15 May 2001
a. General. The recycling of pavement materials has proven to be an economical and feasible
process to rehabilitate worn-out pavements. The use of recycled mixtures for surface courses is not
recommended by either the Army or the Air Force. If an exception to this policy is required, the
Air Force base should contact their MAJCOM pavements engineer and the Army designer should
contact the USACE Transportation Systems Center (TSMCX). Recycling should always be
considered when repairing or rehabilitating existing pavement. The use of recycled materials in
pavement maintenance and rehabilitation has increased for the following reasons:
(1) Environment. The reconstruction of old pavements without recycling often consists of
removing, stockpiling, or disposing of all pavement materials. Recycling of these pavement materials
reuses an available material resource and eliminates the disposal problem.
(2) Material cost. In the last several decades it has been recognized that there is not an
unlimited supply of natural materials. The amount of asphalt and high-quality aggregate available for
construction is limited. This fact, along with economic realities have caused a substantial increase in the
cost of pavement materials and have encouraged the use of recycled materials. Increasing costs of fuel
and equipment have encouraged recycling, especially as haul distances become longer.
(3) Technology and equipment. Increased interest in recycling pavements has brought about
the development of technology and equipment for recycling that can generate an overall reduction in
cost when compared to using new materials. There still exist technical limitations that prevent the
complete recycling of existing pavements into new pavements.
b. Recycling methods. Asphalt pavement recycling methods can be divided into the following three
categories: surface recycling, cold-mix recycling, and hot-mix recycling. Table 7-1 lists the advantages
and disadvantages of the various methods. Many types of distresses can be corrected by one of the
pavement recycling methods identified in table 7-2.
(1) Surface recycling. Hot in-place recycling, rejuvenating, and cold milling are methods of
surface recycling that are used to increase skid resistance, decrease permeability to air and water, and
improve properties of the asphalt binder. Depending on the process used, surface recycling may modify
the top 5 to 40 millimeters (1/4 to 1-1/2 inches) of pavement. However, surface recycling does not
increase the structural strength of the pavement. The existing condition of the pavement surface will
control in the decision whether or not to recycle. The costs involved in the hot in-place recycling of a
pavement to a depth of 25 millimeters (1 inch) will approach the cost of a 25 millimeter (1 inch) overlay.
The existing pavement surface condition will need to be considered when judging the benefits of the
additional 1 inch of overlay versus the benefits obtained from hot in-place recycling.
(2) Cold-mix recycling. Cold-mix recycling is a process which reclaims most or all of the
existing asphalt pavement by breaking it to a maximum particle size of 25 to 40 millimeters (1 to
1-1/2 inches), mixing it with virgin materials, if needed, and reusing the mixture as a pavement material.
Cold recycling material can be used to surface secondary roads, if a seal coat is applied, and as a base
course for high-quality pavements.