15 May 2001
EXAMPLES OF COLD-MIX AND HOT-MIX
B-1. COLD-MIX RECYCLING PROBLEM. The middle 16 meters (50 feet) of an airfield taxiway is to be
removed to a full depth (7.5 to 1.25 centimeters, 3 to 5 inches), replaced with a recycled cold mix, and
overlaid with 7.5 centimeters (3 inches) of new hot mix. The design mix must be developed for the
recycled cold mix.
a. Step 1. Obtain samples of the in-place pavement (use jackhammer or other acceptable means).
b. Step 2. Run an extraction on the old asphalt pavement to determine the following:
(1) Asphalt content. Use the determination of the existing asphalt content as a guide to
calculate how much, if any, additional asphalt binder will be needed.
(2) Asphalt penetration. After recovering the asphalt cement perform a penetration test to
determine if the existing asphalt has become so hard and brittle that it needs rejuvenating. If possible,
avoid using a rejuvenator with recycled cold mixes. Until the rejuvenator penetrates the old asphalt, the
mix is unstable and could remain unstable for as long as 2 months. Generally, a slow-set asphalt
emulsion is preferred for cold-mix recycling.
c. Step 3. Vary the amount of asphalt emulsion added from 0 to 2.5 percent, residual asphalt, in
0.5 percent increments. This range will generally be large enough to bracket the optimum amount of
emulsion to be added. Prepare a set of three samples at each percentage of asphalt emulsion, and
compact at 75-blow compaction effort at a temperature of 121 degrees C (250 degrees F).
d. Step 4. Test the samples obtained in step 3 for stability, flow, unit weight, percent voids total
mix, and percent voids filled with asphalt. Record the test results in plots similar to those shown in
figure B-1. The plots in figure B-1 are used to determine the optimum asphalt emulsion to be added.
e. Step 5. Using figure B-1 and the procedure outlined in TM 5-822-8/ AFM 88-6, Chap. 8 (Future
AFJMAN 32-1028), and TM 5-825-2/AFJMAN 32-1014, select the preliminary optimum asphalt emulsion
to be added from table B-1.
f. Step 6. Determine the optimum water content by preparing a set of samples of various water
contents at the previously determined asphalt content (0.6 percent added asphalt emulsion held
constant) using the 75-blow compaction effort at the approximate temperature at which the reclaimed
asphalt concrete will be during construction.
g. Step 7. Using the data obtained in step 6, plot the dry density versus the water content, as
shown in figure B-2. Pick the peak of the curve to obtain the optimum water content. For the example,
the optimum water content is 2 percent.
h. Step 8. Adjust mix during laydown operations as needed.