ETL 1110-1-177
31 Dec 96
s = percentage of material passing 600-m sieve and
retained on 75-m sieve
f = percentage of material passing 75-m 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.
b.
Specimen production.
Using the five mix design asphalt contents, produce three
100-mm-diameter Marshall specimens at each asphalt content. Use
approximately 800 grams of combined aggregates following the
previously determined aggregate blending formula for each
specimen. Just before mixing, the temperature of the aggregates
should be 145 + 5 oC and the asphalt cement should be 135 + 5
o
C. With normal mixing procedures, the temperature of the
asphalt mixture during compaction is 120 + 5 oC. Compact the
open-graded asphalt concrete specimens with 25 blows from a
4.5-kg 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.
c.
Measuring voids total mix (VTM).
(1) Measure the VTM of each open-graded specimen using the
following formula:
VTM = (1 - WTair/Volume * 1/SGT) * 100
where
Wtair = dry weight of specimen
Volume = B/4 D2H
D = diameter
H = height
SGT = maximum theoretical specific gravity
(2) Calculate the average VTM for each of the five asphalt
cement contents. Select the optimum asphalt content as that
B-2
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