The Criticality of Sieve Size in Asphaltic Concrete Mixes as Measured by Volumetric Properties and Stabilities

About the report:

The purpose of this study was to investigate the effects of deviations from the specified aggregate gradation on the stability and volumetric properties of the S-5 mix. The project involved two phases of experimental work. The first phase consisted of designing a control mix to be used as a standard for comparison with the experimental mixes. The median S-5 specifications were used and an optimum asphalt content of 5.6% was determined through the Marshall design procedure. The second phase involved the molding and testing of specimens using aggregate gradations that varied systematically from the median S-5 gradation but had the same asphalt content as the control mix (5.6%). The results showed that the six sieve sizes in the S-5 gradation could be classified into three groups according to their effects on the stability and volumetric properties of the mix. The coarse sieves (3/8", #4 and #8) displayed similar curves, the #30 appeared to be a transition size, and the fine sieves (#50 and #200) showed characteristics which were generally opposite those of the coarse sieves. The #30 sieve was the most critical size with regard to stability. Another finding was that although the S-5 specifications do not place direct bounds on the volumetric properties of a mix, the gradation requirements seemed to provide fairly consistent control of them.

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