Another way to view the issue is to ask, how sensitive are concrete and asphalt mix designs to the values of the aggre- gate specific gravity? For this analysis, an asphalt mix design
having a gradation of 50 percent passing the No. 4 sieve was considered. The standard deviation for the combined Gsb of the blend would be the average of the standard deviations from T 84 and T 85. Likewise, the acceptable range of two Gsb measurements of the combined aggregate should be within the average of the coarse and fine aggregate
D2S ranges. Therefore, a reasonable precision estimate for Gsb of the blend is (0.032 + 0.025) = 0.0285 = 0.029, which is the practically attainable limit with the current methods. The following calculation illustrates how this acceptable range would affect the calculated VMA for an example asphalt mix.
This clearly shows that VMA is very sensitive to Gsb. This also illustrates one of the serious flaws in using VMA as a mix design or acceptance criterion for asphalt paving mix- tures. The test methods for the materials are so variable that it would be easy to design or accept a mixture that appears to be satisfactory but could have too low or too high a VMA.