15 May 2001
asphalt emulsion, can also be used as a base course for high-quality pavements. The material can be
mixed in place or removed and plant-mixed to produce a satisfactory base course. For high-quality
airfield pavements, this base course should be overlaid with the minimum amount of asphalt concrete
mixture required by design. The hot mix and cold mix prepared from materials obtained by milling are
discussed later in this chapter.
(5) Gradation. The gradation of the milled material obtained from the milling operation is
important when the material is to be used to produce recycled cold or hot mixes.
(a) When the material is to be used in a recycled cold mix, the maximum size of the milled
conglomeration of aggregate and asphalt, should not exceed 38 millimeters (1-1/2 inches). However, a
small amount of material larger than 38 millimeters (1-1/2 inches) is acceptable if it can be removed by
screening prior to mixing. Generally, the milled material, without additional virgin aggregates, is used to
produce recycled cold mix.
(b) When the milled material is to be used in recycled hot mix, the gradation of the milled
material after extraction of the asphalt cement is important. Very little breakdown of the aggregate
should occur during the milling operation. It is important that the maximum size of the material as milled
does not exceed 38 to 50 millimeters (1-1/2 to 2 inches) to ensure that it will break up and satisfactorily
mix with the new materials in the production of recycled hot mix. Some filler material passing the 75 Fm
(No. 200) sieve will be manufactured during the milling operation. Depending on the aggregate type,
1 to 3 percent additional filler may be manufactured. One of the problems in designing a recycled
mixture is not to exceed the maximum amount of filler allowed. Generally, new aggregates that are to
be added to a recycled mixture are required to have little or no filler. Therefore, washing of new
aggregate is often required to remove the filler prior to producing the recycled mixture.
(6) Base course. When the asphalt pavement material is to be removed down to the base
course, care should be taken to prevent damage to the base course. Any damage to the base course
should be corrected prior to placing the recycled mixture. Generally, approximately 1.5 centimeters
(1/2 inch) of asphalt mixture should be left in place to prevent damage to the base course by the milling
equipment or by rain.
3. RECYCLED COLD-MIX ASPHALT.
a. General. When a pavement has deteriorated to a point that the thickness of a conventional
overlay required to satisfactorily provide a solution to the problem is not economical or is prohibited by
existing grades, the use of recycled cold mix should be considered. A recycled cold mix involves the
reuse of the existing pavement structure by reprocessing it and adding an asphalt binder to it without the
use of heat. Recycled cold mix in conjunction with a hot mix overlay can often be used to repair an
existing pavement at lower cost than with a conventional overlay. The basic process is shown on the
flow chart in figure 7-2.
b. Equipment. The equipment required for pavement removal and crushing is either conventional
equipment for ripping or scarifying and crushing or a cold-milling machine. For mixing and placing, a
rotary mixer and grader, a mix-in-place travel plant, or a central plant and a conventional paver are
required. The required equipment includes a distributor, trucks, brooms, rollers, and front-end loaders.
c. Pavement design. The structural design of pavements using recycled cold-mix asphalt should be
the same as that for the asphalt-stabilized materials as provided in TM 5-825-2/AFJMAN 32-1014. The
recycled cold-mix should provide a structure whose performance is equal to that of the asphalt-stabilized
material. Mixture design for recycled cold-mix asphalt concrete is important to ensure proper material
proportions and to obtain maximum field density. When no new aggregates are to be added to the