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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