to evaluate performance, these AR
pavement sections appear to be in the same condition as the conventional (control) sections.
It was concluded that dense-graded AR mixtures can be constructed with little or no
difference from that of a conventional mix. On the first two projects a problem with shoving
and cracking occurred during rolling and sticking (pick up) of the AR mix to the drum of the
roller.(26>28) Segregation was a problem on the third project and it was alleviated by using
flowboy trucks instead of dump trucks.CT The conventional control mix also had the same
segregation problem as the AR mixture.
Maryland designed a dense-graded AR mixture using a 12.5-mm (0.5-in) nominal
maximum size aggregate and an asphalt rubber binder containing 18 percent CRM (4.8-mm
(0.19-in) maximum particle size) with extender oil as necessary (7 percent maximum) to
meet the AR binder specifications.01) The aggregate gradation was altered from the
conventional mix to increase the voids in the mineral aggregate (VMA) from 16.8 to 20.3,
which changed the binder content from 5.5 percent to 7.2 percent for the AR mixture. A
1.61-km (1-mi) long AR test section was constructed with only minimal problems. Initial
performance of the pavement up to 7 months after construction indicates minimal rutting and
visually no difference between conventional and AR test sections. However, average friction
numbers for the AR section are about 10 units lower than for the conventional pavement
immediately after construction.
The McDonald process was used in Missouri to blend an AR binder. ^ An AC-5 with
15 percent (by weight of binder) CRM was used in a dense-graded aggregate blend and
placed as a 1.61-km (1.0-mi) long test section on 1-70 during August 1990. The overall
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performance of the AR concrete mixture was satisfactory over the first 4 months except
friction numbers were 10 to 15 units less than the control section.
In general, the costs for dense-graded AR concrete mixtures using the wet process is two
to three times the cost of conventional mixtures. It appears that costs using the dry process
may be as low as 1.3 to as high as 2.0 times the cost for conventional dense-graded
mixtures.34) A survey by the State of Maryland of State Highway Agencies indicated that
about 75 percent of those using CRM were paying between $48.50 to $97.00/Mg ($40 to
$80/ton) of hot-mix. ;
Gap-Graded Mixtures
A gap-graded aggregate HMA has a gradation that is deficient in or has no material in
one or more of the intermediate sieve sizes. In other words, one or more of the sieves in a
series of sieves used for gradation analysis would not have any retained aggregate. The
purpose of using a gap-graded aggregate blend is to provide space for the rubber aggregate
and to maintain course aggregate contact without dilation when the voids are filled with fine
aggregate and asphalt cement.(5)
Probably the most well-known method for gap-graded rubber aggregate mixtures is that
called PlusRide9. It is a very resilient material that makes it a difficult material to evaluate
using conventional tests in the laboratory/35' However, its potential attributes are improved
skid resistance because of its deicing characteristics resulting from its high resiliency
(deformation under load). Braking tests conducted in Alaska showed a 19-to 25 percent
reduction in stopping distance during icy road conditions.(8>34)
The variable performance history of PlusRide* in Colorado indicated either a problem
with proper formulation and construction, or using it to correct extensively distressed
pavements. The major problem encountered in Colorado was raveling, which appears to be
caused by cohesive failure and is most prevalent in traffic and turn lanes on facilities with
higher volumes of vehicles.a5) Apparently, it is necessary to place these RUMAC mixtures
at air-void contents near 4.6 percent to achieve good performance. ^; This necessitates
laboratory design voids somewhere in the range of 3 to 4 percent. The desired air-void
content is usually achieved by increasing both mineral filler and asphalt cement contents.
The cost per ton of PlusRide* in the Anchorage area exceeds the cost of conventional hot-mix
by 43 percent.(37) •..•..
Open-Graded Mixtures 4
High permeability and high skid resistance are two characteristics of ^open-graded friction
course (OGFC) mixtures. These mixtures are specially designed with a high void content to
minimize hydroplaning and splash/spray by increasing the ability of the water to drain
through the mix and away from the pavement surface. The use of asphalt rubber binder
increases the binder's viscosity and allows for an increase in binder content without the
83
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problem of binder migration (drain-down). The resulting increase in asphalt film thickness is
essential for OGFC mixture durability.
OGFC projects in Florida were constructed using both McDonald and Continuous
Blending methods.(IO'12) Test sections in both projects appear to be performing well after 2 to
3 years of service. A generic dry method with 10 percent CRM (by weight to binder) was
included in one project without any noticeable difference in constructibility or performance to
date. One project on 1-95 involved 57.6 lane-kilometers (36 lane-miles) of conventional
OGFC and 6.4 lane-kilometers (4 lane-miles) of OGFC containing 12 percent CRM in the
asphalt rubber binder. The cost of the AR friction course was 30 percent over the cost per
square yard of conventional OGFC. More recently, a project near Tampa resulted in only a
10 percent increase in cost using terminal blending of the AR binder.
Since 1988, Arizona has constructed seven projects using an asphaltic concrete friction
course (ACFC) to control reflective cracking in severely cracked concrete pavement. Since
the earliest sections were placed in 1988, no cracks have reflected through. Despite the
higher cost of asphalt rubber compounds, the material is more cost effective because a
50-mm (2-in) or less ACFC provides better reflective cracking control than a significantly
larger and more costly layer of HMA.08)
Recycling Pavements Containing Crumb Rubber Modifier
The literature search did not reveal any documented projects or experience relating to the
recycling of asphalt pavements containing CRM. Furthermore, the responses from State
highway agencies as requested in the letter and survey form no. 3 in appendix B indicate that
only three projects have been recycled. These projects were located in New Jersey, the
District of Columbia, and Ontario, Canada.
The Ontario Ministry of Transportation used a drum mixer and batch plant in the
production of a dense-graded hot-mix for pavement rehabilitation in October 1991. After
being in service for 1.5 years, the pavement was cracked and raveling. Overall performance
was rated poor compared to the control.
The New Jersey Department of Transportation used 20 percent RAP containing CRM
(PlusRide") in a dense-graded hot-mix for pavement construction during August 1992. No
difference was observed between the construction of the recycled and control pavement
sections. It is too early to quantify its performance.
An open-graded recycled mix with CRM RAP was used in the construction of a
pavement in the District of Columbia. However, this pavement was overlaid shortly after
being constructed in September 1992.
The lack of information and the concern over the ability to effectively recycle CRM
pavements without technical and environmental difficulties suggest that further research is
essential. If certain types (particle size) and concentrations (amount) of CRM prevented
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effective recycling of pavements, then it would severely impact those State and other
highway agencies that currently have viable asphalt pavement recycling programs.
Results From Survey of State Highway Agencies
Appendix B provides examples of the letter of transmittal, one-page questionnaires that
were sent to State highway agencies in the U.S. and to Ministries of Transportation in
Canada. Thirty-two States and the NY/NJ Port Authority responded to the CRM pavement
survey, including two States that have not used CRM technology. Table 13 presents a
summary of the most important variables of CRM technology, i.e., type of process, type of
application, age of test section, and relative performance rating.
The summary presented at the bottom of table 13 indicates that 70.2 percent of all
reported CRM projects used a wet process and almost 61 percent of the total involved the
McDonald method. The Continuous Blending method, which was developed in the late
1980's, accounted for 7.7 percent of the projects. Methods such as the generic dry (14.2
percent) and PlusRide* (10.3 percent) processes comprised most of the projects that used the
dry process.
The applications portion of the table indicates that almost 40 percent of the projects were
dense-graded HMA mixtures and about 29 percent gap-graded HMA mixtures. Surprisingly,
the number of SAMI projects (27) greatly exceeded the SAM projects (2), This occurred
primarily because numerous SAM projects were not reported. Most of the SAMI projects
were constructed with asphalt rubber using the McDonald method. The performance of the
SAMTs were rated as being about the same as the control sections. Projects that were 8 to
14 years old will be overlayed in the near future, which assumes that they have approached
the end of their service life.
The majority of dense-graded CRM projects have been in service for less than 5 years,
except for numerous older projects in California that have, in general, a performance rating
better than the control sections. These older projects were primarily constructed using the
McDonald method, whereas the younger projects across the country utilized the generic dry,
Continuous Blending, and McDonald methods. Performance rating on projects less than 5 or
6 years old generally were equivalent to the performance of the control sections.
Performance of the gap-graded CRM mixtures with the PlusRide* method varied from
better to worse than conventional mixtures in the control sections. The other wet and dry
methods used with the gap-graded CRM mixtures on the projects performed essentially the
same as the control. The open-graded friction course projects using McDonald and generic
methods are too young to assess performance differences.
The majority of dense-graded CRM projects have been in service for less than 5 years,
except for numerous older projects in California that have, in general, a performance rating
better than the control sections. These older projects were primarily constructed using the
McDonald method, whereas the younger projects across the country utilized the generic dry,
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Table 13. Summary of responses to the surveys on CRM pavements.
STATE/
DISTRICT
Alwki
Alisk«
Arizona
Arizona
California
California
California
California
California
California
California
California
California
California
California
California
California
WET PROCESS
McOon
1
1
T
1
1
i
1
1
1
1
1
1
1
i
1
1
1
i
1
1
i
1
1
1
1
i
1
Continuous
196
198
Ovefflex
DRY PROCESS
Generic
PlwRkfe
1
1
1
Rim Rex
Flomlx
K
§r
SAM
SAMI
•PLICATION
GAP
1
1
OGFC
Ao«
(Mo)
89
137
PERFORMANCE
Perforr
Ruttinc
4
3
nince<
Crack
3
3
;ompi
Rave
2
redtc
Strip
3
Control
Overall
4
3
Ovwlty
in New
N
N
FORMULATION
Compile
SuneW/0
8 • 1 988 ARIZONA HAS CONSTRUCTED OVER 1 0 PROJECTS THAT WERE EVALUATED IN THE DEVELOPMENT OF ASPHALT-RUBBER SYSTEMS
6-1992 OVER BO PROJECTS PLACED. REPORTS AND TABULATED INFORMATION ARE BEING EVALUATED.
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1/U
144
132
120
120
108
84
96
96
84
68
48
B2
62
48
41
36
30
16
IE
1B
16
5
5
3
3
8
8
3
4
3
3
2
3
4
3
3
4
6
4
5
B
B
2
4
2
B
4
B
4
4
K
B
B
2
4
3
2
B
4
B
B
4
4
B
B
B
2
4
4
4
B
4
3
3
3
3
3
3
3
N
N
91
Y
N
Y
N
Y
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
X
X
X
X
X
X
X
X
X
X
X
X
: Te« to Cor
Conv. Mix
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
ttrolSect.
SimeGrd
y
y
n
y
n
y
n
y
V
y
n
y
y
CR
(X)
oo
o\
-------
Table 13. Summary of responses to the surveys on CRM pavements (Continued).
STATE/
DISTRICT
California
California
Caltrans
Caltrans
Caltrans
Florida
Florida
Florida
Georgia (*)
Georgia (*)
Indiana
Indiana
Indiana
owa
($)
Kentucky
WET PROCESS
Method (Trade Name)
McDon
T
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Continuous
1
1
1
1
1
1
1
1
Overflex
DRY PROCESS
Method (Trade Name)
Generic
1
1
1
1
1
1
1
PlusRide
1
Ram Flex
Flomix
APPLICATION
Spray
SAM
SAMI
1
1
1
1
1
1
1
1
1
1
1
1
1
Asphalt Concrete
Dense
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
GAP
1
1
1
1
1
1
1
OGFC
1
1
1
PERFORMANCE
Age
(Mo)
8
18
18
7
300
188
1B
8
96
39
132
144
132
108
146
45
42
162
27
2
2
14
6
29
18
18
18
6
14
14
16
4
18
E
6
172
16
16
17
27
28
Performance Compared to Control
Rutting
3
3
*«
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
4
3
Crack
6
3
3
3
3
4
3
3
6
3
3
3
3
3
3
3
3
3
3
3
3
3
3
1
4
4
2
2
1
Ravel
3
3
3
3
3
3
3
3
3
2
3
3
3
3
3
2
1
3
Strip
3
3
3
3
3
3
3
3
3
3
3
3
3-
3
3
3
3
3
Overall
3
6
4
4
3
3
4
3
3
3
3
3
3
3
3
3
3
3
3
3
3
1
4
4
3
2
2
Overlay
in Near
Future
N
N
N
N
Y
Y
N
N
Y
N
Y
Y
11/89
4/92
88
N
N
N
6/92
N
N
Y
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
Y
N
N
N
N
N
FORMULATION
Compare: Test to Control Sect.
SameW/0
X
X
X
X
X
X
X
.
X
X
X
Conv. Mix
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
• x
X
X
X
X
X
X
X
X
X
X
Same Grd
n
n
n
n
n
n
n
n
n
n
n
n
V
V
v
y
n
v
„«««
n
v
y
y
n
n
n
n
n
n
V
y
n
y
v
v
CR
(%)
1
2
3
-------
Table 13. Summary of responses to the surveys on CRM pavements (Continued).
STATE/
DISTRICT
Louiilina
MaJrw
MicWotn
Michigan
Minnesota
Minnesota
Minnesota
Missouri
Missouri
Nebraska
New Jersey
New Mexico
New York 1
B-Project 1
(NY) 1
(NY! 1
D-Proect 2
INY) 2
(NY) 2
NY/NJ Pt Auth.
North Carolina
North Carolina
North Dakota
Ohio
Ohio
Ohio
Me
McDon
1
1
1
1
1
1
i
1
1
i
1
1
i
1
1
i
i
(thod (Trade N
Continuum
i
i
1
tn»)
Overflex
Genetic
1
1
1
1
1
1
1
1
i
1
* N/A«
Method (T
PlusRkie
1
1
1
1
1
1
1
rade Name]
Rim Rex
Flomtx
S
SAM
jray
SAMI
1
1
1
1
Aipt
Dente
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1 1
1
tit Co
RAP
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
crete
OQFC
I 1
Aoo
(Mo)
0
17
17
17
27
1B6
S
5
101
101
100
29
28
16
15
14
2
24
168
E
27
101
24
166
173
40
40
40
40
40
40
40
40
116
16
19
1
1
1
1
24
24
Perforn
Rutting
3
3
3
4
4
3
3
4
3
3
3
3
3
E
3
3
3
3
3
1
3
3
3
3
3
3
3
3
3
1
3
3
3
Banco <
Crack
3
3
3
3
3
4
3
4
2
3
3
6
4
4
3
3
3
1
3
2
2
3
3
3
3
3
3
3
5
4
3
?ompa
Rave
3
3
3
3
1
1
1
3
1
3
1
4
3
E
3
3
3
3
3
1
3
1
1
3
3
1
3
1
1
2
3
red to
Strip
3
3
3
3
1
3
3
3
3
3
1
3
3
6
3
3
3
3
3
1
3
3
1
3
3
3
1
3
2
3
3
3
Centre-
Overall
3
3
3
1
1
4
3
3
3
E
3
4
3
3
3
3
1
3
3
1
1
3
3
1
3
2
1
3
3
3
Overlay
In Near
Future
N
N
N
N
N
93
N
N
N
Y
N
N
N
N
N
N
N
N
N
10/86
N
N
N
Y
Y
N
N
N
Y
N
N
N
N
N
N
N
N
N
Compare
Same VWO
X
X
X
X
X
X
X
X
X
X
X
FORMULA
: Te*t to Cor
Conv. Mix
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
rioN
troISect.
Sarna Grd
n
y
Y__
y
y
y
y
y
y
y
y
y
n
y
n
n
y
y
y
y
y
y
y
y
y
y
y
n
CR
<»)
1
2
3
2
3
CO
CO
-------
Table 13. Summary of responses to the surveys on CRM pavements (Continued).
STATE/
DISTRICT
Ohio
Ohio
Ohio
Oklahoma
Oklahoma
Oklahoma
Oregon
Oregon
Oregon
Oregon
Oregon
Pennsylvania
Rhode Island
South Carolina
Utah
Vermont
Vermont
Vermont
Wisconsin
Wisconsin
Wisconsin
Wisconsin
Wisconsin
Wisconsin
Wyoming
TOTAL
SECTIONS
PERCENT
WET PROCESS
Method (Trade Name)
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
94
60.6
NOTES: * =
$ =
*« =
**# =
@ =
1
1
1
1
12
7.7
Overflex
1
1
1
1
1
3
DRY PROCESS
Method (Trade Name)
Generic
1
1
1
1
22
1.9 14.2
PlusRide
I 1
16
10.3
Ram Flex
2
1.3
Flomix
1
0.6
APPLICATION
Spray
SAM
1
1
2
1.3
SAMI
1,
1
1
1
27
Asphalt Concrete
Dense
1
1
1
1
1
1
1
1
1
1
1
68
16.9 42.6
GAP
1
1
1
1
1
1
1
1
1
1
1
46
28.8
OGFC
1
1
1
1
12
7.5
Novophalt* (Modified asphalt using CRM)
80-Mesh CRM Used
No Test Section Set Up, Not Considered Experimental
MixContans16%RAP
Bitumar EcoFlex*
PERFORMANCE
Age
(Mo)
6
6
6
127
127
128
15
16
16
8
4
4
5
27
27
4
88
88
14
66
8
6
161
161
164
60
60
60
32
32
32
32
17
Hutting
1
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
2
3
3
3
3
3
3
3
Crack
1
2
2
3
3
3
3
3
3
3
3
3
2
4
4
3
3
1
1
1
1
1
1
1
1
1
1
3
Ravel
1
3
1
3
3
3
3
3
3
3
1
3
3
3
2
1
1
1
?
1
1
3
3
3
3
3
55.2 AVERAGE AGE
(Mo)
Rating
1
2
3
4
5
Total
Rutting
3
2
83
9
1
98
3.0
Crack
14
9
55
16
10
104
3.0
Rave
20
10
52
5
7
94
2.7
Strip
1
3
1
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
1
1
3
3
3
3
3
Overall
1
3
2
3
3
3
3
3
3
3
2
4
4
3
3
3
3
2
1
1
1
1
1
1
1
3
Strip
9
1
68
0
1
79
2.8
Overall
16
11
60
20
8
115
3.0
in Near
Future
N
N
N
Y
Y
Y
Y
Y
Y
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
10/80
1993
Y
Y
Y
Y
Y
Y
N
FORMULATION
Compare: Test to Control Sect.
Same W/O
X
X
X
X
X
X
X
X
X
Conv. Mix
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Same Grd
v
n
y
n
n
n
n
n
n
n
n
n
n
n
y
n
n
n
n
n
y
y
y
y
y
RATING SCALE ,
(1) POOR
(2) SLIGHTLY SUBSTANDARD
(3) AVERAGE
(4) GOOD
(5) EXCEPTIONALLY GOOD
Weighted Average
CR
t%)
RAP
RAP
CO
-------
Table 13. Summary of responses to the survey on CRM pavements (Continued).
SUMMARY OF PERFORMANCE RATINGS ACCORDING TO APPLICATION AND METHOD
WET PROCESS
Application
SAM
SAMI
SAMI
Dense
Dense
GAP
OGFC
OGFC
Method
Overflex
Overflex
McDonald
McDonald
Continuous
McDonald
Continuous
No.
Projects
2~
r
25
32
_
IT"
7
1
Avg.
Age
162.5
161.0
86.8
56.9
12.4
42.1
31.4
5.0
PERFORMANCE (AvBi-nrm Rntinnl
Rutting
3.0
3.0
3.1
3.0
3.3
3.3
2.4
3.0
Cracking
1.0
1.0
3.0
2.9
3.3
3.6
3.2
3.0
Raveling
1.0
1.0
3.0
3.1
4.0
3.0
3.2
3.0
Stripping
3.0
3.0
2.6
2.9
4.0
3.0
3.2
3.0
Overall
2.5
3.0
3.1
3.0
3.3
3.4
3.2
3.0
Application
Dense
Dense
Dense
GAP
GAP
Method
Generic
RamFlex
Flomix
Generic
PlusRide
No.
Projects
20
2
i
2
is
Avg.
Age
29.2
KJ2"F
1 70.0
~mf
~7§T
PE
Rutting
3.1
2.5
3.0
3.0
3.0
KhUKMA
Cracking
3.0
2.0
40
2.5
3.1
VUt (Ave
Raveling
2.3
2.0
4 0
2.0
2.5
age Ratm
Stripping
2.6
2.0
2.6
g)
Overall
2.6
2.0
3.0
3.1
-------
Continuous Blending, and McDonald methods. Performance rating on projects less than 5 or
6 years old generally were equivalent to the performance of the control sections.
Performance of the gap-graded CRM mixtures with the PlusRide* method varied from
better to worse than conventional mixtures in the control sections. The other wet and dry
methods used with the gap-graded CRM mixtures on the projects performed essentially the
same as the control. The open-graded friction course projects using McDonald and generic
methods are too young to assess performance differences.
Assessment
Is CRM technology viable and cost-effective in applications relating to construction and
rehabilitation of asphalt pavements? The answer to this question is not readily apparent in
the literature or from State highway agency responses to the survey on CRM utilization.
States located in the hot, dry, southwestern U.S. (e.g., California and Arizona) have
extensive experience with AR membranes and mixtures. In general, they have had only a
few failures and are generally satisfied with the constructability and performance of pave-
ments containing CRM. However, highway agencies in the northern States, where wet and
cold weather is more prevalent, have not observed any major improvement in performance
over their conventional HMA pavements. In fact, numerous CRM pavements and CRM test
sections performed worse than the conventional pavement or control sections. The exact
causes of early failures were not identified, but they may be a result of weather-affected
construction problems.
Costs are high during initial development and experimentation. This is quite apparent in
CRM applications for asphalt pavement construction. At this time, many experimental CRM
projects have been recently constructed. Costs are high because projects are short in length
and experimental. There are indications that newer processes or adaptations to conventional
production methods may reduce costs and provide reasonably good economic advantage from
a life-cycle cost standpoint.
The information derived from the literature and surveys of State highway agencies
indicates that SAM and SAMI's often give variable performance. This is attributed to
adverse climate conditions, poor mixture design and construction, or trying to correct severe
pavement distress problems (e.g., extensive cracking), which probably could not be corrected
without major reconstruction. The successful use of SAM and SAMI's in the Southwest may
be due to the dry, hot climate, and long construction season, which can be beneficial from
the construction standpoint, but extensive experience also undoubtedly contributes measurably
to their success. The main deterrent to the new user of SAM's and SAMI's is the initial cost
— about twice the cost of a conventional chip seal. Even though problems have occurred,
there are other projects where it has been demonstrated that SMA and SAMI membranes are
cost-effective.
Based on the survey data returned, the recent experimental applications of CRM through-
out the U.S. appear to be predominately in dense-graded hot-mix asphalt (HMA) using the
generic dry, McDonald, and Continuous Blending methods. These projects are of insurfi-
91
-------
cient age to properly evaluate their performance. The use of CRM in dense-graded mixtures
can pose a problem because of insufficient VMA unless the CRM particle size quantity is
small enough or the aggregate gradation is altered.
The major unknown in using these materials is the potential for their influence on the
recycling process. Experience with the recycling of RAP containing CRM is limited.
RUMAC HMA design is based on the premise that the aggregates are properly gap-
graded to accommodate the rubber aggregate particles. The variation in performance of
pavements constructed in this manner suggests that mix formulation, the degree of resiliency,
and effectiveness of construction are affecting the behavior of the material. Since Alaska has
found the PlusRide* method to work well in their climatic conditions, why in some cases has
it performed poorly in other climates and States?
Other recent projects involving gap-graded CRM mixtures using other methods have nof
been in service for a long enough time to evaluate their performance. If rubber aggregate
and gap-graded aggregate blends are to be used effectively for surface mixtures, the effects
of CRM particle size, amount of CRM and aggregate gradation on the properties of the mix,
and the performance of the pavement need to be established.
The various applications/methods for utilization of CRM in asphalt pavements are for the
most part reasonably effective. The greatest deterrents from the use of CRM is the high
initial cost and the variable performance that seems to be associated with climate and
selection of proper application, mix design, and construction. The assessment of information
from the literature and the surveys of highway agencies has provided some insight into the
problems of CRM technology. Specific recommendations are as follows:
• There is a need to evaluate the recyclability of hot mix asphalt pavements containing
CRM. The investigation should encompass the use of RAP that contains AR and
RUMAC paving mixtures. Potential problems that need to be addressed are: (1) the
effect of asphalt-rubber mixtures and membranes on the aggregate gradation and the
degree of fines generation, and other associated problems encountered in the cold milling
process and (2) the degree to which malthenes (light ends) from recycling agents or new
asphalt cements are absorbed by the CRM in the RAP during the hot mixing and in-
service life of the recycled mixture.
• Layer equivalencies and/or test properties associated with mechanistic design for AR
mixtures and membranes should be developed. In either case, the equivalency or
structural design parameters must be related to the degree of distress and the structural
response of the pavement before the application of AR membrane or AR mixtures to
achieve desirable performance and pavement life.
* CRM/asphalt cement interaction should be evaluated to establish absorption of malthenes,
degree of rubber particle swell or solubility, and influence on binder properties in
relation to size and amount of CRM. Processing methods, .both wet and dry, should be
evaluated to determine the effects of time, temperature, pressure, mechanical mixing,
etc., on the CRM/asphalt interaction. Process (reaction) time, storage time, or equilibri-
92
-------
urn conditions must be established for wet processing methods. It should be determined
whether or not the product of the dry process can be made equivalent to the product of
,the wet process based on the fineness and quantity of CRM used in the mixture.
• Mixture design method(s) should be developed to accommodate the use of CRM using
either dry or wet processing methods. The combined influence of CRM particle size and
aggregate gradation needs to be evaluated and suitable criteria established for selection of
amount and size of CRM and total binder contents for each application.
• Test methods and specification guidelines need to be established for effective construction
control. These methods and specifications should be readily adopted or incorporated into
existing quality control and quality assurance procedures.
References
1. Summary of Markets for Scrap Tires, EPA/530-SW-90-074B, United States Environ-
mental Protection Agency, Washington, DC, October 1991.
2. Witczak, M.W., State of the Art Synthesis Report Use of Ground Rubber in Hot Mix
Asphalt, Department of Civil Engineering, University of Maryland, College Park, MD,
June 1991.
3. Ahmed, Imtiaz, Use of Waste Materials in Highway Construction, Final Report,
FHWA/IN/SHRP-91/3, May 1991.
4. Hughes, Chuck, P.E., Scrap Tire Utilization Technologies, National Asphalt Pavement
Association, Lanham, MD, 1992.
5. State of the Practice — Design and Construction of Asphalt Paving Materials with
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6. Takallou, H.B. and A. Sainton, "Advances in Technology of Asphalt Paving Materials
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Research Board, Washington, 1992.
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Department of Transportation and Public Facilities, Juneau, AK, April 1985.
9. Ruth, B.E., Sigurjonsson, S., and C.-L. Wu, Evaluation of Experimental Asphalt-
Rubber, Dense-Graded, Friction Course Mixtures: Materials and Construction of Test
93
-------
Pavements on N.E. 23rd Avenue, Technical Report, prepared for the Florida Department
of Transportation (FDOT), Publication No. 99700-7497-010, May 1989.
10. Ruth, B.E., Evaluation of Experimental Asphalt-Rubber, Open-Graded, Friction Course
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Binder," Proceedings, National Seminar on Asphalt Rubber, Kansas City, Missouri,
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15. Renshaw, R.H., "A Review of the Road Performance of Bitumar-Rubber in South and
Southern Africa," Proceedings, National Seminar on Asphalt Rubber, Kansas City,
Missouri, October 1989, pp. 22-32.
16. Delano, E.B., "Performance of Asphalt-Rubber Stress-Absorbing Membranes (SAM) and
Stress-Absorbing Membrane Interlayers (SAMI) in California," Proceedings, National
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17. Schofield, L., The History, Development, and Performance of Asphalt Rubber at ADOT,
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Phoenix, AZ, December 1989, 37 pp.
18. Turgeon, Curtis M., "The Use of Asphalt-Rubber Products in Minnesota," Proceedings,
National Seminar on Asphalt Rubber, Kansas City, Missouri, October 1989, pp. 311-
327.
19. Stephens, J.E., Nine-Year Evaluation of Recycled Rubber in Roads, JHR 89-183, Civil
Engineering Department, University of Connecticut, Storrs, CT, May 1989, 16 pp.
20. Gupta, P.K., Asphalt-Rubber Surface Treatments and Interlayers, Research Report
FHWA/NY/RR-86/131, Engineering Research and Development Bureau, New York
State Department of Transportation, March 1986, 24 pp.
94
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21. Lorenz, V.M., New Mexico Study of Interlayers Used in Reflective Crack Control,
Research Report MB-RR-84/1, Materials Laboratory Bureau, New Mexico State
Highway Department, September 1984, 47 pp.
22. Murphy, K.E. and C.F. Potts, Evaluation of Asphalt-Rubber as a Stress-Absorbing
Interlayer and a Binder for Seal Coat Construction, Contract No. DOT-FH-15-328,
FHWA, Region 15, Arlington, VA, June 1980, 28 pp.
23. Mellott, D.B., Discarded Tires in Highway Construction, Final Report, Research Project
No. 79-02, Demonstration Project No. 37, Pennsylvania Department of Transportation,
April 1989, 15 pp.
24. Frascoia, R.I., Experimental Use of an Asphalt Rubber Surface Treatment, Interim
Report 83-6, Vermont Agency of Transportation, Materials and Research Division,
September 1983, 16 pp.
25. Correspondence from Wayne J. Brule, Director, Materials Bureau, New York State
Department of Transportation to Byron E. Rath, University of Florida, December 21,
1992.
26. Anderson, C., Evaluation of Recycled Rubber in Asphalt Concrete, Project DTFH71-91-
TE03-1A-30, Highway Division, Iowa Department of Transportation, December 1991,
51 pp.
27. Anderson, C., Evaluation of Recycled Rubber in Asphalt Concrete—Dubuque County,
Project HR-330C, Highway Division, Iowa Department of Transportation, August 1992,
50pp.
28. Anderson, C., Evaluation of Recycled Rubber in Asphalt Concrete—Plymouth County,
Project HR-330A, Highway Division, Iowa Department of Transportation, August 1992,
31pp.
29. Anderson, C., Evaluation of Recycled Rubber in Asphalt Concrete—Black Hawk County,
Project HR-330D, Highway Division, Iowa Department of Transportation, September
1992, 32 pp.
30. Anderson, C., Evaluation of Recycled Rubber in Asphalt Concrete—Black Hawk County,
Project HR-330B, Highway Division, Iowa Department of Transportation, December
1992, 40 pp.
31. Wagner, L.J., Asphalt Rubber Concrete Project—Maryland Route 543, Interim Report
No. MD-92/02, Maryland Department of Transportation, March 1992, 24 pp.
32. Webb, M., Asphalt Rubber Concrete Test Section, Interim Report, Project Number IR-
70-3 (146), Experimental Project M--90-01, Missouri Highway and Transportation
Department, March 1991, 20 pp.
95
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33. Turgeon, C.M., An Evaluation of Dense-Graded Asphalt Rubber Concrete in Minnesota,
Report No. MN/RD-92/01, Minnesota Department of Transportation, November 1991.
34. Stephens, I.E., Recycled Rubber In Roads, Final Report, Report No. FHWA-CT-RD
471-F-80-15, Connecticut Department of Transportation, April 1981.
35. LaForce, R.F., Rubber-Modified Asphalt Concrete, Report No. CDOH-SMB-R-87-15,
Colorado Department of Highways, December 1987, 21 pp.
36. Takallou, H.B. and R.G. Hicks, Development of Improved Mix and Construction Guide-
lines for Rubber-Modified Asphalt Pavements, Transportation Research Record 1171,
Transportation Research Board, Washington, DC, 1988, pp. 113-120.
37. McQuUlen, J.L., Jr., Takallou, H.B., Hicks, R.G., and D. Esch, "Economic Analysis of
Rubber-Modified Asphalt Mixes," Journal of Transportation Engineering, Vol. 114, No.
3, American Society of Civil Engineers, May 1988, pp. 259-277.
38. Fortsie, Douglas A., "Letter to the FHWA Region 9," dated August 21, 1991, Arizona
Department of Transportation, Provided as personal correspondence, March 9, 1993.
RECYCLING OF ASPHALT PAVEMENTS USING AT LEAST 80 PERCENT
RECYCLED ASPHALT PAVEMENT (RAP)
Overview
Recycling of asphalt pavements has been shown to be both technically and economically
viable, and has been among the standard practices of many State and local highway agencies
in the United States in recent years. The benefits of asphalt recycling include cost savings,
conservation of asphalt and aggregate resources, conservation of energy, preservation of
existing highway geometries, and preservation of the environment.
From the standpoint of conservation of natural resources, it is desirable to use as much
RAP (Recycled Asphalt Pavement) as possible in the recycled asphalt paving mixtures.
However, the maximum percentage of RAP that could be incorporated in a recycled mixture
might be limited by the properties of the RAP used. Old asphalt pavement usually contains a
binder that is hard and brittle, and an aggregate that has been degraded to some extent. The
general principle in asphalt recycling is to blend the RAP with a soft asphalt or rejuvenating
agent, and a coarse aggregate in the proper proportions such that the resulting recycled
mixture would have a binder of suitable rheological properties and an aggregate blend of
desirable gradation. A very high percentage (over 80 percent) of RAP could only be used
under the following circumstances:
• The RAP is lean in asphalt, and additional soft asphalt could be incorporated without
addition of virgin aggregate.
96
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• The RAP contains a soft binder that need not be rejuvenated and could allow for some
further hardening from the recycling process.
If the aggregate in the RAP contains an excessive amount of fines, an adequate propor-
tion of virgin coarse aggregate would need to be added to upgrade the aggregate gradation.
This would require a lower percentage of RAP to be used in the recycled asphalt mixture.
Currently, there are only three asphalt recycling processes that can successfully utilize at
least 80 percent RAP. They are: (1) cold in-place recycling, (2) hot in-place recycling, and
(3) hot-central plant recycling by means of the proprietary CYCLEAN* process.
Cold in-place recycled materials are usually used as a stabilized base course to be
covered with a chip seal in low-volume roads, or overlaid with a hot or cold surface mix.
Pavements with excessive patching, weak subgrade due to water damage, or stripping
problems are not recommended for cold in-place recycling.
Hot surface recycling is usually used to correct surface defects such as roughness and
weathering of pavements that are structurally adequate. Currently, this recycling process is
also limited to a depth of 50 mm (2 in).
Among these three recycling processes, the hot central plant recycling can produce mixes
of the highest quality. The hot recycled mixes are usually used as surface structural mixes.
However, due to the problem with smoke emission, utilization of greater than 80 percent
RAP in the recycled mix has been limited to the CYCLEAN* process that uses the micro-
wave technology. For conventional hot mix asphalt plants, the typical maximum RAP is
limited to 30 to 50 percent of the mix. Conventional plants producing hot mix asphalt with
RAP contents exceeding those limits usually fail to meet local air quality requirements.
Definitions of Recycling Categories
The Federal Highway Administration classifies asphalt pavement recycling into surface,
cold-mix, and hot-mix recycling.(1) The definitions for these three categories are as follows:
• Surface Recycling — Reworking in-place of the surface of an asphalt pavement to a
depth of less than about 50 mm (2 in) by any of the suitable machinery available (such as
heater-planer, heater-scarifier, hot-milling, cold-planing, or cold-milling devices). This
operation is a continuous, single-pass, or multistep process that may involve the use of
added materials, including aggregate, modifiers, or asphalt mixtures (virgin or recycled).
• Cold-Mix Recycling — Reuse of untreated base materials and/or asphalt pavement that is
either processed in-place or at a central plant with the addition of asphalt emulsions,
cutbacks, portland cement, lime, and/or other materials as required to achieve desired
mix quality, followed by placement and compaction.
• Hot-Mix Recycling — Removal of more than the top 25 mm (1 in) of an asphalt
pavement with or without removal of underlying pavement layers (e.g., untreated base
97
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materials) that is processed by sizing, heating, and mixing in a central plant with
additional components such as aggregate, bitumen, or recycling agents and then relaid
and compacted according to standard specifications for conventional hot mixtures (e.g.,
hot mix asphalt base, binder, and leveling or surface course).
Results from Survey of Highway Agencies
Currently, 31 State transportation or highway departments in the U.S. and 3 transporta-
tion departments from Canada have responded to the survey on the use of at least 80 percent
RAP in asphalt pavements. A condensed summary of the survey results is displayed in table
14. Of these 34 responses, 8 States in the U.S. and 1 Province in Canada have indicated
experience with the use of at least 80 percent RAP.
Of these seven positive responses, three States have indicated experience with using at
least 80 percent RAP in hot-in-plant mixes. The mixers used were a CYCLEAN" (micro-
wave heater) mixer and a drum mixer with a special heat shield. The reported projects that
used the CYCLEAN* method had ages ranging from 2 to 25 months. The overall condition
of these pavements was good, and no rutting, cracking, raveling, or stripping problems were
reported. However, due to the young age of these pavements, the long-term performance of
these mixtures could not be assessed. The project that used the drum mixer was reported to
have performed well and carried loads in excess of design. Light raveling and moderate-to-
high cracking were reported after 8 years of service.
Serious smoke emission problems have been reported when high percentages of RAP
were used in conventional asphalt mixers. When more than 70 percent RAP was used in
demonstration projects in Oregon, smoke emissions with opacities above 20 percent were
encountered.p>3)
^ Only one State has responded as having had experience with using over 80 percent RAP
in hot surface recycling. The process used a Pyrotech hot in-place recycling train Problems
with excessive numbers of starts and stops, which caused excessive roughness requiring
pavement grinding, were reported. This problem might be due to the inexperience of the
contractor. The reported projects were only 3 to 5 months old, and thus their long-term
performance could not be assessed.
Five States and one Canadian Province have indicated experience with using over 80
percent RAP in cold in-place recycling. The typical equipment used in the recycle train
include a milling machine and a continuous pug mill with emulsion feed. Of the old
pavement, 25 to 127 mm (1 to 5 in) could be milled off and mixed in place with an added
asphalt emulsion and coarse aggregate. The compacted cold-recycled mixtures were usually
covered with a chip-seal or sand-seal for low-volume roads, and. overlaid with a hot-mix
surface course for medium- or high-volume roads. The cold-recycled mixtures generally
performed well. Problems reported included slight raveling, cracking, and bleeding
98
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Table 14. Summary of the survey on pavements using more than 80 percent RAP.
STATE
Florida
Georgia
Georgia
Georgia
Georgia
Georgia
Georgia
Georgia
Idaho
Idaho
Idaho
Idaho
Maryland
Nebraska
METHOD USED (Plant Type)
In situ Travelina
Cold Pit
1
1
1
Hot Pit
1
1
1
1
Conven
Hot Pit
Microwave
Cyclean* Pit
1
1
1
1
1
1
1
1
1
Recovery
Process
& Depth
Stockpile
Stockpile
Stockpile
Stockpile
Stockpile
Stockpile
Stockpile
Stockpile
2" Milled
2" Milled
2" Milled
3.6" Milled
4" Milled
3 • 6" Milled
MIX FORMULATION
WRAP
Used
100
eo
90
90
90
90
SO
90
Additives
Used
4%
4%
4%
% Virg.
Agg.
10
10
10
10
10
10
10
20
0
% Total
Aph Cont
6.42
6.42
6.42
E.42
6.21
5.21
6.21
6.21
6.5$
5.0$
6-6$
unk
6.8
HOT MIX BINDER AND TEMP (F)
% From
RAP
6.45
5.45
5.46
6.46
6.21
5.21
6.21
5.21
5.21
6.5$
6.5$
5.8$
6.8
%NeW
Aphlt
0
0
0
0
0
0
0
0
0
2$
1.6$
1.5$
1
%Total
Binder
6.46
6.46
6.46
6.45
5.21
6.21
5.21
6.21
6.21
6.8
Temp
©Pit
300
300
300
300
300
300
300
300
300
Temp
@Site
290
290
290
290
290
290
290
290
290
17
17
17
17
16
17
20
23
20
3
3
5
6
10
1
2
0-10E
PERFORMANCE
Performance Compared to Control
Rutting
4
4
4
4
4
4
1
3
Crack
4
4
4
4
4
4
1
6
Ravel
4
4
4
4
4
4
1
3
Strip
4
4
4
4
4
4
1
3
Overall
4
4
4
4
4
4
1
4
SEE
NOTE
11
1
2
4
4
4
4
12,$
12,$
12.$
12.$
14
VO
("F-321/1.8 = °C
NOTES:
ALL RESPONSES INDICATED NO SAFETY OR ENVIRONMENTAL PROBLEMS WERE ENCOUNTERED.
ALL PAVEMENT SECTIONS ARE TRAFFIC LANES EXCEPT WHERE NOTED.
ALL PERCENTAGES ARE BY WEIGHT OF MIX UNLESS NOTED OTHERWISE.
PERFORMANCE RATING SCALE:
(1) POOR
(2) SLIGHTLY SUBSTANDARD
(3) AVERAGE
(4) GOOD
(5) EXCEPTIONALLY GOOD
-------
Table 14. Summary of the survey on pavements using more than 80 percent RAP (Continued).
1 - NO EXPERIENCE WITH OVER 80% RAP.
2 - VIRGIN AGG. IS 10% LOCAL SAND.
3 - VIRGIN AGG. IS 10% #89 STONE.
4 - TEST SECTION IS SHOULDER WIDENING.
5 - DRUM MIXER USED. PAVEMENT PERFORMED WELL.
6 - PROJECT DID NOT GO WELL RATING.
7 - PROJECT WAS A SUCCESS RATING.
9 - MARGINAL SUCCESS RATING.
10 - VERY SUCCESSFUL RATING.
11 - ONE-HALF PROJECT PLACED WITH LIME ADDITIVE.
12 - PYROTECH HOT-IN-PLACE RECYCLING TRAIN USED.
13 - THESE ARE GENERAL CONDITIONS ONLY, NEW MEXICO HAS 120 PROJECTS
14 - SC & CRSH = SCARIFY, REMOVE, CRUSH RAP MATERIAL
$ - PERCENT BY WEIGHT OF RAP AGG. & VIRGIN AGG.
-------
Table 14. Summary of the survey on pavements using more than 80 percent RAP (Continued).
STATE
North Carolina
Ohio
Oklahoma
Oregon
Oregon
Oregon
Oregon
Oregon
Oregon
Oregon
Oregon
Pennsylvania
Rhode Island
South Dakota
Vermont
Washington
West Virginia
METHOD USED (Plant Type)
In situ Traveling
Cold Pit
1
1
1
1
1
1
1
1
1
1
Hot Pit
Conven
Hot Pit
1
Microwave
Cyclean* Pit
1
Recovery
Process
& Depth
2" Milled
2" Milled
2" Milled
2" Milled
2 - 4" Milled
1.6 -2" Milled
2" Milled
1.6" Milled
2" Milled
1 .6" Milled
MIX FORMULATION
%RAP
Used
80
100
100
100
100
100
100
100
100
100
90
Additives
Used
AR-2000
1.1%HFE-1BO
1.1%HFE-1EO
1 % CMS-2S
1.4-1.5%
CMS
1 % CMS-2S
1 4% CMS-2S
1 - 2% CMS-
2S
1-2% CMS-
2S
2% CMS-2S
.4% CMS-2S
RenOil-1736
% Wfl.
Agg.
20
10
% Total
Aph Cont
5.2
4.1 -4.6
HOT MIX BINDER AND TEMP (F)
% From
RAP
3.7
% New
Aphlt
1.6
%Total
Binder
6.2
Temp
©Pit
260
Temp
@Site
(mo)
186
64
64
64
78
78
78
78
84
eo
102
30
3
PERFORMANCE
Performance Compared to Control
Rutting
Crack
Ravel
Strip
Overall
Note 6
Note 7
Note?
Note?
Note6
Note 7
Note?
Note 9
Note 10
SEE
NOTE
1
1
1
6
8
8
8
8
11
1
1
1
(°F - 321/1.8 = °C; 1 in = 25.4 mm
NOTES:
ALL RESPONSES INDICATED NO SAFETY OR ENVIRONMENTAL PROBLEMS WERE ENCOUNTERED.
ALL PAVEMENT SECTIONS ARE TRAFFIC LANES EXCEPT WHERE NOTED.
ALL PERCENTAGES ARE BY WEIGHT OF MIX UNLESS NOTED OTHERWISE.
PERFORMANCE RATING SCALE:
(1) POOR
(2) SLIGHTLY SUBSTANDARD
(3) AVERAGE
(4) GOOD
(5) EXCEPTIONALLY GOOD
-------
8
Table 14. Summary of the survey on pavements using more than 80 percent RAP (Continued).
1 - NO EXPERIENCE WITH OVER 80% RAP.
2 - VIRGIN AGG. IS 10% LOCAL SAND.
3 - VIRGIN AGG. IS 10% #89 STONE.
4 - TEST SECTION IS SHOULDER WIDENING.
5 - DRUM MIXER USED. PAVEMENT PERFORMED WELL.
6 - PROJECT DID NOT GO WELL RATING.
7 - PROJECT WAS A SUCCESS RATING.
9 - MARGINAL SUCCESS RATING.
10 - VERY SUCCESSFUL RATING.
11 - ONE-HALF PROJECT PLACED WITH LIME ADDITIVE.
12 - PYROTECH HOT-IN-PLACE RECYCLING TRAIN USED.
13 - THESE ARE GENERAL CONDITIONS ONLY, NEW MEXICO HAS 120 PROJECTS
14- SC & CRSH = SCARIFY, REMOVE, CRUSH RAP MATERIAL.
$ - PERCENT BY WEIGHT OF RAP AGG. & VIRGIN AGG.
-------
was generally attributed to the addition of an excessive amount of asphalt emulsion in the
recycled mix. In most cases, the observed distress, such as cracking or rutting, was
attributed to the problem in the hot-mix surface course or the open-grade friction course that
was placed on top of the cold-recycled mixture, rather than to the cold-recycled mixture
itself.
Performance of Recycled Asphalt Pavements Using At Least 80 Percent RAP
Due to the limited usage of hot central-plant recycled asphalt mixtures using over 80
percent RAP, long-term performance data on these materials are not available. In the
Oregon demonstration project, satisfactory recycled asphalt mixtures incorporating from 80
to 100 percent RAP were able to be designed in the laboratory to meet all the Hveem mix
design criteria.® However, in actual construction, due to problems with emission, only 70
percent RAP was incorporated in the hot recycled mix. Though the new recycled pavement
surface was reported to be rougher than an average new hot mix asphalt pavement, the
recycled pavement was reported to perform well and to have carried traffic well in excess of
the design loadings after 10 years of service.
When properly executed, hot surface recycling is an effective rehabilitation method to
correct surface defects of pavements that are structurally sound. The Ontario Ministry of
Transportation reported that the hot-surface recycled mix surface looked older and drier.(4) It
was thought to be due to the asphalt cement not being rejuvenated sufficiently. The perfor-
mance of these pavements was reported to be comparable to conventionally rehabilitated
pavements. Since all the longitudinal joints were formed hot in the hot surface recycling
process, centerline cracks were reported to be less likely to arise. The typical reported
distresses are coarse aggregate loss from the surface and reflective cracking after 1 year of
service. Reflective cracking is usually expected when a thin overlay (conventional or
recycled) is placed over a cracked pavement.
The overall performance of cold in-place recycled pavements has been very good on a
large percentage of the projects.® Of the 13 recycled projects reported by California DOT,
9 were reported as having good performance after 5 years of service. Poor performance in
the California projects was attributed to moisture damage, nonuniform distribution of binder,
or excessive binder contents in the different projects. The cold in-place recycling project in
Indiana was reported to be performing better than the conventional pavement. Kansas and
Maine DOT'S reported less reflective cracking in the cold-recycled pavements as compared
with conventional and hot-recycled pavements. Of the 54 projects constructed from 1984 to
1986 in New Mexico, only one project showed signs of distress (rutting) as of 1987. Of the
52 cold-recycled pavements evaluated in Oregon, 47 had good or very good performance.
Pavements that had poor performance were attributed to: (1) using too high a recycling
agent content, (2) placing a tight seal or (dense wearing course too soon, (3) placing the cold-
recycled mixture on a delaminated layer of old pavement, and (4) failing to provide some
type of seal before freeze/thaw conditions. Oregon DOT reported service lives for low
volume roads of 6 to 8 years for cold in-place recycled pavements with chip seal when
projects are properly selected.(6)
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First Cost Comparison of Recycled Asphalt Pavements Using At Least 80 Percent RAP
Substantial cost-savings from hot-mix asphalt recycling have been reported and well
documented in the literature. However, the available information deals mainly with recycled
pavements using less than 80 percent RAP. In Florida, where up to 50 percent RAP could
be incorporated in the recycled hot mix, the cost savings from the utilization of hot asphalt
recycling is 15 to 30 percent as compared with the conventional paving approach.m In
demonstration project no. 39 in Oregon, where 74 percent RAP was used in the hot recycled
mixture, a cost savings due to the saving of asphalt cement and aggregate was indicated.*3' A
savings of 2,452 Mg (2,756 tons) of asphalt cement was equated to a cost savings of
$220,472. The unit cost in providing the virgin aggregate was $5.65/Mg ($5.03/ton), while
the crushing cost for the RAP was $1.63/Mg ($1.45/ton). Cost savings were also reported in
the demonstration project in Utah for the utilization of 70 percent RAP.(8)
Substantial cost savings have also been reported in hot in-place and cold in-place
recycling. The Ontario Ministry of Transportation reported an average cost savings of 10
percent to 20 percent when a 40-mm (1.6-in) hot in-place recycled asphalt layer was
compared with a 40-mm (1.6-in) conventional hot-mix overlay.(4) The Oregon Department of
Transportation reported that, with the exception of two failures, the life-cycle costs for cold
in-place recycled projects ranged from 37 percent to 82 percent of the hot-mix overlay
alternative, when no credit is given to the hot-mix overlay for increased structural section.®
Indiana Department of Transportation reported that the cold recycling process was signifi-
cantly less expensive that the hot-mixed material.(9) The cost of a plant-mixed base was three
times that of the cold in-place recycled material.
Assessment
Currently, there are three asphalt recycling processes that can successfully utilize at least
80 percent RAP. They are: (1) cold in-place recycling, (2) hot in-place recycling, and
(3) hot central-plant recycling by means of the proprietary CYCLEAN* process.
Cold in-place recycled materials are usually used as a stabilized base course to be
covered with a chip seal in low-volume roads, or overlaid with a hot or cold surface mix.
When properly executed, cold in-place recycling can produce roads of excellent rideability
with minimal rutting and cracking.(1°-12> Careful selection of projects for cold in-place
recycling is needed to ensure success. Pavements with excessive patching, weak subgrade
due to water damage, or stripping problems are not recommended for cold in-place recy-
cling. a°'n>
Hot-surface recycling is usually used to correct surface defects such as roughness and
weathering of pavements that are structurally adequate.(4>13) The recycling process is also
limited to a depth of 50 mm (2 in). Smoke formation can be a problem in hot-surface
recycling when the pavement surface is overheated.(4) If properly executed, hot in-place
recycling has been shown to be a cost-effective technique for pavement rehabilitation.
104
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Among these three recycling processes, the hot central-plant recycling can produce mixes
of the highest quality. The properly designed and evaluated hot-recycled mixes are equally
good or better than conventional hot mixes, and are usually used as surface structural mixes.
However, due to the problem with smoke emission, utilization of greater than 80 percent
RAP in the recycled mix has been limited in conventional hot-mix plants. The CYCLEAN*
process, which uses the microwave technology, has been used successfully to produce mixes
containing as much as 100 percent RAP without smoke emission problems. Recent develop-
ment in drum mixer technology, such as the counter flow dryer-drum mix coater and the
double-barrel drum mixer, has minimized the smoke emission problem in hot-mix
recycling.(14) However, these pollution-free drum mixers are set up to recycle only up to 50
percent RAP, due to the small demand to produce mixes containing more than 50 percent
RAP. For a RAP material that has been substantially aged and deteriorated, adequate
amounts of virgin aggregate and recycling agent are required to be added to the RAP to
produce a high-quality hot mix. This will limit the percentage of RAP that could be
incorporated in the recycled mix.
References
1. Federal Highway Administration, Pavement Recycling Guidelines for Local Govern-
ments, Washington, DC, September 1987, 33 pp.
2. Dumler, J. and G. Beecroft, Recycling of Asphalt Concrete—Oregon's First Hot Mix
Project, Interim Report, Oregon Department of Transportation, November 1977.
3. Rusnak, J.S., Zhou, H., and S.E. Nodes, Woodburn Hot In-Plant Asphalt Pavement
Recycling Project, Final Report, Oregon Department of Transportation, May 1992.
4. Marks, P. and T.J. Kazmierowski, The Performance of Hot In-Place Recycling in
Ontario, Ministry of Transportation of Ontario, Canada, June 1992.
5. Epps, J.A., Cold-Recycled Bituminous Concrete Using Bituminous Materials, NCHRP
Synthesis of Highway Practice 160, Transportation Research Board, Washington, DC,
July 1990.
6. Scholz, T.V., Hicks, R.G., and D.R Rogge, In-Depth Study of Cold In-Place Recycled
Pavement Performance, Final Report, Volumes I, Oregon Department of Transportation,
December 1990.
7. Page, G.C.,"Florida's Experience in Hot Mix Asphalt Recycling," Hot Mix Asphalt
Technology, National Asphalt Pavement Association, Lanham, MD, Spring 1988, pp.
10-16.
8. Betenson, W.B., Hot Recycling ofAsphaltic Concrete Pavement, Utah Department of
Transportation, October 1980.
105
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9. ElMn, B.L., Evaluation of Recycled Bituminous Pavements, Final Report, Indiana State
Highway Commission, West Lafayette, Indiana, August 1978.
10. O'Leary, M.D. and R.D. Williams, In Situ Cold Recycling of Bituminous Pavements
mth Polymer-Modified High Float Emulsions, Transportation Research Record 1342
1992, pp. 20-25. . '
11. Rogge, D.R, Hicks, R.G., Scholz, T.V., and D. Allen, Use of Asphalt Emulsions for
In-Place Recycling: Oregon Experience, Transportation Research Record 1342 1992
PP- i-8- '
12. Harmelink, D.S., Cold-Recycling of Asphalt Pavement—U.S. 24, Colorado Department
of Highways, June 1990.
1
13. Vollor, T.W., Asphalt Pavement Recycling Primer, Final Report, Waterways Experi-
mental Station, Corps of Engineers, Vicksburg, MS, February 1986.
14. Brock, J.D., Dryer Drum Mixer, Technical Paper T-119, ASTEC Industries, Chatta-
nooga, Tennessee, 1989.
CRUSHED GLASS APPLICATIONS
Overview
As with most solid wastes, the exact amount currently being generated is not known, but
it was estimated that in 1988 approximately 10.9 million Mg (12 million tons) of glass were
discarded and about 1.46 million Mg (1.5 million tons) were used primarily as cullet for
glass manufacturing.
In the late 1960's only 3.4 million Mg/yr (3.5 million tons/yr) were being generated,
which included about 26 to 30 billion glass bottles and jars.(1~3) This constitutes an average
increase of almost 0.49 Mg/yr (0.5 million tons/yr) since 1968.
Glass recovered from the solid waste stream for recycling into glass products must be
sorted by color and be free from contaminants that tend to be cost prohibitive. (See
references 1, 4, 5, and 6.) In general, few sources of recycled glass exist, although cullets
from bottling plants, dairies, breweries, etc., or glass cleaned and separated at the source
(e.g., household separation) has proven to be economically feasible.(6) However in 1990,
glass that had been separated and crushed for recycling into glass containers sold for about
$62/Mg ($60/ton).(5) Even crushed, sorted glass selling for $31 to $62/Mg ($30 to $60/ton)
and unsorted glass costing as much as $34/Mg ($33/ton) for disposal in landfills is expensive
relative to conventional fine aggregate at $1.1 to $4.1/Mg ($1 to $4/ton) and high quality
coarse aggregate usually at less than $15.5/Mg ($15/ton).(5>6) Obviously, the availability,
cost, and proximity to the source of utilization will influence the economics.
106
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Glass has been used primarily on an experimental basis in the construction of highways,
therefore no established specifications for its use exist. Approximately nine States have set
specifications covering the incorporation of crushed glass into conventional highway
materials. ^ Applications include its use or disposal for:
• Partial replacement of fine aggregate in asphalt paving mixtures.
• Substitution of fine aggregate in unbound base courses.
• Mixing with embankment soils.
• Glass beads in line striping.
• Pipe bedding and filter materials in pavement edge drains.
Its direct use in portland cement concrete (PCC) is not feasible because of poor bonding
(adhesion), adverse chemical reaction, and reduction in concrete strength.® However, the
introduction of zirconosilicate glass and manufacturing of glass fibers or foamed glass for use
in PCC may provide benefits, but at a substantial increase in cost.
Specific applications of disposed, crushed glass in highway construction are presented
and discussed in the following sections.
Asphalt Paving Mixtures
The results of research on the use of recovered glass in bituminous concrete by Malisch
et al. is among the first reported attempts to utilize glass in highway pavements. (1'3) Their
findings indicated that mixtures composed entirely of glass aggregate could be designed by
the Marshall test, but degradation of elongated glass particles occurred during compaction,
and when exposed to water, loss of asphalt films (stripping) from the glass aggregate
occurred. The use of antistripping compounds or slow-setting cationic emulsions tended to
improve the resistance to stripping. Inspection of the test results for two different mixtures
indicated that the Marshall stability was low, being generally comparable to a sand asphalt
hot mix, and the flow was excessively high, except when the gradation was altered to
increase the voids in the mineral aggregate.
Opinions of researchers on the suitability of glass aggregate are quite different. In
Israel, 10 to 30 percent ground glass was used successfully as an admixture to increase skid
resistance of their limestone and dolomitic aggregates.(9) The key advantage was that the
crushed glass admixture was economically viable as compared to the prohibitive costs for
basaltic and granitic aggregates. However, Heinrich and Lindemann did not recommend the
use of glass because of poor adhesion between bitumen and glass, and also, because the price
of used glass was high, thereby offering no benefits for highway use.(10) The Vermont
Agency for Transportation constructed, without any apparent problems, 0.29 lane-kilometers
(0.48 lane-miles) of pavement containing 10 percent crushed glass crushed to 92 percent,
passing the 9.5-mm (3/8-in) sieve.(11) Glasphalt has been successfully mixed and placed on
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low-volume or low-speed roads in at least 45 locations in the U.S. and Canada between 1969
and 1988, but no high-speed highway application currently exist.2 <12)
Most Glasphalt has been placed on city streets, driveways, and parking lots. One
advantage for major parking areas is the increased reflectivity during nighttime conditions.
A commercial establishment's parking lot in Wisconsin was paved using 10 percent crushed
glass at additional cost to improve reflectivity.P) However, visibility of painted line striping
may be impaired by the reflectivity of asphalt mixtures containing glass.(12)
Hughes concluded from laboratory tests that it was feasible to use glass providing:®
• It is crushed to < 9.5-mm (S/s-in) size with no more than 6 percent minus no. 200 sieve.
• The amount of glass does not exceed 15 percent of the total mix.
• The tensile strength ratio (TSR) is 0.9 or greater because of the propensity to suffer
moisture damage.
These findings were based upon partial replacement of sand and greenstone aggregates in
the conventional mix with crushed glass that did not change the gradation significantly.
However, the use of crushed glass as an admixture could have a substantial influence on the
gradation and mixture's properties.
A similar laboratory study was conducted by Murphy et al. using a control mix, a mix
with 15 percent replacement with coarse crushed glass, and a third mix with 15 percent fine
crushed glass.® The crushed glass produced a 15 to 20 percent reduction in Marshall
stability and a 20 percent lower dry tensile strength. When the tensile strengths of the three
mixtures were evaluated after moisture conditioning, the control, coarse glass, and fine glass
mixtures had reductions of 25 to 30, 15, and 50 percent, respectively. However, the coarse
glass mixture had a 1.0 percent lower air-void content than the control mix, and moisture-
conditioned coarse glass mixtures with and without the antistripping additive had the same
tensile strength. Probably, the increased surface area of the fine crushed glass mixture
combined with its propensity for stripping caused the 50 percent reduction in tensile strength.
The tensile test results indicated that the moisture-conditioned specimens for the three
mixtures were not affected by the antistripping additive. The authors' recommendations
allowed the use of crushed glass in asphalt mixtures with the following restrictions:
* Maximum of 15 percent crushed glass (by weight of total aggregates).
• Requirement of 100 percent passing the 9.5-mm (S/s-in) sieve with no more than 8
percent passing the no. 200 sieve.
• Asphalt mixtures containing crushed glass shall contain an antistripping additive that can
be demonstrated to satisfactorily improve the moisture damage resistance of the mixture.
2Glasphalt is a term adopted for asphalt paving mixtures that contain crushed glass.
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• Crushed glass shall not be used in dense-graded or open-graded friction course mixtures.
Also, they recommended that these special provisions could be included in specific
contracts involving asphalt paving where a source of glass is available. However, the use of
glass should be optional to the contractor to allow the most economical materials to be used.
Several reports that were written on the use of waste materials in highway construction
have emphasized different aspects of glass in asphalt paving mixtures.(8>14) The loss of
adhesion between asphalt and glass as well, as the fracture of glass under traffic and the fact
that it crushes more easily than quality aggregate is noted in both reports. A maximum of 15
percent glass in HMA is considered as acceptable, except that it should be used only in the
base course to minimize potential skid resistance and surface raveling problems. Because of
the various problems with glass, it is preferred that glass in wearing courses be limited to use
on low-speed and low-volume streets and highways.(14)
Embankment and Base Materials
The use of glass in unbound aggregate base layers and in embankment construction has
been considered by several States. ^'^ The Washington State DOT has prepared a proposed
general special provision that allows aggregate base with reclaimed glass to be processed and
used as crushed surfacing base course, gravel backfill, pipe bedding material, etc.(14)
However, the blended material (aggregate and crushed glass) must conform to all specifica-
tions in section 9-03 of the standard specifications, except that the Los Angeles abrasion
requirement is waived in certain applications. Furthermore, the blended material cannot have
more than 15 percent reclaimed glass and no more than 10 percent larger than 6.4 mm (l/4
in) shall be glass. In essence, they have accommodated the use of glass providing the
aggregate-glass blend conforms to the conventional aggregate specifications.
Maine's special provisions, section 203, allow the disposal of crushed glass in place of
common borrow in subgrades or embankments. They require the crushed glass to be placed
and compacted in a maximum thickness of 200 mm, loose measure. The top of the layer
must be a minimum of 600 mm below the finished surface of the subgrade and 600 mm
above the natural original ground elevation. It is paid for on the basis of common borrow.
This approach allows for disposal of glass, but it does not really provide for use as a
substitute material as is done by the Washington State DOT.
The literature pertaining to glass in highway construction was evaluated by Halstead who
concluded that the preferred use of waste glass is in the construction of embankments and
fills.w More research and field experimental projects are needed before crushed glass can be
used as a partial replacement for aggregates.
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Other Applications
Crushed glass has been used directly as an aggregate replacement for highway subdrain
(french drain) construction.a5) In most cases, even when using conventional aggregates, a
geotextile must be used to act as a filter to prevent clogging by fine-grained soil particles.
Many other applications require the processing of glass into specialized products such as
mineral wool insulation, tiles, and glass beads. The U.S. Bureau of Mines Ceramic
Research Laboratory in Tuscaloosa, Alabama, has made glass beads in the 100- to 200-mesh
range using the glass fraction from incinerator residue.(15) These types of products are
generally experimental or of limited production and cannot be considered accepted as
commercially operational systems. However, glass beads made from 100 percent recycled
soda lime window glass for use in highway striping paints are manufactured in Oregon by
Potters Industries (documented on page 1-68, appendix I of reference 13).
Results From Survey of State Highway Agencies
Five of the twenty-three States responding to the survey on crushed glass in highway
construction reported no experience with the use or recycling of glass. Of the remaining
States, 12 test pavements were constructed with crushed glass being used as a soil additive or
as an admixture to hot-mix asphalt. All test sections were less than 28 months old, so long-
term performance information was not available. Florida is evaluating glass in a hot-mix
asphalt surface course, structural mix, and as an aggregate for soil stabilization. No
difference between test sections was observed after 4 months of service.
Similarly, Pennsylvania constructed an asphalt pavement and a stabilized subgrade using
100 mm (4 in) of glass covered by 200 mm (8 in) of soil. The section proved to be
unstable, but showed that blending of soil and glass appears to have provided satisfactory
results. Raveling of small glass pieces occurred and after 27 months they reported that this
asphalt pavement section exhibited poor performance. They reported that glass should be
limited to base and binder courses if it is used in asphalt pavements. Furthermore, they
believe the only benefit of using glass in pavements was the avoidance of landfill costs that
range from $52 to $72/Mg ($50 to $70/ton) of glass. The cost of processing glass prior to
use was $15 to $21/Mg ($15 to $20/ton), which does not include transportation, handling,
and additional construction costs.
New Jersey has constructed five projects using glass in the binder course and one in the
friction course. To date, no difference has been observed between glass sections and
conventional sections. No benefits are expected from the use of glass other than removal of
this material from the waste stream. However, New York allows glass as a replacement for
up to 5 percent of aggregate weight as an option in all contracts other than for wearing
course asphalt mixtures. Conversely, Connecticut does not use glass as an additive to hot
mix asphalt due to potential safety and/or performance problems of inadequate skid resis-
tance, raveling, broken glass, or glare. They do allow glass to be used as a fill material for
embankments.
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Hawaii and Maryland permit glass in hot-mix asphalt base courses, but they have not
used glass as yet. The city and county of Honolulu has two experimental Glasphalt parking
lots in current use.
New Hampshire uses glass for soil stabilization in base and subbase construction.
Minnesota's test section used glass to successfully stabilize a sandy soil for use as a base
course. In Missouri, the availability of good aggregates makes the costs associated with
using glass prohibitive.
Assessment
The quantity of crushed glass is relatively small with respect to potential uses in the
highway network. Also, the availability of crushed glass for highway construction is limited
to areas near cities that are major generators of glass. Because of its value, glass that has
been sorted is best suited for recycling back into glass products.
Crushed glass has been used successfully as an aggregate replacement in base course
materials, as a drainage media, and in asphalt pavements subjected to light traffic volumes.
Some States already allow its use as a partial replacement of granular materials providing the
materials containing glass meet the test requirements as specified for the application (e.g.,
base course, subgrade, etc.) This approach can be utilized in States that do not currently
allow the use of crushed glass as a partial replacement of granular material.
In summary, glass has been incorporated into the base and subbase layers of highway
pavements. However, at this time it should be considered experimental as an aggregate
replacement in surface coarse mixtures. The use of glass typically increases the cost of the
pavement without imparting any beneficial attributes to a pavement other than reflectivity. It
can generally be considered as being non-beneficial to the properties of conventional
construction materials and to the performance of highway pavements.
References
1. Malisch, W.R., Delbert, E.D., and E.G. Wixson, Use of Domestic Waste Glass as
Aggregate in Bituminous Concrete, Highway Research Record 307, Transportation
Research Board, 1970, 9 pp.
2. Malisch, W.R., Delbert, E.D., and B.G. Wixson, Use of Domestic Waste Glass for
Urban Paving, Final Report, Civil Engineering Department, University of Missouri-
Rolla, July 1973, 106pp.
3. "250,000 Crushed Bottles Help Pave Parking Area," Construction Digest, July 16, 1970,
p. 70. '•-...;•-•
4. Murphy, Robert J., Research Requirements for the Recycle and Reuse of Solid Waste
Materials, Florida Highway Technology and Industry Council, February 1989.
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5. Hughes, C.S., Feasibility of Using Recycled Glass in Asphalt, Final Report, Virginia
Transportation Research Council, March 1990, 24 pp.
6. Murphy, K.H., West, R.C., and G.C. Page, Evaluation of Crushed Glass in Asphalt
Paving Mixtures, Research Report FL/DOT/SMO/91-388, State of Florida Department of
Transportation, State Materials Office, April 1991, 15 pp.
7. Halstead, Woodrow J., Use of Waste Glass in Highway Construction (Update-1992),
VTRC93-TAR2, Virginia Transportation Research Council, January 1993.
8. Imtiaz, Ahmed, Use of Waste Materials in Highway Construction, Final Report,
Synthesis Study, Joint Highway Research Project, FHWA/IN/JHRP-91/3, May 1991, pp.
45-55.
9. Peleg, M., Study of Road Friction, R&D Report, Technion Research and Development
Foundation, Ltd, Israel, December 1972, 116 pp.
10. Heinrich, P. and B. Lindemann, Used Glass as an Aggregate for the Production of
Rolled Asphalt, Transpress, VEB fuer Verkehrswesen Strasse, Vol. 17, No. 3, March
1977, pp. 106-109.
11. Frascoia, Ronald I., Glasphalt Pavement Construction on VTRoute 12, Number 092-4,
Research Update, Materials and Research Division, Vermont Agency of Transportation,
October 1992.
12. Larsen, D.A., Feasibility of Utilizing Waste Glass in Pavements, Connecticut DOT,
Bureau of Highways, Office of Research and Materials, Report No. 343-21-89-6, June
1989.
13. Weigel, John L., Quality Control Supervisor, Payne and Dolan, Inc., P.O. Box 781,
Waukesha, WI 53187, Personal Communication, February 1, 1993.
14. Swearingen, D.L., Jackson, N.C., and K.W. Anderson, Use of Recycled Materials in
Highway Construction, Final Report, Washington State Department of Transportation,
WA-RD252.1, February 1992, pp. 10-13.
15. Abrahams, J.H., Jr., Recycling Container Glass—An Overview, Solid Waste Resource
Conference, Columbus, Ohio, May 1971, Printed by Glass Container Manufactures
Institute, Inc., 330 Madison Avenue, New York, NY 10017.
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RECYCLED PLASTIC APPLICATIONS
Overview
Plastics constitute over 7 percent by weight of the municipal solid waste (MSW) stream
or approximately 12 to 20 percent of the volume.(1>2) Estimates of the total amount of
plastics generated yearly range from 12.7 to 22.7 million Mg/yr (14 to 25 million tons/yr).
Most plastic materials are derived from petroleum. Therefore, the value of plastics are
strongly related to petroleum prices. For instance, a 2-liter soft drink bottle, which consists
of a polyethylene terephthalate (PET) bottle and a polyethylene (PE) basecup, may sell for up
to $1.76/kg ($0.80/lb) for the PET plastic.a) This is about twice the price of aluminum.
One organization recycles approximately 45,400 Mg (50,000 tons) of soda bottles returned
by consumers in those States with bottle deposit laws.(1)
Other types of resins and plastic products in the MSW stream include: a'3)
• Low-density polyethylene (LDPE): film and trash bags.
• High-density polyethylene (HDPE): 1-gal milk jugs.
• Polystyrene (PS): egg cartons, plates, and cups.
• Polyvinyl chloride (PVC): siding, flooring, and pipes.
• Polypropylene (PP): luggage and battery casings.
As with any high-cost material, the key to recycling appears to be the availability of sorted
and reasonably clean material that is acquired prior to co-mingling with other materials in the
MSW stream. Therefore, emphasis should be placed on the collection of sorted material to
maximize utilization rather than attempting to sort from co-mingled materials.
The use of plastics in highway construction includes products or uses for the following
products or applications and their approximate recycled plastic content: ^
Geotextiles
Traffic control barricades
Fence posts
Guard rail posts
Flexible delineator posts
Posts (sign and supports)
Speed bumps
Concrete grade stakes
Curb edging
Concrete cylinder molds
Drainpipe
Lumber (plastic)
Parking bollards
60 percent to 100 percent PET, PP
100 percent
100 percent
(experimental)
50 percent to 100 percent
100 percent ,
100 percent
100 percent
100 percent HDPE, LDPE, or PP
97 percent PP
20 to 60 percent
100 percent HDPE, LDPE, or PP
97 percent, HDPE, LDPE, PE, PET
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Parking stops
Fencing (plastic)
Park benches
Signs (roadway)
Temporary curbing
Modifier for hot-mix asphalt pavements
100 percent
100 percent
100 percent
100 percent
100 percent
0 to 100 percent
The use of plastics in highway construction is being examined by seven States.00 Most
post-consumer and co-mingled plastics that are recycled go into the manufacturing of
products. Some of these products find application to highway construction, e.g., traffic
cones, rebar spacers, and those previously listed.® The literature research has shown that
the primary use of plastics in highway construction is in the fabrication of construction and
traffic safety products.
Asphalt and Mixture Modifier Applications
There are numerous processes that blend virgin plastics (polymers) with asphalt cements
to produce polymer-modified asphalt cements and mixtures. Considerable technical informa-
tion is available in the literature on this subject. Numerous highway rehabilitation projects in
Europe, the U.S., and other countries have been successfully paved with asphalt mixtures
containing these polymers.® The only two known products that include recycled plastic
polymer-modified asphalt cement are Novophalt* and Polyphalf, both of which meet new
SHRP asphalt pavement specifications.3'4®
The properties of conventional paving grade asphalt cements compared with those
processed into Novophalt* indicate that the viscosity and stiffness of the binder are increased
substantially by polymer modification. Laboratory rutting/wheel-tracking tests performed by
Nievelt Laboratories in Austria and the Transport and Road Research Laboratory (TRRL) in
Crowthorne, England resulted in much lower rutting of the polymer-modified asphalt
mixtures than the original asphalt mixtures.® Although it is a different process, Polyphalt™
uses polyethylene in similar concentrations so the properties of the asphalt and mixtures
should be similar to that achieved using Novophalt*.
3A trade name for a polymer-modified asphalt that is produced by the high-shear blending
of 4 to 6 percent polyolefins (by weight of asphalt cement), primarily LDPE (virgin with 85
to 95 percent recycled), with asphalt cement. Marketed by Novophalt* America, Inc.
4A trade name for a polymer-modified asphalt cement using an emulsifying agent that
keeps the PE in suspension for storage. It was developed under the auspices of the Universi-
ty of Toronto Innovations Foundation. This process uses 100 percent recycled polyethylene
that is blended with the asphalt cement in concentrations ranging from 3 to 10 percent (by
weight of asphalt cement).
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Highway pavements constructed in Georgia with Novophalt* are performing well after
one year of service. On 1-75, polymer- (plastic) modified test sections had considerably less
rut depth than the control.(Q Also, Novophalt* was used in the construction of SMA test
sections, but their age is insufficient to assess differences in performance. A project in
Canada had 6- to 7-mm-deep ruts in both conventional and polymer-modified sections. No
difference was observed in crack resistance or overall performance of the pavement test
section.® In general, beneficial properties and improved performance can be achieved using
polymers. However, polymers are not a cure-all. Proper selection and proportioning of
asphalt cements and aggregates is still an essential element in achieving good performing
pavements.
A Novophalt'-modified hot mix asphalt pavement costs about $6.35 to $7.26/Mg ($7.00
to $8.00/ton) of hot-mix over that for the conventional mix, or about a 30 percent increase in
cost. If increased service life and lower maintenance costs can be realized, the life-cycle
cost of polymer-modified binders will be lower than that of conventional mixtures.®
Other Uses of Plastics
The list of products given in the overview represent those produced by manufacturers
that are useable directly in highway structures (geotextiles, drainpipe, etc.),.for construction
(traffic control barricades, cones, concrete cylinder molds, etc.) and for appurtenances to the
highway system (fence, fence posts, delineator posts, signs). Some States have specifications
for plastic fence posts and delineator posts (Florida, New York, Nevada, Tennessee).®
Maine specification 652.02 was amended to include "All barricades, cones, drums, and
construction signs may be constructed from new or recycled plastic."
Collection of post-consumer plastics by resin type rather than co-mingled plastics would
enhance manufacturers' product quality and provide greater incentive for utilization of
recyclable plastics assuming demand from the consumer (highway agencies) also expanded.
Results from Survey of State Highway Agencies
Nineteen States responded to the survey on recycled plastics for highway construction.
Of those responding, six States have not utilized recycled plastics. In 1991, Georgia used
approximately 2.7 Mg (3 tons) of recycled LDPE in the construction of Stone Matrix Asphalt
(SMA) and Porous European Mixtures (PEM) test sections on 1-85 in Jackson County. Also,
45.4 Mg (50 tons) of recycled LDPE was used in 15,300 Mg (18,000 tons) of open-graded
friction course (OGFC) mix that was placed on 1-75 in Bartow County in 1992. Both
projects used the Novophalt* process to produce the polymer-modified asphalt cement. No
"drain down" problems occurred even though a higher binder content was used on the
polymer-modified section. There has been insufficient time to assess the performance of
these test sections.
Connecticut is conducting studies to evaluate, under field conditions,-delineator posts
containing 46 percent recycled plastic. Also, traffic barricades made of 100 percent recycled
HDPE were tried on an Interstate construction project. Their light weight and inability to be
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anchored caused excessive blowdown of the barricades. However, traffic cones made from
PLV or LDPE are being purchased for maintenance and construction detours. The supplier
does not specify recycled content even though the State has a standard specification on
recycled plastic content of traffic cones.
Michigan uses delineator posts, landscape timbers, and picnic table boards containing
recycled plastic. Research into plastic guardrail posts, including dynamic load tests and
ultraviolet warping behavior tests, are currently underway. Guardrail post pendulum tests
will be performed at -3 °C, 20 °C, and 49 °C to determine if posts conform to a minimum
fracture energy of 7510 N-M (5,500 ft-lb). If successful, crash tests will be performed.
The current cost disparity between wood and recycled plastic guardrail posts is substantial,
$16.00 for wood vs. $62.00 for plastic (approximately four times greater). Another major
problem with recycled plastic posts is the variability in strength parameters due to impurities.
Oregon has used about 5.5 Mg (5 tons) of recycled plastic sign and fence posts, snow
poles, and sound barrier walls on an experimental basis to evaluate their performance
throughout various locations in Oregon. When these products were installed, the increased
weight of the recycled plastic necessitated increased personnel and machinery.
Assessment
In summary, recycled plastic guardrail posts and other experimental posts that are not
currently a manufactured product, have insufficient performance data to evaluate their
suitability for use in highway construction. Impurities, which affect strength properties and
densities that are greater than those found in wood products, suggest that it may be
impractical to use recycled plastics in certain applications. Increased costs, as much as four
times greater than wood, may result in life-cycle costs that are excessively high if service life
is not dramatically increased.
However, it seems reasonable to assume that State highway agencies can utilize currently
manufactured recycled plastic products providing they meet standard requirements/
specifications. Although many manufacturers label their products with the recycled content,
all producers should have similar labeling to facilitate purchasing of products according to
specifications.
The use of virgin plastic polymers for modification of asphalt cements is not a new
technology. However, the chemical variability in recycled plastics has been a deterrent to
the use of waste plastics in pavements. Other than differences in processing and type of
polymer, those processes using recycled plastics (Novophalt* and Polyphalt™) are similar.
Test sections are not yet old enough to determine if lower life-cycle costs will offset
increased initial expense.
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References
1. Smith, I.L., "Are There Plastics in Your Future?," ASTM Standardization News,
October 1988, pp. 34-37.
2. Adams, M., "Beatty: 'Develop Markets for Recycled Plastics'," Materials World,
Department of Materials Science and Engineering, University of Florida, Vol. 8, No. 1,
Fall 1990.
3. Recycling and Use of Waste Materials and By-Products in Highway Construction,
NCHRP Project 20-5, Topic 22-10, Transportation Research Board, Washington, DC,
1992.
4. Whitmill, M.E., Recycled Products and Solid Waste Materials Incorporated in Project
U-2003AA, NC Department of Transportation, February 1991.
5. Flynn, L., "Recycled Plastics Find Home in Asphalt Binder," Roads and Bridges,
March 1993, pp. 41-47.
6. Personal Communications, Bulletins, and Performance Information Releases from
Novophalt* America, Inc., Sterling, VA.
7. Swearingen, D.L., Jackson, N.C., and K.W. Anderson, Use of Recycled Materials in
Highway Construction, Appendix I, Report No. WA-RD252.3, Washington State
Department of Transportation, February 1992, pp. 1-174.
8. "Plastic Firms See Miles of Opportunity on U.S. Highways," Plastics News,
September 17, 1990.
OTHER MATERIALS
Coal Ash
Overview
There are three basic forms of ash produced in the combustion of coal for power
generation: fly ash (FA), dry bottom ash, and wet-bottom boiler slag.(1) In 1991, 65 Mg
(72 million tons) of ash were produced, with a breakdown of 74 percent fly, 20 percent
bottom, and 6 percent boiler slag.a>3>5) Fly ash consists mostly of the noncombustible mineral
material that is removed from the combustion chamber with the hot combustion gases.
Electrostatic precipitators or baghouses collect the ash. FA is a very fine, light
dust—primarily rock detritus that has collected in the fissures of coal seams, and constitutes
from 8 to 14 percent of the coal's weight. Bottom ash can be either dry or wet, depending
on the type of boiler in which the coal is burned. Bottom ash is the heavier, noncombustible
particles that collect in the bottom of a dry-bottom boiler. If a wet-bottom boiler is
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employed, the molten ash is tapped from the boiler and cooled using water that produces a
slag material.
The primary constituents of coal fly ash are silicon dioxide (SiO2) and aluminum oxide
(A12O3). In bituminous coal, the relative percentages are 55 percent and 26 percent,
respectively. For lignite and subbituminous coals, the ratios are 40 percent, 17 percent with
an additional 24 percent of calcium oxide (CaO). Other ingredients common to all coals
include ferric oxide (Fe^) and magnesium oxide (MgO). Trace elements of arsenic,
barium, cadmium, chromium, lead, mercury, selenium, and silver also occur, but in
extremely small amounts. ^
Applications
Fly ash has been incorporated into a number of highway-related construction activities.
In general, the six areas most often cited include:
• Lime (or cement)/fly ash/aggregate base course.
• Stabilized fly ash pavement.
• Lime/fly ash/soil subbase material.
• Fly ash embankments.
• Fly ash structural fill.
• Fly ash in grouts.
The amount of ash used in the U.S. varies. In 1986 for example, approximately 18
percent of the fly ash, 27 percent of the bottom ash, and 52 percent of the boiler slag was
used in all applications.® Of this amount, 26 percent was used by the electric utilities
themselves.® However, due to the much greater amounts of fly ash being produced, it is the
primary material used today in highway construction activities. Fly and bottom ashes are
used primarily as additives in cement and concrete products, road bases, and in structural
fills. Boiler slag is used as blasting grit, roofing granules, or for snow and ice control.
Approximately 9 percent of the annual generation is incorporated into cement and
concrete products.® Furthermore, the adoption of other uses in highway construction will
further reduce the amount of ash for disposal. Several southern States (Alabama in particu-
lar) have used the ash as a base material. In a demonstration, 36,300 Mg (40,000 tons) of
ash were placed as a 152- to 203-mm (6- to 8-in) layer under an asphalt paving course.
Georgia used it by combining it with cement and placing it as subgrade, base, and with the
blacktop.®
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Table 15 illustrates the wide variety of uses of coal ash, while several States have
specifications or guidelines that deal specifically with the use of ash as shown in table 16.
While incorporating ash into the above areas can improve the particular characteristics,
there is also an economic benefit as well. In 1987, the average price of coal ash was
$22/Mg (SlO/ton).^ [This figure varies by region—lower in the Southwest, $13/Mg
($12/ton) and higher in the Northwest, $77/Mg ($70/ton).](3) If used as a replacement,
substantial costs-savings may be incurred since the typical cost of cement averages $143/Mg
(SBO/ton).®
While FA is nonuniform in composition as outlined above, its major constituents are
present in relatively standard proportions. Thus, it can be said that in general, all fly ashes,
in the presence of lime and moisture, exhibit pozzolanic properties. Some FA contain
sufficient free lime to self-harden without the addition of lime or cement. Generally, lime is
added to a lime-fly ash-aggregate mixture from a low of 2 percent to a high of 8 percent.®
FA values range from 8 to 36 percent. Typical proportions are 2.5 to 4 percent lime and 10
to 15 percent FA. Aggregate sizes range from fine to coarse. In general, a fine-grained
aggregate will produce better durable mixes, but coarser-grained aggregate exhibits higher
strength and is more mechanically stable.
Curing conditions can greatly affect the final properties. The two primary variables are
time and temperature. For example, at temperatures below 4 °C (40 °F), the reaction
process ceases. Thus, as the temperature rises, the pozzolanic reaction rate increases. It has
been found that the chemical reactions will continue as long as there is sufficient lime and
FA available to react. Cores taken over a 10-year period have shown continued strength
gain.
Admixtures have been added to lime/fly ash (LFA) mixtures in order to accelerate
strength development as well as to improve the short-term durability. As is the case of most
of these types of materials, the compressive strength is substantially greater than the tensile
strength. Since tension is difficult to measure, it is common to combine tension and
compression into the flexural strength. In general, flexural strength is approximately 20
percent of the compressive strength. Other factors that are considered in the evaluation of
LFA mixtures include durability, bending resistance (stiffness), fatigue, and the coefficient of
thermal expansion. Another very interesting characteristic of LFA is its autogenous healing
or the ability to repair itself across internal cracks that may form.
Lime and fly ash added to aggregates (LFAA mixtures) have been used to produce a
high-quality base course in flexible pavement systems, and a high-quality subbase in rigid
pavement systems. Lime-fly ash-aggregate (LFAA) mixtures are used as base or subbase
courses. Compressive strength up to 2.1 kgVmrn2 (3,000 lbf/in2) have been found from a
number of sites, however, 0.35- to 0.70-kgf/mm2 (500- to 1000-lbf/in2) values are more
common. A wearing surface must be applied in order to protect the material from abrasive
effects of traffic from weather and water infiltration.
The LFA and LCFA mixtures lend themselves to conventional construction techniques.
The primary requirements needed to produce a good base or subbase include: thorough
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Table 15. Uses of coal ash (from reference 3).
FLY ASH
1. Raw material in portland cement.
2. Replacement for cement in concrete.
3. Cement replacement in precast concrete products.
4. Ingredient in aerated concrete.
5. Mineral filler in asphaltic concrete.
6. Aggregate for the stabilization of highway subgrades.
7. Aggregate for road base material.
8. Raw material in the manufacture of lightweight aggregates.
9. Material for structural fill.
10. Material for flowable fill or backfill.
11. Raw material for metal reclamation.
12. Filler material in plastics.
13. Sanitary landfill cover or liner.
14. Backfill for controlling subsidence in abandoned mines.
15. Backfill for fighting mine fires.
16. Amelioration of soils.
17. Raw material in brick manufacture.
18. Ingredient in the manufacture of roofing felt.
19. Raw material for making mineral wool insulation.
20. Source of cenospheres.
21. Ingredient in grouts.
22. Material for absorbing oil spills.
23. Medium for filtering insulating oils used by utilities.
24. Absorbent for dewatering sewage sludge.
25. Fixation ingredient for sulfate sludge.
26. Flowability agent in molding sand.
USES OF BOTTOM ASH
1. Aggregate in cold-mix asphalt.
2. Ingredient in bituminous stabilized bases for highways.
3. Aggregate in portland cement stabilized bases for highways.
4. Grit for ice-covered roads.
5. Filter material.
6. Structural fill.
USES OF BOILER ASH (Slag)
1. Sand-blasting grit.
2. Filter material for water treatment.
3. Raw material for mineral wool insulation.
4. Roofing granules in asphalt shingles.
5. Grit for ice-covered roads.
6. Structural fill and road bases.
7. Aggregate in highway construction.
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Table 16. States with guidelines for use of ash (from reference 3).
STATE
Arkansas
Georgia
Illinois
Kansas
Mississippi
Montana
New Jersey
New York
North Carolina
North Dakota
Ohio
Oklahoma
Pennsylvania
Tennessee
Texas
Wyoming
USE OF ASH
Soil stabilization - lime/fly ash pressure injection
Pressure-grouting concrete pavement
Lime-fly ash-soil construction
Soil cement construction
Mineral filler
Pozzolanic aggregate mixture
Mineral Filler
Pozzolan
Fine aggregate for trench backfill and bedding and French drains
Pozzolanic base course - type A
Pozzolanic-aggregate mixture (PAM)
Aggregate for bituminous mixtures
Aggregate for ice control
Aggregate for bituminous maintenance and repair
Lime-fly ash-treated courses
Mineral filler
Aggregate-lime-pozzolan stabilized base course
Subsealing concrete pavement
Mineral filler
Aggregates for bituminous plant mixes (mineral filler)
Portland cement concrete
Lime-fly ash-treated subbase
Econocrete
Aggregate base
Ash embankment
Aggregate base
Supplemental specification for aggregate-lime fly ash base
Fly ash modified subgrade
Aggregate-lime-fly ash stabilized base course
Anti-skid materials
Aggregate-lime-fly ash stabilized base course
Test method for sampling fly ash
Departmental materials specification for fly ash
Portland cement-fly ash-treated base
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mixing, uniform spreading with a minimum of segregation, and compaction to a high relative
density.
Assessment
Based on the literature and the results of the spreadsheet surveys, the following general
statements may be made regarding coal ash utilization.
• Fly ash has been used as an additive/partial replacement in PCC for over 50 years.(6)
Over 5.5 million Mg (6 million tons) annually are used in transportation-related concrete
materials.(6)
• The quantity of ash in a particular application is limited by either a percentage of
absolute volume (e.g., 20 to 30 percent) or weight (e.g., maximum 15 percent) of
cementitious material. In HMA, typical percentages of ash to asphalt cement is 0.6 to
1.2 by weight.
• Primary usage involves one of the following areas:®
- In PCC, both as an additive and/or cement replacement.
- Mineral filler in HMA pavements.
- As a fine aggregate.
- Embankment/fill material.
- Stabilized base course component.
- Flowable backfill component.
As a general rule, the low cost and enhancing properties of coal ash make it an excellent
material for highway construction.
References
1. Emery, John and Michael MacKay, "Use of Wastes and Byproducts as Pavement
Construction Materials," Proceedings, 1991 Canadian Technical Asphalt Association
Annual Conference, Winnipeg, Manitoba, 1991, pp. A125-A146.
2. Meyers, J.F., Pichumani, R., and B.S. Kapples, Fly Ash, A Highway Construction
Material, U.S. Department of Transportation, FHWA IP-76-16, Washington, DC, June
1976.
3. Overview of the Use and Storage of Coal Combustion Ash in the United States, U.S.
Department of Commerce, Office of Energy, Washington, DC, November 1988.
4. Annable, J.A., Use of Fly Ash in Highway Construction, Final Report, Federal Highway
Administration, Report No. FHWA/AR-86/005, Washington, DC, October 1986.
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5. Liyang, H.I. and K.L. Bergeson, "Utilization of Waste Materials in Civil Engineering
Construction," Proceedings, 1992 Materials Engineering Division, ASCE, pp. 140-148.
6. Collins, R.J. and S.R. Ciesielski, Use of Waste Materials and By-Products in Highway
Construction, First Draft, National Cooperative Highway Research Program (NCHRP),
Project 20-5, Topic 22-10, Washington, DC, May 1992, 205 pp.
Incinerator Ash
Overview
The disposal of domestic (household and commercial) garbage results in the generation of
approximately 181 million Mg (200 million tons) per year of solid waste.(1) Of this, 14.5
million Mg (16 million tons) is incinerated producing 7.3 million Mg (8 million tons) of
waste ash. Approximately 90 percent of this is bottom ash.(4)
The waste ash generated in the incineration of municipal solid wastes (MSW) is similar
to that generated in coal-fired power plants. However, the properties of the MSW ash tend
to vary significantly depending on the source.®
Raw samples of MSW ash contain cans, wire, organics, and other materials not fully
reduced in the initial incineration. Multiple screening is necessary to remove unreduced
particles.
Applications
MSW bottom ash stabilized with lime or portland cement concrete has been used in
highway construction. It is also felt that the bottom ash could be used to replace sand or
gravel completely in mix designs.® The use of ash in this application would be favorable
due to the fact that it has a lower unit weight than conventional sands.
MSW fly ash is more suitable for incorporation into pavements at a rate of approximately
25 to 50 percent by weight due to its finer gradations and fewer contaminates (unburned
particles). Concrete produced using MSW fly ash has been shown to meet ASTM compres-
sive strength standards.®
Assessment
The use of MSW incinerator ash is made attractive by the low material cost, savings in
landfill requirements, and potential availability. Early estimates placed economic savings of
MSW ashes at $5/Mg ($4.50/ton) of in-place material.® Although ash contains high levels
of leachable contaminants such as heavy metals, testing has shown that MSW ash concretes
are below established toxicity limits.®
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References
1. "Utilization of Waste Materials in Civil Engineering Construction," Edited by Hilary I.
Inyang and Kenneth L. Bergeson, Proceedings, ASCE, Materials Engineering Division,
September 13-17, 1992.
2. Rashid, R.A. and G.C. Frantz, "MSW Incinerator Ash as Aggregate in Concrete and
Masonry," Journal of Materials in Civil Engineering, Vol. 4, No. 4, November 1992.
3. Haynes, J. and W.B. Ledbetter, Incinerator Residue in Bituminous Base Construction,
Federal Highway Administration, Report No. FHWA-RD-76-12, Washington, DC,
December 1975.
4. Collins, Robert J. and Stanley K. CiesielsM, "Highway Construction Use of Wastes and
By-Products," Proceedings, American Society of Civil Engineers National Convention on
Utilization of Waste Materials in Civil'Engineering Construction, New York, NY,
September 13-17, 1992, pp. 140-152.
Slags
Overview
The predominant form of slag is blast furnace-produced during the process of separating
iron from the rock ore. It is formed when the iron ore, coke, and a flux (dolomite and/or
limestone) are melted together in a blast furnace. Once smelting is complete, the aluminates
and silicates of the ore and coke ash have been chemically bonded to the lime. The other
types of slags include steel, nickel, and copper. Annually, approximately 21 million Mg (23
million tons) of slag is produced. Of this, 67 percent [14 million Mg (15.4 million tons)] is
iron slag and the remainder [7 million Mg (7.6 million tons)] is steel slag.(1) Nickel and
copper slags are usually combined into a single category since they are both iron silicate
nonferrous material. Their use is not widespread—however, there is interest in using it in
blended cement, base stabilization, and as fine aggregate in HMA.®
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Applications
There are five types of slag produced from blast furnace operations :P)
• Air-cooled — Produced by simply pouring the molten blast-furnace slag into pits and
permitting it to cool under ambient conditions. It is usually then crushed and screened
and used as an all-purpose construction aggregate. Its primary uses include:
- Concrete (plain and reinforced).
- Bituminous pavements (skid-resistance).
- High stability base course (macadam surfaces and bases, dense-graded aggregate,
bituminous stabilized base, or soil-aggregate base).
Unscreened slag is also used for construction of bases and fills. Air-cooled slag is the
predominant form of processed slag accounting for 89 percent of slag sales in 1989.(1)
• Expanded — By applying water, steam, or compressed air to the molten slag, a
lightweight, expanded aggregate is produced. It is not commonly used in highway
construction, except for producing light-weight concrete products.
• Granulated — Suddenly quenching the molten material in water results in a non-
crystalline, granular material. It will gain strength with time, and it exhibits good
compaction characteristics. This is used frequently for embankment fill or highway
bases. When used as a base material, it exhibits excellent insulative properties and can
be used effectively in frost-heavy situations. Due to its strength-gaining characteristics,
it can be used in slag cement manufacturing. The three primary types of cementitious
materials include:
- Combining portland cement and slag to produce portland blast furnace slag cement.
- Mixing slag, anhydrite, and portland cement to produce a super-sulfated cement.
- Ground slag alone used as a partial replacement for portland cement.
• Pelletized — The molten slag is solidified in a spinning drum while subjected to water
and air quenching. It is a lightweight material used as an aggregate for concrete. It can
be vitrified to assume strength-gain properties as in granulated slag.
Steel furnace slag is produced in the making of steel. It typically exhibits high bulk
density, and is frequently used as base course and for highway shoulders. The additional
unit weight of steel mill slag produces higher skid resistance when used in asphalt mixes for
wearing surfaces. Other benefits derived from its use in both dense- and open-graded
HMA's, include high stability and good striping resistance.
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Assessment
The use of blast furnace slag is generally accepted in highway construction. A 1991
survey cited its use as the third most popular material following old asphalt and old
concrete.® This rank was based on material availability, technical suitability, favorable
economics, and positive environmental impact. Approximately 35 percent of the States and 2
Provinces use it, and 14 States have specifications that govern its use.® Of the various
types, air-cooled and granulated are the most widely used. The surveys that have been
received from the current requests have not supplied any substantial additional updated usage
information at this time.
One of the potential problems associated with its use as granular material is that of
leachate production. However, based on test results, the EPA has not to date classified it as
a solid waste.®
Steel slag is ranked number five, behind fly ash in overall usage.® Eighteen States and
four Provinces use it. It has been used extensively in HMA's to enhance skid resistance,
however currently, southern Ontario is considering excluding this application due to
extensive map cracking performance properties. a>4) It is thought that the cracking is related
to deleterious soft lime and/or lime-oxide agglomerations, however this has not been verified.
Another restriction that steel slag has, compared to blast furnace slag, is its expansive
properties (up to 10 percent by volume due to the hydration of calcium and magnesium
oxides). This negates its use in confined applications and in portland cement concrete.
References
1. Owens, Judity R, "Iron and Steel Slag in 1989," Mineral Industry Surveys, U.S.
Department of the Interior, Bureau of Mines, Washington, DC, 1989, 15 pp.
2. Emery, John and Michael MacKay, "Use of Wastes and Byproducts as Pavement
Construction Materials," Proceedings, 1991 TAG Annual Conference, Winnipeg
Manitoba, 1991, pp. A125-A146.
3. Slag, The All Purpose Construction Aggregate, National Slag Association, Washington,
DC, 1968.
4. "Utilization of Waste Materials in Civil Engineering Construction," Edited by Hilary I.
Inyang and Kenneth L. Bergeson, Proceedings, ASCE, Materials Engineering Division,
September 13-17, 1992.
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Paper/Cellulose in Stone Matrix Asphalt (SMA)
Overview
Stone Matrix Asphalt (SMA) is an asphaltic concrete mixture concept developed in
Europe primarily to minimize rutting of pavements that carry large volumes of heavy truck
traffic. SMA mixtures differ from typical dertse-graded hot-mix asphalt (DGHMA) mixtures
conventionally used in the U.S. in two important ways: SMA mixtures utilize a coarser
aggregate gradation than that used in DGHMA, and SMA mixtures contain a rich stabilized
asphaltic mastic to hold the aggregates together compared to simple asphalt cement binders
used in conventional DGHMA.
SMA mixtures are now commonly used on many highways in Germany, France,
Belgium, Austria, Holland, and the Scandinavian countries/1' In response to the success of
the SMA mixtures in Europe, several States in the U.S. have constructed test pavements with
SMA mixtures. The Federal Highway Administration has encouraged the development of the
SMA technology. In addition to improved resistance to rutting, other pavement performance
benefits of SMA mixtures may include improved skid resistance, greater cracking resistance,
and improved durability.a>3) At the present, the greatest disadvantage of SMA mixtures is a
10 to 30 percent higher cost (European estimates), which is due to the use of asphalt
additives and select high-quality aggregates, and increased production costs.0>4) However,
the higher initial cost of SMA mixtures may be offset by a longer pavement service life.
Another potential benefit of SMA mixtures is as an outlet for certain recycled materials.
Many SMA mixtures have used cellulose fibers, which can be derived from high-quality
waste paper, as a stabilizing agent in the mastic. Recycled plastics and crumb rubber have
also been used to improve the mastic in SMA mixtures.®
Material Characteristics
• Aggregates
The most striking feature of SMA mixtures is the coarse aggregate content. SMA
mixtures contain approximately 65 to 70 percent coarse aggregate, which is predominately of
one size (> 4.75 mm). By contrast, conventional dense-graded asphalt concrete mixtures
contain from 25 to 55 percent coarse aggregate. Typically in an SMA mixture, the maxi-
mum particle size is about 11 to 13 mm (~ V2 in), and the dominant size is 8 to 10 mm
(~ 3/8 in). The coarse aggregate serves as a stone skeleton, or matrix, in which contact
between the large particles provides a rigid framework to withstand heavy loads. The fine
aggregate fills in gaps in the coarse aggregate skeleton. Approximately one-third of the fine
aggregate is mineral filler (> 75 pm), which combines with the stabilized binder to create a
stiff mastic.
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European aggregate requirements for SMA mixtures have been rather stringent, limiting
aggregates to very high-quality, well-crushed materials. Carbonate aggregates such as
limestone are prohibited. The restrictive European aggregate specifications are intended in
part to minimize wear on the pavement surface due to abrasion by studded tires.(5>6) In the
U.S., lesser quality and more economical aggregates will be evaluated. The FHWA has
attempted to translate the European specifications into guidelines for aggregate properties
using U.S. standard tests.00 Whether or not the tough European specifications are necessary
or if the translated properties are valid is an important issue to be resolved in the U.S.
evaluation of the SMA technology.
• Asphalt Cement
Although the asphalt cement properties used in SMA mixtures are the same as in
conventional dense-graded mixtures, the asphalt content of SMA mixtures is typically higher
by 1 to 2 percent of the total mix.(4) The higher asphalt content gives SMA mixtures greater
durability and cracking resistance, but makes it necessary to add a stabilizer to the mix to
prevent the asphalt from draining through the mixtures during production, transport, and
placement.
• Stabilizing Additives
The most common form of stabilizing agent used to reduce drainage of the binder in
SMA mixtures is some type of fiber. Cellulose fibers are the most economical and the most
often used stabilizer.® Cellulose fibers are usually added at a rate of 0.3 percent by weight
of mix. Mineral fibers such as rock wool and asbestos have been used in Europe, although
the use of asbestos is now discontinued. Dosage rates for mineral fibers are often as much
as twice that of cellulose fibers. Other stabilizing agents that have been used include carbon
black, rubbers, artificial silica, and a number of different polymers.® Some of these
additives may provide benefits in addition to stabilizing the asphalt. For example, some
polymers may improve the resistance of the pavement to deformations at high summer-time
temperatures.
Production and Placing of SMA Mixtures
Production of SMA mixtures at hot-mix asphalt facilities is also different than
conventional DGHMA production. In Europe, SMA mixtures are nearly always produced in
batch plant facilities. Asphalt plants are equipped with additional cold bins to separate
aggregates into different size fractions for greater gradation control.(4) Mineral filler and
fiber packaged in meltable plastic bags are added at the pugmilL Mixing time is extended to
ensure dispersion of the fiber throughout the mixture. ® The longer mixing time reduces the
production rate of the plant.
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In the U.S., drum mixer plants are more often used because they have greater production
rates and are therefore more efficient than batch plants. To introduce fibers into a drum
mixer plant, it is necessary to use fibers in a pelletized form to avoid blowing the loose
fibers out through the plant exhaust system. Pelletized fibers, which are fibers encapsulated
in an equal amount of asphalt cement by weight, can be added in drum plants through the
drum mixer's recycled asphalt pavement (RAP) slot. Since pelletizing more than doubles the
cost of the fibers, an alternative technique was developed to inject and blend loose, air-blown
fibers into the asphalt cement line just before the asphalt cement enters the drum mixer.
This technique has been used on four of the SMA projects constructed in the U.S.
Paving with SMA mixtures is similar to paving with conventional mixtures. Compaction
operations are kept close to the paver. Both static and vibratory steel wheel rollers have
been used successfully. Pneumatic rollers, however, tend to pump the mastic to the surface
and track the mastic on the surface of the pavement. Density levels specified are usually
around 94 percent of the theoretical maximum density, which can normally be achieved with
four to six roller passes.
SMA Performance
The SMA technology has continually evolved since it was originally developed over
20 years ago. It has been reported that the European SMA pavements have a 12- to 15-year
life, which is generally beyond the life of conventional asphalt concrete pavements.(4)
Although the U.S. projects are all fairly young, the short-term performance of these projects
has been excellent.® Initially, five SMA projects were constructed in different States during
1991. Ten more SMA projects were constructed in 1992. Georgia, which has constructed
two SMA projects using several material variables and has another major project scheduled
to begin soon, is considering the use of SMA throughout the rehabilitation of one of its
Interstate highway corridors.(9)
Potential Cellulose Consumption
Cellulose fibers are used extensively in SMA mixtures in Germany and Sweden. Of the
15 SMA projects constructed in the U.S. to date, 11 have contained at least a section with
cellulose fibers.(1)
Currently, the primary source of cellulose fibers used in SMA construction comes from a
German manufacturing company that derives the fibers from natural raw materials, i.e.,
wood.(1Q) However, there appears to be no technical limitation on using recycled paper for
making cellulose fibers. In fact, cellulose fibers are currently being produced for use in
SMA mixtures by a company in Michigan.(11)
If the SMA technology continues to gain acceptance in this country, and if cellulose
fibers continue as the predominant stabilizing agent, the market for the fibers may see
tremendous growth. It is estimated that every lane-mile of pavement constructed with a
cellulose-stabilized SMA would consume nearly 1.45 Mg (1.6 tons) of fiber. An optimistic
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forecast of 322 lane-km (200 lane-miles) of SMA construction per State each year would
result in an estimated annual U.S. consumption of 14,515 Mg (16,000 tons) of cellulose
fiber. However, this amount is insignificant when considering the total yearly generation of
waste paper [approximately 50 million Mg (55 million tons)] of which about 33 percent [16
million Mg (18 million tons)] were recycled in 1988.(12-14)
References
1. BukowsM, J.R., SMA in America: Past, Present and Future, Transportation Research
Board, Washington, DC, January 11, 1993.
2. BukowsM, J.R., Stone Mastic Asphalt, SMA, Technology Synopsis and Work Plan Test
and Evaluation Project No. 18, FHWA, Office of Technology Applications, Washington
DC, April 1991 (draft).
3. Bellin, P.A.F., Use of Stone Mastic in Germany, State-of-the-An, Transportation
Research Board, Washington, DC, Jan. 1992.
4. European Asphalt Study Tour, 1990 (draft).
5. Stuart, K.A., Stone Mastic Asphalt (SMA) Mixture Design, Federal Highway Administra-
tion, Publication No. FHWA-RD-92-006, Washington, DC, March 1992.
6. Brown E.R., Experience with Stone Matrix Asphalt in the United States, National Center
for Asphalt Technology, Auburn University, Auburn, AL, March 1992.
7. Stone Mastic Asphalt (SMA) Surface Course, Model Specification, FHWA, Office of
Technology Applications, Washington, DC, July 1992.
8. Scherocman, J.A., "The Design, Construction and Performance of Stone Mastic Asphalt
Pavement Layers," Canadian Technical Asphalt Association Proceedings, Nov. 1992.
9. Campbell, B.E., Evaluation of a Stone Matrix Asphalt Overlay Over PCC, Georgia
Department of Transportation Research Project No. 9202, Jan. 1993.
10. An Introduction to Stone Mastic Asphalt, J. Tettenmaier and Sons GmbH Co Germanv
Jan. 1991. 3'
11. Karnemaat, R.J., Vreibel, D.J., and C.H. VanDeusen, Stone Matrix Asphalt: Introduc-
tion of Loose Cellulose Fibers into Drum Mix Plants, TRB, Washington, DC, Jan. 1993.
12. Franklin Associates, Inc., Characterization of Municipal Solid Waste in the United
States, Franklin Associated Ltd, Prairie Village, KS, 1993.
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13. National Solid Waste Management Association, Landfill Capacity in the Year 2000,
Washington, DC, 1989.
14. National Solid Waste Management Association, Recycling in the States, 1990 Review,
Washington, DC, 1990.
Carbon Black
Overview
Carbon black is a material derived from petroleum and natural gas furnaces. There are
over 40 different grades of carbon black. Only the higher purity carbon black from natural
gas furnaces is suitable in the manufacturing of rubber products including truck and
automobile tires. Carbon black can also be used as a modifier to improve the properties of
paving-grade asphaltic cements.
The pyrolization of used tires—heating in the absence of oxygen—yields gas, liquid
fuels, and carbon black. Tires processed this way yield approximately 40 percent carbon
black and 60 percent fuels by weight. The gases obtained are used to fuel the pyrolization
process and the liquid fuels can be reclaimed leaving a carbon black residue that is free of
volatile components such as oils. The carbon black can then be ground to a 60-/tm powder
suitable for use as an asphaltic cement modifier/0
Asphalt Paving Mixtures
Carbon black has been used as a modifier for many years and has been shown to increase
stiffness and improve rutting resistance/0 Other testing of carbon black-modified asphalt has
shown increased resistance to low-temperature cracking and longer fatigue life as compared
to conventional asphalt.®
Since carbon black is nonvolatile, there is little danger of pollution when incorporated
into asphalt. Carbon black can be added using mechanical agitation, therefore no special
tanks or heaters are necessary for the asphalt or aggregate.
Economic Considerations
The cost of recovering suitable carbon black as an asphalt modifier is estimated at less
than $1 per tire. This is compared to the cost of obtaining suitable CRM at $15 per tire.
The recovered carbon black has an approximate value of $0.50 to $0.80 per tire.(1) If all of
the approximately 242 million waste tires generated in the United States each year were
pyrolized, approximately $150 million worth of carbon black would be obtained. It would
cost approximately $750 million dollars to realize this same quantity as crumb rubber. These
figures do not account for the value of the energy used and obtained from pyrolization.
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Assessment
The pyrolization of tires to obtain carbon black appears promising as a method of
resource recovery since raw material in the form of useable energy sources and carbon black
are produced. Further consideration is necessary to realize the full benefit of the use of
carbon black-modified asphalt.
References
1. King, Gayle N., Letter to the Federal Highway Administration in response to certain
recycling mandates in the 1991ISTEA Act, February 1993.
2. Khosla, N. Paul and S.Z. Zahran, "A Mechanistic Evaluation of Carbon Black Modified
Mixtures," Canadian Technical Asphalt Association Proceedings, Toronto, Ontario,
1987.
Recycled Portland Concrete Cement
Overview
The use of recycled portland cement concrete (PCC) has been facilitated in recent years
by the increasing costs of hauling and disposing of used PCC. In situ recycling of concrete
results in a 45 percent savings compared to transporting and dumping.(1)
Recycling of PCC is currently being practiced by several State and Provincial transporta-
tion administrations. In Connecticut, State DOT projects recycle approximately 75 percent
of the PCC removed. The remaining 25 percent is disposed. The Manitoba Ministry of
Transportation also reports a 75 percent recycling rate for PCC. Michigan DOT projects
recycle PCC for use as course aggregate in open-graded drainage courses under pavement
and course aggregate for shoulders. Michigan currently recycles 90 recycle of the PCC
removed on freeway projects. Ontario employs a riprap gabion filler as reprocessed
aggregate. Excess material is made available to commercial recycling facilities.
Applications
• Aggregate in PCC Pavement
Recycled PCC aggregate may be preferential to virgin aggregates if careful control is
maintained during the crushing operation to ensure uniformity of gradation. The crushed
particles tend to be more angular than conventional crushed stones due to the cement mortar
adhering to the aggregate surfaces. It should be noted that concrete recycled from PCC
pavements makes better aggregate than that derived from structural concrete.® The presence
of cement mortar decreases the likelihood of failure along the interface between aggregate
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and mortar that is commonly experienced in PCC with virgin aggregate. Since the chance of
this common mode of failure is decreased, the flexural fatigue strength of recycled PCC
concrete tends to be higher.®
Despite this higher flexural fatigue strength in recycled aggregate concrete, the compres-
sive strength is generally 15 to 40 percent lower. However, the development of strength
gain with age is similar to virgin aggregate concrete.0)
• Aggregate Base Material
When applied as a base material, the density of the compacted recycled aggregate will
often be lower than that of virgin aggregate, primarily due to the internal voids of the
concrete mortar. This can result in a lower initial bearing capacity that will improve, and
may exceed, virgin aggregate due to the presence of cement liberated during crushing and
compaction.(1)
Research has shown that high fly ash lean concretes with recycled aggregate have
potential as a base course. The material shows good workability, strength development,
rigidity, and low drying shrinkage.0
• Other Uses
In a practice commonly known as cracking and seating, a concrete pavement is broken
into chunks approximately 0.14 to 0.19 m2 (1.5 to 2 ft2) and then seated using a heavy
rubber tire roller to serve as a base course for an asphalt overlay. The intent of the process
is to prevent the reflective cracking that can be prevalent in asphalt overlays on intact PCC
pavement.
The initial step of breaking the pavement into chunks is accomplished with either a
standard diesel hammer, a guillotine hammer, or a whip hammer. The chunks are then set
using a 30,000- to 45,000-kg (66,000- to 99,300-lb) rubber-tired roller prior to the applica-
tion of the asphalt overlay.(4)
This in situ use of PCC is more logically called "reuse" rather than recycling since the
material is not removed from its place of origin.
Assessments
The potential use of recycled aggregate concrete should not be ignored. The savings in
money, landfill space, and reduced virgin aggregate quarrying through increased use of
recycled aggregate are adequate to justify expanded use of the material. Although cost data
was not located, the minimization of transportation costs by on-site processing may, in many
instances, prove to be a cost advantage. Recycling of PCC pavements is undoubtedly
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effective when cost savings of 40 to 50 percent over the cost of transportation and disposal
are realized.
The use of recycled aggregate in base courses has been shown to have better properties
than virgin bases. On this basis, the use of recycled aggregate bases will probably be
expanded.
References
1. Gorle, D. and L. Saeys, "Reuse of Crushed Concrete as a Road Base Material," Reuse
of Demolition Waste, Vol. 2, Cambridge, MA: University Press, 1988.
2. Kowamura, M. and K. Torii, "Reuse of Recycled Concrete Aggregate for Pavement "
Reuse of Demolition Waste, Vol. 2, Cambridge, MA: University Press, 1988.
3. Ikida, T., Yamane, S., and A. Sakamota, "Strengths of Concrete Containing Recycled
Concrete Aggregate," Reuse of Demolition Waste, Vol. 2, Cambridge, MA- Universitv
Press, 1988. J
4. Welke, R.A., Webb, A.B., and C. Van Deusen, Cracking and Seating of Jointed
Portland Cement Concrete Pavements in Michigan, Association of Asphalt Paving
Technologists, Minneapolis, MN, 1984.
Roofing Materials
Overview
Each year approximately 8,618,000 Mg (9,500,000 tons) of roofing shingles are
manufactured in the United States. Approximately 65 percent of these are used for
reroofing. Thus, 6,350,400 Mg (7,000,000 tons) of used material is left for disposal. Since
roofing shingles contain approximately 33 percent asphalt by weight, approximately
1,814,000 Mg (2,000,000 tons) of asphalt or about 20 percent of the annual usage in the
U.S. could be recovered.
The savings in economic terms are also favorable. By incorporating shingles into
asphaltic concrete at 5 percent by weight, the cost of the mix can be reduced by $3.08/Mg
($2.79/ton).(1) Manufacturers estimate that the cost of cold-mix patching asphalts with
asphaltic shingles can be as much as 50 percent less than standard cold mixes.® Recycling
of shingles also reduces landfill volume as well as saving landfill disposal fees that ranee
from $19.50 to $49.60/Mg ($18 to $45/ton).
134
-------
Asphaltic Concrete Paving Mixtures
• Cold-Mix Patching Compounds
Cold-mix asphaltic concrete patching compounds are currently manufactured by two
companies. These cold mixes are routinely used in eastern municipalities for such applica-
tions as patching pot holes, driveways, utility cuts, repairing bridge decks, and as a replace-
ment for aggregate subbase.
Cold-mix patching compounds such as RePave1" , which is manufactured by ReClaim
Inc., contain as much as 20 percent dry roofing material.® This shingle material contains
asphalt, filler, and fiber, which have been found to perform similarly to many current
modifiers, such as polymers and mineral fillers.
• Hot-Mix Asphalt (HMA)
The benefits of adding waste roofing material to HMA's are similar to those of cold mix.
After the raw waste material is shredded to particles 12.7 mm (V2 in) or smaller, it can be
easily added to the pug mill in the same manner as is used to introduce recycled asphaltic
pavement. An addition of 5 percent to 10 percent by weight has been shown to help
pavement resist rutting, shoving, reflective cracking, and aging due to oxidation.
Assessment
The use of waste roofing materials in asphaltic concrete is justified both by the cost
savings and the desirable material properties it produces. The material has been used
successfully in several projects including high-volume, heavy truck roadways and has shown
favorable performance.®
For these benefits alone, the recycling of roofing waste could be expanded. By
landfilling the approximately 6,350,000 Mg (7,000,000 tons) of roofing waste produced in
the U.S. each year, 1,814,000 Mg (2,000,000 tons) of raw asphalt, a non-renewable resource
is being wasted.
References
1. Brock, Don J., From Roofing Shingles to Roads, Astec Industries, Inc., Technical Paper
T-120, Chattanooga, TN, 1989.
2. Flynn, Larry, "Roofing Materials Hold Promise for Pavements," Roads and Bridges,
Vol. 31, No. 4, April 1993.
135
-------
Tire Chip and Whole Tire Applications
Overview
_ In addition to the uses of crumb rubber-modified asphaltic concrete, numerous possibili-
ties exist for the use of tires and tire scraps as lightweight fill, retaining walls, insulator and
other applications. The large quantities of tires available at low cost make their use
attractive.
Lightweight Fill Material
In many embankment situations, the weight of the fill used to create the embankment
creates a potential for failure. Typical densities for tire chip fill ranges from 480 to 722
kg/m (30 to 45 lb/ft3) after compaction versus a typical soil density of 1926 kg/m3 (120
Ib/ft3)/ By replacing the heavy soils used in many embankments with tire chips—50- to
100-mm (2- to 4-in) gradation—the static weight of the fill is significantly reduced thus
reducing the potential for slope failure. '
In areas where roads cross low-strength subgrades such as peats, the weight of a
conventional base material will cause substantial long-term settlement. This problem can be
alleviated through the use of layers of tire chips that are then covered with compacted
structural fill.
One concern in the use of tire fill is leaching of chemicals and oils into the water table
One method of dealing with this problem is to use wood chips below the water table and tire
chips above the water table. Using tire chips above the water table also alleviates the
problems associated with rotting of wood in the unsaturated zone.® After a substantial base
has been created using wood and tire chips, 0.6 to 0.9 m (2 to 3 ft) of conventional structur-
al base is added in preparation for the asphaltic surface.
Retaining Walls
Although a tire-surfaced retaining wall may not be as aesthetically pleasing as other
conventional materials, in many applications they will not be noticeable to the user. The use
of whole tires for retaining walls is enhanced by the fact that used tires are a cheap,
nonbiodegradable, ultraviolet-resistant material.
Tire retaining walls are created by placing tires in alternating rows and backfilling in
small lifts with a geotextile between lifts to serve as a tie back. The rows of tires are also
staggered back from the front edge to add stability and to prevent backfill from falling
through the spaces between tires.
The cost of tire retaining walls is significantly lower than the cost of conventional
material walls. Tire-faced walls can be constructed for under $140/m2 ($13/ft2) of face area
136
-------
while the cost of a typical wall can range from $161/m2 ($15/ft2) to as high as $323/m2
Insulation Layer Beneath Road Surfaces
In cold weather regions, base-course shrinking and swelling can lead to significant
surface cracking. Rubber, which has a significantly lower thermal conductivity than soils,
can be used to insulate the base to prevent shrinking and swelling. Research is currently
underway in Maine to determine: the thickness of tire chips needed to insulate adequately,
the thickness of gravel cover over the tire chips to provide a stable surface, and the effects of
tire chips on ground water.(4)
The test section has been subjected to fully loaded double- and triple-axle dump trucks
with significant initial rutting. Rutting under subsequent loads was substantially less. The
chip layers have shown encouraging results in reducing depth of frost penetration.(4)
Assessment
The potential cost savings available through the use of used tires in retaining walls
justifies the continued exploration of usage. However, the low aesthetic value of the tire
surface may limit the scope of application.
The value of tire chips, both as insulation and as a lightweight fill, warrants expanded
usage—not for economic reasons, but for their structural properties. Tire chips have the
potential to provide a cheap, durable substitute for lower-quality materials.
References
1. Hughes, Chuck, Scrap Tire Utilization Technologies, National Asphalt Pavement
Association and State Asphalt Pavement Association, Lanham, MD, 1993.
2. Keller, Gordon, "Retaining Forest Roads," Civil Engineering, December 1990, pp. 50-
53.
3. Oswer, Oppe, Markets for Scrap Tires, U.S. Environmental Protection Agency, Report
No. EPA/530-SW-90-074a, Washington, DC, October 1991.
4. Humphrey, Dana N. and Robert A. Eaton, Tire Chips as Insulation Beneath Gravel-
Surfaced Roads, Second International Symposium on Frost in Geotechnical Engineering,
Anchorage, Alaska, June 1993.
137
-------
DISPOSAL, REUSE, AND RECYCLING OF HIGHWAY MATERIALS
Introduction
The results of survey 1 pertaining to the disposal, reuse, and recycling of highway
materials are presented in table 17. The original intent of the survey form was to distinguish
between materials disposed of by burying on the project, landfilled, sold as scrap metal, or
disposed of as contractor property from materials recycled, and functionally reused on the
roadway. Unfortunately, there is some degree of confusion between these categories (e.g.,
recycling or disposal when steel is sold for scrap and recycling or reuse when concrete
bridge deck is used for riprap). Descriptive information provided with the survey form by
some States and Canadian Provinces proved to be valuable in assessing the actual deposition
of highway materials.
Another problem was that exact answers were difficult to provide because of the
variations between contracts in specifying reuse, recycling, or in some instances when the
contractor is responsible for disposal. In general, the information provided in the discussion
of different highway materials and appurtenances provides a realistic overview of current
practice for those States and Provinces that provided supplementary detailed information.
The response to this survey indicates that most States are putting forth considerable effort
to minimize waste, reduce operational costs, and to improve quality while emphasizing
recycling and reuse of materials and appurtenances in their highway maintenance and
rehabilitation programs. Numerous comments and letters received from the highway
agencies confirmed their concern for effective recycling/reuse of materials. One example
provided here is an excerpt from a letter by Richard R. Stapp, State Construction and
Materials Engineer, Wyoming Department of Transportation:
"The decision whether or not to recycle pavements or base materials basically
depends upon economics. Our state has many areas in which suitable materials
sources are a significant distance from our construction projects, which makes
recycling highly attractive. We also have many areas in which aggregate sources are
numerous and virgin mixes are less expensive to use than the recycled materials.
The haul of the removed material is the significant expense in this case. Very little
material is wasted, however. The removed materials are either used as a part of
subgrade reconstruction, stockpiled for our maintenance forces to use in their
patching and repair work, or used as a portion of various stabilized material tapers
along the roadway shoulders. We have even used milled asphalt concrete to stabilize
unsurfaced parking lots at various government and civic agency locations. The little
material that is disposed of is usually used as landfill material by the contractors."
The ensuing discussion on roadway materials, culverts, guardrail systems, signs, and
sign/signal structuring bridges, and other recycling activity provide insight into the diversity
of approaches followed by different highway agencies.
138
-------
Table 17. Summary of disposal/utilization survey.
U.S. SOURCE:
ALABAMA
ALASKA
ARIZONA
ARKANSAS
COLORADO
CONNECTICUT
FLORIDA
GEORGIA
IDAHO
LOUISIANA
MAINE
MASSACHUSETTS
MARYLAND
MICHIGAN
MISSISSIPPI
MISSOURI
OREGON
PENNSYLVANIA
RHODE ISLAND
S. CAROLINA
S. DAKOTA
VIRGINIA
WYOMING
Mean Value
Range
No. of Responses
ONTARIO
Mean Value
Range
No. of Responses
ROADWAY MATERIAL
% Dispos
6
5
0
70
0
30
0
0
0
0
5
80
10
10
0
1
0
0
so
17.7
0,90
- o
1
0,6
Notes
(2.3)
(31
(3)
(3)
13)
(3)
(3)
(3)
(2,3)
(3)
Notes -
% Recycl
16
100
30
76
80
20
90
30
10
10
26
100
10
30
56.3
0, 100
96
95
100
97
95, 100
Notes
(5)
(5,4)
(5)
(5)
(6)
(6)
(6)
(5)
(5)
(4,6)
(4,5)
(6)
(6)
% Reused
80
0
0
20
80
10
90
0
38
20
24.6
0,94
0
2
0,6
Notes
<6'
161
(6)
(6)
(6)
ROADWAY MATERIAL
Asphalt Concrete
1.1.2 Structural or Base Course
6
0
80
>:v:-x*:*:*:*x*
30
0
0
0
o
80
10
0
0
75
0
26
0
48
60
18.1
0,90
0
0
5
0
0
1
0,5
6
Notes
(2,3)
(3)
(3)
(3)
(3)
(3)
(2,3)
(3)
N/A
% Recycl
15
100
20
0
80
20
96
100
20
90
100
99
15
0
25
100
25
100
0
16
30
64.5
0, 100
30
% Recycl
100
95
96
0
100
78
0,100
6
Notes
(6)
(5,1)
(5)
(4)
ls'
(5)
(6)
(5)
14,5)
(4,6)
(5)
Notes
N/A
(6)
% Reused
80
0
0
^
70
80
5
•:•:•:•:•:•:•:•:•:•:;:•:•:•:::•
0
0
10
0
0
,
100
0
100
26.0
0, 100
29
% Reused
0
6
0
0
0
1
0,6
5
Notes
(6)
(6)
(61
Notes
N/A
ROADWAY MATERIAL
Stabilized Base
% Dispos
0
0
100
60
0
0
100
60
0
1
%
0
20
10
I 28.6
0, 100
| 28
0
0
0
NONE
6
N/A
(2,3)
(3)
(3)
(3)
(3)
(2,3)
(3)
Notes
N/A
N/A
60
20
40
0
0
60
0
99
0
100
0
10
30.7
0,100
28
0
100
0
40
0, 100
5
2
N/A
(5)
(S)
(6)
(5)
"TO"
(6,13)
(4,6)
(4,5)
(5)
N/A
N/A
0
80
100
0
100
S«SSSS*s:
100
100
10
34.3
0, 100
28
0
0
0
20
0, 100
6
~N/A
N/A
(6)
(6)
(6)
N/A
N/A
-------
Table 17. Summary of disposal/utilization survey (Continued).
. U.S. SOURCE:
ALABAMA
ALASKA
ARIZONA
ARKANSAS
CONNECTICUT
FLORIDA
GEORGIA
IDAHO
INDIANA
KANSAS
MAINE
MARYLAND
MICHIGAN
MISSOURI
NEBRASKA
OHIO
RHODE ISLAND
S. CAROLINA
S. DAKOTA
TENNESSEE
TEXAS
UTAH
Mean Value
Range
No. of Responses
CANADA SOURCE:
NOVA SCOTIA
SASKATCHEWAN
Mean Value
Range
No. of Responses
0
0
0
30
-.^f...:-: ::j
25
GO
65
0
0
0
0
0
0
100
30
0
0
SSWS*:**
BO
0
0
1
WSSSWSS?::
0
20
0
0
0
28
BO
17.1
0, 100
28
% Dispos
0
0
0
0
0
NONE
B
N/A
(2.3)
(3)
12)
'3>
13)
N/A
N/A
(3)
N/A
(3)
(3)
(3)
Notes 1
N/A :
1
Crushed E
1
0
0
100
70
70
BO
0
0
0
100
0
0
B
0
0
100
0
0
100
0
99
XfSi*iSf!X!Z
0
0
0
BO
0
65
0
28.9
0. 100
28
% Recycl
0
100
100
0
0
40
0, 100
5
tooeBaw
3
Note*
N/A
15'
IB)
IB.4)
(B)
N/A
N/A
(5)
N/A
(B)
(B)
(4,61
(6)
Notes
N/A
N/A
1
U.
100
0
0
B
0
B
0
9B
0
0
10
100
BO
38.7
0, 100
29
0
0
20
0,100
B
Notes
N/A
(6)
(61
N/A
N/A
N/A
16)
(61
(6)
(6)
Notes
N/A
N/A
% Dbpos
0
0
30
2B
0
0
100
0
100
0
:•:•:-:-:•:•:•:•:•:":•:•:•:•:
BO
1
0
_
BO
18.B
0,100
27
% Dispos
0
0
0
NONE
B
Notes
(2,3)
»'
(2)
N/A
(31
(31
(3)~
(3)
Notes
N/A
ROADWAY
1_
%Recyc
0
0
70
70
0
0
0
100
90
0
B
0
B
0
19
•:-:v:::::V:-:::W:%:
0
0
BO
78
29.2
0, 100
27
% Recycl
0
100
100
26
4B
0, 100
MATERM
rivelBiM
Notes
(b)
(6)
(6,4)
N/A
IB)
(B)
(4)
(B)
IB)
(4,6)
(B)
Notes
N/A
1
100
100
0
0
6
0
100
0
0
10
0
1B
60
0
80
100
100
100
AWSawiSK
BO
48.6
0, 100
27
% Reused
0
0
0
76
36
0, 100
"»'
N/A
(6)
(3)
(6)
(6)
(6)
(6)
(6)
Notes
N/A
(6)
I
% Dfipo
0
0
0
30
'/
26
100
0
100
0
2B
0
0
100
30
80
0
60
0
0
1
0
20
0
0
S¥:W4WSWi
60
0
23.0
0,100
27
0
0
0
0
0.0
NONE
Notes
(2,3)
(3)
(2)
(3)
(8)
131
(3)
'3'
<3'
N/A
Notes
N/A
ROADWAY
Granular
1
SBccycl
0
100
100
70
70
'"• \?
0
0
0
0
76
B
100
0
9
0
0
32
0
26.6
0,100
27
% Recycl
0
100
0
26
46.0
0, 100
MATEHI/
Subbm
5
Notes
(61
(6)
'51
(6.41
16)
(4)
161
16)
IB)
14.61
IB)
N/A
Notes
N/A
(6)
|
J.
*R*uaed
100
0
0
0
f
6
'".'''' '' ••"
0
100
0
100
96
70
16
0
60
60
100
8
0
46.4
0, 100
27
% Reused
0
76
36.0
0, 100
Note*
(61
(3)
18)
(6)
16)
(4.6)
(6)
N/A
Notes
N/A
(6)
-------
Table 17. Summary of disposal/utilization survey (Continued).
U.S. SOURCE:
ALASKA
ARKANSAS
COLORADO
CONNECTICUT
FLORIDA
GEORGIA
IDAHO
INDIANA
LOUISIANA
MAINE*
MASSACHUSSETTS
MARYLAND
MISSISSIPPI
MISSOURI
NEBRASKA
OHIO
OREGON
PENNSYLVANIA
RHODE ISLAND
S. CAROLINA
S. DAKOTA
TENNESSEE
TEXAS
UTAH
VIRGINIA
VERMONT
WASHINGTON
WYOMING
Mean Value
Range
No. of Responses
CANADA SOURCE:
NOVA SCOTIA
SASKATCHEWAN
N. BRUNSWICK
MANITOBA
ONTARIO
Mean Value
Range
No. of Responses
0
0
0
100
0
10
100
'100
100
0
0
0
0
100
80
0
0
0
0
1
J
0
0
',
0
0
44
0
24.7
0,100
% Dispos
0
0
0
0
0
0.0
NONE
F
Notes
N/A
(2,3)
(3)
N/A
(3)
(3)
N/A
(3)
N/A
N/A
(3)
N/A
Notes
N/A
N/A
tOADWAY t
Stabilized
1.6
% Recycl
0
0
100
0
0
SO
0
0
0
100
0
0
0
0
10
100
•; ••
0
100
0
99
*:
0
0
60
0
44
0
25.6
0, 100
% Recycl
0
100
100
0
0
40.0
0, 100
MATERIAL
Subbase
Notes
N/A
IB)
N/A
(5)
N/A
(6)
(5)
(B)
N/A
I5)
N/A
(4,6)
(S)
N/A
Notes
N/A
N/A
% Reused
100
0
0
0
0
0
0
0
0
100
100
0
10
0
0
100
^ .
100
•111
12
0
27.4
0, 100
% Reused
0
0
20.0
0,100
Notes
N/A
N/A
N/A
(6|
16)
N/A
(6)
(61
(61
N/A
Notes
N/A
N/A
% Dispos
0
0
0
20
96
0
10
0
0
40
0
0
•1
\
i
14
10
=
12.8
0, 100
% Dispos
0
; s
1.7
0,6
R
Notes
N/A
(31
(2)
'31
191
(31
N/A
(11)
(2.3)
(31
Notes
N/A
1.7
% Recycl
0
100
10
100
0
60
0
20.6
0,100
27
100
0
33.3
0, 100
3
N/A
(B)
(6,4)
(4,5)
N/A
IB)
(6)
N/A
(4,6)
(6)
N/A
100
0
0
' J
10
90
6
100
90
100
100
96
100
60
60
0
100
100
0
0
0
0
60
100
60
90
66.6
0,100
27
0
0
95
I 31.7
0,96
3
Notes
N/A
(6)
(6)
(6)
N/A
(6)
13)
(6)
(6)
N/A
(6)
(6'
N/A
% Dispos
10
6
:y
20
100
0
16
0
0
0
100
6
0
10
0
( ',
1
0
76
26
0
70
0
23.7
0, 100
26
0
100
0
33.3
0, 100
3
R
Notes
(3)
(2)
(3)
(3)
(3,14)
(3)
(3)
13)
(2,3)
N/A
N/A
Shoulders:
1.8.
0
15
%
76
70
0
6
80
20
0
95
75
20
100
99
50
25
26
0
30
38.2
0, 100
26
0
f f
46.0
0, 100
4
ATERIAL
Hot Mix
Notes
(5,4)
lb)
(3,14)
(5)
W
(5)
(4,6)
(6)
N/A
N/A
(51
% Reused
90
80
- v ,
26
10
0
80
95
6
100
6
0
0
0
60
6o
100
0
34.2
0,100
26
0
0.0
NONE
3
~~iei
(6)
(3,14)
""iei
N/A
N/A
-------
Table 17. Summary of disposal/utilization survey (Continued).
U.S. SOURCE:
ALABAMA
_ ALASKA
ARIZONA
ARKANSAS
COLORADO
CONNECTICUT
FLORIDA
GEORGIA
IDAHO
INDIANA
KANSAS
MAINE
MASSACHUSSETTS
MARYLAND
MISSOURI
NEBRASKA
RHODE ISLAND
S. CAROLINA
S. DAKOTA
TENNESSEE
UTAH
VIRGINIA
WASHINGTON
WYOMING
Mean Value
Range
No. of Responses
CANADA SOURCE:
SASKATCHEWAN
N. BRUNSWICK
MANITOBA
Mean Value
Range
No. of Responses
%Ditpoi
10
6
100
0
0
0
0
20
0
0
95
0
0
23.6
0, 100
14
^ Dispos
0
0
x-x*:-x:xx*
10
0
2.6
0, 10
4
SI
(3)
(3)
(3,14)
(3)
N/A
Notes
N/A
houWert: F
1.
0
18
S s*
0
"• : *.
0
90
0
95
0
100
0
100
0
0
0
28.6
0, 100
14
% Recycl
0
100
0
100
50.0
0, 100
4
iw Aooro
5.2
(3,14)
(5)
(5)
N/A
N/A
(B)
«.
qit«
90
80
1 *
5
jfxWftxxxsx
0
40.7
0, 100
14
% Reused
0
22.5
0,90
4
Holes
(3,14)
N/A
Notes
N/A
X Dltpoi
100
50
7B
90
100
100
70
50
2B
BO
100
50
100
95
:*X-x-:-:*x*x-:*
100
50
81
99
75.9
0,100
29
% Dispos
25
BO
55
0, 100
6
Note*
N/A
(2,3)
(3)
(21
(2,3)
(3)
(8)
(3)
(3)
(2)
(3)
(21
(2,3|
Notes
CULV
2
% Recyc
0
0
0
0
25
10
0
0
0
0
0
0
0
0
8
6.0
0, 100
29
% Recycl
BO
50
20
0,60
6
EHTS
1
Notes
N/A
16,4)
(5)
(6)
(3)
(4,B)
Notes
(6)
% Reuud
0
0
50
0
•!\ /
0
0
0
0
0
30
BO
75
0
60
B
10
B
0
1
14.7
0,76
29
% Reused
0
50
0
zi
0,75
6
Note*
N/A
(6)
(6)
(6)
(6)
Notes
=====
%Diipo»
100
80
90
7's <
0
90
100
80
60
90
100
90
80
100
100
100
90
80
95
100
100
73
95
87.0
0, 100
29
100
0
90
52
0, 100
Cor
Nclet
'31
(2,3)
(31
(9,2)
(3)
(31
(81
13)
'3'
(3)
(2)
'31
(1,21
(1)
(3!
(1,3)
(3)
CULV
tucjtted Stw
2
% Recycl
0
0
0
0
95
10
0
0
0
0
0
0
0
0
0
0
7
0
3^9
0,95
29
0
60
0
0
10
0, BO
•ERTS
:IP(paCul
2
Note«
'Ml
'*'
'31
(4,6)
^^— "
Verti
X Rawed
0
0
20
10
V.
5
0
0
0
0
20
10
60
0
10
0
:X:x*xXx:;:;x:.::
10
•:*:*:X:XxX:->:>:
6
9.3
0, BO
29
1
% Reused
60
70
10
38
0,70
Notes
(6)
(6)
'61
(6)
(6)
Notes
(6)
-------
Table 17. Summary of disposal/utilization survey (Continued).
U.S. SOURCE:
ALABAMA
ALASKA
ARIZONA
ARKANSAS
COLORADO
CONNECTICUT
FLORIDA
GEORGIA
IDAHO
INDIANA
KANSAS
LOUISIANA
MAINE
MASSACHUSSETTS
MARYLAND
MICHIGAN
MISSISSIPPI
MISSOURI
NEBRASKA
OHIO
OREGON
PENNSYLVANIA
RHODE ISLAND
S. CAROLINA
S. DAKOTA
TENNESSEE
TEXAS
UTAH
VIRGINIA
VERMONT
WASHINGTON
WYOMING
Mean Value
Range
No. of Responses
CANADA SOURCE:
NOVA SCOTIA
SASKATCHEWAN
N. BRUNSWICK
MANITOBA
ONTARIO
Mean Value
Range
No. of Responses
CULVERTS
Wood
2.3
% Dispos
100
0
100
0
$ f
0
0
100
100
100
0
100
0
100
sw«s
0
100
100
100
100
0
, :
100
•• ;
0
100
0
0
100
100
0
- BE .6
0,100
27
% Dispos
100
100
100
100
100
100
NONE
6
Notes
N/A
N/A
(3)
N/A
N/A
N/A
N/A
N/A
few
few
N/A
N/A
N/A
N/A
(3)
(3)
N/A
Notes
burn
% Recycl
0
0
0
0
0
ff
0
0
0
0
0
0
0
0
JSpSSSSii
0
0
0
0
0
0
mmzm
0
mmmm
o
0
0
0
0
0
0
0.0
NONE
27
% Reoycl
0
0
0
0
0
0
NONE
B
Notes
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
Notes
% Reused
0
0
0
0
'•
0
0
0
0
0
0
0
0
0
mmmm
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0.0
NONE
27
% Reused
0
0
0
0
0
0
NONE
5
Notes
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
Notes
CULVERTS
Multiplate Underpass or Culvert
2.4
% Dispos
100
100
0
0
10
100
0
100
0
20
. 100
60
100
60
100
0
100
100
100
100
••
100
:
0
0
100
BO
70
100
61.4
0, 100
27
% Dispos
60
26
76
0
90
48
0,90
6
Notes
N/A
(3)
(2)
(3)
(3)
N/A
(3)
(1)
(3)
(9)
(3)
N/A
(3)
(1)
(3)
(3)
(3)
Notes
(1)
N/A
(3)
% Recycl
0
0
•f
60
95
10
0
60
0
0
80
0
0
0
0
0
0
0
0
0
0
0
: > '
0
100
0
0
20
0
1B.O
0,95
27
% Recycl
50
50
0
0
0
20
0,60
5 .
Notes
N/A
(6,4)
(6)
N/A
N/A
(6)
(6)
(6)
Notes
N/A
(6)
% Reused
0
0
5
50
' f
5
80
0
60
0
0
0
0
60
0
40
0
100
0
0
0
0
•, . ,
0
0
0
0
50
10
0
16.1
0, 100
27
% Reused
0
25
25
0
10
12
0,26
6
Notes
N/A
(6)
(6)
N/A
few
N/A
(6)
Notes
N/A
(6)
GUARDRAIL SYSTEMS
Guardrails
3.1
% Dispos
76
40
15
80
•;
0
40
0
10
60
60
80
30
40
40
80
100
60
BO
90
0
60
S '
80
0
90
26
0
100
50
32
10
45.6
0,100
30
% Dispos
60
90
20
0
90
60
0,90
6
Notes
(3)
(2,3)
(3)
(21
(3)
(9)
(1)
(3)
(1)
(3)
(9)
(3)
(1)
(3)
(1,3)
Notes
(1)
(3)
% Recycl
0
0
0
10
50
30
26
0
0
0
0
0
0
0
0
0
0
0
0
60
0
SSSSS:^
0
0
0
0
100
0
0
42
10.6
0,50
29
% Recycl
60
0
80
0
0
26
0,80
6
Notes
(5,4)
(4)
(4)
(B)
(4,6)
Notes
% Reused
25
60
85
10
60
30
75
90
60
60
20
70
60
60
20
0
50
60
10
60
40
.,*!..::
20
100
10
76
100
0
60
26
90
47.6
0,100
30
% Reused
0
10
0
100
10
24
0, 100
6
Notes
(6)
(6)
(6)
(9)
(6)
Notes
(6)
-------
Table 17. Summary of disposal/utilization survey (Continued).
U.S. SOURCE:
ALABAMA
ALASKA
ARIZONA
ARKANSAS
COLORADO
CONNECTICUT
aORIDA
GEORGIA
INDIANA
KANSAS
LOUISIANA
MAINE
MASSACHUSETTS
MARYLAND
MICHIGAN
MISSISSIPPI
MISSOURI
NEBRASKA
OHIO
OREGON
PENNSYLVANIA
RHODE ISLAND
S. CAROLINA
TENNESSEE
TEXAS
UTAH
VIRGINIA
VERMONT
WASHINGTON
WYOMING
Mean Value
Range
CANADA SOURCE:
NOVA SCOTIA
N. BRUNSWICK
MANITOBA
Mean Value
0
•> ' J
10
10
*
GO
17.B
0, BO
4
0
NONE
0
13)
(9)
Steel Qutf
3
%Recye
26
0
90
30
36.3
0,90
4
•-"-•-• _LI1_L
0
NONE
0
LSYSTEI.
drill Poru
2
Note*
(4)
S
t
SRCLMCC
7B
A rj?
0
f f
20
46.3
0,90
4
0
NONE
0
Neie»
% DItBOf
60
L^.A. "'
,%
,#
70
^ f f
EO
B6.7
60,70
3
0
NONE
0
Hotel
(3)
(21
(91
GUARORAIt
3
XRecycl
h-frrt, -
•" J * /
>;
0
10.0
0,30
3
0
NONE
0
.SYSTEM
3
Note*
Notes
S
% Roused
60
'* ft-
"• v"-" -.
30
f
20
33.3
20, BO
0
NONE
Notes
(6)
Notes
1
KDIspot
BO
BO
9B
90
\
60
0
100
BO
•"!, f'r
30
40
100
30
100
60
60
100
::¥Sfft::SS::¥r::¥
EO
mmmm
80
0
90
76
100
50
mm®®
10
60.3
0, 100
% Dispos
100
100
90
10
90
7B
0, 100
On
Notes
(3)
I2-3'
(3)
(31
(1)
(3)
(9)
13)
(2)
~
Notes
(1)
(3)
1
GUARORAI1
destgnMed (
3.
% Reeye
0
0
5
0
2B
0
0
i ^
0
0
0
0
0
0
0
0
0
SKSiSiSSKs
0
0
0
0
0
0
*:*i-#>:*:8$
0
2.6
0,33
% Recycl
0
0
0
0
0
0
NONE
.SYSTEM
3tu»M!F
4
Note*
(4)
Notes
==
S
ottt
%n
-------
Table 17. Summary of disposal/utilization survey (Continued).
U.S. SOURCE:
ALABAMA
ARIZONA
ARKANSAS
COLORADO
CONNECTICUT
FLORIDA
GEORGIA
IDAHO
INDIANA
KANSAS
LOUISIANA
MAINE
MASSACHUSSETTS
MARYLAND
MICHIGAN
MISSISSIPPI
MISSOURI
NEBRASKA
OHIO
OREGON
PENNSYLVANIA
RHODE ISLAND
S. CAROLINA
S. DAKOTA
TENNESSEE
TEXAS
UTAH
VIRGINIA
VERMONT
WASHINGTON
WYOMING
Mean Value
Range
No. of Responses
CANADA SOURCE:
NOVA SCOTIA
SASKATCHEWAN
N. BRUNSWICK
MANITOBA
ONTARIO .
Mean Value
Range
No. of Responses
SIGNS
4.1
% Dispos
30
60
5
10
0
10
75
40
0
20
60
26
80
100
60
100
0
•.
100
60
60
.. t
0
96
0
60
100
25
27
100
44.7
0. 100
28
% Dispos
30
100
20
0
20
34
0, 100
6
Notes
(2,3)
(3)
(3)
(1)
(1)
(1)
(3)
(3)
(1,2)
(1)
(3)
(1,3)
(3)
Notes
(1)
(1)
% Recycl
70
10
5
86
J.
90
0
25
60
100
30
60
0
0
0
0
0
60
0
50
0
100
0
100
6
0
26
62
0
33.1
0, 100
28
% Recycl
70
0
40
0
30
28
0,70
6
Notes
(4)
(4)
(4)
(12)
(6)
(4,6)
Notes
% Reused
0
30
90
5
,
10
90
0
0
0
50
0
75
20
0
60
0
40
0
0
60
0
5
0
0
0
60
11
0
20.6
0,90
28
% Reused
0
0
40
100
60
38
0,100
6
Notes
(6)
(6)
(6)
Notes
SIGNS
Sign Posts
4.2
% Dispos
30
75
10
80
0
60
100
100
60
60
40
26
50
100
80
100
25
100
20
20
't
'
0
95
0
50
100
25
68
100
66.8
0, 100
28
% Dispos
10
60
20
5
10'
19.0
5,50
5
Notes
(2,3)
(3)
(3)
(1,10)
111
(3)
(1)
(3)
(9)
(3)
(9)
(1,2)
(1)
(3)
(2,3)
(3)
Notes
(10)
% Recycl
0
6
6
10
£ 1
90
0
0
0
40
0
0
0
0
0
0
0
0
0
60
0
0
0
0
60
0
26
17
0
10.4
0,90
28
% Recycl
90
0
0
0
30
24.0
0,90
5
Notes
(4)
(6)
(4,5)
Notes
(10)
% Reused
70
20
85
10
mzmm
10
60
0
0
0
40
60
76
50
0
20
0
76
'
0
30
80
100
6
100
0
0
60
15
0
33.8
0, 100
28
% Reused
0
50
80
SB
60
67.0
0,95
6
Notes
(6)
(6)
(6)
(6)
Notes
(10)
SIGNS
Sign or Signal Poles and Structures
4.3
% Dispos
60
100
6
5
BBSSSSaSBSSSS
0
60
50
60
60
85
90
26
60
0
100
26
95
100
20
95
5
76
100
0
76
50
42
60
61.8
0,100
28
% Dispos
10
75
10
25
0
24.0
0,76
6
Notes
(3)
(2,3)
(3)
(3)
(3)
(1)
(3)
(3)
(9)
(2)
(3)
(11)
(3)
(3)
(3)
Notes
(10)
n-type
% Recycl
0
0
6
80
#:¥:¥:?:¥£:?;*
90
10
60
0
40
0
0
0
0
20
,
0
0
0
0
60
0
'
0
0
0
80
0
0
28
0
16.2
0,90
28
% Recyol
90
0
0
0
0
18.0
0,90
5
Notes
(4,6)
(4)
(5)
(4,6)
Notes
% Reused
60
0
90
10
40
0
60
0
16
10
75
60
80
vmsmw
0
75
6
0
30
5
. V
95
26
0
20
26
50
30
60
32.0
0,96
28
% Reused
0
26
90
76
100
58.0
0, 100
6
Notes
(6)
(6)
(6)
(6)
Notes
(10)
n-type
-------
Table 17. Summary of disposal/utilization survey (Continued).
ON
U.S. SOURCE;
ALABAMA
ALASKA
ARIZONA
ARKANSAS
COLORADO
CONNECTICUT
FLORIDA
GEORGIA
IDAHO
INDIANA
KANSAS
LOUISIANA
MAINE
MASSACHUSSETTS
MARYLAND
MICHIGAN
MISSISSIPPI
MISSOURI
NEBRASKA
OHIO
OREGON
PENNSYLVANIA
RHODE ISLAND
S. CAROLINA
TENNESSEE
TEXAS
UTAH
VIRGINIA
VERMONT
WASHINGTON
WYOMING
Mean Value
Range
No. of Responses
CANADA SOURCE:
NOVA SCOTIA
SASKATCHEWAN
MANITOBA
ONTARIO
Mean Value
Range
No. of Responses
BRIDGES
Steel Rtilfnos
KDlipot
J-.4'
"Vs
go
% •*
66.7
10, 100
3
^%
0
NONE
0
Note*
(3)
&T~
E
SRocyd
\' '{
'>- '• '',
f: •.'
10
3.3
0, 10
3
0
NONE
0
1
Notes
(4)
XReuwc
0
0
' < t.
V
SO
30.0
0,90
3
A -,
0
NONE
0
Naias
BRIDGES
MDlipos
•V
'£
BO
f f
30
46.7
0,90
3
f
0
NONE
0
(3)
<3I
6.
Sfocycl
' y\ '••
' •.? v
* ' J
EO
0
16.7
0, BO
3
0
NONE
0
2
Note*
(4)
Notes
XReuied
..V
0
20
0
0
EO
1
1E
40
EO
0
90
0
0
0
0
E
0
0
20
10
9
76
19.4
0, 100
% Reused
0
0
90
100
10
40
0,100
Notes
(S)
(6)
(6)
(6)
Notes
-------
Table 17. Summary of disposal/utilization survey (Continued).
U.S. SOURCE:
ALABAMA
ALASKA
ARIZONA
ARKANSAS
COLORADO
CONNECTICUT
FLORIDA
GEORGIA
IDAHO
INDIANA
KANSAS
LOUISIANA
MAINE
MASSACHUSSETTS
MARYLAND
MICHIGAN
MISSISSIPPI
MISSOURI
NEBRASKA
OHIO
OREGON
PENNSYLVANIA
RHODE ISLAND
S. CAROLINA
S. DAKOTA
TENNESSEE
TEXAS
UTAH
VIRGINIA
VERMONT
WASHINGTON
WYOMING
Mean Value
Range
' No. ef Responses
CANADA SOURCE:
NOVA SCOTIA
SASKATCHEWAN
N. BRUNSWICK
MANITOBA
ONTARIO
Mean Value
Range
No. of Responses
BRIDGES
Steel Superstructure
6.4 .
% Dispos
76
100
86
6
•. ,
0
100
0
60
100
0
95
60
90
99
0
100
60
95
100
100
90
0
100
60
0
100
0
68
99
62.1
0, 100
29
% Dispos
30
0
10
26
90
31
0, 90
6
Notes
(3)
(3)
(2,3)
(3)
(9,2)
(3)
(1)
(3)
(3)
(3)
(3)
(1)
(1)
(3)
(3)
(3)
% Recycl
0
0
6
76
S4W&&:
80
0
90
0
0
90
0
0
0
0
60
0
0
0
0
;
0
•" .,
0
90
0
0
100
0
0
31
0
21.1
0,90
29
% Recycl
70
50
0
0
0'
24
0, 70
6
Notes
(5,4)
(41
(6)
(6)
Notes
% Reused
26
0
10
20
', ^
20
0
10
60
0
10
5
40
10
1
60
0
60
5
0
0
..
10
10
0
60
0
0
100
(11)
• . 1
16.8
0, 100
, 29
% Reused
0
50
90
75
10
46
0, 90
6
Notes
(6)
(6)
(6)
(6)
(6)
Notes
BRIDGES
Concrete Beams
5.5
% Dispos
90
100
86
96
30
60
100
60
100
100
100
0
f •
100
60
100
0
100
100
100
100
100
100
Smmsm
100
100
100
88
100
82.8
0, 100
27
% Dispos
0
100
0
100
90
I 68
0, 100
Notes
(3)
(2,3)
(3)
(2)
(3)
(3)
N/A
(3)
(3)
(2)
(3)
(2)
(3)
(2,3)
(3)
Notes
N/A
(2)
N/A
% Recycl
0
0
10
0
: f
70
60
0
0
0
0
0
0
O
0
0
100
0
0
t
0
'
0
0
0
;••
0
0
0
0
0
8.6
0, 100
27
% Recycl
0
0
0
0
10
2
0, 10
5
Notes
(5)
(6,4)
(6)
N/A
(6)
Notes
N/A
N/A
(5)
% Reused
10
0
5
6
issssss:;*;
0
0
0
60
0
0
0
0
0
60
0
0
0
0
m®®m
0
mmms
0
0
0
••
0
0
0
12
0
4.9
0,60
27
% Reused
0
0
0
0
0
0
NONE
5
Notes
(61
N/A
(6)
Notes
N/A
N/A
BRIDGES
Concrete Decks
5.6
% Dispos
90
100
60
100
40
60
100
100
100
100
100
100
90
100
90
80
0
75
100
wsassfsfssfs
100
gg*;*
100
100
100
' ' '
100
100
100
100
100
88.0
0, 100
28
% Dispos
100
100
0
75
30
61
0, 100
6
Notes
(3)
(2,3)
(3)
(2)
(3)
(3|
(3)
(3)
(2)
(3)
(2)
(3)
(2,3)
(3)
Notes
(2)
N/A
(2)
% Recycl
0
0
50
0
60
60
0
0
0
0
0
0
0
0
10
20
60
25
0
0
..
0
0
0
msMm
0
0
0
0
0
9.8
0,60
28
% Recycl
0
0
0
25
70
19
0,70
6
Notes
(6)
(5,4)
(5)
(5)
(5)
(6)
Notes
N/A
(5)
% Reused
10
0
0
0
«• v
0
0
0
0
0
0
0
0
10
0
0
0
40
0
0
0
0
0
0
J
0
0
0
0
0
2.1
0,40
28
% Reused
0
0
0
0
0
0"
NONE
6
Notes
Notes
N/A
-------
Table 17. Summary of disposal/utilization survey (Continued).
Legend
NOTE
DISPOSAL:
1
2
3
8
9
11
RECYLED:
4
5
REUSED:
6
DESCRIPTION
Sold as scrap.
Disposed of In landfill, etc.
Material becomes contractor's property to be recycled, reused, or sold as scrap.
Becomes property of others.
Only unusable items are disposed of.
Only unsuitable material is removed.
Reused, or stored for subsequent use after straightening, painting, or minor repair.
Crushed, broken, or modified for recycling for use in a different highway application.
Used in the same application or function.
NOTE
OTHER:
10
12
13
14
N-Type
f
DESCRIPTION
Entry applicable to steel only. For wood:
State/Province
Georgia
Saskatchewan
Ontario
Wood
Aluminum
Concrete Shoulder
% Dispos
50
25
80
75
0
10
Notes
(2)
burned
% Recyc
50
0
10
0
100
90
New type of poles.
Notes
(2)
% Reused
0
75
10
25
0
0
Notes
oo
-------
Roadway Materials
Roadway materials are comprised of different material layers extending from the asphalt
pavement's surface course to the subgrade and those material layers used to construct the
shoulders. Ten different material/application layers are identified in table 17. The response
to the survey indicated that, on the average, at least 75 percent of all roadway materials were
either reused or recycled. The ensuing discussion presents a more detailed evaluation for
each category of roadway materials.
Most States and Provinces do not distinguish between asphalt surface and asphalt
structural layer/base course for pavement recycling purposes. The majority of the highway
agencies recycle between 75 and 100 percent of their asphalt surface and asphalt base courses
and the remainder is reused except for a small percentage (e.g., 5 to 10 percent) of RAP that
is disposed of because it was not recoverable from stockpile or was of poor quality. Several
States (e.g., Oregon, Alaska, Vermont) recycle less than 30 percent and primarily reuse the
RAP for embankment fill. In Vermont, the contractor, with written approval, may use on
the project such stone, gravel, sand, and other materials as may be found in the excavation,
for other construction items, providing the materials meet the specifications. Alaska removes
asphalt pavement and stockpiles about 80 percent for later use or for local reuse. The
Province of Alberta often provides designs for pavement rehabilitation that allow for the use
of all the RAP excluding that which is of poor quality.
The amount of recycling performed by the highway agencies is affected by the cost and
availability of commercial aggregates, the type or category of highway, the pavement design,
and existing policy and specifications for recycling of asphalt pavements. Table 18 provides
a summary of specifications for hot-mix recycling in 50 States and the District of
Columbia.a) Typically, most States allow a maximum of 50 percent or less RAP, except
Arkansas and Utah where the maximum amount of RAP allowed in surface or binder courses
is 70 percent.
Other roadway materials such as crushed stone base, crushed gravel base, and granular
subbase are commonly reused or disposed of into embankments or fills. In Louisiana, 90
percent of old crushed gravel base courses are improved by stabilization. Granular subbase
is used as fill, although 25 percent is used as aggregate in HMA and approximately 25
percent is donated to adjacent property owners. Crushed stone is used in Kansas as a
subgrade modifier or stabilized subbase.
Stabilized base course materials are conventionally used in embankments, although other
methods have been adopted by several States. Louisiana pulverizes and restabilizes about 40
percent of the time. When cement-treated bases are encountered in Idaho, they are disposed
of rather than attempting to recycle. Arizona breaks all stabilized base materials and
incorporates them into embankment fills where future excavation is not anticipated. In
Alberta, stabilized base containing 4 percent asphalt and/or crushed gravel is reused to
improve the properties of subgrade and granular bases on the rehabilitation project.
Stabilized subbases are generally reused or disposed of in embankments.
149
-------
Table 18. Summary of recycling specifications of 50 States and the District of Columbia (from reference 3).
STATE
Alabama
Alaska
Arizona
Arkansas
California
Colorado
Connecticut
Delaware
t— »
Ot
o
District of
Columbia
Florida
Georgia
MAX
BASE
40
RAP <£ R
BIND
40
ATCH
SURF
12
MAX RAP %— DRUM BLENDED RECYCLING AGENTS
BASE
50
(Developmental projects only at this time — no
40
70
50
30
40
35
60
60
25
40
70
50
30
40
35
60
40
70
50
30
40
25
NO
50 50
See note #1
25
25
40
70
50
30
40
50
60
60
40
BIND
50
1UF Slit STOCKPILE
SURF FOR RAP ALLOWED? A/C
12 2 in YES AC 5-20
MOD- NOTES
NO RAP must meet specs.
standard specifications)
40
70
50
30
40
50
60
40 1% in NO AC 10-20
70 3 in NO YES
50 2 in NO YES
30 114 in OPEN YES
40 95% < 2 in YES YES
30 See note #1 See note #2 AC 10
NO 1 in NO AC 10
50 50 See note YES YES
See note #1
40
40 2 in YES YES
NO 100% RAP must pass I'A-ia screen.
Oversize must be crushed.
YES
YES Only RAP milled from rehabilitation
project can be used in recycled mix
YES In most cases, less than 30% used.
NO 15 % RAP may be routinely used
after notifying DOT.
NO Note#l: 100% RAP must pass 2-in
sieve with 90% passing 1-in sieve.
Note #2: When using blended
stockpile, maximum RAP allowable
is 10%.
YES When RAP contains sheet asphalt,
the practice is to limit the RAP to
'0*6
YES Note#l: All mixes must meet stan-
dard spec requirements.
Note #2: Equal to top size of mix
NO Specs allow use of contractor's stock-
pile of RAP; RAP stockpile must be
-------
Table 18. Summary of recycling specifications of 50 States and the District of Columbia (Continued).
STATE
Hawaii
Idaho
Illinois
Indiana
Iowa
Kansas
MAX RAP %-BATCH MAX RAP %-DRUM BLENDED
• ' TOP SIZE STOCKPILE'
BASE BIND SURF BASE BIND SURF FOR RAP ALLOWED?
30 NONE NONE 40 NONE NONE 1V4 in NO
OPEN OPEN 2 in OPEN
25 25 15 25 25 15 See note NO
See note #1 See note #2 See note #1 See note #2
50 50 See note 50 50 See note 2 in NO
OPEN 1'Ain NO
50 50 50 50 50 50 See note YES
RECYCLING AGENTS
A/C MOD.
AR6000 OPEN
YES OPEN
AC 2.5 to 20 NO
AC 2.5 to 20 AE60
AE90
YES OPEN
YES YES
NOTES
Limited to AC base.
Specs tailored to each project 20%
to 40% max.
Grizzly required for RAP bin.
Note#l: No Interstate use. Top
size for RAP, maximum size
allowed in mixture.
Note #2: For ADT less than 2,000.
Open to modifying specs for given
project. Surface recycling is by spe-
cial provision only. RAP percentage
limited to 20% when not salvaged
from DOH project. Homogenous
aiwCtvjjliC i. iv \jtIifCu*
At least 70% of asphalt cement in
final surface course mix shall be new
material.
100% must pass 2W-in scalper,
10% RAP routinely may be used.
Kentucky
30/20 30/20 30/20 30/20 30/20 30/20 NONE
See notes #1,
See notes #1, #2
OPEN
See note #2
YES OPEN Note#l: RAP used in open-graded
portion, sand surface asphalt, or any
surface course must meet aggregate
requirements when originally placed.
Same is true with mixes requiring
polish-resistant sand.
Note #2: When RAP not salvaged
from DOT projects, RAP percentage
limited to 20%.
Louisiana
30 30 NO 30
30 NO
2 in
OPEN AC 10,30 NO
Shoulder-wearing course maximum
of 20%.
-------
Table 18. Summary of recycling specifications of 50 States and the District of Columbia (Continued).
U)
Ni
MAXRAP56-BATCH
STATE
Maine
Maryland
Massachusetts
Michigan
Minnesota
Type 32 Mix
Type 42 Mix
Mississippi
Missouri
Montana
Nebraska
Nevada
New Hampshire
BASE
40
50
20
50
50
50
30
50
50
BIND
40
50
20
50
50
30
30
50
50
SURF
NO
30
10
50
30
30
NO
50
0
Batch plants not commonly used
50
35
50
35
15
0
MAXRAP56-DRUM
BASE
40
50
40
50
50
50
30
50
50
50
50
50
BIND
40
50
40
50
50
30
30
50
50
50
50
50
SURF
NO
30
10
50
30
30
NO
50
0
50
15
0
TOP SIZE
FOR RAP
VAin
See note #1
VAin.
2-in Base
1-in Top
See note
See note
2in
l'/4in
2 in
2in
Itein
See note
BLENDED
STOCKPILE ~
ALLOWED?
NO
See note #2
NO
YES
YES
YES
NO
OPEN
YES
OPEN
NO?
NO
RECYCLING AGENTS
A/C
AC 5, 10
YES
AC 5, 10
AC 1-10
MOD.
NO
YES
NO
NO
Modifiers not required
AC120/150
YES
YES
85-100
120-150
200-300
YES
YES
YES
NO
NO
NO
NO
YES
NO
NOTES
20% max RAP allowed in all base
and binder mixtures on all projects.
Up to 40% RAP on specific projects
Note #1: All mixes must meet IMF.
Note #2: Not after the approval of
All salvaged asphaltic pavement
materials to be used in type 32 mix,
no particle greater than 3 in; for
Specifications tailored to each proj-
ect. May be less to meet air quality
RAP percentage may vary if order
for combined gradation is to meet
Modifier required when RAP percent-
-------
Table 18. Summary of recycling specifications of 50 States and the District of Columbia (Continued).
Ui
STATE
New Jersey
New Mexico
New York
North Carolina
North Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
MAX RAP %— BATCH MAX RAP %— DRUM BLENDED
TOP SIZE STOCKPILE"
BASE BIND SURF BASE BIND SURF FOR RAP ALLOWED?
50 50 10 50 50 10 2% in YES
OPEN* OPEN 2 in NO
See note #1 See note #1
50 50 NO 70 70 NO 2 in NO
60 60 60 60 60 60 2 in YES
See note
50 50 50 50 50 50 l'/4 in NO
50 50 30 50 50 30 Base 95% NO
< 2 in,
•^4 in for surface
25 25 25, 0 25 25 25, 0 95% < 2 in YES
See note See note
30 20 20 30 20 20 1 in NO
See note #1 See note #1
OPEN OPEN 10 OPEN OPEN 10 95% < 2 in YES
RECYCLING AGENTS
A/C MOD. NOTES
AC 20, 10 NO Specs are for RAP used from same
reconstruction project; otherwise,
from blended stockpile, 10% RAP in
surface and 50% in base and binder
courses allowed.
YES YES RAP must be screened and stock-
piled 2 in to 3/8 in.
Note#l: By mix design.
YES NO Maximum RAP % linked to RAP
moisture content.
YES NO Subject to approval. AC-20 may be
allowed with 15% or less RAP, sub-
ject to approval.
YES OPEN
YES YES When RAP % is less than 10%,
Marshall mix design not required.
These figures okay for contractor
mix designs.
AC-20 NO 25% for low volume roadways (less
than 1,000 ADT); 0% for all other
roadways.
YES OPEN 20% RAP allowed in shoulders.
The combination of RAP, new mate-
rials, and recycling agents must pro-
duce mixture with recovered asphalt
properties equal to new asphalt.
Note#l: Non-Interstate jobs;
0% RAP on Interstate projects.
YES YES Minimum 11% RAP required for
base and binder, 5% for surface.
-------
Table 18. Summary of recycling specifications of 50 States and the District of Columbia (Continued).
MAX RAPE-BATCH
STATE
Rhode Island
South Carolina
South Dakota
Tennessee
BASE BIND
35 35
20 15
SURF
NO
10
Batch plants not commonly used.
OPEN
See note
0
MAXRAP56-DRUM
BASE BIND
50 50
20 15
50 50
See note
OPEN
See note
SURF
NO
10
50
0
TOP SIZE
FOR RAP
IK in
2 in
VA in
NONE
BLENDED
STOCKPILE —
ALLOWED?
NO
NO
NO
OPEN
RECYCLING AGENTS
A/C
YES
YES
YES
YES
MOD.
Optional
NO
NO
YES
NOTES
Minimum 10% RAP required.
Percentage specified on project basis
by plan note.
At least 65% of asphalt cement in
final mix shall be new material.
Texas
OPEN
See note
OPEN
See note
2 in OPEN YES YES Specification limits RAP percentage
to 20% when not salvaged from
TxDOT project. Only RAP from
TxDOT projects allowed in surface
courses. RAP percentages above
20% require analysis of blended
asphalt quality.
Utah
70 70 70 70 70 70 95% < IVS in NO
100% < 2 in
YES YES Minimum 50% RAP Required:
recovered asphalt after recycling has
to meet same requirements as if new
asphalt was used, and gradations
have to meet same requirements as
new material. Up to 15% RAP
allowed without recovered analysis
of aggregate gradation and asphalt
cement.
Vermont
Virginia
Washington
West Virginia
See note
25 (see note)
OPEN
See note #1
OPEN
See note
25 (see note)
OPEN
See note #1
OPEN
N/A
2in
OPEN
See note #1
OPEN
NO YES NO All recycled mixes must meet stan-
dard specifications.
YES YES NO Unless otherwise approved hi
writing by the engineer.
YES YES YES Up to 20% RAP allowed without
analyzing gradation of RAP.
Mixture containing RAP must
conform to standard specs.
Note#l: By mix design.
OPEN OPEN OPEN Penetration not less than 60.
-------
Table 18. Summary of recycling specifications of 50 States and the District of Columbia (Continued).
MAX RAP %-BATCH MAX RAP %-DRUM
STATE
Wisconsin
Wyoming
BASE BIND
OPEN
50 50
SURF BASE BIND SURF
OPEN
50 50 50 50
BLENDED
'lOP SJ1ZE &1OCKP1LE
FOR RAP ALLOWED?
lin NO
2 in NO
RECYCLING AGENTS
A/C
YES
YES
MOD. NOTES
NO RAP source limited to reconstruction
project for surface courses.
NO Percent of RAP specified by State on
a project basis.
1 in = 25.4 mm
-------
Subgrade materials are always reused except in certain situations where the material is
wet or contaminated and does not meet the agency's specifications.
Shoulders constructed with HMA are mostly reused and recycled. Very little is disposed
of except into fills. Similarly, compacted aggregate shoulders are reused, possibly stabilized
or re-manipulated most of the time. '
Culverts
The primary function of a culvert is to transfer surface drainage water from one side of a
roadway to the other and to provide structural support for the overlying roadway fill,
pavement, and vehicular traffic. In some cases, large culverts also function as vehicle or
pedestrian underpasses. The materials used in the construction of small culverts usually
range from wood, concrete pipe, corrugated steel pipe, to concrete box. Larger culverts and
underpass structures are often constructed using multiplate.
The information on culverts from the survey indicated 100 percent disposal of wood
culverts. In most States, multiplate underpasses were disposed of 100 percent of the time,
either being sold as scrap or as the contractor's property for reuse, recycling, or disposal or
scrap. A few States and Provinces indicated reuse ranging from 10 to 50 percent (one State
cited 100 percent reuse). The limited demand for multiplate structures and the difficulties
encountered in erection using bent, damaged, or rusted plates and fittings often make it more
practical to sell as scrap or designate as contractor salvage. One State mentioned that the
lack of storage space made it impractical to recycle or reuse multiplate units.
About one-half of the respondents indicated that they dispose of 90 to 100 percent of the
concrete culvert pipe. Missouri crushes all old concrete pipe and recycles it into roadway
fill. Arizona and Manitoba recycles about 50 percent in this manner and disposes of the
remaining 50 percent in other ways. In general, in the remaining one-half of those respond-
ing to the survey, concrete culvert reuse ranged from 10 to 75 percent. One State donated
about half of the old concrete culverts to property owners and the remainder were used as
temporary culverts. Recycling usually involved use in roadway fill, ,but in Ontario 30
percent is consumed as riprap, 20 percent is reused, and 50 percent is buried or used as fill.
Corrugated steel culvert pipe is predominantly disposed of directly or by the contractor
as scrap for recycling into steel products. On the average, 87 percent is disposed of as
compared to 74 percent for concrete culverts. About 15 percent (ranging from 5 to 70
percent) was reused on State highways, given to local municipalities for local roads, or either
sold or donated to landowners, sometimes as part of right-of-way negotiations for use as
storage bins or culverts. In numerous instances, scrap steel is the property of the contractor.
156
-------
Guardrail Systems
The survey form did not identify the different types of guardrails. Although the implica-
tion was for conventional rolled steel, there was one or two responses that indicated
aluminum and steel cable. Similarly, the guardrail posts were generally steel posts,
however, aluminum and wood posts were utilized in three and five States, respectively.
As would be expected, on the average, 57 percent of wood guardrail posts were disposed
of by the contractor or maintenance crew. Wood posts may be landfilled, used as landscap-
ing timbers, sold to landscapers, or disposed of by the contractor. Salvageable wood posts
are generally reused when guardrails are raised, but are seldom stockpiled for reuse except in
regions where rotting is not a major problem and wood is predominately used.
Steel posts are reused or recycled depending upon conditions and State highway agency
procedures. In some States and Provinces, the removed material becomes the property of the
contractor (e.g., 100 percent disposal), which may be reused elsewhere or sold as scrap and
recycled into new steel products. On the average, the States reuse about 37 percent of the
steel guardrail posts and recycle about 5 percent. These values are not truly representative
because of the variability in which the different States handle contractor salvage. One State
recycles about 90 percent of the steel posts removed from the highways for construction of
storage racks. Most States reuse steel posts, or if damaged, sell it for scrap rather than
recycle (refurbish) damaged posts. Similarly, damaged aluminum posts are sold for scrap
since it is not practical to straighten them.
Typically, guardrails are reused and recycled about 50 percent of the time and the
remaining 50 percent are sold as scrap or contractor salvaged. However, cable guardrails in
Connecticut are 100 percent recycled. Most States and Provinces reuse guardrails unless
they are damaged excessively. A few States straighten (recycle) bent guardrail. In some
instances, the recycled or removed guardrails are stockpiled in maintenance yards for
subsequent use in guardrail repair. In Michigan, aluminum and galvanized guardrails are
used by maintenance crews but Cor-Ten™ guardrail is scrapped. Similarly, in Oregon,
ungalvanized guardrail is sold for scrap. In Canada, the policy varies between Provinces,
such as removed steel becoming the property of the contract (agency) to reuse unless bent or
damaged excessively.
Comments received from States having high wind and snowfall conditions indicate they
have encountered a major problem with guardrails causing snow drifts. The guardrail is
considered a roadside hazard in these conditions. Therefore, except for those locations
where a guardrail is essential, there is a tendency to minimize guardrail installation.
In summary, State highway agency policies, climate conditions, type of material used in
guardrails and posts, availability of facilities for straightening, and probably the degree of
corrosion produced by deicing salts or saltwater spray influences the amount of disposal,
recycling, and reuse of guardrail systems.
157
-------
Signs and Sign Signal Structures
Sign and sign post replacement is usually the responsibility of maintenance and opera-
tions with the State highway agencies. On the average, about 46 percent of all signs are
disposed of, 34 percent are recycled, and the remaining 20 percent are reused. The actual
values for each State vary substantially because of different materials used in sign construc-
tion and operational procedures. Arizona and Maine predominantly reuse their signs Maine
disposes of 15 percent, reuses 75 percent, and recycles 10 percent as scrap metal. Oregon
and Louisiana recycle (resurface and reuse) 50 percent of their signs and dispose of the
remaining signs as scrap metal. All plywood signs in Oregon are discarded. In Missouri, 40
percent of the signs are reused and the remaining 60 percent resurfaced (recycled) in the sign
reclamation plant. Similarly, the Province of Alberta recycles 60 percent of their aluminum-
backed signs by removing old reflective sheeting and sign messages from the aluminum blank
which is then covered with new sheeting and message. In some cases, States and Provinces
dispose of all signs either by selling as scrap metal or by becoming the property of the
contractor.
The disposal, recycling, and reuse of sign posts varied depending upon material type and
highway agency. Ohio, Wisconsin, Wyoming, and Virginia dispose of 100 percent of their
sign posts either through maintenance forces or as contractor's property. About one-half of
the respondents reuse between 50 to 100 percent of their sign posts. In Saskatchewan, 75
percent of wood posts are reused, the remainder are burned, and 50 percent of the steel sign
posts are reused, the remainder are disposed of as scrap steel. Ontario was similar except
they recycled approximately 30 percent of the metal posts.
Sign and signal poles or structures, usually aluminum or steel, are disposed of about 50
to 95 percent of the time by most of the responding States. This material is sold as scrap
except in those States (e.g., Alaska, Virginia, Vermont) where it is designated as the
contractor's property for subsequent sale as scrap (recycling) or reuse. The amount of reuse
tends to be associated with type and age of the sign structures. Ontario reuses 100 percent of
their new type poles and sign structures whereas only 20 percent of the older type is reused
the remainder being property of the contractor. Saskatchewan disposes of 75 percent as
scrap metal, but reuses about 25 percent of all sign poles and structures. Wyoming and
Alberta primarily reuse sign poles unless structurally unsound, and recycle about 50 percent
of the sign structures, the rest being scrapped.
It is apparent that the amount of disposal, recycling, and reuse is dependent upon each
State's policy, type of materials used, and regional conditions that affect suitability for
recycling or reuse. Transportation and competitive cost of new signs, posts, poles, and sign
structures make it impractical to recycle in some areas.
Bridges
The survey response for major bridge components (railing, steel superstructure, concrete
beams, and concrete deck) indicated that most States dispose of 80 percent or more of the
concrete obtained from the rehabilitation and demolition of bridges. Similarly, over half of
158
-------
the States dispose of 80 percent or more for the steel superstructure and bridge railings. At
least five States and one Province indicated that almost all bridge materials were the
contractor's property for reuse, recycling, or disposal, as considered appropriate by the
contractor.
Bridge railings are reused or recycled unless they are excessively damaged, corroded, or
do not meet current standards. The amount of reuse ranges from between 1 and 15 percent,
although Indiana, Maine, and Wyoming indicated 50, 40, and 75 percent reuse, respectively.
Missouri and Arizona essentially reused all bridge railings (90 to 100 percent), except where
the condition required sale as scrap. In Alberta, steel tube railings are commonly recycled
by sand blasting and galvanizing in their shop. The excessively corroded railings are
disposed of in landfills. Only three States differentiated between steel and aluminum
railings. Maryland and Michigan reuse 50 percent of their aluminum railings, but dispose of
almost all steel railings. No comments were provided to identify the difference in reuse
between aluminum and steel, although it may be related to the corrosion resistance of
aluminum.
Steel superstructure members and trusses were reused by about two-thirds of the
respondents. The amount of reuse generally varied between States from 1 to 50 percent.
The response may be misleading because reuse may involve being reused by local or
municipal agencies. For example, Missouri reuses about 50 percent of its steel bridges, but
part of this is sold to counties. Similarly, in the Province of Alberta, steel trusses with
insufficient load capacity are either sold through Government Services Surplus sales or sold
to the public for reuse or recycling. Otherwise, they reuse trusses at other suitable locations
or put them into salvage steel truss inventory for repair or modification of inservice trusses.
Occasionally, they are reused on similar bridges by doubling the trusses to increase load
capacity.
Those States that indicated a high percentage of recycling were in several instances
disposing of the steel as scrap for recycling into new steel products. This, combined with
disposal practices in many States, suggests that most bridge superstructure steel is removed
and sold as scrap by either the contractor or the highway agency.
Concrete beams and concrete bridge decks are, for the most part, disposed of with very
little recycling or reuse. Broken concrete is frequently used as embankment fill or buried
within limits of construction. Reinforcing steel is generally removed and sold as scrap. In
Pennsylvania, all bridge materials are the contractor's property, but when concrete bridge
demolition is near suitable commercial facilities, the concrete rubble is generally recycled.
In Alberta, concrete beams are occasionally used in storage yards for stockpiling planks and
other materials or sold to the public for use as sleepers or in small bridge construction for
landowner access. Concrete bridge decks are reused by some States and Provinces for slope
protection (Missouri) or riprap (Nebraska, Manitoba, Ontario).
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Other Recycling Activities
Traffic paint and cracksealer are supplied, in accordance with the Alberta Transportation
Department's specifications, in returnable drums with plastic liners. After the material is
used, the liner and drum are returned to the manufacturer.
Arizona recycles about 95 percent of chain-link fences and posts. Sidewalk/curb and
gutter concrete is used in embankments.
Summary
The results of this survey would have been enhanced had the knowledge gained here
been applied in the development of an improved survey form or questionnaire. However, the
results obtained and inferred suggest that numerous regional or local factors influence the
operational aspects of maintenance and rehabilitation. In some cases, policies and specifica-
tions governing the disposal, recycling, and/or reuse of highway materials have evolved to fit
these situations. It seems that substantial effort has been and is being exerted by the agencies
to find more effective ways to utilize highway materials. Finally, since highway materials
often differ from one locality to the next, there are, as evidenced by this survey, different
approaches to materials utilization that are effective under a specific set of conditions.
References
1. "Three States OK More RAP in Recycling Specs," Roads and Bridges, October 1992
pp. 31-34.
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CHAPTER 4. SUMMARY OF FINDINGS
ENVIRONMENTAL ASSESSMENT
Crumb Rubber Modifier
Environmental and Human Health Effects
The available data are inadequate to develop a quantitative characterization of absolute or
relative human health or environmental risks associated with the production, application,
recycling, or disposal of paving asphalt modified with CRM. Critical data gaps are as
follows.
There are no environmental monitoring data that can be used to define "mixtures of
concern" or "similar mixtures," or to assess exposure to humans or other organisms to
components of these mixtures. Data on emissions are limited to a few studies of stack
emissions from asphalt mixing plants and two preliminary studies of occupational exposure.
The results of these studies and other similar studies of emissions from conventional asphalt
production suggest that, in general, the addition of CRM to the mix does not significantly
contribute to changes in emissions of major classes of pollutants (e.g., polyaromatic hydro-
carbons (PAH), volatile organic compounds, etc.). However, at least one chemical,
4-methyl-2-pentanone (methyl isobutyl ketone or MIBK), may be released in greater
quantities during mixing of asphalt pavements modified with CRM. Although the source of
MIBK has not been identified, a plausible source is thermal degradation of isoprene, a
component of rubber. This is consistent with the observation of higher rates of emission of
MIBK at higher mixing temperatures.
The significance of the detection of MIBK in the emissions from mixing of asphalt
pavements modified with CRM is that it suggests that components of rubber and reaction
products of these components may be emitted during asphalt production (and perhaps at other
stages in the life of the asphalt product). If this is the case, then mixing temperature may be
an important factor in determining relative risk associated with modified asphalt pavement
production vs. conventional asphalt production. It also is possible that other components of
rubber and thermal reaction products may be emitted in the production of modified asphalt
paving mixtures. Consideration should be given to conducting studies in which emissions of
rubber chemicals and probable reaction products are monitored. Once the emission profile
for rubber chemicals has been defined, it might be possible to define potential "mixtures of
concern" or "similar mixtures" that could be used in risk characterization.
It needs to be emphasized that measurements of stack emissions such as those conducted
in the Thamesville (Ontario), Haldimand-Norfolk (Ontario), Farmer County (Texas), and San
Antonio (Texas) studies provide only a rough index of potential exposures resulting from
production of asphalt pavements. They do not provide information about exposures that
might result from leaching of materials from pavement, or from emissions during removal,
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recycling, or disposal of paving. Such information can be obtained from environmental
monitoring in the vicinity of these operations.
In the absence of environmental monitoring studies, some limited estimates of exposure
potential can be made from evaluations of environmental fate. For example, it may be
possible to evaluate the potential for MIBK to be transported to various environmental media
and to estimate its persistence in these media. Such evaluations depend on the availability of
nigh-quality data on the composition of modified asphalt pavement and the environmental fate
of the chemicals of greatest concern. The chemical composition of asphalt pavements
modified with CRM has not been adequately defined to support a comprehensive
components" approach to environmental fate assessments. Furthermore, although there is
information on the environmental fate and toxicity of some of the major hazardous
components of conventional asphalt cement and rubber, this data has not been evaluated to
assess the adequacy of the data base for estimating exposure potential.
Dose-response assessments have not been developed for "mixtures of concern" or
similar mixtures" since these have not been defined. Dose-response assessments are
available for some of the major components of asphalt cement and rubber. The toxicologic
interactions that occur between the chemical components of modified asphalts have not been
adequately characterized.
Recycling
A characterization of relative risk associated with recycling of asphalt paving mixtures
modified with CRM vs. conventional asphalt pavement is not feasible at this time.
Other Recycled Materials
Environmental and Human Health Effects
The available data are inadequate to develop a characterization of absolute or relative
human health or environmental risks associated with the production, application, recycling
or disposal of asphalt pavements modified with other recycled materials.
Recycling
The available data are inadequate to develop a characterization of absolute or relative
human health or environmental risks associated with the recycling of asphalt pavements
modified with other recycled materials.
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ENGINEERING ASSESSMENT
Crumb Rubber Modifier (CRM)
Approximately 242 million tires that are comprised of over 1.8 million Mg (2 million
tons) of rubber are discarded annually. Currently, about 11 percent of these scrap tires are
used as a tire-derived fuel (TDF) source for heat or power generation. About 5 percent are
exported and less than 7 percent are recycled or processed for other products. Of this 7
percent, about 2 percent is used in tire manufacturing, 3 percent is turned into rubber
products, and 2 percent is used as crumb rubber in asphalt pavements.
The answer to the question of whether the CRM technology is viable and cost-effective is
not readily apparent. States located in the hot, dry, southwestern U.S. have extensive
experience with rubber-modified asphalt membranes and mixtures. In general, they have had
only a few failures and are generally satisfied with the constructability and performance of
pavements containing CRM. However, highway agencies in the northern States, where wet
and cold weather is more prevalent, have not observed any major improvement in perfor-
mance over their conventional HMA pavements.
The major unknown in using these materials is the potential for their influence on the
recycling process. Experience with the recycling of RAP containing CRM is limited. The
greatest deterrents from the use of CRM is the high initial cost and the variable performance
that seems to be associated with climate and selection of proper application, mix design, and
construction.
There is an urgent need to evaluate the recyclability of asphalt concrete pavements
containing CRM. The investigation should encompass the use of recycled asphalt pavement
(RAP) that contains stress-absorbing membrane (SAM), stress-absorbing membrane interlayer
(SAMI), and other asphalt rubber (AR) paving mixtures, including combinations (e.g.,
SAMI, asphalt concrete, SAM).
There is also a need to develop mixture design methods to accommodate the use of CRM
using either dry or wet processing methods. The combined influence of CRM particle size
and aggregate gradation needs to be evaluated and suitable criteria needs to be established for
selection of amount and size of CRM and total binder content for each application.
The CRM/asphalt cement interaction needs to be evaluated to establish absorption of
malthenes, degree of rubber particle swell or solubility, and influence on binder properties in
relation to size and amount of CRM. Processing methods, both wet and dry, should be
evaluated to determine the effects of time, temperature, pressure, mechanical mixing, etc.,
on the CRM/asphalt interaction. Process (reaction) time, storage time, or equilibrium
conditions must be established for wet processing methods. It should be determined whether
or not the dry process is equivalent to the wet process once a certain fineness and amount of
CRM is achieved.
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Recycling of Pavements Using 80 Percent RAP
Currently, there are only three asphalt recycling processes that can utilize successfully at
least 80 percent RAP. They are: (1) cold in-place recycling, (2) hot in-place recycling, and
(3) hot central plant recycling by means of the proprietary CYCLEAN* process.
Cold in-place recycled materials are usually used as a stabilized base course to be
covered with a chip seal in low volume roads, or overlaid with a hot or cold surface mix
Pavements with excessive patching, weak subgrade due to water damage, or stripping
problems are not recommended for cold in-place recycling.
Hot surface recycling is usually used to correct surface defects such as roughness and
weathering of pavements that are structurally adequate. The recycling process is also limited
to a depth of 50 mm (2 in).
Among these three recycling processes, the hot central plant recycling can produce mixes
of the highest quality. The hot recycled mixes are usually used as surface structural mixes
However, due to the problem with smoke emission, utilization of greater than 80 percent
RAP in the recycled mix has been limited to the CYCLEAN* process that uses the micro-
wave technology. For a RAP material that has been substantially aged and deteriorated
adequate amounts of virgin aggregate and recycling agent are required to be added to the
RAP to produce a high-quality hot mix. This will limit the percentage of RAP that could be
incorporated into the recycled mix. Recycling specifications of State highway departments
have set limits on the maximum allowable percentage of RAP to be used in hot-mix
recycling.
Crushed Glass
The quantity of crushed glass is relatively small with respect to potential uses in the
highway network. Also, the availability of crushed glass for highway construction is limited
to areas near cities that are major generators of glass. Because of its value, glass that has
been sorted is best suited for recycling back into glass products,.
Crushed glass has been used successfully as an aggregate replacement in base and
subbase course materials, as a drainage media, and in asphalt pavements subjected to light
traffic volumes. The use of glass as an aggregate supplement should be considered experi-
mental in the surface coarse since its performance in this capacity is unknown.
In summary, glass has been used in portions of the highway pavement structure Its use
may not be cost-effective nor may it impart any beneficial attributes to a. pavement other than
reflectivity. It can generally be considered as being nonbeneficial to the properties of
conventional construction materials and to the performance of highway pavements.
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Plastic
In summary, recycled plastic guardrail posts and other experimental posts that are not
currently a manufactured product, have insufficient performance data to evaluate their
suitability for use in highway construction. Impurities that affect strength properties and
densities that are greater than wood products suggest that it may be impractical to use
recycled plastics in certain applications. Also, costs that may be four times greater than
wood may result in life-cycle costs that are excessively high.
However, it seems reasonable to assume that State highway agencies can utilize currently
manufactured recycled plastic products provided they meet their requirements/specifications.
Although many manufacturers label their products with the recycled content, all producers
should have similar labeling to facilitate purchasing of products according to specifications.
The use of virgin polymers for modification of asphalt cements is not a new technology.
Other than differences in processing and type of polymer, those processes using recycled
plastics (Novophalt* and Polyphalf) are similar and should be expected to provide greater
resistance to rutting and possibly greater life provided the properties of the binder and
mixture are suitable for the imposed traffic and climatic conditions. The approximate 30
percent increase in cost for polymer-modified hot-mix asphalt appears justifiable based upon
life-cycle costs.
Other Materials
Coal Ash
Coal-fired power generating plants produce as byproducts, fly ash and bottom ash. Both
have been used extensively in highway construction. Fly ash in particular is one of the most
abundant and useful "waste" products available.
For over 50 years, fly ash has been used as a replacement/additive in portiand cement
concrete where it enhances sulfate resistance, raises strength, and reduces permeability.
Forty-five States either incorporate it in or have specifications governing its use. Another
benefit derived is the potential cost savings of $1.3 to $2.6/m3 ($1 to $2/yd3) when used as a
cement replacement.
Fly ash added to aggregates has been used to produce a high-quality base course in
flexible pavement systems, and a high-quality subbase in rigid pavement systems. Lime-fly
ash-aggregate mixtures are also commonly used as a base or subbase course. Other uses
include mineral filler in HMA pavements, fine aggregate, embankment material, soil
stabilizer, and flowable backfill component.
Bottom ash accounts for 15 percent of total coal ash production (fly ash is 85 percent).
It has been extensively used as an anti-skid material, granular backfill and embankment
material, as a coarse aggregate in asphalt paving, and as a component of cement-stabilized
base material.
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Slag
As is the case with fly ash, blast furnace (primarily iron) slag has been used extensively
as an all purpose aggregate material for over 30 years. There are four primary types of slag:
air-cooled, expanded, granulated, and pelletized. The other types include steelfurnace
nickel, and copper slags.
_ Air-cooled slag is used as an aggregate in a variety of materials such as concrete (both
plain and reinforced) and bituminous pavements (enhances skid-resistance). It has been used
as a high-stability base course for macadam surfaces and bases, dense-graded aggregate,
bituminous stabilized bases, and as a soil-aggregate base.
^ Expanded slag and pelletized slag are lightweight aggregates, and are not used extensive-
ly in highway construction, except for producing lightweight concrete products.
^ Granulated slag gains strength with time and it exhibits good compaction characteristics.
It is used frequently for embankment fill or highway bases. When used as a base material, it
exhibits excellent insulative properties and can be used effectively in frost prone areas. Due
to its strength-gaining characteristics, it has also been used as an additive/replacement for
cement in slag cement.
Steel furnace slag, produced in the making of steel, exhibits high bulk densities, and is
frequently used as base course and for highway shoulders. The additional unit weight
produces higher skid resistance when used in asphalt mixes for wearing surfaces. Other
benefits derived from its use in both dense and open-graded HMA include high stability and
good stripping resistance.
Nickel and copper slags are usually combined into a single category since they are both
iron silicate, nonferrous materials. Their use is not widespread; however, there is interest in
using it in blended cement, base stabilization, and fine aggregate in HMA.
The use of blast furnace slag is generally accepted in highway construction. It is the
third most popular material following recycled or reused asphalt and concrete. Its popularity
is based on its availability, technical suitability, favorable economics, and positive environ-
mental impact. Approximately 35 percent of the States and 2 Provinces use it, and 14 States
have specifications that govern its use. Of the various types, air-cooled and granulated are
the most widely used.
The only potential problem associated with the use of slags as granular material is
leachate production. However, based on test results, the EPA has not, to date, classified it
as a solid waste.
Steel slag is ranked behind coal fly ash in overall usage. Eighteen States and four
Provinces use it primarily in HMA to enhance skid resistance. Caution is advised when
using steel slag due to its expansive properties, and thus, it should not be used in confined
applications or in portland cement concrete.
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Municipal Solid Waste Ash (MSW)
Approximately 15 percent of the 181 million Mg (200 million tons) of domestic waste
produced each year is burned in incineration plants. The 7.8 million Mg (8.6 million tons)
of residue or ash left (bottom - 90 percent and fly - 10 percent) have been successfully used
as a partial replacement for coarse aggregate in asphalt paving mixes as well as combined
with portland cement in base courses. Currently five States have used MSW either as
subbase, embankment material, or as aggregate in asphalt or concrete.
During the late 1970's, several research projects were conducted to evaluate the use of
MSW in highway construction. Several researchers found that the material, when used as an
aggregate in a bituminous base (termed "littercrete"), performed as well as conventional
aggregates. Thus, in terms of engineering properties, it appears to be promising.
The primary concerns with the use of this material however, are the variability of the
product and the potential for leachate problems associated with excess lead and cadmium
present in the fly ash. Most plants combine the two ashes together, thereby reducing the
concentrations to acceptable limits. Nevertheless, the concern for leachate contamination—
primarily heavy metals—has prevented the widespread use of this material in highway
construction.
Paper/Cellulose in Stone Matrix Asphalt
Cellulose fibers are used extensively in SMA mixtures in Germany and Sweden.
Currently, the primary source of cellulose fibers used in SMA construction comes from a
German manufacturing company that derives the fibers from natural raw materials, e.g.,
wood. However, there appears to be no technical limitation on using recycled paper for
making cellulose fibers. Cellulose fibers are currently being produced for use in SMA
mixtures by a company in Michigan. If the SMA technology continues to gain acceptance in
this country, and if cellulose fibers continue as the predominant stabilizing agent, the market
for the fibers may see tremendous growth. An optimistic forecast of 322 lane-km (200 lane-
miles) of SMA construction per State each year would result in an estimated annual U.S.
consumption of 14,500 Mg (16,000 tons) of cellulose fiber. However, this amount is
insignificant when considering the total yearly generation of waste paper, which is approxi-
mately 65 million Mg (72 million tons).
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Carbon Black
The pyrolization of tires to obtain carbon black appears promising as a method of
resource recovery since raw material in the form of useable energy sources and carbon black
are produced. Further consideration is necessary to realize the full benefit of the use of
carbon black-modified asphalt.
Recycled Portland Cement Concrete
Recycled portland cement concrete (PCC) can be used as aggregates in PCC pavement or
as a base material. Recycled PCC aggregate may be preferential to virgin aggregates if
careful control is maintained during the crushing operation to ensure uniformity of gradation
The use of recycled PCC aggregate in base courses has been shown to have better properties
than virgin bases.
Roofing Materials
The use of waste roofing materials in asphalt concrete is justified both by the cost
savings and the desirable material properties it produces. The material has been used
successfully in several projects, including high-volume, heavy truck roadways, and has
shown favorable performance.
Tire Chip and Whole Tire Applications
Tires and tire scraps have been used as retaining walls, lightweight fill, and insulation
layers beneath road surfaces. The use of whole tires for retaining walls is enhanced by the
fact that used tires are a cheap, nonbiodegradable, ultraviolet light-resistant material. The
value of tire chips, both as insulation and as a lightweight fill, warrants expanded usage not
only for economic reasons, but for their structural properties.
Roadway Materials
Roadway materials are comprised of different material layers extending from the asphalt
pavement's surface course to the subgrade and those material layers used to construct the
shoulders. The response to the survey indicated that, on the average, at least 75 percent of
all roadway materials were either reused or recycled. The majority of the highway agencies
recycle between 75 and 100 percent of their asphalt surface and asphalt base courses
Crushed stone base, crushed gravel base, and granular subbase are commonly reused or
disposed of into embankments or fills. Stabilized base course materials are conventionally
used in embankments. Subgrade materials are always reused except in certain situations
where the material is wet or contaminated and does not meet the agency's specifications
Shoulders constructed with HMA are mostly reused and recycled. Compacted aggregate
shoulders are reused, possibly stabilized, or re-manipulated most of the time.
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Culverts
The materials used in the construction of small culverts usually range from wood,
concrete pipe, corrugated steel pipe, to concrete box. Larger culverts and underpass
structures are often constructed using multiplates. The information from the survey indicated
wood culverts and multiplate units are usually disposed of as scrap. Concrete culverts have
been used as roadway fill or riprap. Corrugated steel culvert pipe is predominantly disposed
of as scrap for recycling into steel products.
Guardrail Systems
Guardrail posts are generally made of steel. However, a few States also use aluminum
and wood posts. Most States reuse steel posts, or if damaged, sell it for scrap rather than
recycle (refurbish) damaged posts. Similarly, damaged aluminum posts are sold for scrap
since it is not practical to straighten them. Wood posts may be landfilled, used as
landscaping timbers, sold to landscapers, or disposed of by the contractor.
Signs and Sign Signal Structures
Sign and signal poles or structures, usually aluminum or steel, are either reused or
disposed of as scrap. The amount of disposal, recycling, and reuse is dependent upon each
State's policy, type of materials used, and regional conditions that affect suitability for
recycling or reuse. Transportation and competitive costs of new signs, posts, poles, and sign
structures make it impractical to recycle in some areas.
Bridge
Major bridge components include railing, steel superstructure, concrete beams, and
concrete deck. Bridge railings are reused or recycled unless they are excessively damaged,
corroded, or do not meet current standards. A small portion of steel superstructure members
and trusses were reused. Most bridge superstructure steel is removed and sold as scrap by
either the contractor or the highway agency. Concrete beams and concrete bridge decks are,
for the most part, disposed of with very little recycling or reuse.
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APPENDIX A. LETTER OF TRANSMITTAL AND SURVEY FORM NO. 1
November 20, 1992
345 Weil Hall
Tel.: (904)392-6590
FAX: (904)392-3394
Dear2~:
We are currently working on the documentation of information on the Use of Recycled
Materials in Highway Construction. This investigation is being conducted for the Federal
Highway Administration to address certain aspects of the Intermodal Surface Transportation
Efficiency Act (ISTEA).
The information that I am requesting relates to the use of materials, structural units,
appurtenances, etc., that are removed from the highway system for disposal, recycling, or
reuse. Table 19 provides a general guide (not necessarily complete) as to the materials/
appurtenances that may be removed in the process of rehabilitation, reconstruction, or
removal of abandoned structures. Please furnish any documented information and comments
relating to how the materials are reused, recycled, or disposed of. The table may be used to
furnish the relative percentage of reuse, recycling, or disposal for each type of removed
material, structural element, or appurtenance.
In the event that the utilization of disposed materials is unknown, then please furnish
the names, addresses, and telephone numbers of two or three contractors that have recently
been involved in the removal and disposal of highway materials. Examples of disposal
include landfilling, land reclamation, reclaimed for building materials, etc.
Your assistance in providing this information will be greatly appreciated. If possible,
send the information to me by mail or FAX prior to January 8, 1993.
The information you provide will be compiled with the responses from other State
highway agencies in the final report that should be available before the fall of 1993.
Thank you again for your consideration in this matter.
Sincerely,
Byron E. Ruth
Highway Engineer/Professor
BER/ckl
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Table 19. Disposal/utilization of materials removed from highways.
Material/Appurtenance
Type
Asphalt Concrete: Surface Course
Structural or Base
Stabilized Base (Specify)
Crushed Stone Base
Crushed Gravel Base
Granular Subbase
Stabilized Subbase
Subgrade
Shoulders (Specify Type)
Concrete Culverts
Corrugated Steel Pipe Culverts
Wood Culverts
Multiplate Underpass or Culvert
Guardrails
Guardrail Posts
Signs - Advisory and Regulatory
Sign Posts
Sign or Signal Poles and Structures
Bridges: Aluminum or Steel Railing
Steel Members for Super-
Structure, Deck, etc.
Concrete Beams
Concrete Deck
Percent of Material, Structural Unit, or Appurtenance Disposed,
Recycled, or Reused
Disposed %
Recycled %
Reused %
Use the following code numbers as applicable:
Disposal: (1) sold as scrap; (2) disposal in landfill, etc.; (3) contractor's property—recycled, revised, or
scrap
Recycled: (4) reused or stored for subsequent use after straightening, painting, or minor repair
(5) crushed, broken, or modified for recycling for use in a different highway application
Reused: (6) used in the same application or function
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APPENDIX B.
LETTER OF TRANSMITTAL, SURVEY FORM NOS. 1 AND 2,
AND ONE-PAGE QUESTIONNAIRES
December 4, 1992
345 Weil Hall
Tel. 904-392-6590
FAX 904-392-3394
1 ~
Dear2~:
We are currently working on the documentation of information on the Use of Recycled
Materials in Highway Construction. This investigation is being conducted for the Federal
Highway Administration to address Section 1038 of the Intermodal Surface Transportation
Efficiency Act (ISTEA).
Attached are copies of two (2) one-page questionnaires relating to "Crumb Rubber-
Modified Asphalt Paving Mixtures," and to "Recycling of Pavements Containing Crumb-
Rubber," Please complete a questionnaire for each test project within your jurisdiction
(State, municipality, etc.). These forms may be duplicated if additional copies are needed.
The information you provide is critical in establishing the status, feasibility, and/or
future needs of this technology. In the event your agency has not constructed or planned to
construct crumb rubber-modified test sections, so note on the form after filling in lines 1 and
2 (similarly for recycling with RAP containing crumb rubber). It is essential that I receive
the requested information as soon as possible, but no later than January 15, 1993. Please
mail all responses in the attached self-addressed envelope.
In addition to these one-page questionnaires, I have enclosed one copy or packet of
each of the following questionnaires (spread sheets) for the purpose of acquiring more
detailed information on utilization of waste/byproduct materials in highway construction:
A1A Crumb Rubber-Modified Asphalt Paving Mixtures
A IB Crumb Rubber-Modified Spray Applications
A1C Recycling of Pavements Containing Crumb Rubber
B1A Recycling of Pavements Using Over 80 Percent RAP
BIB Plastics in Highway Construction
B1C Crushed Glass in Highway Construction
BID Reuse, Recycling, and Disposal of Other Recycled Materials Used in Highway
Construction
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2~
December 4, 1992
Page Two
The detailed information requested in these packets will be analyzed to establish
current practice, types of technologies being used, feasibility of utilization/technology, and
future research needs. These packets may be duplicated as necessary to provide sufficient
copies for each project. Please return the completed forms to me no later than February 5
1993.
In the event that test projects have been thoroughly documented in published or in-
house reports for any of the subject areas (A1A through BID), please furnish copies of these
reports along with the questionnaire (spread sheets) for each project.
Your assistance in providing this information will be greatly appreciated. Contact me
by telephone or FAX if you need clarification of any questions in the packets.
Thank you again for your consideration in this matter.
Sincerely,
Byron E. Ruth
Highway Engineer/Professor
BER/ckl
enclosures
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INFORMATION URGENTLY NEEDED AND CRITICAL TO OUR SURVEY OF CRUMB RUBBER
MODIFIED (CRM) ASPHALT PAVING MIXTURES
1. State DOT/Agency (Specify):
2. State Agency Contact Name:
Phone:
3. Project Location:
Route Number , Beginning Milepost.
FAX:
, Ending Milepost
Project between or at what cities:
Project No. (Research or Constr. I.D.): "
4. Date Constructed Age vrs/mos.
Control Section / / /
CRM Test Sections
I /
5. Control section for comparison:
Same mixture without addition of crumb rubber Q/):
Mixture that is conventionally used by the State (V):
Does control have same aggregate and gradation as test section (Y/IM):
6. General assessment of performance compared to control:
(1) worse, (2) slightly substandard, (3) no difference, (4) slightly improved, (5) improved
Rutting , Cracking , Raveling , Stripping , Overall
7. Wet Processing Technology Used (V): McDonald , Continuous (Rouse)
8. Dry Processing Technology Used (\/): PlusRide* , Generic , Chunk Rubber
9. Application Used (V): Dense , GAP , OGFC , SAM , SAMI
10. Do you anticipate the test sections being overlaid in the near future (%/): yes
no
11. Would your agency consider including the test sections as part of a long-term national study
(V): yes , no
12. Can your agency provide construction records and a complete performance history of the test
section (/): yes , no
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INFORMATION THAT IS NEEDED AND CRITICAL TO OUR SURVEY ON RECYCLING
OF PAVEMENTS CONTAINING CRUMB RUBBER
1. State DOT/Agency (Specify):
2. State Agency Contact Name:
Phone:
3. Project Location:
Route Number
FAX:
Beginning Milepost
Ending Milepost
Project between or at what cities:
Project No. (Research or Constr. I.D.):
4.
Date Constructed Age vrs/mos.
Control Section
Test Sections
5. Control section for comparison:
Same aggregate, gradation, and binder content as test sections (V):
Mixture that is conventionally used by the State (V):
6. General assessment of performance compared to control:
(1) worse, (2) slightly substandard, (3) no difference, (4) slightly improved, (5) improved
Rutting , Cracking , Raveling , Stripping , Overall
7. Type of Plant {/)
Batch:
Continuous:
Drum Mixer:
(Single Drum)
(Dual Drum)
8. Type/Method used for recycling of pavements containing crumb rubber
Hot-mix recycling (V):
Cold-mix recycling ft/):
Surface recycling/traveling plant (V):
Other (specify):
9. Application Used (v'): Dense
GAP
OGFC
Other (Specify):
10. Do you anticipate the test sections being overlaid in the near future (\/): yes , no
11. Would your agency consider including the test sections as part of a long-term national study
(V): yes , no
12. Can your agency provide construction records and a complete performance history of the test
section (vO: yes , no
176
-------
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Project No. IR 8-2(91), "Route 1-8 Located in the South Central Part of the State "
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188
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Prelect FIR 40-2(108), "Route 1-40 Located East of Kingman,"
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Project F 060-1-908, "Route SR 264 Located East of Second Mesa,"
Project F 068-1-510, "Route SR 68 Located East of Bullhead City,"
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Transportation, Las Vegas, NV, October 1989.
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Demonstration Project No. 39, Federal Highway Administration, Washington, DC, March
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Topeka, KS, not dated.
Donnelly, D.E. and K.L. Wood, Cold Recycling of Asphalt Pavements, Project 170-(54)
Debeque East and West, Federal Highway Administration, Colorado Department of High-
ways, Denver, CO, not dated.
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Research Board, National Research Council, Washington, DC, 1990.
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Proceedings of the National Seminar on Asphalt Pavement Recycling, Transportation
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Frascoia, R.I. and D.N. Onusseit, Cold Recycling Asphalt Pavement US RTE 4, Sherburne
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Mosey, J.R., Cold Recycling—Michigan Experience, Ontario Municipal Seminar on Asphalt
Pavement Recycling, Ontario, Canada, November 1981.
Mosey, J.R. and J.H. DeFoe, "In-Place Recycling of Asphalt Pavements," Proceedings,
Association of Asphalt Paving Technologists, Vol. 48, 1979.
Muncy, S., "Rejuvenators for Recycling: A Case History in Dickinson County, Kansas,"
AEMA Proceedings (Pavement Recycling with Asphalt Emulsions), Asphalt Emulsion
Manufacturers Association, Washington, DC, Nov. 1984.
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Heavy Construction, Vol. 132, Oct. 1989, pp. 70-72.
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University of Nevada, Reno, NV, Sept. 1988.
Peters, A., Review of Cold Recycling ACP Paving, Washington State Dept. of Transportation
and FHWA, not dated.
Phillips, K., Cowherd Road Cold Asphalt Recycling Project, Demonstration Project No. 39,
Federal Highway Administration, Washington, DC, Nov. 1979.
Phillips, K., "In-Place Recycling Saves County Road $45,000," Rural and Urban Roads,
March 1980.
Pickett, J.B., In-Place Recycling of Asphalt Roads with Calcium Chloride, paper prepared for
4th International Conference on Low Volume Roads, Ithaca, NY, August 1986.
»o, M.J., Presentation on Cold In-Place Recycling, University of Wisconsin, Madison,
£ 1984.
Santucci, L.E. and M.T. Hayashida, "Design and Testing of Cold Recycled Asphalt Mixes,"
Proceedings, Association of Asphalt Paving Technologists, Vol. 52, 1983.
Scherocman, J.A., "Cold In-Place Recycling of Low-Volume Roads," Transportation
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tation Research Board, National Research Council, Washington, DC, 1983, pp. 308-315.
Scherocman, J.A., Barber, P.A., and V. Abbott, Cold Planning and Recycling-Economical
Pavement Maintenance Technology, Proceedings of the Canadian Technical Asphalt Associa-
tion, Vol. 26, Montreal, Quebec, Nov. 1981.
Scholz, T. V., In-Depth Study of Cold In-Place Recycled Pavement Performance, Oregon
Dept. of Transportation, Materials and Research Section, Salem, OR, 1990.
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Spelman, S.R., "Rural Cold Recycling," Transportation Research Record 780: Proceedings
of the National Seminar on Asphalt Pavement Recycling, Transportation Research Board,
National Research Council, Washington, DC, 1980, pp. 107-114.
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Steward, D.A., Cold In-Place Asphalt Pavement Recycling, paper prepared for the 4th
International Conference on Low Volume Roads, Ithaca, NY, Aug. 1986.
Stewart, J., Cold Recycling of a Soil-Asphalt Roadway, Beaver County, Oklahoma,
Demonstration Project No. 39, Federal Highway Administration, Washington, DC, April
TTia>
No.
Laboratory Investigation of Cold-Mix Recycled Bituminous Pavements, Report
-78-23, Indiana State Highway Commission, Dec. 1978.
Tia, M., Characterization of Cold-Recycled Asphalt Mixtures, Bieport No. FHWA/IN/JHRP-
82-5, Indiana State Highway Commission, Aug. 1982.
Tia, M., lida, A., McKinney, J., and L. Wood, An Investigation of Recycling Bituminous
Pavements, Report No. FHWA-RD-IN-83-4, Indiana Department of Highways, Federal
Highway Administration, March 1983.
Van Wijk, A.L, Wood, L.E., and P.E. Kercher, "The Use of Asphalt Emulsions in Cold
Recycled Asphalt Paving," AEMA Proceedings (Pavement Recycling with Asphalt Emul-
sions), Asphalt Emulsions Manufacturers Association, Washington, DC, Nov. 1984.
Wood, J.F., "Cold-Asphalt Recycling Equipment," Transportation Research Record 780:
Proceedings of the National Seminar on Asphalt Pavement Recycling, Transportation
Research Board, National Research Council, Washington, DC, 1980, pp. 101-102.
Wood, L.E., White, T.D., and T.B. Nelson, "Current Practice of Cold In-Place Recycling
of Asphalt Pavements," Transportation Research Record 1178: Flexible Pavement Construc-
#0«, Transportation Research Board, National Research Council, Washington, DC, 1988,
pp. 31-37.
Wright, J.J., Cold Bituminous Pavement Recycling in Montana, Demonstration Project No.
39, Federal Highway Administration, Washington, DC, May 1979.
RECYCLING OF ASPHALT—HOT MIX
Betenson, W.B., Hot Recycling of Asphalt Concrete Pavement Experimental Test Section
Near Cove Fort, Utah Department of Transportation, Materials and Research Section,
Pavement Design and Bituminous Mix Design Unit, Salt Lake City, Utah, July 1984.
"i. i „ , ,
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Construction, Vol. 134, January 1991, pp. 34-35.
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Highway Administration, Region 15, Washington, NY, April 1977.
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Engineers, Geotechnical Laboratory, Vicksburg, MS, 1984.
Brown, E.R., Hot Mix Recycling at Pope AFB, paper presented at New Mexico Paving
Conference, Albuquerque, NM, January 1981.
Brown, E.R., Insuring Quality in Hot Mix Recycling, paper presented at Transportation
Research Board Annual Meeting, Washington, DC, Jan. 1982.
Epps, J.A., Mixture Properties of Recycled Central Plant Materials, American Society for
Testing and Materials, STP 662, Dec. 1977, pp. 68-103.
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Howard, P.D., "Microwave Recycling of Reclaimed Asphalt Pavement," Public Works,
Vol. 120, October 1989, pp. 53-55.
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Vol. 92, July 1989, p. 13.
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RECYCLING OF ASPHALT — SURFACE
Barnes, W.D., Surface Recycling Asphaltic Concrete Pavement, Dept. of Transportation,
Federal Highway Administration, Region 15, Demonstration Projects Division, Arlington,
VA, 1977.
Betenson, W.B., "Surface Recycling," The Study of Heater Scarification and Heater
Repaying, Produced by the Utah Department of Transportation, April 1985.
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Asphalt Concrete Implemented on the Al Motorway in the North of France in 1984 and 1985,
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Waterways Experiment Station, Vicksburg, MS, 1990.
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ber 1988, pp. 118-119.
ROOFING MATERIALS
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120, Chattanooga, TN, 1989.
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209
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SLAGS
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Das, B.M., Terquin, A.J., and A.D. Jones, Geotechnical Properties of a Copper Slag,
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Douglas, Ev Malhotra, V.M., and J.J. Emery, "Cementitious Properties of Nonferrous Slags
from Canadian Sources," American Society for Testing and Materials, Cement, Concrete,
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Eggleston. H.E., "The Successful Utilization of Iron and Steel Slags," Proceedings of Second
Mineral Waste Utilization Symposium, IIT Research Institute, Chicago, IL, 1970, pp. 15-22.
Emery, J.J., "Slag Utilization in Pavement Construction," Extending Aggregate Resources,
ASTM Special Technical Publication No. 774, Philadelphia, PA, 1982, pp. 95-118.
Emery, J.J., "Slags," Proceedings of Fifth Mineral Waste Utilization Symposium, IIT
Research Institute, Chicago, IL, 1970, pp. 291-300.
Fernandez, L. and V.M. Malhotra, "Mechanical Properties, Abrasion Resistance, and
Chloride Permeability of Concrete Incorporating Granulated Blast-Furnace Slag," American
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George, H.D., "The Handling, Processing and Marketing of Steel-Making Slag," Proceed-
ings of First Mineral Waste Utilization Symposium, IIT Research Institute, Chicago, IL,
19%8, pp. 80-83. s r > , 5 , ,
Hogan, F.J., "The Effect of Blast Furnace Slag on Alkali Aggregate Reactivity: A Litera-
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gates, Vol. 7, No. 2, Winter 1985, pp. 100-107.
Hogan, FJ. and J.W. Mensel, "Evaluation for Durability and Strength Development of a
Ground Granulated Blast Furnace Slag," American Society for Testing and Materials,
Cement, Concrete, and Aggregates, Vol. 3, No. 1, Summer 1981, pp. 40-52.
Hughes, M.L. and T.A. Haliburton, Use of Zinc Smelter Waste as Highway Construction
Material, Highway Research Board, Record No. 430, Washington, DC, 1973, pp. 16-25.
Idorn, G.M. and D.M. Roy, "Factors Affecting the Durability of Concrete and the Benefits
of Using Blast-Furnace Slag Cement," American Society for Testing and Materials, Cement,
Concrete, and Aggregates, Vol. 6, No. 1, Summer 1984, pp. 3-10.
Kandahl, P.S., Wenger, M.E., and G.E. Schmidt, Expansive Characteristics of Open Hearth
Slagf" Commonwealth of Pennsylvania Department of Transportation, Bureau of Materials,
Testing and Research, Project No. 69-11, Harrisburg, PA, 1970.
Maslehuddin, M., Al-Mana A.I., Caricimen, I., and M. Shamin, "Corrosion of Reinforcing
Steel in Concrete Containing Slag or Pozzolans." American Society for Testing and Materi-
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210
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Moulton, L.K., "Bottom Ash and Boiler Slag," Proceedings of Third International Ash
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8640, Washington, DC, 1974, pp. 148-169.
National Slag Association, Blast Furnace Slag, A.I.A: File Number 3-D-3, Arlington, VA,
National Slag Association, Blast Furnace Slag Concrete, Publication Number NSA 168-5,
Arlington, VA, 1968, p. 26.
National Slag Association, Processed Blast Furnace Slag, Publication Number NSA 178-1,
Arlington, VA, 1978, p. 15.
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Asphalt, Transportation Research Board, Record No. 1269, Washington, DC, 1990,
Noureldin, A.S. and R.S. McDaniel, "Performance Evaluation of Steel Furnace Slag-Natural
Sand Asphalt Surface Mixtures," Proceedings of the Association of Asphalt Paving Technolo-
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Owens, J.F., "Slag-Iron and Steel," Mineral Yearbook, U.S. Bureau of Mines, Washington,
DC, 1989.
Ozyildirim, C., Evaluation of Hydraulic Cement Concretes Containing Slag Added at the
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Mineral Waste Utilization Symposium, IIT Research Institute, Chicago, IL, 1972, pp. 51-54.
Standard Specification for Ground Iron Blast Furnace Slag for Use in Concrete and Mortars,
American Society for Testing and Materials, Designation D989, Philadelphia, PA, not dated.
Walter, P.D., Simpson, J.F., and S.J. Murrie, "Development of Blast Furnace Slag as an
Aggregate on Road Surfacing," Proceedings of the Utilization of Steel Plant Slags
Symposium, Australian Institute of Mining and Metallurgy, Parkville, Australia, February
TIRE CHIP AND WHOLE TIRE APPLICATIONS
Hughes, Chuck, Scrap Tire Utilization Technologies, National Asphalt Pavement Association
and State Asphalt Pavement Association, Lanham, MD, not dated.
Humphrey, Dana N. and Robert A. Eaton, Tire Chips as Insulation Beneath Gravel Surfaced
Roads, Second International Symposium on Frost in Geotechnical Engineering, Anchorage,
AK, June 1993. B &, & ,
Keller, Gordon, "Retaining Forest Roads," Civil Engineering, December 1990.
211
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Oswer, Oppe, Markets for Scrap Tires, U.S. Environmental Protection Agency, Report No.
EPA/530-SW-90-074a, Washington, DC, October 1991.
•U.S COVEXNMtNTPRJKTINCiOFFICE 1993 -3"t3 • 120/ 95730
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