Lesson 5/Learning Event 1
FIGURE 16
FIGURE 17
Step 2
Percentage asphalt content for the properties are then tabulated:
Peak of Stability
4.3%
Peak of Unit-Weight
4.5%
4% Voids in Total Mix
5.0%
75% Total Voids Filled with AC
4.9%
and an average of the four obtained: 18.7% 4 = 4.7. ( Trial optimum asphalt content).
Step 3
In this step you check the trial OAC value to see that the criteria given in column 3 of Table 9
are met. This is done by entering all five of the curves at the Trial OAC, 4.7 percent, and
drawing vertical lines up to intersect the curves.
Stability. Entering this curve at 4.7 percent, the value of stability is read at approximately 2000
pounds, which meets the requirement of 1800 pounds or higher as given in column 3 of Table 9.
Unit Weight. Table 9 indicates there is no definite criteria for the unit weight. This is because
various types of aggregate would give various unit weights in the compacted mix. However, the
unit weight is used as a factor in the determination of the optimum asphalt content. In this case,
on entering the unit weight curve, the unit weight at 4.7 percent (OAC) is 151.35 pounds per
cubic foot. On a contract job, this should be determined with great care as the contractor will be
held to a certain percentage of this value as the required density in the final compacted
pavement.
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