Evaluation of the effect of superpave aggregate gradations on marshall mix design parameters of wearing course

Abstract

The purpose of this study was to evaluate the effect of the Superpave specified aggregate gradation on Marshall mix design parameters. Twenty eight (28) asphalt concrete mixtures were prepared in three types of gradations such that the gradations were above, through and below the Superpave restricted zone. Samples were prepared for Marshal mix design and tested in the laboratory to evaluate the Marshall stability, flow and volumetric properties. Statistical analysis showed that all three types of mixtures, above, through and below the restricted zone, did not have any significant difference on Marshall stability and void in mineral aggregate (VMA). The mixtures with gradation passing below the restricted zone showed higher air voids (Va ) and lower flow values than gradation passing above and through the restricted zone. The results indicated that Superpave specified aggregate gradation could be used as a guide to select aggregate gradations for wearing courses. Aggregate gradation below the restricted zone requires 0.5 % less bitumen than typical mix designs and has a lower binder tolerance limit. Keywords: Aggregate gradation, Marshall parameters, restricted zone, Superpave gradation, wearing course.