more than 160 degrees C 325 degrees F when added to the aggregates.
Performance Graded (PG) asphalts shall be within the temperature range of
[_____] to [_____] degrees C F when added to the aggregates.
3.2
PREPARATION OF MINERAL AGGREGATE
The aggregate for the mixture shall be heated and dried prior to mixing.
No damage shall occur to the aggregates due to the maximum temperature and
rate of heating used. The temperature of the aggregate and mineral filler
shall not exceed 175 degrees C 350 degrees F when the asphalt cement is
added. The temperature shall not be lower than is required to obtain
complete coating and uniform distribution on the aggregate particles and to
provide a mixture of satisfactory workability.
3.3
PREPARATION OF HOT-MIX ASPHALT MIXTURE
The aggregates and the asphalt cement shall be weighed or metered and
introduced into the mixer in the amount specified by the JMF. The combined
materials shall be mixed until the aggregate obtains a uniform coating of
asphalt binder and is thoroughly distributed throughout the mixture. Wet
mixing time shall be the shortest time that will produce a satisfactory
mixture, but no less than 25 seconds for batch plants. The wet mixing time
for all plants shall be established by the Contractor, based on the
procedure for determining the percentage of coated particles described in
ASTM D 2489, for each individual plant and for each type of aggregate used.
The wet mixing time will be set to at least achieve 95 percent of coated
particles. The moisture content of all hot-mix asphalt upon discharge from
the plant shall not exceed 0.5 percent by total weight of mixture as
measured by ASTM D 1461.
3.4
PREPARATION OF THE UNDERLYING SURFACE
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NOTE: If the underlying surface to be paved is an
unbound granular layer, a prime coat should be
applied, especially if this layer will be exposed to
weather for an extended period of time prior to
covering with an asphalt mixture. Benefits derived
from a prime coat include an additional
weatherproofing of the base, improving the bond
between the base and HMA layer, and preventing the
base from shifting under construction equipment. If
the prime coat requirement is not a separate pay
item and is waived from this contract, an adjustment
to the contract price should be made. Environmental
laws in certain states may not allow prime coats to
be applied.
If the underlying surface to be paved is an existing
asphalt or concrete layer, a tack coat should always
be used to ensure an adequate bond between layers.
Tack and prime coat requirements will need to be
covered in the contract documents.
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Immediately before placing the hot mix asphalt, the underlying course shall
be cleaned of dust and debris. A [prime coat] [and/or] [tack coat] shall
be applied in accordance with the contract specifications.
SECTION 02749
Page 20
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