Fatigue Characteristics of Stone Matrix Asphalt Mixes in Warm Climate

Abstract

Tropical countries like India with predominantly warm climates,  face problems of excessive rutting in flexible pavements with bituminous wearing courses. In order to provide rut resistant wearing courses, Stone Matrix Asphalt (SMA) mixes, which are basically gap graded mix, characterized by high coarse aggregates, high asphalt contents and polymer or fiber additives
as stabilizers, have been suggested. High concentration of coarse aggregate maximizes stone–to–contact and interlocking in the mix which provides strength, and the rich mortar binder provides durability. The stabilizing additives composed of cellulose fibers, mineral fibers, or polymers are added to SMA mixtures to prevent draindown from the mix. In comparison to dense graded mixtures SMA has higher proportion of coarse aggregate, lower proportion of middle size aggregate and higher proportion of mineral filler.
The present study presents the details of a laboratory study of stone mastic asphalt mixes, with emphasis on engineering characteristics under repeated load conditions. In this study, conventional binders namely locally used penetration grade bitumen 80/100 and 60/70, with locally available aggregates and cement as filler have been used. A non-conventional natural
fiber, namely coconut fiber to the extent of 0.3% by weight, have been added to the mix to act as a stabiliser. It is observed that the natural fibres improve the engineering properties of the SMA mixes considerably.