Evaluation of the performance of aggregate in hot-mix asphalt

Abstract

Paper presented at the 33rd Annual Southern African Transport Conference 7-10 July 2014 "Leading Transport into the Future", CSIR International Convention Centre, Pretoria, South Africa.

The overall performance of an asphalt mix is dependent on, amongst others, the properties of the constituent materials, which include aggregate, binder and filler. The aggregate for production of asphalt mixes is usually sourced from a quarry, which is established through a long and expensive process. A quick evaluation of a new aggregate source will give some indication of its future performance as well as facilitate its introduction into the market place. This paper presents a study of the comparative performance of two aggregates; a granite aggregate of known good performance and a relatively unknown quartzite aggregate containing up to 30% shale. The basic properties of the quartzite aggregate were assessed; following which, the performance of the aggregate in an asphalt mix was evaluated. The design grading of the asphalt mixes was similar; the only difference being that the coarse granite fractions (6.7 and 9.5 mm) of the asphalt mix of known good field performance were replaced by coarse quartzite fractions. The same binder type and crusher sand was used in both asphalt mixes, allowing for a comparative evaluation of the mixes in the laboratory. The asphalt performance-related tests conducted on the mixes included Repeated Simple Shear Test at Constant Height (rutting indicator), beam fatigue test (cracking indicator), dynamic modulus (stiffness indicator) and modified Lottman test (durability indicator). The test results were analysed statistically, to establish whether the performance of the asphalt mixes differed.