TM 5-822-10/AFM 88-6, Chap. 6
After the asphalt concrete has been broken down to the desired particle size, it can be mixed with asphalt or other
stabilizers and water in place or at a central plant. The in-place mixture produced by a travel plant is less expensive than
the mixture produced at a central plant, but control of the quality is not as good. Either type of plant should be acceptable
as long as the contractor can demonstrate that material meeting the specification requirements can be produced. To meet
the specification requirements, the contractor must be able to control the amount of additional asphalt and water as well
as the mixing time.
a. Recycled cold mix. The recycled cold mix should be placed to the desired grade and compacted to meet the
minimum density requirements. The layer thickness should not be less than 2 inches compacted nor greater than 4 inches
compacted. In order to ensure that satisfactory density is obtained, a vibratory roller and a pneumatic- tired roller should
be available. The pneumatic-tired roller should weigh at least 20 tons and be capable of tire inflation pressures of at least
90 pounds per square inch.
b. Density. Since it is difficult to establish a laboratory density for comparison with field density, the theoretical
maximum density (TMD) should be used to establish field density requirements. The theoretical maximum density is that
density at which there would be zero air voids in the mixture. At least 86 percent of the theoretical maximum density
should be obtained in the field to ensure that the voids in the field mixture are not excessive.
c. Cure time. Each layer of recycled cold mix should be allowed time to cure prior to being overlaid. The time
needed to cure depends on many things such as air temperature, wind, type of asphalt used, layer thickness, and humidity,
but as a general rule each layer of recycled cold mix should be allowed to cure for 10 days before being overlaid.
Field density measurements.
The field density should be determined from cores removed from the in-place pavement. With some mixes it will be
difficult to obtain undamaged cores prior to curing the cold mix for a few days. When cores cannot be obtained within 24
hours of paving, other methods of obtaining samples should be considered. For example, ice placed on the sample
locations for 1 to 2 hours prior to coring samples will cool the material and reduce damage caused by heat developed
during the coring operation. Another approach is to use a concrete saw to cut small cubes from the pavement. Nuclear
density gages can be used to obtain an indication of density, but actual samples should be taken to determine acceptability
of the density of the in-place mixture.