TM 5-822-10/AFM 88-6, Chap. 6
The equipment required for pavement removal and crushing is either conventional equipment for ripping and crushing
or a cold-milling machine. For mixing and placing, 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.
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/AFM 88-6, chapter 2. 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 reclaimed materials, the mix design should be performed on the reclaimed materials as recovered.
The maximum-size particles of the reclaimed asphalt concrete should not exceed the requirement, which is usually 1.5
inches. When new aggregates are to be added, the design should be performed on the desired mix of reclaimed aggregate
and new aggregate.
Development of the mix design accomplishes two objectives: (a) determines the amount of new binder and rejuvenator
required to obtain a durable and stable mixture, and (b) fixes the amount of moisture needed to provide maximum density.
a. Rejuvenator. A rejuvenator can be used in place of new asphalt in some instances to improve the old asphalt
properties. A thorough blending of the rejuvenator and oxidized asphalt does not immediately occur when mixing the
recycled cold mix. In fact, the rejuvenator initially coats the old asphalt and with time, probably months, will penetrate
the old asphalt binder and produce an improved binder. During the first few months, the recycled cold mix may be unstable
because of the film of rejuvenator around the oxidized asphalt and aggregate. After the rejuvenator penetrates the old
asphalt and the binder material becomes more homogeneous, the recycled cold mix should perform satisfactorily. Because
of the initial instability and increased costs created by rejuvenators, asphalt emulsions are usually used in recycled cold
b. Asphalt content. The amount of new asphalt needed in the recycled cold mix should be determined by conducting
a conventional hot-mix design on the recovered aggregate. The laboratory density obtained in the hot-mix design is
approximately equal to the maximum density that will be obtained in the field under traffic. The amount of asphalt added
should be varied by 0.5 percent increments from 0 percent to the high side of optimum asphalt content. The samples
should be compacted by the required effort, either 50 blows for low-pressure tires or 75 blows for high-pressure tires, and
determinations should be made for density, stability, flow, voids total mixture, and voids filled with asphalt. These
determinations should be plotted and curves drawn to select the optimum asphalt content. The optimum additional asphalt
will often be between 0 and 1 percent. When the optimum additional asphalt to be selected is 0 percent, no additional
asphalt should be added since it may cause the mixture to become unstable. When no asphalt is needed, only water should
be added to lubricate the mixture so that the needed density can be obtained in the field.
c. Compacted samples. After the optimum asphalt content has been determined, samples should be made at the
optimum asphalt content with varied water contents. These samples should then be compacted at room temperature using
the same compaction effort as that used to determine optimum asphalt content. Next, the dry density for each of the
compacted samples should be determined, a moisture/density curve should be plotted, and the moisture content that
provides maximum dry density should be selected as the optimum moisture content. A design example is given in
Removal of in-place material.
The material to be used in the recycled cold mix can be removed from the in-place pavement by a number of methods.
Two of the more common methods are identified. As discussed in paragraph 2-5, milling machines can be used to remove
existing materials. When a 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, and no further crushing is necessary. Another procedure
for removing the pavement involves using a ripper tooth to remove the asphalt concrete (fig 3-2). When a ripper tooth
is used, the asphalt concrete is removed full depth since there is no way to control the depth of material removed. When