Influence of the Aggregate Gradation on the Rutting Resistance of Bituminous Mixtures

Rutting in bituminous pavements predominantly depends on the aggregate gradation. In particular, for fine graded mixtures, the aggregate gradation below 2.36 mm play a critical role since more than 60% of aggregates will pass through this sieve. The present work is focused on quantifying the rut resistance of three different fine aggregate gradations. The control gradation is the well-graded gradation used in India, and the other two gradations were obtained following Bailey method. The Bailey gradations were designed in such a way that the gradation below 2.36 mm sieve size was varied while the gradation above this sieve size was kept the same as that of the control gradation. The mixtures were fabricated using an unmodified binder (binder content kept constant at 5.4%) at 6% air voids using a shear box compactor. The influence of aggregate gradation on the creep and recovery response of bituminous mixtures was investigated at two temperatures by applying 10,000 repetitions of a repeated trapezoidal loading and recovery cycles. From the resulting residual strain curve, the Bailey mixture designed towards the coarser side below 2.36 mm sieve was found to have a higher resistance to rutting when compared to the conventional bituminous concrete-middle gradation.