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.
