Compaction of Granular Soils Using Superpave Gyratory Compactor at Higher Confining Pressures

Post construction densification of subbase material underneath flexible asphalt surfaces is believed to lead to the failure of pavements. The compaction characteristics for granular soils have been tested for decades using standard ASTM testing methods such as the Modified Proctor test. In an attempt to find an acceptable alternative testing method, base and subbase materials were tested using the Superpave Gyratory Compactor (SGC). The Modified Proctor test is the current standard method for determining the optimal moisture content (OMC) and maximum dry density of soils. However, only vertical work is done on the soil sample with this method. When the SGC is used to compact granular soils, vertical work is complemented by shear work applied to the soil sample due to the gyration angle. Effects of the combination of vertical and shear work on final density were examined analytically by observing compaction curves and final densities. The confining pressure and number of gyrations were the varied parameters. Densities achieved with the SGC were compared to the densities found using the Modified Proctor. With reliable field data, relatively high confining pressures and gyration counts could be used to simulate construction and trafficking of pavements experiencing higher loads. Increasing the number of gyrations appears to increase the densification of subbase materials. When increasing the confining pressure applied to samples, an increase in densification of the materials is not immediately distinguishable indicating that most of the post construction densification of flexible pavements is due to shear work.