15 May 2001
blend has been prepared from the available materials, then samples of these materials can be
processed for used for use in the laboratory design tests as specified in CRD-C 649.
(3) Determination of optimum asphalt cement content. The optimum asphalt cement content
will be taken as the average of the asphalt contents corresponding to the mix properties in table 6-7.
The optimum asphalt cement content will be the amount of asphalt cement that will be incorporated into
the mix. The percent of cut-back asphalts and emulsified asphalts will be corrected to give a residual
asphalt content equal to the optimum asphalt content determined by the tests. Because all of the
volatiles do not evaporate, the amount of bitumen to be added as determined by this mix design
procedure should be decreased slightly. When the asphalt cement and kerosene type mix is to be used,
the desired amount of kerosene will be added to the actual paving mix in addition to the optimum asphalt
content determined from the laboratory design.
Selection of Optimum Asphalt Content
Value for Determining Optimum Asphalt Content
Unit weight of mix, pcf
Peak of curve
Voids total mix, percent
Voids filled with asphalt, percent
(4) Plant control. Plant control is discussed in chap 2.
(5) Plant operation. The plant operation varies with the type of asphalt material used in the
mix. For mixes using asphalt cement and kerosene, the kerosene and asphalt cement must be
introduced onto the aggregate at different times. Drying of the aggregate is not necessary with asphalt
emulsions, but for cut-back binders the aggregates should be heated to between 380E and 107EC (100E
and 225EF). Aggregates should not be hotter than 93EC (200EF) when mixed with cut-back asphalts or
asphalt cement and kerosene. The asphalt materials should be in the temperature ranges given in
table 6-8 when introduced into the pugmill.
(6) Plant laboratory. Use of a plant laboratory will insure that the aggregate is of the proper
gradation and that the mix contains the prescribed percentage of asphalt material. The plant laboratory
should contain the following major equipment:
-- Hand- or power-driven mechanical sieve shaker. The sieve shaker shall have a capacity of not
less than eight full-height 20 millimeter (8-inch)-diameter sieves.
-- Full-height 200 millimeter (8-inch)-diameter sieve for each of the following sieve openings:
12.7 millimeter (1/2 inch), 9.5 millimeter (3/8 inch), 4.75 millimeter (No. 4), 2.36 millimeter (No. 8),
1.18 millimeter (No. 16), 600 Fm (No. 30), 300 Fm (No. 50), 150 Fm (No. 100), and 75 Fm (No. 200).
The sieves shall have square openings and shall conform to requirements of ASTM E 11.
-- Extractor suitable for obtaining bitumen content within close tolerances.
-- Balance having a capacity of 2 kilograms and sensitive to 0.1 gram.
-- Marshall equipment for compacting and testing samples to verify mixture design.