15 May 2001
mixture is to be used. Penetration is used because of the relative ease of use in a field laboratory.
Viscosity or performance graded binder properties can also be used, provided the necessary testing is
accomplished to produce an asphalt mixture with binder properties approaching those of new in-place
hot-mix asphalt pavement. The amount of recycling agent should be selected so that the recovered
asphalt penetration meets the desired limits. It is important that the penetration of the recovered asphalt
be measured during plant production and that adjustments be made if necessary to ensure proper
asphalt consistency. Paragraph B-2 in appendix B gives a design example of a hot-mix design for a
recycled asphalt pavement. The JMF supplied by the contractor should contain all the information given
for hot-mix asphalt in Chapter 2. This information should also include the properties of the asphalt and
aggregate in the RAP.
g. Production of recycling hot-mix. Most recycled asphalt concrete is produced with a drum mixer
designed or modified to produce recycled mixtures. Modified batch plants have also been used
successfully to produce recycled hot mix.
(1) Drum mixer. When a drum mixer is used for recycling, the new aggregate is added at the
high side of the drum near the flame. The aggregate absorbs much of the heat from the burner and acts
as a shield to protect the reclaimed asphalt concrete, new asphalt binder, and recycling agent. The
reclaimed asphalt concrete is added to the drum near the midpoint followed by the recycling agent and
new asphalt. The flights inside the drum should be in good condition so that the veil of new aggregate
will properly protect the asphalt materials from heat damage. The final recycled mixture is generally
heated to between 125 and 145 degrees C (260 and 290 degrees F) to produce a mixture that can be
compacted to meet density requirements. Air pollution is sometimes a problem, but generally the mix
design can be modified by lowering the percent of reclaimed asphalt pavement to bring the emissions
within an acceptable range.
(2) Batch plant. Batch plants have been modified for the production of recycled mixtures. The
modification consists of adding a feeder and conveyor to carry the reclaimed asphalt pavement directly
to the weigh bucket. The new aggregate that passes through the dryer is usually superheated to
between 260 and 315 degrees C (500 and 600 degrees F) so that when the materials are blended, the
resulting temperature is suitable for mixing and compaction. An increase in the amount of reclaimed
asphalt concrete used in the mix would require an increase in the new aggregate temperature. Also,
additional moisture in the new aggregate or reclaimed asphalt pavement stockpiles will require
additional heat. Therefore, to save energy both stockpiles should be kept as dry as possible.
(3) Stockpiling. Prior to production of recycled asphalt concrete, the stockpile of reclaimed
materials should be inspected to ensure that no significant segregation of material exists. Many
pavements have been patched during their lives, causing variation in the type of materials at various
locations in the pavements. Therefore, the materials should be removed from the pavement and
stockpiled in such a way as to ensure proper mixing of these localized material with the other reclaimed
materials. When the asphalt pavement is removed in two lifts, the properties of the material in the top lift
will probably vary from the properties of the materials in the bottom lift. In this case, the materials should
be stockpiled separately, or some acceptable procedure for blending these materials must be used.
(4) Cold feeds. In order to remove all material larger than 50 millimeters (2 inches), a screen
should be placed over the bin or cold feeder from which the reclaimed materials will be fed to the plant.
When conglomerations of asphalt and aggregate exceed this size, they will not break down enough in
the asphalt plant to produce a homogeneous mixture. Consequently, these oversize pieces may cause
problems with pulling and tearing of the mat during lay-down operation.
(5) Control testing. During production of recycled asphalt concrete, a number of tests must be
conducted to ensure that a satisfactory product is produced. The tests used to evaluate recycled