stockpile and 15 L 4 gal of asphalt cement.
(2) Oven dry aggregate stockpile samples and conduct a sieve
analysis (ASTM C 136) on each sample. Determine the combination
of aggregate stockpiles that results in a gradation closest to the
center of the limiting gradation band. This stockpile combination
will become the blending formula for the open-graded asphalt
concrete.
(3) Measure apparent specific gravity of aggregates (ASTM C 127
and ASTM C 128) from each stockpile used in the final gradation.
Calculate apparent specific gravity of combined aggregates using
the blending formula percentages. Measure specific gravity of
asphalt cement (ASTM D 70).
(4) Estimate the optimum asphalt content using the following
equation:
Optimum asphalt content = 8.61(0.21G + 5.4S + 7.2s + 135f)0.2 SG
where
SG = apparent specific gravity of the combined aggregates
G = percentage of material retained on the 4.75 mm No. 4 sieve
S = percentage of material passing the 4.75 mm No. 4 and retained
on the 0.6 mm No. 30 sieve
s = percentage of material passing the 0.6 mm No. 30.sieve and
retained on the 0.075 mm N0. 200 sieve
f = percentage of material passing 0.075 mm No. 200 sieve
(5) Round the calculated optimum asphalt content value to the
nearest tenth of a percent. Use this asphalt content value along
with two asphalt contents above this amount and two asphalt
contents below this amount in the production of mix design
samples. Use 0.5 percent above and below the optimum and 1.0
percent above and below the optimum as the four additional asphalt
contents. Calculate maximum theoretical specific gravities for
each of these five asphalt cement contents using ASTM D 2041.
2.6.1.2
Specimen Production
Using the five mix design asphalt contents, produce three 100 mm 4 inch
diameter Marshall specimens at each asphalt content. Use approximately 800
grams 1.8 lbs of combined aggregates following the previously determined
aggregate blending formula for each specimen. Just before mixing, the
temperature of the aggregates should be 145 5C 290 9F and the asphalt
cement should be 135 5C 275 9F. With normal mixing procedures, the
temperature of the asphalt mixture during compaction is 120 5C 250 9F.
Compact the open-graded asphalt concrete specimens with 25 blows from a
4.5 kg 10 lbs Marshall hand hammer on one side of each specimen. Allow the
specimens to air cool for a minimum of 4 hours before carefully removing
from molds.
2.6.1.3
Measuring voids total mix (VTM)
(1) Measure the VTM of each open-graded specimen using the
following formula:
SECTION 02746
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