Effect of mix gradation on rutting potential of dense-graded asphalt mixtures

A study was conducted to evaluate the effect of mix gradations, both complying with and violating the Superpave restricted zone, on rutting potential of hot-mix asphalt Superpave gyratory samples of mixes with granite, limestone, and gravel aggregates were used. The following gradations were used: gradation above the restricted zone, gradation through the restricted zone in close proximity to the maximum density line, and gradation below the restricted zone. Rut tests were conducted at 64degreesC with the asphalt pavement analyzer under 689-kPa contact pressure and 45.2-kg wheel load. Rut depths were measured at the end of 8,000 cycles. Repeated shear tests at a constant height were also conducted with the Superpave shear tester. Statistical analysis of rut data generally indicates a significant difference between rut depths obtained in mixes using different aggregate types and gradations. The gradations violating the restricted zone did not necessarily give relatively higher rut depths compared with the gradations in compliance with the zone.