15 May 2001
Mixing Temperatures for Asphalt Materials
Bituminous Material Type
Note: MC = medium curing; RC = rapid curing; MS = medium set; and SS = slow set.
(7) Adjusting mix proportions. Mix proportions shall be adjusted whenever tests indicate that
specified tolerances are not being met. Fully automated plants should produce consistent mixtures,
provided they are correctly calibrated and in good working condition. Improper weighing or faulty scales
may be detected readily and corrective measures taken by maintaining a close check or load weights.
The total weight of each load of mixture produced shall not vary more than plus or minus 2 percent from
the total of the batch weights dumped into the truck. Figure 2-15 presents other probable causes of
paving-mixture deficiencies due to improper plant operations.
e. Preparation of construction specifications.
(1) Specifications. Cold-laid asphalt mixtures will be produced according to provisions of guide
specifications except when small quantities of mix, less than 100 metric tons, may be necessary for
limited use in repairs. In these cases, the procedures specified in the guide specification would not be
economical. When such an exception is deemed necessary, locally available cold-laid bituminous mix
produced according to local state highway department specifications may be used when approved by
the Division Engineer. When the quality exceeds 100 metric tons for Army projects, approval from the
USACE Transportation Systems Center (CENWO-ED-TX) will be required. A copy of the specification or
proper reference thereto and information regarding traffic conditions and facilities to be paved will
accompany the request for approval.
(2) Placing. Although closer control of layer thickness and better prevention of segregation of
the mix can be achieved with a mechanical spreader, a motor grader is sometimes desirable for
spreading plant-mix cold-laid pavements. Aeration of the mix to remove some of the volatile material is
often necessary to bring the mix to the proper condition for compaction. A motor grader can aerate the
mix by balding it back and forth across the roadbed.
(3) Compaction of mixture. At the time of compaction, the asphalt material in the mixture must
provide a proper amount of cohesion, so that the desired density can be reached. Cohesion of the
mixture will be controlled by the type of asphalt material, volatile content, and temperature of the
mixture. Low cohesion will cause the mix to be unstable under the roller, while high cohesion will cause