Table 17-7.—Marshall Test Specifications and Determination of Optimum Asphalt Content5. Calculate the voids by using the adjustedspecific gravity, and apply the design criteria for thisvalue.6. Use stability and flow values as measured on thecompacted specimens.JOB-MIX FORMULA (AC MIXES)When the mix has proven itself to be satisfactory,the percentages by weight of the aggregate and theaveraged optimum bitumen content should be combinedto establish the job-mix formula. Figure 17-6A lists thefinal percentages of the aggregate for a given job mix.By plotting the test results (figs. 17-9A and 17-9B) onDD Form 1219 (fig. 17-10) and applying the Marshalltest criteria for determining optimum bitumen content,you make the determination that the mix requires4.7 percent of asphalt cement. Accordingly, theaggregates must be 95.3 percent of the total mix. Theselected blend contained 45-percent coarse aggregate(CA), 30-percent fine aggregate (FA), 20-percent fineriver bar sand (FRBS), and a 5-percent limestone dust(LSD) mineral filler. The job-mix formula is computedas follows:CA= 95.3 x .45FA= 95.3 x .30F R S= 95.3 x .20Mineral filler= 95.3 x .05Asphalt cement =Total == 4 2 . 9%= 2 8 . 6%=19.0%=4.8%95.3%4.7%100.0%MODIFIED TEST FOR COLD-MIXPAVEMENTSThis method is used as an aid in determining theasphalt content for cold-mix design of light-dutypavement. It can be used where asphalt cutbacks will be17-21
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