TM 5-6635-386-12&P
Use this to good advantage by extending the use of the
tester to become a good AC content tester for field use.
Some additional hardware is required
a.
Metal pan, approximately 16" x 16" x 4".
b.
Compaction plate...5" x 5" x 1/2" with a rod
welded to it and a sliding weight to slide on the rod and
permit a controlled compaction effort on the plate.
c.
Accurate scale to approximately 30 pounds.
d.
Straight edge and a finely graduated metal ruler.
.. C-clamp to clamp the ruler to the straight edge. The
straight edge should be approximately twice as long as
the pan’s longest dimension.
Procedure
Establish an initial calibration curve in the laboratory.
After that, the same procedure is used in the field to
establish the desired asphalt content value.
Prepare a sample of asphaltic concrete at a specific
weight each time. This weight will be selected at the
outset and will be used for the initial calibration as well as
for all subsequent field tests.
This weight should be approximately 95% of optimum for
the typical asphalt weights used in the user’s locale.
Round it off to a practical value for ease of preparation
and calculations.
Initially prepare a sample at a known density, evenly
compacted in the pan in one inch thick layers.
Thereafter prepare the sample in the same one inch
layers for all field work using the same technique exactly.
a.
Measure the pan and determine precisely the
volume in each inch for the bottom three inches. The
fourth inch will merely become a catch basin for the light
material that is compacted into the third inch.
If a 16" square pan was used, then each inch would
hold precisely 0.1481 cubic feet.
Establish a density to be compacted in the pan
each time. . this is 135 pounds/cubic feet, a value that
is about 95% of optimum for the region that is going to
use this test. It will vary, of course, for different parts of
the world.
If the desired density is 135 PCF, and if each inch in
the pan represents 0.1481 cubic feet then a one inch
layer compacted to 135 PCF would actually weigh 19.99
pounds.
135 PCF x 0.1481 CF = 19.993 pounds.
b.
Measure out exactly 19.99 pounds of hot AC mix
and dump this into the pan.
Spread it around evenly and then compact it down to
a depth of exactly one inch.
A 1/16th inch error in height is equal to a 6% error in
final compaction. . an error of 8.1 PCF, something not
accepted or calibration work.
c.
Compact a second and third lift in the same
manner.
Weigh the final pan of material and it should weigh
exactly 3 x 19.99 = 59.97 pounds plus tare.
d.
Set the pan atop the tester shipping case in the
same manner as you would take a standard count.
Remove the reference standard from the case.
e.
Take several tester moisture readings on the
compacted surface, revolving the tester 900 each time.
Record the readings.
f.
Run an extraction of a sample of the compacted
material to determine asphalt content.
g.
Plot the tester reading (in ratio) on the vertical
axis of a calibration sheet similar to that used fur the
CPN moisture curve, and plot the asphalt content
PERCENTAGE across the bottom.
This curve is now an accurate asphalt content curve.
Zero is obtained by compacting a
bone
dry
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