Table 17-7.—Marshall Test Specifications and Determination of Optimum Asphalt Content
5. Calculate the voids by using the adjusted
specific gravity, and apply the design criteria for this
value.
6. Use stability and flow values as measured on the
compacted specimens.
JOB-MIX FORMULA (AC MIXES)
When the mix has proven itself to be satisfactory,
the percentages by weight of the aggregate and the
averaged optimum bitumen content should be combined
to establish the job-mix formula. Figure 17-6A lists the
final percentages of the aggregate for a given job mix.
By plotting the test results (figs. 17-9A and 17-9B) on
DD Form 1219 (fig. 17-10) and applying the Marshall
test criteria for determining optimum bitumen content,
you make the determination that the mix requires
4.7 percent of asphalt cement. Accordingly, the
aggregates must be 95.3 percent of the total mix. The
selected blend contained 45-percent coarse aggregate
(CA), 30-percent fine aggregate (FA), 20-percent fine
river bar sand (FRBS), and a 5-percent limestone dust
(LSD) mineral filler. The job-mix formula is computed
as follows:
CA
= 95.3 x .45
FA
= 95.3 x .30
F R S
= 95.3 x .20
Mineral filler
= 95.3 x .05
Asphalt cement =
Total =
= 4 2 . 9%
= 2 8 . 6%
=
19.0%
=
4.8%
95.3%
4.7%
100.0%
MODIFIED TEST FOR COLD-MIX
PAVEMENTS
This method is used as an aid in determining the
asphalt content for cold-mix design of light-duty
pavement. It can be used where asphalt cutbacks will be
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