15 May 2001
(1) Cold milling. When a cold-milling machine is used, the existing asphalt pavement can be
removed to any desired depth. Generally, the particle size of the removed material is satisfactory for
recycling, and no further crushing is necessary.
(2) Ripping. The last procedure for loosening the pavement involves using a ripper tooth or
sacrificer to loosen the asphalt mixture. When a ripper tooth is used, the asphalt mixture is removed full
depth since there is no way to control the depth of material loosened. When the asphalt concrete is
removed by ripping, it must be further broken down by crushing in place with a pulverizer or other
equipment or be carried to a crusher. When this method is used, a significant amount of base repair will
be required. While the old pavement is being removed, consideration should be given to drainage of the
area to prevent unnecessary delays caused by rain. The exposed surface should be sloped to promote
good drainage, and outlets or other means should be provided to prevent the ponding of water.
(3) Pulverizing. Another procedure for loosening the pavement is to pulverize it in place,
generally with a rotary mixer. This piece of equipment can reduce the pavement into nearly individual
aggregate size particles. Additional passes can be used to reduce the particle sizes down to the
individual aggregates as required. This procedure can be very effective except on thicker asphalt
sections where ripping or scarifying the surface may be most effective.
f. Construction. After the asphalt mixture has been broken down to the desired particle size, it can
be mixed with asphalt or other additives and water at a central plant or in place. Any procedure should
be acceptable as long as the contractor can demonstrate that material meeting the specification
requirements can be produced. Construction should not continue during rainfall or when rain is
expected. The ambient temperature should be at least 10EC (50EF) and freezing temperatures should
not be expected for at least 5 days. Generally the warmer the weather the better will be the final
properties of the cold recycled mixture.
(1) Mixing. The in-place mixture produced by a rotary mixer or a traveling plant is less
expensive than the mixture produced at a central plant, but control of the quality is not as good. To meet
the specification requirements, the contractor must be able to control the amount of additional asphalt,
additives, and water as well as the mixing time.
(a) Central plants. Central plants generally consist of a mixer, asphalt cement and additives
storage, a water supply, and a system of cold feeds for RAP and new aggregates (if required). The
mixer may be either a batch, drum, or continuous type with suitable equipment for feeding the asphalt,
additives, water, and aggregate as required. Continuous mix plants are most commonly used for cold-
mix recycling. Existing hot-mix asphalt plants can usually be adapted to produce cold-mix recycled
material. Mixing times for cold-mix recycling are usually shorter than those for hot-mix. Mixing time and
procedures should achieve a uniform dispersion of the binder and complete coating of fine aggregate.
The coarse aggregate may not be completely coated; however, additional coating and mixing will occur
during transit and placement. These blades not only loosen or pulverize the pavement to the required
particle size but they also mix the asphalt and water into the reclaimed material. The rotary mixers may
have their own spray apparatus in the chamber or the asphalt and water may be applied ahead of it by a
distributor. Even when all materials are added during the initial break up pass, additional passes are
usually made to assure desired sizing and complete mixing. Travel plant mixers are usually self-
propelled pugmill plants that mix the loosened and sized reclaimed material with asphalt and water at a
prescribed rate. They may discharge the mix into a windrow or the mixture may be placed with a screed
that is attached to the back of the travel plant mixer.
(b) In-place mixing. In-place mixing may be accomplished by graders, rotary (pulverize)
mixers, or travel plant mixers. Mixing with graders is requires that the pavement be properly sized and
loosened to the required depth prior to mixing. Water and asphalt are usually added with a distributor