Fine aggregate properties vs asphalt mechanical behavior: An experimental investigation

Aggregates make up around 95% of the total mass of Hot Mix Asphalt (HMA). Therefore, aggregates quality has been recognized as a key parameter for enhancing HMA performance under traffic loadings. In particular, the Superpave-SHRP mixture design specifications recommend to investigate on the Fine Aggregate Angularity (FAA), as a function of the ESAL’s (Equivalent Single Axle Loads), in order to optimize HMA rutting potential. More specifically, the FAA value is defined as the percent air voids in a loosely compacted sample of fine aggregate: the higher the percentage of voids the more angular the fine aggregate. In addition, more angular particles in the mix result in a larger interlock between grains thus leading to higher shear strength and fatigue resistance. This paper presents the results from FAA tests performed on three different types of crushed sand. Each of them was used as fine aggregate (2,36÷0,150 mm size) for the production of three traditional HMA wearing courses. Several mechanical tests were carried out on laboratory samples to measure asphalt performance in terms of Marshall stability, Marshall stiffness and Indirect Tensile Strength. Mechanical tests were also performed on slab samples by a wheel tracker machine in order to better investigate on the relationship between fine aggregate quality and asphalt rutting resistance. Results show that fine aggregate features influence asphalt mechanical properties, confirming that higher FAA values seem to enhance asphalt rutting resistance. These findings are consistent with previous studies.