EPA-650/2-73-046
December 1973
Environmental Protection Technology Series
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EPA-650/2-73-046
ATMOSPHERIC EMISSIONS
FROM
THE ASPHALT INDUSTRY
by
L. L. Laster
ROAP No. 21AXM10
Program Element No. 1AB015
Control Systems Laboratory
National Environmental Research Center
Research Triangle Park, North Carolina 27711
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
December 1973
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This report has been reviewed by the Environmental Protection Agency and
approved for publication. Approval does not signify that the contents
necessarily reflect the views and policies of the Agency, nor does
mention of trade names or commercial products constitute endorsement
or recommendation for use.
11
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CONTENTS
Page
Figures iv
Abstract v
Introduction 1
The Asphalt Industry 9
Hot-Mix Asphalt Plants 9
Major Sources of Pollutant Emissions
from Hot-Mix Plants 14
Available Control Methods for Hot-
Mix Plants 15
Control Technology Needed for Hot-
Mix Plants 17
Asphalt Roofing Manufacture 18
Major Sources of Pollutant Emissions
from Roofing Manufacture 22
Available Control Methods for
Roofing Manufacture 22
Control Technology Needed for
Roofing Manufacture 24
References 26
Appendix A - Terms Relating to Asphaltic
Materials 27
Appendix B - Terms Relating to Asphalt
Pavements and Surface Treatments 31
iii
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FIGURES
No.
1 Flow Diagram of Vacuum Distillation Unit 5
2 Flow Diagram of Propane Deasphalting Unit 7
3 Flow Diagram of Hot-Mix Batch Asphalt Plant 8
4 Flow Diagram of Continuous-Mix Asphalt Plant 13
5 Flow Diagram of Airblown Asphalt Manufacture
(Batch Process) 19
6 Flow Diagram of an Asphalt Roofing Felt Saturator 21
7 Flow Diagram of Scrubbing System 25
iv
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ABSTRACT
This report summarizes the air pollution problem of the two
segments of the asphalt industry—hot-mix asphalt plants and roofing
manufacture—with emphasis on particulate emissions. It provides a
general outline of the industrial processes, sources, types of pollutant
emissions,and present and needed control methods.
The asphalt industry has developed into one of the leading industries
of the nation with sales revenues approaching $2 billion in 1970 from
the hot-mix asphalt plants and the roofing manufacture. Its annual
growth rate is predicted to be 3 or 4 percent. Air pollution problems
have increased with the industry's growth; however, as a result of
research and development, the corporations involved have control
methods for some of the pollutants. Particulates are the principal
emission from the two industrial segments; sulfur oxides, nitrogen
oxides, odors, and hydrocarbons are emissions of minor importance.
The estimated emissions of these pollutants (except for odor, per se)
in the United States in 1968 were 197,726 metric tons (218,000 short
tons) with substantial control exercised only for particulates. Emissions
from the aggregate drier in the asphalt hot-mix operation and from the
saturator and "blowing" still in the roofing manufacture are the chief
sources of pollution. In spite of control methods developed for some
of these pollutants, the asphalt industry still has air pollution
problems. The pollutants emitted contribute to a dense and foggy fume
and cause a majority of the public's complaints. Particulates can
be controlled by wet or dry methods (or a combination of the two),
by fabric filters, or by baghouses. Emissions of sulfur oxides,
nitrogen oxides, and hydrocarbons are not significant qualitatively,
but each contributes to the odor and smog problems and should be
controlled.
Control devices can be used in asphalt plants. Electrostatic precipita-
tors are not usually considered because of their initial cost and rather
high volume. Control methods are available for the principal pollutant,
particulate; however, as in many other industries, available control
equipment is often not being installed.
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INTRODUCTION
The asphalt industry, with sales revenues approaching $2 billion
in 1970, is economically among the leading U. S. industries.
Demands for asphalt and asphaltic products have increased
immensely as home building, industrial activity, and highway construc-
tion have increased. Increased demands for the past 3 years are shown
in Table l.(1)
The production data do not include imports, exports, or fluctuations
in year-end stocks. The shipments data include, in addition to refinery
production and imports, various emulsifiers and blenders.
The asphalt industry is divided into two segments: hot-mix asphalt
plants and roofing manufacture. Major sources of emissions from
the hot-mix plants are the rotary drier, fuel burners, and truck
transportation; lesser sources are the elevators, screens, heating
system, storage bins, and loading facilities. The major sources
of emissions from roofing manufacture are the "blowing" stills and
saturators. Factors contributing to these emissions include ash and
sulfur content of the fuel oil used, control equipment and methods
used, and the efficiency of blowing operations.
Table 1. DEMAND FOR ASPHALT AND ASPHALTIC PRODUCTS
Category
Production
Shipments:
Paving
Roofing
Others
1969
Metric
tons
(000)
22,377
25,538
19,349 '
3,701
2,488
Short
tons
(000)
24,671
28,156
21,333
4,080
2,743
1970
Metric
tons
(000)
24,185
26,949
21,400
3,853
1,696
Short
tons
(000)
26,665
29,712
23,594
4,248
1,870
1971a
Metric
tons
(000)
25,898
27,869
22,176
4,011
1,682
Short
tons
(000)
28,553
30,727
24,450
4,422
1,855
Preliminary
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Although control methods have been developed for some of the
pollutants, the asphalt industry still has air pollution problems.
The pollutants emitted contribute to a dense and foggy fume and
cause a majority of the public's complaints. Progress has been
made in controlling particulates, with the cost partially offset
by using the recovered aggregate. Particulates can be controlled by
wet or dry methods (or a combination of the two), by fabric filters,
or by baghouses. The emissions of SC^, NOX, and hydrocarbons are not
significant qualitatively, but each contributes to the odor and smog
problems. These pollutants should be controlled,
The trade organizations and equipment manufacturers related to
the asphalt industry have collaborated to develop equipment and tech-
nology for controlling, or at least reducing, all pollutants from
the plants on a limited scale. That smaller independently owned
plants will be hard pressed financially to install this expensive
equipment has delayed the installation of the necessary controls;
however, since performance standards for emissions are to be promulgated,
plants without control equipment will be required to make the necessary
installations.
The estimated particulate emissions from each segment in 1968 were
182,307 metric tons (201,000 short tons) from the hot-mix asphalt
plants and 15,419 metric tons (17,000 short tons) from the roofing
manufacture, or a total of 197,726 metric tons (218,000 short tons)
from the two segments of the asphalt industry. The emission factors
are estimated to be 18 kg/0.91 metric ton (40 Ib/short ton) fr0m the
hot-mix plants and 4 kg/metric ton (8 Ib/short ton) from the roofing
(2)
manufacture.
Asphalt is one of the oldest construction materials. Some of
the earliest records tell of its use to preserve the dead, to
waterproof material, as a mortar for stone-built structures, and as
a "cement" for roads. Asphalts used by ancient peoples were the
"natural" asphalts found in pits and lakes.
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The development of the petroleum industry, Beginning late in
the nineteenth century, provided the processes of refining and pro-
ducing asphaltic materials in huge quantities' and in various types and
grades under carefully controlled operating conditions. Technology
and research also developed and furthered the use of these products.
Today, their various applications number literally in the thousands.
About 70 percent of the asphalt production is used for paving.
The first effective asphalt pavement was laid in France in 1810;
within a decade, asphalt pavements were accepted throughout the
(4)
United States as an excellent road surfacing material.
In addition to their use in pavement surfaces for highways and
airfields, asphaltic products apply to other features of highway
construction: stabilizing the upgrading of soils and aggregates in
base construction, shoulder treatments, undersealing and joint
sealing of Portland cement concrete slabs, and mulch treatment of
cut-and-flll slopes.
In recent years, asphalt has been used extensively in various
types of hydraulic structures. Hot asphalt paving nixes are used
to face the upstream side of large dams and to line reservoirs, canals,
and rivers for the prevention of both erosion and, in some cases,
seepage losses. Prefabricated asphaltic membranes, asphalt-fiber
panels, and sprayed asphaltic materials are also used to line reservoirs
and canals. Hot-mix sand asphalt is used in building groins both to
prevent beach erosion and to build up eroding shore lines. Asphalt
mixes are also used in storm-water channels where rapid runoff of
debris-laden water normally results in severe erosion.(3,4)
As a roofing material, asphalt far exceeds all other types
combined. Asphalt shingles are prepared by impregnating roofing
felt with an asphalt saturant; after both sides of the felt are
coated with a harder tougher asphalt, mineral granules are embedded
in the surface of one side, and the material is cut into shingles or
strips. Two types of asphalt roll roofing are in common use: smooth
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and mineral surfaced. These, too, are asphalt-saturated felts,
coated with a harder grade of asphalt. Asphalt built-up roofing is
composed of several layers of asphalt-saturated felt applied to
a flat or sloping roof deck. Asphalt is applied between the felt
layers for adhesion. A flood coat of asphalt is applied over the top
layer and usually covered with gravel or slag.
Asphalts are used extensively for industrial and specialty
purposes, including battery cpses, automobile undercoating, tire
manufacture, a wide variety of waterproofing and dampproofing appli-
cations, as a base for paints and lacquers, printing inks, and in the
manufacture of floor coverings and building insulation.^ '
Asphalt used in making the hot mix for paving and in air-
blowing for roofing material is normally prepared at refineries;
however, some is found in naturally occurring deposits. Over 90
percent of the asphalt used in the United States is recovered from
crude oil,, with the method depending on the type of crude oil
being processed. The "crude" is distilled at atmospheric pressure
to remove the lower boiling materials such as gasoline, kerosene,
diesel oil, and gas oil. Nondistillable asphalt may then be recovered
from selected topped crude by vacuum distillation.
/0\
A typical vacuum distillation unit is shown in Figure 1. '
This unit uses a heater, preflash tower, vacuum tower, and auxiliary
equipment for processing the topped crude to yield the desired
product. Distillation of topped crude under a vacuum removes oil
and wax as distillates, leaving the asphalt as a residue. The asphalt
properties are controlled by the amount of distillates removed:
the more removed, the harder the asphalt. Many grades are produced
depending on their ultimate uses and local specifications. The
grades are based on such properties as softening point, penetration,
and ductility. Asphalt prepared from petroleum is sometimes
referred to as artificial asphalt: it is dark-brown to black, solid
or semi-solid, and used as-is for various types of paving or processed
further for building materials.
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EJECTOR
ACCUMULATOR
I
Ul
NONCONDENSABLE
GAS TO TREATER UNIT
INCINERATED IN
FURNACE FIREBOX
TOPPED
CRUDE OIL
WATER-OIL TO
COVERED
SEPARATOR
GAS OIL
ASPHALT
HEATER
Figure 1. Flow diagram of vacuum distillation unit.
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Asphalt is also produced as a secondary product in solvent
extraction processes as shown in Figure 2. This process separates
the asphalt from remaining constituents of topped crude by differences
in chemical types and molecular weights, rather than by boiling
(3)
points as in vacuum distillation processes. The solvent, usually
a light hydrocarbon such as propane or butane, is used to remove
selectively a gas-oil fraction from the residual asphalt.
Analytical methods have been used to separate asphalt into
three component groups—asphaltenes, resins, and oils. A particular
grade of asphalt may be characterized by the amounts of each group
it contains. The asphaltene particle provides a nucleus about which
the resin forms a protective coating. The particles are suspended
in an oil that is usually paraffinic but can be naphthenic or
naphthenoaromatic.
The most significant pollutant from the asphalt plants is
particulates. The emission, factors (without controls) are 18 kg/0.91
metric ton (40 lb/short ton) for the hot-mix plants and 4 kg/0.91
(2\
metric ton (8 Ib/short ton) for the roofing segment. These
quantities represent about 0.65 percent of the national total of
particulate emissions. The control efficiency is 96 percent without
a baghouse and 99 percent with a baghouse filter on the hot-mix
plants and about 50 percent on the roofing.
The asphalt industry has developed efficient control technology
and equipment which are effective in controlling emissions of particulates.
Sulfur oxides, nitrogen oxides, odors, and hydrocarbons are controlled
somewhat in the scrubbing system or baghouse filters used for particulate
control. '
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PROPANE
ACCUMULATOR
J
REDUCED CRUDE OIL
f
STEAM
EVAPORATORS
STEAM
OEASPHALTED OIL
I
PROPANE
COMPRESSOR
JET CONDENSER
DEASPHALTING
TOWER
OIL
STRIPPER
HEATER
FLASH
TOWER
TO COVERED EFFLUENT
WATER SEPARATOR
STEAM
ASPHALT
ASPHALT
STRIPPER
Figure 2. Flow diagram of propane deasphalting unit.
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CYCLONE ,
o>
SAND AND
AGGREGATE
BINS
FAN DUST-LADEN GASES
COLD AGGREGATE
BUCKET ELEVATOR
AGGREGATE
STORAGE
BINS
WEIGH
HOPPER
,SCRUBBER
tZh
STACK
HOT AGGREGATE
BUCKET ELEVATOR
Figure 3. Flow diagram of hot-mix batch asphalt plant.
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THE ASPHALT INDUSTRY
The manufacturing processes of the asphalt industry should be
considered in order to understand the air pollution problems of the
industry. Basically, the industry is divided into two segments or
divisions: hot-mix asphalt plants and roofing manufacturing. Each
will be discussed separately.
HOT-MIX ASPHALT PLANTS
The asphalt hot-mix segment is characterized by a large number
of small firms: many have only one plant; and others have two or
three. Most of the firms are small in comparison with the giant
firms of some of the other industries. Since paving asphalt must
be delivered hot to the Job site, plants are limited to their area
of operations; although some have been designed to be moved from
site to site at a small cost, stationary plants are set up for efficient
operation at a permanent location.
The road paving material commonly called asphalt (referred to
as hot-mix asphalt) is a heated mixture of crushed stone aggregate,
sand, and asphalt. It is commonly produced by a batch process with
an average production rate of 91-182 metric tons (100-200 short tons)
per hour, per plant. There are currently 4500 asphalt hot-mix plants
operating in the United States.
Hot-mix asphalt plants are classified either as batch mix or
continuous mix. Both types have the same flow up to measuring
(a)
the hot aggregate from the bins into the mixer.
Figure 3, a flow diagram for hot-mix batch asphalt plant, shows
(3\
equipment and sources of emissions for this process. The equip-
ment usually consists of:
1. A rotary drier for removing moisture from the sand and
crushed stone.
2. Conveyors for loading the drier and removing the dried
material to the storage bins.
3. Mixing and weighing equipment for the proper proportioning
of the asphalt with the sand and aggregate.
-------
4. Vibrating screens for separating the aggregate.
5. A fan and cyclone for exhausting the fines and dust from
the drier.
(8)
The actual process consists of:
1. Conveying proportioned quantities of cold aggregate to
a drier.
2. Heating and drying the aggregate at 121 to 177°C
(250 to 3508F).
3. Screening and classifying hot aggregate and storing it in
hot bins.
4. Heating the asphalt to 135 to 165°C (275 to 325°F).
5. Measuring and mixing the asphalt in proper proportions.
6. Delivering the hot mixture to trucks which haul it to
the paving site.
Asphalt paving mixes may be produced from a wide range of
aggregate combinations, each having particular characteristics and
suited to specific design and construction uses. Aside from the
amount and grade of asphalt used, the principal characteristics of
the mix are determined by the relative amounts of coarse aggregate
(retained on a No. 8-mesh sieve), fine aggregate (passing a No. 8-mesh
sieve), and mineral dust (passing a No. 200-mesh sieve). '
Aggregates of all sizes up to 6 cm (2-1/2 inches) in diameter
are used in hot-mix asphalt paving. The coarse aggregates usually
consist of crushed stone, slag, gravel, decomposed granite (or other
material occurring naturally in a fractured condition), or highly
angular material with a pitted or rough surface texture. The fine
aggregates usually consist of natural sand. All aggregates must be
free from coatings of clay, silt, or other objectionable matter and
meet tests for soundness (ASTM Method C88) and wearability (ASTM
Method C131).(3)
Mineral filler (dust) is used in some types of paving. It
usually consists of finely ground particles of crushed rock, lime-
stone, hydrated lime, Portland cement, or other nonplastic mineral
10
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matter. A minimum of 65 percent of this material must pass a No. 200-
mesh sieve.
Asphalt, a solid at ambient temperature, is usually used as a
liquid at 135 to 163°C (275 to 325*F). One property measurement used
in selecting an asphalt is penetration, determined by ASTM Method D5.
The most common penetration grades used in asphalt paving are 60 to
70, 85 to 100, and 120 to 150. The grade used depends upon the type
of aggregate, the type of pavement, and the climatic conditions.
Typical paving mixes are given in Table 2.
Table 2. TYPICAL PAVING MIXES
Paving mix designation
Type
I
II
III
IV
V
VI
VII
VIII
Description
Macadam
Open graded
Coarse graded
Dense graded
Fine graded
Stone sheet
Sand sheet
Fine sheet
Maximum sizea
aggregate normally used
Surface and
leveling mixes
3/8 to 3/4 in.
1/2 to 3/4 in.
1/2 to 1 in.
1/2 to 3/4 in.
1/2 to 3/4 in.
3/8 in.
No. 4
Base, binder,
and leveling mixes
2-1/2 in.
3/4 to 1-1/2 in.
3/4 to 1-1/2 in.
1 to 1-1/2 in.
3/4 in.
3/4 in.
3/8 in.
No. 4
For the reader's convenience, non-metric units are used here, in spite
of EPA's general policy of using metric units. To convert these units to
metric (cm), multiply each by 2.54.
11
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1. The continuous-mix plant transfers a preblended mixture of
the dried and graded aggregate from the hot bins to the mixer, using
(8)
a bucket elevator. (Dry mixing is not required, as it is in the
batch plant.)
2. The hot asphalt is sprayed onto the aggregate continuously,
as it falls into the mixer.
3. The mixing time is altered by the volume of the mixer. This
is done by raising or lowering a dam (adjustable weir) on the discharge
/Q\
end of the mixer.
Mixing time can be varied without changing the hourly tonnage
output by varying the height of the adjustable dam. A typical
continuous plant is shown in Figure 4 with potential sources of
(Q)
pollutants.v '
Uses for asphalt and its products include:
1. Paving — Highways, streets, parking areas, driveways,
service station lots, sidewalks, railroad beds and crossings, air-
field areas, and seal coats.
2. Hydraulics — Linings for canals, drainage ditches, and
reservoirs, and erosion control along rivers and lakes.
3. Recreational — Tennis courts, swimming pools, and playgrounds.
4. Roofing — Shingles and smooth and mineral-surfaced roll
roofing.
5. Miscellaneous — Farms (feed lots, barn lots, and floors),
loading areas, and pipe covering and coating.
12
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INDICATES FUGITIVE DUST LOSSES
IF NOT WELL ENCLOSED
J
t
PRIMARY
DUST
COLLECTOR
TO SECONDARY
COLLECTOR
I I
COLD
AGGREGATE
BINS
ASPHALT
STORAGE
Figure 4. Flow diagram of continuous-mix asphalt plant
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Major Sources of Pollutant Emissions from Hot-Mix Plants
The major sources of pollutant emissions in the hot-mix asphalt
plant are the rotary drier, burners, and truck transportation. Emissions
from the aggregate drier are the chief source of pollution in the
asphalt hot-mix operation. The discharge consists of very fine dust
under a No. 200-mesh particle size and amounts to approximately 5
percent of the total weight of the material processed. Moreover, the
total emissions increase direccly with any increase of air velocity
(8)
passing through the rotary drier. ' Other pollution sources are the
elevators, screens, heating system, storage bins, and loading and
transportation facilities; in other words, each operation can be a
potential source of pollution If controls are not employed. The
quantity of dust emitted from the rotary drier varies with the
operations. The hot gases from the drier contain moisture from the
aggregate and, with temperature ranging from 177 to 232°C (350 to 450°F),
absorb odors and hydrocarbons from the operations resulting In the
formation of a dense and foggy plume.
The pollutants emitted are particulates, S00, NO , odors, and
(ft R) "
hydrocarbons.
Particulates
The rotary drier is the primary source of particulate emissions.
The estimated uncontrolled emissions from this one source is 15 kg/0.91
metric tons (32 Ib/short ton) of aggregate; emissions from all other points
of the operation are estimated at 4 kg/0.91 metric tons (8 Ib/short ton).
The fuel used for heating the aggregate and asphalt may emit some
particulate if fuel with a high ash content is burned. The quantity
emitted will be affected by the rotary drier gas velocity, the type of
fuel used (gas or oil), and the efficiency of the combustion process.
Burning oil in the drier will Increase particulate emissions by an
estimated 2 kg/hr (5 Ib/hr) more than with gas.
14
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Sulfur Dioxide
S02 emissions are from the combustion process when fuel oil is
burned to dry the aggregate or heat the asphalt. The amount actually
emitted can be decreased by water scrubbers or the type of aggregate
being dried (limestone or marble). The emission factor is not available.
Nitrogen Oxides
NO^ is emitted from the combustion process only. The quantity
is not available.
Odors
There are three potential sources of odors in a hot-mix plant:
hot asphalt, inefficient burner operation, and the fuel oil used on
truck beds to prevent the asphalt from adhering. The odors from the
asphalt and fuel oil could cause problems in urban areas, but normally
do not. The efficiency of the combustion process will determine the
emission of aldehydes and odoriferous organic acids. Quantitative
data are not available.
Hydrocarbons
Hydrocarbons are emitted from the combustion process, but in
insignificant quantities: estimated to be 64 kg/1600 hectoliters (140 lb/
1000 bbl) of fuel oil burned.
Asbestos
Asbestos is now being added to hot-mix used for highways and
streets to develop non-skid surfaces. Information on this emission
is not available.
Available Control Methods for Hot-Mix Plants
Without question, asphalt mixing plants will emit pollutants if
/Q\
operated without some controls.v ' These plants are numerous and
are located in residential communities, industrial areas, rural areas,
and even in arid desert areas. Those located in the residential areas
are sources of many nuisance complaints.
15
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Practically any control device can be used on asphalt plants.
Electrostatic precipitators are not usually considered because of their
initial cost and their rather large volume. Control methods are
available for the principal pollutant from asphalt plants, particulates.
However, as in many other industries, available control equipment is
often not being installed.
Particulates
Control equipment for particulates falls into two categories,
/g\
wet or dry. In some plants both methods are used. Until very
recently, the accepted method of controlling emissions from the
drier consisted of wet collectors installed in series with conven-
tional dry collectors, such as simple cyclones. The wet collectors
are usually the spray impingement type (with collecting efficiencies
of 90 - 95 percent) or the high-energy, high-efficiency venturi type
(with efficiencies upward of 95 percent). However, wet collector
performance in many instances fails to meet the Equivalent Opacity
regulations that are often written into metropolitan area codes.
The wet process uses water to wet the dust particles; recovering
them as a sludge creates a water disposal problem. Since the
efficiency of the wet scrubber is only about 95 percent, the emissions
may not meet local requirements. The dry process employs cyclones and
multiple cyclones to reduce the emissions to the required local
control level. If necessary, some plants use a baghouse filter to
obtain the necessary limit. The materials recovered in the dry process
can be used in the hot-mix as aggregate. Without the baghouse, this
control method is about 95 percent efficient; with the baghouse,
efficiency is about 99 percent.
Usually the gas from the drier and the emissions from other
sources in the asphalt plant are collected in a vent line and sent
through a cyclone dust collector.
All wet collectors, regardless of kind, carry with them the
problem of sludge disposal. Federal and state water pollution
regulations prevent disposal to natural drainage systems. This water
16
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may carry odors leached from the aggregate raw material drier.
Recirculation of pond water, as it is sometimes called, tends to
increase the odor potential from this phase.
Up to a few years ago, dry collectors for asphalt mixing plants
consisted of cyclones and multiclones, which yielded efficiencies of
approximately 75 - 80 percent at best and did not collect the greater
percentage of the dust (200 microns or less). These dry collectors
were modified into primary collectors, followed by the installation
of the more efficient wet collectors in series with them, thereby
increasing the overall efficiency to above 95 percent. As control
regulations become more severe fabric filters or baghouses will be
required.
Inherently, the two main factors hindering optimum collection
efficiencies of any baghouse are temperature and moisture. Both of
these conditions are prevalent in the exhaust stream from an asphalt
hot-mix plant. Latest technology has proven that properly designed
bag collectors can comply with any of the stringent regulations.
Collection efficiencies of over 99 percent can be achieved and
"clear stacks" are not uncommon. Costwise, the baghouse will range
20-30 percent higher than the cyclone and/or scrubber. Recovered
dust is returned to the process. Savings realized from the recovery
of these fines offset the cost of the equipment.
Control Technology Needed for Hot-Mix Plants
SO. and NO are emitted in such insignificant quantities that
£* X
controls are not employed. Hydrocarbon emissions, which can cause a
serious odor problem,can be reduced slightly by wet scrubbers and
baghouse filters. At present they do not present pollution problems.
Research work is needed to develop controls for odors (and
perhaps for hydrocarbons) from the potential emission sources.
Improvements of controls for these two pollutants would reduce public
complaints. Recently asbestos has been added to the weigh hopper
along with the aggregates, hopefully to develop non-skid surfaces on
17
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highways and streets. There could be some health hazards attached
to asbestos handling and emissions. Emission factors for this
process should be developed.
ASPHALT ROOFING MANUFACTURE
The manufacture of asphalt roofing felts and shingles involves
saturating a fiber medium with asphalt by dipping and/or spraying.
While not always done at the same site, an integral part of the
(3)
operation is preparing the asphalt saturant. This preparation
consists of oxidizing the asphalt by bubbling air through liquid
asphalt for 8-16 hrs at 221 to 260°C (430 to 500°F). This operation
is known as "blowing."
Airblowing is a dehydrogenation process. Oxygen in the air
combines with hydrogen in the oil molecules to form water vapor.
The progressive loss of hydrogen results in polymerization of the
(3)
asphalt to the desired consistency. Although blowing may be
continuous, it is usually carried out batch-wise in horizontal or
vertical stills equipped to steam-blanket the charge for safety.
Vertical stills are more efficient because of longer air/asphalt
contact time. The asphalt is heated to 149 to 205°C (300 to 400°F)
either by an internal fire-tube heater or by circulating the charge
material through a separate tube-still before the injection of 0.14-
0.57 m of air/min/0.91 metric ton (5-20 ft of air/min/short ton) of
asphalt. Little additional heat is necessary: the reaction becomes
(3)
exothermic.
Figure 5 is a flow diagram of airblown asphalt manufacture
(batch process).
Pollutants from the airblowing stills include particulates,
sulfur and nitrogen compounds, hydrocarbons, odors, and water vapors.
The time required for blowing depends on the desired properties
of the saturant. It had been the practice to blow the asphalt in
horizontal stills where the material loss ranges from 3 to 5 percent.
Most of this material is recovered by venting the exhaust gases
through oil knockout tanks which are an integral part of the process.
18
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RESIDUAL
OIL
A
STEAM
BLANKET
HEATER
AIR
(RECYCLE)
WATER
OFF GAS TO
BLOWING STILL
INCINERATOR
EFFLUENT TO
AIR BLOWN COVERED OIL-WATER
ASPHALT " SEPARATOR
SCRUBBER
KNOCKOUT DRUM
Figure 5. Flow diagram of airblown asphalt manufacture (batch process).
-------
The recovered liquid is either reprocessed or used as fuel oil. The
gas may be charged to afterburners. In horizontal stills,0.95 metric
tons (1.05 short tons) of asphalt is required to produce 0.91 metric
tons (1.00 short ton) of saturant. Currently firms are using vertical
stills with a material loss of 1 to 2 percent.
Because finished roofing materials must withstand severe weather
conditions and changes in temperature, extreme caution must be taken
in selecting the asphalt for airblowing. Although physical tests of
the unblown asphalt may meet manufacturing specifications, if the
airblown saturant becomes brittle, the finished products will crack
and deteriorate on exposure to weather conditions. Manufacturers may
have accelerated weathering tests to determine if the products are
suitable for industrial uses.
After the asphalt has been airblown to meet requirements, it
is transferred to the second operation: saturating asphalt roofing
felt for manufacturing the roofing products. Asphalt-saturated felt
is manufactured in high-speed, continuous-operating machines, referred
(3)
to as asphalt saturators. The saturator consists of a dry looper,
asphalt spray section, saturating tank, and wet looper. The felt is
continuously fed from rolls into the dry looper where it passes over
rollers into a series of vertical loops used as live storage in the
process to permit maintenance of feed at a uniform rate to the saturating
process during roll changes. The liquid asphalt at 205 to 232°C
(400 to 450°F) is sprayed on one side of the felt. This spray of hot
asphalt drives moisture in the felt out the unsprayed side and prevents
the moisture from forming blisters when the felt is saturated. After
being sprayed, the felt passes through a tank of hot asphalt that
saturates the felt. The saturated felt then enters the wet looper
where it passes over another set of rollers into long vertical loops
to permit cooling of the asphalt. The web of saturated felt is then
rolled up from the discharge end of the wet looper either for use as
roofing felt or building paper, or (after applying a small quantity
of bituminous material and mica schist or rock granules—sand—to
the surface) as composition roofing paper and shingles. Figure 6
(3)
is a flow diagram of an asphalt roofing saturator.
20
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DRY
LOOPER
SPRAY
SECTION
WET
LOOPER
TO ROLL PRODUCT
OR SHINGLE
PRODUCT OPERATION
Figure 6. Flow diagram of an asphalt roofing felt saturator.
-------
The felt containing 5-10 percent water is made from fibrous
vegetable matter. The final felts are made in varying weights: 7, 14,
and 25 kg/0.9 m2 (15, 30, and 55 lb/100 ft2). Regardless of the
weight of the asphalt saturant, the final makeup is approximately
40 percent dry felt and 60 percent saturant (blown asphalt).
Major Sources of Pollutant Emissions from Roofing Manufacture
Although the principal sources of particulate emissions from
roofing manufacture are the saturator and "blowing" stills, all
operations are potential sources. The relatively high application
temperature results in the vaporization of the, lower boiling components
of the asphalt and of the moisture in the felt, producing a highly
opaque mist. Additional vapors and mists are emitted from the saturated
felt in the wet looper. This emission rate is a function of felt feed
rate, felt moisture content, number of sprays used, and asphalt temper-
ature. ^ Limited test data are available on emission rates, and
emission totals for roofing manufacture are conservative estimates.
Available Control Methods for Roofing Manufacture
Control methods have been developed for some of the pollutants from
asphalt roofing manufacture, but the necessary control equipment has
not been installed except to meet local regulations.
Particulates
Although emissions may not meet standards, particulates can
be controlled by:
1. Enclosing the spray area and the saturator and ventilating
through one or more collection devices including combina-
tions of two-stage low-voltage electrostatic precipitators,
fabric filters,scrubbers, and incinerators. Hoods for
collecting the emissions should be Installed so that there
is a single continuous enclosure around the points of emission,
extending down to the floor. Since operating personnel
must have access to the saturator for operating adjustments,
doorways or other entry provisions in the hood must usually
be supplied. These should be kept as small as possible.
22
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In addition, openings in the hoods must be provided for
the entrance of felt and exit of the saturated material.
These openings should be as close to the floor as possible.
Experience indicates that a minimum indraft velocity of
60 m/min (200 ft/min) is required at all hood openings.
Air volumes handled by the exhaust system vary with hood
design and saturator size but are about 283-566 stdm3/min
(10,000-20,000 scfm). The large volume of air required in
controlling the saturator equipment generally makes incin-
(2)
eration impractical.
Using electrostatic precipitators. The low-voltage
(or two-stage) electrostatic precipitator, preceded by
a spray scrubber as a pre-cleaner, gives relatively high
collection efficiency as well as substantial reduction in
the opacity of the saturator effluent.
Using fabric filters or baghouse filters. Baghouse filters
are occasionally used as air pollution control devices for
asphalt saturators, but their use is limited as a result
of maintenance problems associated with filter bag upkeep
and their high power requirements. Oil collected by the
filter fabric is oxidized and polymerized by the air stream,
plugging the fabric and increasing the pressure drop across
the filter unit. The air volume handled by the exhaust
system then decreases because of increased pressure drop,
resulting in loss of mist capture at the saturator hood open-
ings. «>
Using scrubbers. Spray-type scrubbers have met with limited
success as air pollution control devices for saturators.
Although some spray scrubbers may have an efficiency,
based on weight removed, as high as 90 percent, their
effluent may be from 50 to 100 percent opaque. This opaque
discharge is due to the extremely low collection efficiency
23
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of spray scrubbers for particles less than 1 micron in diameter.
These small-diameter particles, when emitted(from the scrubber
discharge, cause maximum light scattering and, therefore,
high opacities.^
Sulfur Dioxide and Nitrogen Oxides
Limited efforts have been made to control these pollutants:
scrubbers to control particulates, and using low-sulfur fuel for heating.
Proper burner design and efficient operation of the heating system will
greatly reduce these pollutants.
Odors and Hydrocarbons
Effluents from asphalt airblowing stills have been controlled by
scrubbing and incineration, singly or in combination. Most installations
use the combination. Potential air pollutants can be removed from
asphalt still gases by scrubbing alone. One effective control installation
in Los Angeles County uses sea water for single-pass scrubbing of effluent
gases from four asphalt airblowing stills. The fume scrubber is a standard
venturi-type unit. The scrubber effluent is discharged into an enclosed
oil/water gravity-type separator for recovery of oil, which is reprocessed
or used as fuel. Effluent gases from the covered separator that collects
the scrubber discharge are not incinerated but flow through a steam-
blanketed stack to the atmosphere. The system, Figure 7, removes
essentially all potential air pollutants from the effluent stream. A
limiting factor in the application of this method of control is the
water supply. Since a high water/vapor scrubbing ratio (379 liters/28
3
stdm —100 gal/1000 scf) is necessary, an economical source of water
should be readily available to supply the large volume required for
(3)
single-pass operation.
Control Technology Needed for Roofing Manufacture
Pollutant control methods are available to asphalt roofing manu-
facturers. Improvement of odor control is needed. The odor study
is expected to be underway by EPA in the near future.
Roofing manufacturers have not been as aggressive as hot-mix
plant operators in combating air pollution due perhaps to the former's
smaller production and older plants. As stated, control technology is
available; it is a question of installing available equipment.'
24
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OCEAN WATER
(80 psi)
(5.6 kg/cm2)
EXHAUST GASES
TO ATMOSPHERE
ro
Cn
KNOCKOUT
DRUM
FUME
SCRUBBER
STEAM
BLANKET
MIST ELIMINATOR
COVERED SEPARATOR
AIR BLOWN
ASPHALT STILLS
(BATCH OPERATION)
CONDENSATE
TO STORAGE
SKIMMED OIL
TO STORAGE
EFFLUENT WATER TO
COVERED SEPARATOR
Figure 7. Flow diagram of scrubbing system.
-------
REFERENCES
1. U. S. Dept of the Interior. Minerals Yearbook. U. S. Govt
Printing Office, 864 and 950 (1971).
2. Midwest Research Institute. Particulate Pollutant System Study,
Vol I, Mass Emissions, NTIS No. PB 203-128. 160 (May 1W1) . '
3. Environmental Protection Agency. Air Pollution Engineering Manual
(2nd Ed). U. S. Govt Printing Office. EPA.9:40/2. 325-333, 378*-
390, and 685-689 (1973).
4. The Asphalt Handbook, MS-4. The Asphalt Institute (April 1965).
5. Skinner, C. F. New Use for Baghouse Filter: Handling Hot Effluent.
Plant Engrg. 23(13):57-59 (June 26, 1969).
6. EPA. The Economics of Clean Air. U.S. Senate Document 92-67,
U. S. Govt Printing Office, Sec 4, p. 27 (March 1972).
7. EPA. The Cost of Clean Air. U. S. Senate Document 93-40, U. S.
Govt Printing Office, Sec 5, p. 44 (October 1973).
8. Loquercio, P. A. and C. F. Skinner. Abating Pollution from Asphalt
Mixing Plants Especially by Means of a Baghouse. Environmental
Pollution Control Systems. (Presented at 63rd Annual APCA Meeting.
St. Louis. 16 p.) (June 14-18, 1970).
9. Asphalt Batch Plants, Environmental Engineering, Inc. (March 1971)..
26
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Appendix A
TERMS RELATING TO ASPHALTIC MATERIALS
Asphalt - A dark-brown to black cementitious material (solid, semi-
solid, or liquid in consistency) in which the predominating constituents
are bitumens which occur in nature as such or which are obtained as
residue in refining petroleum. Asphalt is a constituent in varying
proportions of most crude petroleums.
Asphalt Blocks - Asphalt concrete molded under high pressure. The
type of aggregate mixture composition, amount and type of asphalt,
and the size and thickness pf the blocks may be varied to suit usage
requirements.
Asphalt, Blown or Oxidized - Asphalt that is treated by blowing air
through it at elevated temperature to give it characteristics desired
for certain special uses such as roofing, pipe coating, undersealing
Portland cement concrete pavements, membrane envelopes, and hydraulic
applications.
Asphalt, Catalytically Blown - An air-blown asphalt produced by using
a catalyst during the blowing process.
Asphalt Cement - Asphalt that is refined to meet specifications for
paving, industrial, and special purposes.
Asphalt. _Cutb_a_ek - See Asphalt, Liquid, A, below.
Asphalt, Emulsified - See Asphalt, Liquid, B, below.
Asphalt, Hard - See Asphalt, Solid, below.
Asphalt Joint Filler - An asphaltic product used for filling cracks
and joints in pavement and other structures.
Asphalt Joint Fillers, Preformed - Premolded strips of asphalt mixed
with fine mineral substances, fibrous materials, cork, sawdust, etc.;
manufactured in dimensions suitable for construction joints.
Asphalt, Lakef- See Asphalt, Natural, below.
Asphalt, Liquid - An asphaltic material having a soft or fluid
consistency that Is beyond the range of measurement by the normal
penetration test. Liquid asphalts include cutback asphalts and
emulsified asphalts.
A. Cutback Asphalt - Asphalt cement which has been liquefied
by blending with petroleum solvents (diluents), as for
the RC and MC liquid asphalts (a and b, below). Upon
exposure to atmospheric conditions the diluents evaporate,
leaving the asphalt cement to perform its function.
27
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a. Rapid-Curing (RC) Asphalt - Liquid asphalt composed of
asphalt cement and a naphtha or gasoline-type diluent
of high volatility.
b. Medium-Curing (MC) Asphalt - Liquid 'asphalt composed of
asphalt cement and a
volatility.
pha
ker
osene-type diluent of medium
c. Slow-Curing (SC) Asphalt - Liquid asphalt composed of
asphalt cement and oils^of low volatility.
d. Road-Oil - A heavy petroleum oil, usually one of the SC
grades of liquid asphalt.
B. Emulsified Asphalt - An emulsion of asphalt cement and water
which contains a small amount of an emulsifying agent; a
heterogeneous system containing two normally immiscible
phases (asphalt and water) in which the water forms the
continuous phase of the emulsion, and minute globules of
asphalt form the discontinuous phase.
Asphalt, Medium-Curing (MC) - See Asphalt, Liquid, A.b, above.
Asphalt, Mineral-Filled - Asphalt containing finely divided mineral matter,
Asphalt, Natural (Native) - Asphalt, occurring in nature, which has
been derived from petroleum by natural processes of evaporation of
volatile fractions, leaving the asphalt fractions. The native asphalts
of most importance are found in the Trinidad and Bermudez Lake
deposits. Asphalt from these sources often is called Lake Asphalt.
Asphalt Paint - A liquid asphaltic product sometimes containing small
amounts of other materials such as lampblack, aluminum flakes, and
mineral pigments.
Asphalt Panels. Premolded - Generally made with a core of asphalt,
minerals, and fibers, covered on each side by a layer of asphalt-
impregnated felt or fabric , and coated on the outside with hot-
applied asphalt. The panels are made under pressure and heat to a
width of 9 to 12 meters (3 to 4 feet) by 0.3 to 2.5 cm (1/8 to 1 inch)
thick, and to any desired length.
Asphalt, Petroleum - Asphalt refined from crude petroleum.
Asphalt Planks - Premolded mixtures of asphalt fiber and mineral
f iller , somet imes reinforced with steel or fiberglass mesh. They are
usually made 9 to 24 meters (3 to 8 feet) long and 15 to 30 cm (6 to
12 inches) wide. Asphalt planks may also contain mineral grits which
maintain a sandpaper texture throughout their life.
28
-------
Asphalt, Powdered - Solid or hard asphalt, crushed or ground to a fine
state of subdivision.
Asphalt Primer - A liquid asphalt of low viscosity which penetrates
a non-bituminous surface upon application.
Asphalt, Rapid-Curing (RC) - See Asphalt, Liquid, A. a, above.
Asphalt, Rock - Porous rock, such as sandstone or limestone, that has
become impregnated with natural asphalt through geologic process.
Asphalt, Semisolid - Asphalt which is intermediate in consistency
between liquid asphalt and solid or hard asphalt; that is, it normally
has a penetration between 10 and 300.
Asphalt, Slow-Curing (SC) - See Asphalt, Liquid, A. c, above.
Asphalt, Solid^ - Asphalt having a normal penetration of less than 10.
Also referred to as hard asphalt.
Bitumen - A mixture of hydrocarbons of natural or pyrogenous origin, or
a combination of both; frequently accompanied by nonmetallic derivatives
which may be gaseous, liquid, semisolid, or solid; and which are completely
soluble in carbon disulfide.
Flux Oil - A thick, relatively nonvolatile fraction of petroleum
which may be used to soften asphalt to a desired consistency; often
used as base stock for manufacture of roofing asphalts. Also
referred to simply as flux.
Gilsonite - Trade name for a form of natural asphalt, hard and brittle,
occurring in rock crevices or veins from which it is mined. Also see
Uintaite, below.
Road Oil - See Asphalt, Liquid, A.d, above.
Uintaite - A black lustrous asphalt, occurring especially in Utah,
that is used in the manufacture of paints, varnishes, inks, and
waterproofing. Also see Gilsonite, above.
29
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Appendix B
TERMS RELATING TO ASPHALT PAVEMENTS AND SURFACE TREATMENTS
Aggregate - Any hard, inert, mineral material used for mixing in
graduated fragments. It includes sand, gravel, crushed stone,
and slag.
Aggregate, Coarse - That retained on the No. 8-mesh sieve.
Aggregate, Coarse-Graded - One having a continuous grading in sizes
of particles from coarse through fine with a predominance of coarse
sizes.
Aggregate, Fine - That passing the No. 8-mesh sieve.
Aggregate, Fine-Graded - One having a continuous grading in sizes of
particles from coarse through fine with a predominance of fine sizes.
Aggregate, Macadam - A coarse aggregate of uniform size usually of
crushed stone, slag, or gravel.
Aggregate, Open-Graded - One containing little or no mineral filler
or in which the void spaces in the compacted aggregate are relatively
large.
Aggregate, Well-Graded - Aggregate that is graded from the maximum
size down to filler, used to obtain an asphalt mix with a controlled
void content and high stability.
Aggregate Seals - See Asphalt Seal Coat, below.
Armor Coat Treatment - See Multiple Surface Treatments, below.
Asphalt Base Course - A foundation course consisting of mineral
aggregate, bound together with asphaltic material.
Asphalt Binder Course - See Asphalt Intermediate Course, below.
Asphalt Block Pavements - Pavements in which the surface course is
constructed of asphalt blocks. These blocks are laid in regular courses
as in the case of brick pavements.
Asphalt Concrete - High quality, thoroughly controlled hot mixture of
asphalt cement and well-graded, high quality aggregate, thoroughly
compacted into a uniform dense mass.
31
-------
Asphalt Emulsion Slurry Seal - A mixture of slow-setting emulsified
asphalt, fine aggregate, and mineral filler, with water added to
produce slurry consistency.
Asphalt Fog Seal - A light application of liquid asphalt without
mineral aggregate cover. Slow-setting asphalt emulsion diluted with
water is the preferred type.
Ajsphalt Intermediate Course - A course between a base course and an
asphalt surface course.Also called binder course.
Asphalt Leveling Course - A course (asphalt aggregate mixture) of
variable thickness used to eliminate irregularities in the contour
of an existing surface prior to superimposed treatment or construction.
Asphalt Macadam - A type of pavement construction using a coarse,
open-graded aggregate that is usually produced by crushing and screening
stone, slag, or gravel. Such aggregate is called Macadam Aggregate.
Asphalt may be incorporated in macadam construction either by
penetration or by mixing.
Asphalt Mastic - A mixture of asphalt and fine mineral material in
such proportions that it may be poured hot or cold into place and
compacted by troweling to a smooth surface.
Asphalt Overlay - One or more courses of asphalt construction on
an existing pavement. The overlay generally includes a leveling
course to correct the contour of the old pavement, followed by a uni-
form course or courses to provide needed thickness. When overlaying
rigid-type pavements, the overlay should be not less than 10 cm
(4 inches) thick to minimize reflection of cracks and joints through
the overlay. Greater thickness of overlay may be required depending
upon both the condition of the old pavement and traffic to be served.
Asphalt Pavement - Pavement consisting of a surface course of
mineral aggregate coated and cemented together with asphalt cement on
supporting courses such as asphalt bases; crushed stone, slag, or
gravel; or on portland cement concrete, brick, or block pavement.
Asphalt Pavement Structure - Courses of asphalt/aggregate mixtures,
plus any non-rigid courses between the asphalt construction and the
foundation or subgrade. The term "flexible," sometimes used in
connection with asphalt pavements, denotes the ability of such a
pavement structure to conform to settlement of the foundation.
Also called flexible pavement structure.
Asphalt Prime Coa^ - An application of low-viscosity liquid asphalt
to an absorbent surface. It is used to prepare an untreated base
for an asphalt surface. The prime penetrates the base and plugs the
32
-------
voids, hardens the top, and helps bind it to the overlying asphalt
course. It also reduces the necessity of maintaining an untreated
base course prior to placing the asphalt pavement.
Asphalt, Sand - A mixture of sand and asphalt cement or liquid asphalt
prepared with or without special control of aggregate grading with
or without mineral filler. Either mixed-in-place or plant-mix
construction may be employed. Sand asphalt is used in construction of
both base and surface courses.
Asphalt Seal Coat - A thin asphalt surface treatment used to waterproof
and improve the texture of an asphalt wearing surface. Depending on
purpose, seal coats may or may not be covered with aggregate. The
main types of seal coats are aggregate seals, fog seals, emulsion
slurry seals,and sand saals.
A.sphalt, Sheet - A hot mix of asphalt cement with clean angular,
graded sand and mineral filler. Its use is ordinarily confined to
surface course, usually laid on an intermediate or leveling course.
Asphalt Soil Stabilization (Soil Treatment) - Treatment of naturally
occurring non-plastic or moderately plastic soil with liquid asphalt
at normal temperatures. After mixing, aeration and compaction provide
water resistant base and subbase courses of improved load bearing qualities.
Asphalt Surface Course - The top course of an asphalt pavement, some-
times called asphalt wearing course.
Asphalt Surface Treatment - Application of asphaltic materials to
any type of road or pavement surface, with or without a cover of
mineral aggregate, which produces an increase in thickness of less
than 2.54 cm (1 inch).
Asphalt Tack Coat - A very light application of liquid asphalt applied
to an existing asphalt or portland cement concrete surface. Asphalt
emulsion diluted with water is the preferred type. It is used to
ensure a bond between the surface being paved and the overlying course.
Asphalt Wearing Course - See Asphalt Surface Course, above.
Base Course - The layer of material immediately beneath the surface
or intermediate course. It may be composed of crushed stone, crushed
slag, crushed or uncrushed gravel and sand, or combinations of these
materials. It also may be bound with asphalt.
Basement Soil - See Subgrade Soil, below.
Cold-Laid Plant Mixture - Plant mixes which may be spread and compacted
at atmospheric temperature.
Deep-Lift Asphalt Pavement - One in which the asphalt base course is
placed in one or more lifts of 10 cm (4 inches) or more compacted
thickness.
33
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peep-Strength - A term registered by The Asphalt Institute with
U. S. Patent^Office. The term Deep-Strength (also called "mark")
certifies that the pavement is constructed of asphalt with an asphalt
surface on an asphalt base and in accordance with design concepts
established by the Institute.
Dry Sieve Analysis - See Sieve Analysis, below.
Emulsion Slurry Seals - See Asphalt Seal Coat, above.
Flexible Pavement Structure - See Asphalt Pavement Structure, above.
Fog Seals - See Asphalt Seal Coat, above.
Foundation Soil - See Subgrade Soil, below.
Full-Depth Asphalt Pavement - One in which asphalt mixtures are used
for all courses above the subgrade or improved subgrade. It is laid
directly on the prepared subgrade. (The mathematical symbol Ta
denotes full-depth or total asphalt.)
Hot-Laid Plant Mixture - Plant mixes which must be spread and compacted
while at an elevated temperature. To dry the aggregate and obtain
sufficient fluidity of the asphalt (usually asphalt cement), both
must be heated prior to mixing, giving origin to the term "hot mix."
Inverted Penetration Treatment - See Multiple Surface Treatments,
below.
Macadam Aggregate - See Asphalt Macadam, above.
Mineral Dust - The portion of the fine aggregate passing the No. 200-
mesh sieve.
Mineral Filler - A finely divided mineral product at least 65 percent
of which will pass a No. 200-mesh sieve. Pulverized limestone is the
most commonly manufactured filler; although other stone dust, hydrated
lime, portland cement, and certain natural deposits of finely divided
mineral matter are also used.
Mixed-in-Place - An asphalt course produced by mixing mineral
aggregate and liquid asphalt at the road site by means of travel
plants, motor graders, drags, or special road-mixing equipment. Also
called road mix.
Multiple Lift Treatment - See Multiple Surface Treatments, below.
Multiple Surface Treatments - Commonly two or three successive
applications of asphaltic material and mineral aggregate. (Treat-
ments designated "Armor Coat," "Multiple Lift," and "Inverted
Penetration" are essentially multiple surface treatments.)
34
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Pavement Structure - All courses of selected material placed on the
foundation or subgrade soil, other than layers or courses constructed
In grading operations.
Pavement Structure, Combination (or Composite) Type - When the asphalt
pavement is on an old portland cement concrete base, or other rigid-
type base, the pavement structure is referred to as a combination
(or composite) type pavement structure.
Penetration - The penetration test determines the relative hardness
or consistency of an asphalt cement by measuring the distance that
a standard needle will penetrate vertically into a sample of asphalt
under known conditions of temperature, loading, and time. When
other conditions are not specifically mentioned, it is understood
that penetration value or measurement is made at 258C (77°F); that
the needle is loaded to 100 grams; and that the load is applied for
5 seconds. This is known as standard penetration. The unit of
penetration is 1/10 mm (about 1/254 inch). It is evident that the
softer asphalt cement will have a greater number of penetration units.
Using penetration limits, asphalt cements are classified on the basis
of hardness or consistency. The Asphalt Institute has adopted
four grades of asphalt cement for paving, with penetration ranges of
60-70, 85-100, 120-150, and 200-300. The Institute also has specifica-
tions for a 40-50 penetration grade, used for special and industrial
purposes.
Plant Mix - A mixture, produced in an asphalt mixing plant5 which
consists of mineral aggregate uniformly coated with asphalt cement or
liquid asphalt.
Road-Mix - See jlixed-in-Place, above.
Rock Asphalt Pavement - Pavement constructed of rock asphalt, natural
or processed, and treated with asphalt or flux.
Sand Seals - See Asphalt Seal Coat, above.
Sieve Analysis - There are two methods of determining the relative
proportions of various particle sizes in a mineral aggregate: dry
sieve analysis, and washed sieve analysis.
A. Dry Sieve Analysis - A weighed quantity of thoroughly
dried aggregate is shaken over a set of sieves each with
different sizes of square openings. The sieves are nested
together: the one with the largest opening is on top; and
those with successively smaller openings are below it. A
pan under the bottom sieve collects all material passing
35
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through it. The shaking is normally accomplished with a
mechanical sieve shaker. The weight of material retained
on each sieve size is expressed as a percentage of the
weight of the original or total sample. Commonly used with
asphalt paving mixes are 6.4, 5.1, 3.8, 2.5, 1.9, 1.3, and
1.0 cm (2-1/2, 2, 1-1/2, 1, 3/4-, 1/2-, and 3/8-inch) square
opening mesh sieves and No. 4-, 8-, 16-, 30-, 50-, 100-, and
200-raesh sieves.
B. Washed Sieve Analysis - This method of testing determines the
particle size distribution of fine and coarse aggregates by
washing. This method should always be used if the aggregate
contains extremely fine dust, or clay which may cling to
the coarser aggregate particles. In such instances, results
using dry sieve analysis will be in error.
Subbase - The course in the asphalt pavement structure immediately
below the base course is called the subbase. If the subgrade soil
is of adequate quality it may serve as the subbase.
Subgrade Soil - The uppermost material placed in embankments or
not removed from cuts in the normal roadbed grading. It is the foun-
dation for the asphalt pavement structure. Subgrade soil sometimes
is called basement or foundation soil.
Subgrade. Improved - Any course or courses of select or improved
material between the foundation soil and the subbase is usually
referred to as the improved subgrade. The improved subgrade can
be made up of two or more courses of different quality materials.
Washed Sieve Analysis - See Sieve Analysis, above.
36
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BIBLIOGRAPHIC DATA
SHEET
4. Title and Subtitle
1. Report No.
EPA-650/2-73-046
2.
~3. Recipient's Accession No.
Atmospheric Emissions from the Asphalt Industry
5. Report Date
December 1973
6.
7. Author(s)
L.L. Laster
8. Performing Organization Rept.
No.
9. Performing Organization Name and Address
EPA, Off ice of Research and Development
NERC-RTP, Control Systems Laboratory
Research Triangle Park, North Carolina 27711
10. Projeci/Task/Work Unit No.
ROAP 21AXM10
11. Contract/Grant No.
Pgm El em 1AB015
12. Sponsoring Organization Name and Address
NA
13. Type of Report & Period
Covered
In-house (Final)
14.
15. Supplementary Notes
The report summarizes the air pollution problem of the asphalt industry--
hot-mix asphalt plants and roofing manufacture—emphasizing particulate emissions
It outlines industrial processes, types and sources of pollutant emissions, and
current and required controls. Particulates are the principal emission from the
industry; sulfur oxides, nitrogen oxides, odors, and hydrocarbons are emissions of
minor importance. Approximately 200,000 metric tons of these pollutants (except
for odor, per se) were emitted in the U.S. in 1968, with substantial control only
for particulates. In spite of developed controls, the industry still has air pollution
problems. Emitted pollutants contribute to a dense and foggy fume and cause most
of the public's complaints. Particulates can be controlled by wet or dry methods (or
a combination of the two), by fabric filters , or by baghouses. Emissions of sulfur
oxides . nitrogen oxides . and hydrocarbons are not significant qualitatively, but each
" " " contributes to the odor and smog prob-
lems and should be controlled. Control
devices can be used on asphalt plants.
Electrostatic precipitators are not
usually considered because of their
initial cost and rather high volume.
Control methods are available for the
principal pollutant, particulates; how-
ever , as in many other industries,
available controls are often not being
installed.
17. Key Words and Document Analysis
Air Pollution
Asphalt Plants
Roofing
Odors
Smog
Contaminants
Control Equipment
Filtration
I7b. Identificrs/Open-Ended Terms
Air Pollution Control
Stationary Sources
Particulates
Industrial Processes
Fabric Filters
Baghouses
7e. COSAT1 Field/Group
17o. IVscnpior1:
13B, 13H
8. Availability Statement
Unlimited
19. Security Class (This
Report)
UNCLASSIFIED
20. Security Class (This
Page
UNCLASSIFIED
21. No. of Pages
42
22. Pricr
FORM NTIS-39 (REV. 3-72)
37
USCOMM-DC I4BS2-P72
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