For hot-mix, hot-laid asphaltic concrete mixtures, if the asphaltic content is specified as 5 to 7 percent, how is the optimum percentage determined?
What will be an ideal response?
To determine the optimum asphalt content, each potential mix would be
evaluated. Mixes created with asphalt contents of 5%, 5.5%, 6%, 6.5%, and 7%
would be developed. For these mixes, test results would be used to plot curves for
each of the following five variables as function of the range of asphalt content
values used in the test mixes: Marshall stability, flow, voids in mineral
aggregates, voids filled with asphalt, and percent air voids in the compacted
mixture. Curves, such as those shown in Figure 18.13, could then be developed by
plotting these values are also against the corresponding asphalt percentages. The
five plots are now used to determine the optimum asphalt percentage. A suitable
starting point would be to identify the asphalt content that would result in 4% air
voids. While this value of asphalt content may represent that optimal asphalt
content value when examining the other four curves, if would result in a mix that
meets the criteria in Table 18.7, then this design would be acceptable. If all of the
criteria in Table 18.7 are not met using the asphalt content value associated with
4% air voids, then adjustments to asphalt content can be made in attempt to meet
these criteria.
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