Laboratory characterization of compaction and damping properties of Stone Matrix Asphalt

Abstract

Stone Matrix Asphalt (SMA) is referred to gap graded Hot Mix Asphalt (HMA) that is designed to maximize rutting resistance and durability by using a structural basis of stone-on-stone contact. SMA mixture designs with gap graded aggregate gradations and polymer modified binders often have special field compaction requirements. To better understand differences in compaction behavior between SMA and dense graded HMA mixtures, laboratory tests were conducted on field collected loose samples at typical field densities and loading conditions. The goal of the first phase of this study was to investigate the growth of density and the mobilized shear stress in the specimen as a function of applied normal stress, gyration numbers, and the compactive effort. In the second phase, damping ratio tests were performed on the compacted samples at close to field compaction temperatures by applying dynamic loading at various frequencies and different confining pressures to determine the mixture damping properties. The test results indicated that SMA mixtures with the gap graded aggregate structure achieved higher densities in comparison to HMA mixtures. The frequency of dynamic loading had a significant effect on the damping ratios of the SMA mixtures and the effect of confining pressure, linked to proper lift thicknesses in the field, was found to be dependent on compaction pressure levels as well as mixture properties.