U.S. Department of Transportation
Federal Highway Administration
TECHNICAL ADVISORY
ASPHALT CONCRETE MIX DESIGN AND FIELD CONTROL
T 5040.27
March 10, 1988
Par.
- Purpose
- Cancellation
- Background
- Materials
- Mix Design
- Plant Operations
- Laydown and Compaction
- Miscellaneous
- PURPOSE. To set forth guidance and recommendations relating to asphalt
concrete paving, covering the areas of materials selection, mixture design,
and mixture production and placement. The procedures and practices outlined
in the Technical Advisory (TA) are directed primarily towards developing quality
asphalt concrete pavements for high-type facilities. The TA can also be used
as a general guide for low-volume facilities.
- CANCELLATION. Federal Highway Administration (FHWA) Technical Advisory
T 5040.24, Bituminous Mix Design and Field Control, dated August 22, 1985,
is canceled.
- BACKGROUND
- Over one-half of the Interstate System and 70 percent of all highways
are paved with hot-mix asphalt concrete. Asphalt concrete is probably
the largest single highway program investment today and there is no evidence
that this will change in the near future. However, there is evidence that
the number of premature distresses in the nation's recently constructed
asphalt pavements is increasing. Heavier truck axle weights, increased
tire pressures, and inadequate drainage are some of the factors leading
to the increase in premature distress. The FHWA has been concerned with
the deterioration in quality of asphalt concrete pavements for many years
and in 1987 a special FHWA Ad Hoc Task Force studied two of the most common
distresses existing today and subsequently issued a report titled "Asphalt
Pavement Rutting and Stripping." The report contained both short-term
and long-term recommendations for improving the quality of asphalt pavements.
- With the variables of environment, component materials, and traffic
loadings found throughout the United States, it is not surprising that
there are many State-to-State or regional variations of design and construction
requirements. No one set of specifications can achieve the same results
in all States because of the factors mentioned above. However, there are
many things that States can do to improve their current mix design and
field control procedures to ensure that quality asphalt pavements will
be constructed. This TA incorporates many of the FHWA Task Force recommendations
and presents the current state-of-the-art in materials, mix design, plant
operation, laydown and compaction, and other areas relating to quality
hot-mix asphalt pavements.
- MATERIALS
- Aggregate is the granular material used in asphalt concrete mixtures
which make up 90-95 percent of the mixture weight and provides most of
the load bearing characteristics of the mix. Therefore, the quality andphysical
properties of the aggregates are critical to the pavement performance.
The following is recommended:
(1) Aggregates should be nonplastic. The presence of clay fines in
an asphalt mix can result in problems with volume swell and adhesion
of asphalt to the rock contributing to stripping problems. The minus
#4 sieve material should have a minimum sand equivalent value of 45
using the test method described in the American Association of State
Highway and Transportation Officials (AASHTO) specification (AASHTO
T-176).
(2) A limit should be placed on the amounts of deleterious materials
permitted in the aggregates. Specifications should limit clay lumps
and friable particles to a maximum of one percent.
(3) Durability or weathering resistance should be determined by sulfate
soundness testing. Specifications should require a sodium or magnesium
sulfate test using the limits described in the AASHTO specification
M-29.
(4) Aggregate resistance to abrasion should be determined. Specifications
should require a Los Angeles abrasion loss of 45 percent or less (AASHTO
T-96).
(5) Friction between aggregate particles is dependent on aggregate
surface roughness and area of contact. As surface friction increases,
so does resistance of the mix to deformation. Specifications should
require at least 60 percent of the plus #4 sieve material to have
at least two mechanically induced fractured faces.
(6) The quality of natural sand varies considerably from one location
to another. Since most natural sands are rounded and often contain
a high percentage of undesirable materials, the amount of natural
sand as a general rule should be limited to 15 to 20 percent for high
volume pavements and 20 to 25 percent for medium and low volume pavements.
These percentages may increase or decrease depending on quality of
the natural sand and thetypes of traffic to which the pavement will
be subjected.
(7) For adequate control, aggregate gradations should be specified
from the maximum particle size to the #200 sieve so each successive
sieve opening is about 1/2 the previous sieve opening (for example,
1 inch, 1/2 inch, #4, #8, #16, #30, #50, #100, #200). The only accurate
method to determine the amount of minus #200 sieve material is to
perform a wash gradation in accordance with AASHTO T-27 and AASHTO
T-11.
(8) The ratio of dust (minus #200 sieve material) to asphalt cement,
by mass, is critical. Asphalt concrete mixes should require a maximum
dust asphalt ratio of 1.2 and a minimum of 0.6.
(9) A tool which is very useful in evaluating aggregate gradations
is the 0.45 power gradation chart. All mixes should be plotted on
these charts as part of the mix design process (Attachment 1).
(10) An aggregate's specific gravity and absorption characteristics
are extremely important in proportioning and controlling the mixture.
It is recommended that AASHTO T-209 be used to determine the maximum
specific gravity of asphalt concrete mixes. States not using AASHTO
T-209 should be aware of the difficulty of determining the theoretical
maximum density using individual ingredient specific gravities and
their percentages in the mixture. These difficulties will result in
inaccuracies in determining the specific gravity of the mixture. These
inaccuracies will carry through to the calculation of the densities
in the compacted mat and may result in improperly compacted pavements.
It is also necessary to determine the bulk dry specific gravity of
the aggregate in order to determine the voids in the mineral aggregate
(VMA).
The target value for VMA should be obtained through the
proper distribution of aggregate gradation to provide adequate asphalt
film thickness on each particle and accommodate the design air void
system. In addition, tolerance used inconstruction quality control
should be such that the mix designed is actually produced in the field.
- Asphalt grade and characteristics are critical to the performance of
the asphalt pavement. The following is recommended:
(1) Grade(s) of asphalt cement used in hot-mix paving should be selected
based on climatic conditions and past performance.
(2) It is recommended that asphalt cement be accepted on certification
by the supplier (along with the testing results) and State project
verification samples. Acceptance procedures should provide information
on the physical properties of the asphalt in a timely manner.
(3) The physical properties of asphalt cement that are most important
to hot-mix paving are shown below. Each State should obtain this information
(by central laboratory or supplier tests) and should have specification
requirement(s) for each property except specific gravity.
(a) Penetration 77° F
(b) Viscosity 140° F
(c) Viscosity 275° F
(d) Ductility/Temperature
(e) Specific Gravity
(f) Solubility
(g)Thin Film Oven (TFO)/Rolling TFO; Loss on Heating
(h) Residue Ductility
(i) Residue Viscosity
(j)Low temperature cracking is related to the physical properties
of the asphalt and may beincreased by the presence of wax in the
asphalt. The low temperature ductility test at 39.2° F (4°
C) can indicate where this may be a problem. The test is performed
at a pull speed of 1 cm/min. Typical specification requirements
are:
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AASHTO
M-226 |
Table 2 |
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AC 2.5 |
50 + cm |
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AC 5 |
25 + cm |
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AC 10 |
15 + cm |
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AC 20 |
5 + cm |
(4) The temperature viscosity curves or absolute and kinematic viscosity
information should be available at the mixing plant for each shipment
of asphalt cement. This can identify a change in asphalt viscosity
which necessitates a new mix design. Each State should provide temperature/viscosity
information on the asphalt used in the laboratory mix design to the
projects. Differences in the viscosity (as well as the penetration)
of the asphalt from the asphalt used in the mix design may indicate
the necessity to redesign the mix (Attachment 2).
- MIX DESIGN
- Asphalt concrete mixes should be designed to meet the necessary criteria
based on type of roadway, traffic volumes, intended use, i.e., overlay
on rigid or flexible pavements, and the season of the year the construction
would be performed. Each State's mix design criteria should be as follows.
PROPERTY |
|
HEAVY TRAFFIC DESIGN
(>1,000,000 ESAL*) |
MEDIUM TRAFFIC DESIGN
(10,000 - 1,000,000 ESAL) |
LIGHT TRAFFIC DESIGN
(<10,000 ESAL) |
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Marshall |
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Compaction Blows |
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75 |
50 |
35 |
Stability (min.) |
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1,500 |
750 |
500 |
Flow |
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8-16 |
8-18 |
8-20 |
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Hveem
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Stability (min.) |
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37 |
35 |
30 |
Swell |
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0.030 in. |
0.030 in. |
0.030 in. |
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Void Analysis |
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Air Voids |
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3-5 |
3-5 |
3-5 |
* Equivalent Single Axle Load
MINIMUM PERCENT VOIDS IN MINERAL AGGREGATE (VMA)
|
Nominal Maximum Particle Size, USA Standard Sieve Designation |
Minimum Voids in Mineral Aggregate Percent |
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No. 16 |
23.5 |
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No. 8 |
21 |
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No. 4 |
18 |
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3/8 in. |
16 |
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½ in. |
15 |
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3/4 in. |
14 |
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1 in. |
13 |
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1 ½ in. |
12 |
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2 in. |
11.5 |
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2 ½ in. |
11 |
- Standard mix design procedures (Marshall, Hveem) have been developed
and adopted by AASHTO, however, some States have modified these procedures
for their own use. Any modification from the standard procedure should
be supported by correlation testing for reasonable conformity to the design
values obtained using the standard mix design procedures.
- Stripping in the asphalt pavements is not a new phenomenon, although
the attention to it has intensified in recent years. Moisture susceptibility
testing should be a part of every State's mix design procedure. The "Effect
of Zero on Compacted Bituminous Mixtures" (immersion compression
test) (AASHTO T-165) and "Resistance of Compacted Bituminous Mixture
to Moisture Induced Damage" (AASHTO T-283) are currently the only
stripping test procedures which have been adopted by AASHTO. The AASHTO
T-283, commonly known as the LottmanTest, requires that the test specimens
be compacted so as to have an air void content of 7 ± 1 percent,
while AASHTO T-165 does not. This air void content is what one would expect
in the mat after construction compaction. There is considerable research
underway on developing better tests for determining moisture damage susceptibility
of the aggregate asphalt mixtures. One of the most promising test procedures
is that developed by Tunnicliff and Root as reported in the National Cooperative
Highway Research Program (NCHRP) Report 274. This test is similar to AASHTO
T-283, but it takes less time to perform. In the majority of cases hydrated
lime and Portland cement have proven to be the most effective antistripping
additives.
- The determination of air voids in the laboratory mix is a critical step
in designing and controlling asphalt hot-mix. In order to determine air
voids, the theoretical maximum density or the maximum specific gravity
of the mix must be determined. This can be accomplished by using the "Maximum
Specific Gravity of Bituminous Paving Mixtures" (Rice Vacuum Saturation)
(AASHTO T-209).
- Proper mix design procedures require that each mix be designed using
all of the actual ingredient materials including all additives which will
be used on the project.
- The complete information on the mix design should be sent to the plant.
The following information should be included in the mix design report
and sent to the plant.
(1) Ingredient materials sources
(2) Ingredient materials properties including:
(3) Mix temperature and tolerances
(4) Mix design test property curves
(5) Target asphalt content and tolerances
(6) Target gradations for each sieve and tolerances
(7) Plot of gradation on the 0.45 power gradation chart, and
(8) Target density
- Formal procedures should be established to require that changes to mix
designs be approved by the same personnel or office that developed the
original mix design.
- After startup, the resulting mixture should be tested to verify that
it meets all of the design criteria.
- PLANT OPERATIONS
- In order to assure proper operation, an asphalt plant must be calibrated
and inspected. Plant approval should be required and should cover each
item on the asphalt plant checklist (Attachment 3).
- To avoid or mitigate unburned fuel oil contamination of the asphalt
mixture, the use of propane, butane, natural gas, coal or No. 1 or No.
2 fuel oils is recommended.
- If the asphalt cement is overheated or otherwise aged excessively, the
viscosity of the recovered asphalt will exceed that of the original asphalt
by more than four times. However, if the viscosity of the recovered asphalt
is less or even equal to the original viscosity, it has probably been
contaminated with unburned fuel oil.
- For drum mixer and screenless batch plants there should be three separate
graded stockpiles for surface courses and four for binder and base courses.
Each stockpile should contain between 15 to 50 percent by weight of the
aggregate size in the mix design. The plus #4 sieveaggregate stockpile
should be constructed in lifts not exceeding 3 feet to a maximum height
of 12 feet. There should be enough material in the stockpiles for at least
5 days of production. The plant should be equipped with a minimum of four
cold feed bins with positive separation.
- Control testing of gradation and asphalt content should be conducted
to assure a quality and consistent mixture. In many States, the contractor
or supplier is required to do this testing.
- Acceptance testing should be conducted for gradation and asphalt content
of the final mixture.
- The plotting of control and acceptance test results for gradation, asphalt
content, and density on control charts at the plant provides for easy
and effective analysis of test results and plant control.
- The moisture content of the aggregate must be determined for proper
control of drum mixer plants. The asphalt content is determined by the
total weight of the material that passes over the weigh bridge with the
correction made for moisture. Sufficient aggregate moisture contents need
to be performed throughout the day to avoid deviations in the desired
asphalt content.
- Moisture contents of asphalt mixtures is also important. The extraction
and nuclear asphalt content gauge procedures will count moisture as asphalt.
For this reason, a moisture correction should be made. In addition, high
moisture contents in asphalt mixtures can lead to compaction difficulty
due to the cooling of the mix caused by evaporation of the moisture. This
is particularly important with drum mixer mixes which require moisture
for the mixing process. Some States specify a maximum moisture content
behind the paver. A recommended maximum moisture content behind the paver
is 0.5 percent.
- LAYDOWN AND COMPACTION
- Prior to paving startup, equipment should be checked to assure its suitability
and proper function. Projectequipment approval should include the items
shown on the project inspection checklist (Attachment 4).
- Paving startup should begin with a test strip section. This will allow
for minor problems to be solved, establishment of roller patterns and
number of passes, and will assure that proper placement and compaction
can be attained.
- In order to assure proper placement and compaction, it is essential
that the mat be placed hot. Establishment of and compliance with the following
items should be included: minimum mix, underlying pavement, and ambient
temperatures. Cold weather and early or late season paving should be avoided.
The practice of raising the temperature of the mixture to combat the cold
conditions should not be permitted, as this will contribute to excessive
aging of the asphalt cement.
- The use of a pneumatic roller in the compaction process is strongly
encouraged. When used in the intermediate rolling it will knead and seal
the mat surface and aid in preventing the intrusion of surface water into
the pavement layers. It will also contribute to the compaction of the
mat.
- Density requirements should be established to result in an air void
system in the mat of 6-8 percent immediately after construction. This
allows for the inherent additional densification under traffic to an ultimate
air void content of about 3-5 percent. Density acceptance specifications
should require a percentage of maximum density as determined by AASHTO
T-209. A percentage of test strip density or Marshall laboratory density
can be used provided each is related to the maximum density. The specified
density should be attained before the mat temperature drops below 175° F.
- Density measurement should be accurate, taken frequently, and the results
made available quickly for each day of production. Density should be determined
by test cores, or by properly calibrated nuclear test gauges. Specifications
should require several tests to be averaged to determine density results
for acceptance.
- Successive hot-mix courses should not be placed while previous layers
are wet. To avoid, or minimize the penetration of water into base and
binder courses, paving operations should be scheduled so that the surface
layer(s) is placed within a reasonable period after these courses are
constructed. To the greatest extent possible, construction should be planned
to avoid the necessity of leaving layers uncovered during wet seasons
of the year.
- MISCELLANEOUS
- Some States have established procedures to accept out-of-specification
material and pavement with a reduction in price. These procedures include
definition of lot size/ production time, tolerances, and pay factor reductions
for ingredient materials, combined mixture properties, pavement density,
pavement smoothness, and lift thickness.
- Prior to the start of production and placement operations, a preplacement
conference, including all the paving participants, should be held. This
conference would define duties and responsibilities for each phase of
the operation as well as problem-solving procedures.
- During startup it is very effective to have a construction and/or materials
specialist at the project site to assist in identifying and solving any
problem that develops.
- Because asphalt hot-mix pavement construction is complex, it requires
that each person involved understand his/her function thoroughly. It is
also helpful if each person has a basic understanding of each of the many
phases involved. It is recommended that States develop or use existing
training to address these phases of asphalt paving.
/S/
Ronald E. Heinz
Associate Administrator for
Engineering and Program Development
AGGREGATE GRADATION
It has long been established that gradation of the aggregate is one of the
factors that must be carefully considered in the design of asphalt paving mixtures,
especially for heavy duty highways. The purpose in establishing and controlling
aggregate gradation is to provide sufficient voids in the asphalt aggregate
mixture to accommodate the proper asphalt film thickness on each particle and
provide the design air void system to allow for thermal expansion of the asphalt
within the mix. Minimum voids in the mineral aggregate (VMA) requirements have
been established and vary with the top aggregate size.
Traditionally, gradation requirements are so broad that they permit the use
of paving mixtures ranging from coarse to fine and to either low or high stability.
To further complicate matters, different combinations of sieve sizes are specified
to control specific grading ranges. Standardization of sieve sizes and aggregate
gradations, which has often been suggested, is not likely to occur because of
the practice of using locally available materials to the extent possible.
In the early 1960's, the Bureau of Public Roads introduced a gradation chart
(Figure 1) which is especially useful in evaluating aggregate gradations. The
chart uses a horizontal scale which represents sieve size openings in microns
raised to the 0.45 power and a vertical scale in percent passing. The advantage
in using this chart is that, for all practical purposes, all straight lines
plotted from the lower left corner of the chart, upward and toward the right
to any specific nominal maximum particle size, represent maximum density gradations.
The nominal maximum particle sieve size is the largest sieve size listed in
the applicable specification upon which any material is permitted to be retained.
An example is shown in Figure 2.
The gradations depicted in Figures 3 and 4 are exaggerated to illustrate the
points being made. By using the chart, aggregate gradations can be related to
maximum density gradation and used to predict if the mixture will be fine or
coarse textured as shown in Figure 3.
Soon after the chart was developed, it was used to study gradations of aggregate
from several mixtures that had been reported as having unsatisfactory compaction
characteristics. These mixtures could not be compacted in the normal manner
because they were slow in developing sufficient stability to withstand the weight
of the rolling equipment. Such mixtures canbe called "tender mixes."
This study identified a consistent gradation pattern in these mixes as is illustrated
in Figure 4.
Most notable is the hump in the curve near the #40 sieve and the flat slope
between the #40 sieve and the #8 sieve. This indicates a deficiency of material
in the #40 to #8 sieve range and an excess of material passing the #40 sieve.
Mixtures with an aggregate exhibiting this gradation characteristic are susceptible
to being tender, particularly if the fines are composed of natural sand.
As part of the bituminous mix design process, the aggregate gradation should
be plotted on the 0.45 power gradation chart.
Figure number is given above each thumbnail graphic (click on graphic to link
to larger image).
Figure 1: Gradation Chart
Figures 2 and 3: 0.45 Power Gradation Charts
Figure 4: 0.45 Power Gradation Chart
ASPHALT VISCOSITY
Each particular asphalt has a unique temperature-viscosity relationship. This
relationship is sometimes described as temperature susceptibility. This temperature-viscosity
relationship can be plotted on a modified semilog chart as shown on the attached
chart. These charts are very useful in determining the optimum mixing and compacting
temperature of a particular asphalt. Past research has identified the optimum
mixing tempera ture as that corresponding to a viscosity of 170 ± 20 centi
stokes, and the optimum compaction temperature as that corre sponding to a viscosity
of 280 ± 30 centistokes for laboratory mix design. The optimum mixing temperature
should be identified for the asphalt used in the mix design and included in
the mix design report which is sent to the production plant.
Prior to the oil embargo, there was a relatively fixed distribu tion system
for crude oil. This allowed for a relatively uniform asphalt cement from each
refinery. Highway agencies became familiar with the handling and performance
characteristics of those asphalt cements. As a result of the embargo, a new
vari able distribution system is in place which allows shifting and blending
of crude oils resulting in production of asphalt cements with very different
temperature viscosity characteristics.
The attached chart will allow plotting the temperature-viscosity curve for
the asphalts used in a State or a particular asphalt from a project. If the
kinematic viscosity (275° F) of the asphalt being used changes from the
kinematic viscosity of theasphalt used in the mix design by a factor of more
than about two, a new mix design should be required.
Attachment 2: Asphalt Viscosity Chart
MODEL CHECKLIST FOR
ASPHALT PLANT
COMPANY _______________________________
LOCATION __________________ INSPECTED BY __________ DATE ________
TYPE PLANT AND MANUFACTURER NAME ________________________________
MAXIMUM BATCH ____________________ LBS.
RATED TONS PER HOUR ______________
PROJECT NO. ______________________ COUNTY _______________________
- Stockpiles
- Properly separated.
- Material segregated.
- Has contractor submitted and received approval of intended materials
sources and job mix formula?
- Is area clean and properly kept?
- General Requirements for all Plants
- Are tanks for storage of asphalt cement equipped for heating the material
under effective and positive control at all times?
- Are tanks or storage material properly heated?
- Is a circulating system for the asphalt cement of adequate capacity
to provide proper and continuous circulation between storage tank and
proportioning units during the entire operating period?
- Is the discharge end of the asphalt cement circulating pipe kept below
the surface of the material in the storage tank?
- Are all pipe links and fittings steamed, oil jacketed, or otherwise
properly insulated to prevent heat loss?
- Is storage tank capacity such as to ensure continuous operation of the
plant and uniform tem perature of the asphalt cement when it is mixed
with the aggregate?
- Are tanks accurately calibrated to 100 gallons (378.5 L) and accessible
for measuring the volume of the asphalt cement?
- Is a sampling outlet provided in the asphalt feed lines?
- Is a drainage receptacle provided for flushing the outlet prior to sampling?
- Antistrip and Other Additive Systems
- Is antistrip material added at plant site?
- If antistrip material is added at plant site, does the antistrip system
meet specifications?
- If other approved additives are used, are they handled in accordance
with an established proce dure?
- Cold Feed System
- Number of cold bins. ____________
- Does plant have mechanical or electrical means for uniformly feeding
the aggregates into the dryer?
- Does cold feed have a synchronized proportioning method when blending
aggregates from two or more bins?
- If mineral filler is required, is a separate bin provided?
- Is the feeder for mineral filler furnished with the feeder drive positively
interlocked and syn chronized with the aggregate feeds?
- Drier
- Number of driers. ___________
- Is a drier of satisfactory design provided?
- Dust Collectors and Emission Controls
- What type dust collector is provided?
- Can the material collected in the dust collector be wasted or any part
or all of the material be returned to the aggregate mixture?
- Does the plant meet applicable limitations on emissions?
- Has company received a permit to operate from EPA?
- Thermometric Equipment
- Is a recording pyrometer or armored thermometer located in the asphalt
cement feed line near the discharge end at the mixer unit?
- Is the plant equipped with recording pyrometers, or armored thermometers
or other approved thermometric instruments at the discharge end of the
drier?
- Has accuracy of pyrometers or thermometers been checked?
- Surge and Storage Bins
- Is plant equipped with surge or storage bins?
- What type bin? Surge or storage?
- Is unit enclosed, insulated, weather proof?
- Is unit equipped with material level indicator?
- Is the indicator visible from plant operator or weigh master's station?
- Does unit have approved thermometric instrument so placed to indicate
automatically the temperature of mixture at discharge?
- Is conveyer system covered and insulated (if necessary) so as to prevent
excessive loss of heat during transfer of material from mixing plant to
storage bin?
- Does storage bin have acceptable heating system?
- Has surge or storage bin received prior evaluation and approval before
using?
- Safety and Inspection Provisions
- Are gears, pulleys, chains, sprockets, and other dangerous moving parts
thoroughly protected?
- Is an unobstructed and adequately guarded passage provided and maintained
in and around the truck loading space for visual inspection purposes?
- Does plant have adequate and safe stairways or guarded ladders to plant
units such as mixer platforms, control platforms, hot storage bins, asphalt
storage tanks, etc. where inspections are required?
- Is an inspection platform provided with a safe stairway for sampling
the asphalt mixture from loaded trucks?
- Truck Scales
- Are scales capable of weighing the entire vehicle at one time?
- Do scales have digital printing recorder or automatic weight printer?
- Have scales been checked and certified by a reputable scale company
in the presence of an authorized representative of the highway department?
- Date checked
Agency Name
- Is copy of certification available?
- Remarks
- Transportation Equipment
- Are truck bodies clean, tight, and in good condition?
- Do trucks have covers to protect material from unfavorable weather conditions?
- Is soapy water or other approved products available for coating truck
bodies to prevent material from sticking? Diesel fuel should not be used.
- Type of material used.(_________)
- Provisions for Testing
- Does size and location of laboratory comply with specifications?
- Is laboratory properly equipped?
- Is laboratory acceptable?
SPECIAL REQUIREMENTS FOR BATCH PLANTS
- Weigh Box or Hopper
- Is weigh box large enough to hold full batch?
- Does gate close tightly so that material cannot leak into the mixer
while a batch is being weighed?
- Aggregate Scales
- Are scales equipped with adjustable pointers or markers for marking
the weight of each material to be weighed into the batch?
- Are ten 50-lb. (22.7 kg) weights available for checking scales?
- Has accuracy of weights been checked?
- Have scales been checked and certified by a reputable scales company
in the presence of an authorized representative of the highway department?
- If the plant is equipped with beam type scales, are the scales equipped
with a device to indicate at least the last 200 lb. (97 kg) of the required
load?
- Asphalt Cement Bucket
- Is bucket large enough to handle a batch in a single weighing so that
the asphalt material will not overflow, splash or spill?
- Is the bucket steamed, or oil-jacketed or equipped with properly insulated
electric heating units?
- Is the bucket equipped to deliver the asphalt material over the full
length of the mixer?
- Asphalt Cement Scales
- Have scales been checked and certified by a reputable scale company
in the presence of an authorized representative of the highway department?
- Are scales equipped with a device to indicate at least the last 20 lb.
(9.1 kg) of the approaching total load?
- Screens
- Condition of screens.
(Satisfactory or Unsatisfactory)
- Do the plant screens have adequate capacity and size range to properly
separate all the aggregate into sizes required for proportioning so that
they may be recombined consistently?
- Hot Bins
- Number of bins? _____________________
- Are bins properly partitioned?
- Are bins equipped with overflow pipes?
- Will gates cut off quickly and completely?
- Can samples be obtained from bins?
- Are bins equipped with device to indicate the position of aggregate
at the lower quarter point?
- Asphalt Control
- Are means provided for checking the quantity or rate of flow of asphalt
material?
- Time required to add asphalt material into pugmill.
- Mixer Unit for Batch Method
- Is the plant equipped with an approved twin pugmill batch mixer that
will produce a uniform mixture?
- Can the mixer blades be adjusted to ensure proper and efficient mixing?
- Are the mixer blades in satisfactory condition?
- What is the clearance of the mixer blades? (___ in.)
- Does the mixer gate close tight enough to prevent leakage?
- Does the mixer discharge the mixture without appreciable segregation?
- Is the mixer equipped with time lock?
- Does timer lock the weigh box gate until the mixing cycle is completed?
- Will timer control dry and wet mixing time?
- Can timer be set in 5-second intervals throughout the designated mixing
cycles?
- Can timer be locked to prevent tampering?
- Is a mechanical batch counter installed as part of the timing device?
- Automation of Batching
- If the plant is fully automated, is an automatic weighing, cycling and
monitoring system installed as part of the batching equipment?
- Is the automatic proportioning system capable of weighing the materials
within ± 2 percent of the total sum of the batch sizes?
SPECIAL REQUIREMENT FOR DRUM MIXERS
- Aggregate Delivery System
- Number of cold feed bins? __________________
- Are cold feed bins equipped with devices to indicate when the level
of the aggregate in each bin is below the quarter point?
- Does the cold feed have an automatic shut-off system that activates
when any individual feeder is interrupted?
- Are provisions available for conveniently sampling the full flow of
material from each cold feed and the total cold feed?
- Is the total feed weighed continuously?
- Are there provisions for automatically correcting the wet aggregate
weight to dry aggregate weight?
- Is the flow of aggregate dry weight displayed digitally in appropriate
units of weight and time and totaled?
- Are means provided for diverting aggregate delivery into trucks, front-end
loaders, or other containers for checking accuracy of aggregate delivery
system?
- Is plant equipped with a scalping screen for aggregate prior to entering
the conveyor weigh belt?
- Asphalt Cement Delivery System
- Are satisfactory means provided to introduce the proper amount of asphalt
material into the mix?
- Does the delivery system for metering the asphalt material prove accurate
within ± 1 percent?
- Does the asphalt-material delivery interlock with aggregate weight control?
- Is the asphalt material flow displayed in appropriate units of volume
or weight and time and totaled?
- Can the asphalt material be diverted into distributor trucks or other
containers for checking accuracy of delivery systems?
- Drum Mixer
- Is the drum mixer capable of drying and heating the aggregate to the
moisture and temperature requirements set forth in the specifications,
and capable of producing a uniform mix?
- Does plant have provisions for diverting mixes at startup and shutdowns
or where mixing is not complete or uniform?
- Is plant approved for use?
PROJECT INSPECTION CHECKLIST
Compaction of Foundation
- Have all courses of the foundation been compacted to required density?
Old Asphalt Pavement
- Have all potholes been patched?
- Have all necessary patches been made?
- Have all loose material and "fat" patches been removed?
- Have all depressions been filled and compacted?
- Has fog seal been used on surface that has deteriorated from oxidation?
- Has an emulsified asphalt slurry seal been applied on old surfaces with
extensive cracking?
Rigid Type Pavement
- Has pavement been under sealed where necessary?
- Has premolded joint material and crack filler been cleaned out?
- Have all "fat" patches been removed?
- Has badly broken pavement been removed and patched?
- Have all depressions been filled and compacted?
Incidental Tools
- Do incidental tools comply with specifications?
- Are all necessary tools on job before work begins?
The Engineer and the Contractor
- Have the engineer and inspectors held a preliminary conference with the
appropriate contractor personnel?
- Has continuity of operations been planned?
- Has the number of pavers to be used been determined?
- Have the number and type of rollers to be used been determined?
- Has the number of trucks to be used been determined?
- Has the width of spread in successive layers been planned?
- Is it understood who is to issue and who is to receive instructions?
- Have weighing procedures and the number of load tickets to be prepared been
determined?
- Have procedures for investigation of mix been agreed upon?
- Has method of handling traffic been established?
Preparation of Surface
- Have all surfaces that will come into contact with the asphalt mix been
cleaned and coated with asphalt?
- Has a uniform tack coat of correct quantity been applied?
Asphalt Distributor
- Does the asphalt distributor comply with specifications?
- Are the heaters and pump in good working condition?
- Have all gauges and measuring devices such as the bitumeter, tachometer,
and measuring stick been calibrated?
- Are spray bars and nozzles unclogged and set for proper application of asphalt?
Hauling Equipment
- Are truck beds smooth and free from holds and depressions?
- Do trucks comply with specifications?
- Are trucks equipped with properly attached tarpaulins?
- For cold weather or long hauls, are truck beds insulated?
- When unloading, do trucks and paver operate together without interference?
- Is the method of coating of contact surfaces of truck beds agreed upon?
Paver
- Does the paver comply with specifications?
- Is the governor on the engine operating properly?
- Are the slat feeders, the hopper gates, and spreader screws in good condition
and adjustment?
- Are the crawlers adjusted properly?
- Do the pneumatic tires contain correct and uniform air pressure?
- Is the screed heater working properly?
- Are the tamper bars free of excessive wear?
- Are the tamper bars correctly adjusted for stroke?
- Are the tamper bars correctly adjusted for clearance between the back of
the bar and the nose of the screed plate?
- Are the surfaces of the screed plates true and in good condition?
- Are mat thickness and crown controls in good condition and adjustment?
- Are screed vibrators in good condition and adjustment?
- Is the oscillating screed in proper position with respect to the vibrating
compactor?
- Is the automatic screed control in adjustment and is the correct sensor
attached?
Spreading
- Are the required number of pavers on job?
- Is the mix of uniform texture?
- Is the general appearance of the mix satisfactory?
- Is the temperature of the mix uniform and satisfactory?
- Does the mix satisfy the spreading requirements?
- Has proper paver speed been determined?
- Is the surface smoothness tolerance being checked and adhered to?
- Is the depth of spread checked frequently?
- Has the daily spread been checked?
Rolling
- Are the required number of rollers on the job?
- Is proper rolling procedure being followed?
- Is the proper rolling pattern being followed?
- Are joints and edges being rolled properly?
Miscellaneous
- Are all surface irregularities being properly corrected?
- Is efficient control of traffic being maintained?
- Are sufficient samples being taken?
- Are samples representative?
- Have assistant inspectors been properly instructed?
- Are inspection duties properly apportioned among assistants?
- Are records complete and up-to-date?
- Are safety measures being observed?
- Has final cleanup and inspection been made?
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