Compaction Effort Evaluation of Crumb Rubber Modified Hot Mix Asphalt

Abstract

The primary goal of this study was to obtain the same performance from an asphalt mixture made using a Marshall impact hammer (MIH) as from asphalt made using a Superpave gyratory compactor (SGC). This was due to the expense of Superpave equipment compared with Marshall equipment. A wet process was used to blend the CR with PG 70-16 asphalt. A crushed stone aggregate was used with a 19 mm nominal maximum aggregate size, and the samples were prepared using an SGC and an MIH. The results show that nine percent CR was determined to be the optimum crumb-rubber content (OCRC). In addition, the SGC provided excellent performance in Marshall stability, density, tensile strength, and compressive strength at different numbers of blows and gyrations compared with the MIH. Moreover, the MIH required approximately 21, 21, 18, and 24 extra blows to obtain the same stability, density, tensile strength, and compressive strength, respectively, as the SGC at the design number of gyrations (Ndesign). Furthermore, modified mixtures at the OCRC increased the compressive strength in the range from 16 to 48 percent and had higher values on the index of retained strength than unmodified mixtures. As a result, they provided mixtures with less susceptibility to moisture damage. The significance of this study is that asphalt that performed the same as Superpave samples was obtained using only Marshall equipment.