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.

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      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).

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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.

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     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.

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                              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

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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

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 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

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 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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