EFFECT OF AGGREGATE GRADATION VARIATION ON ASPHALT CONCRETE MIX PROPERTIES

Six asphalt concrete mixes were tested to investigate the effects of variation in the aggregate gradation on mix properties. The asphalt contents of the mixes were maintained at the job mix design contents. The gradation variations were representative of typical construction extremes. Five gradations were tested from each mix: (a) the job mix formula (JMF) gradation, (b) a fine gradation, (c) a coarse gradation, (d) a coarse-fine gradation, and (e) a fine-coarse gradation. The fine and coarse gradations deviated from the JMF gradation by the maximum amount to the fine or coarse side. The fine-coarse and coarse-fine gradations crossed over the JMF gradation curve from the maximum fine (or coarse) amount on the largest size fraction to the maximum coarse (or fine) amount on the smallest size fraction. Properties investigated were creep stiffness, split tensile strength, resilient modulus, Marshall stability, Marshall flow, air voids, and voids in mineral aggregate. Analysis of the data revealed that the fine-coarse and coarse-fine gradation variations had the greatest impact on mix properties but that none of the variations had a significant effect on resilient modulus. The data also showed that within the range normally encountered, air void content had a greater impact on split tensile strength than did gradation variation.