Numerical Investigation of Aggregate Segregation of Superpave Gyratory Compaction and Its Influence on Mechanical Properties of Asphalt Mixtures

In the laboratory, there are significant differences in mechanical properties of asphalt mixtures with the same size gradation and asphalt binder, which is not conducive to evaluating and designing the pavement structure accurately. Meanwhile, the influence of aggregate segregation in height on the mechanical properties of asphalt mixtures is unclear. This study developed a new method to generate a three-dimensional (3D) model of the real composition and aggregate shape to characterize the aggregate segregation during Superpave gyratory compaction (SGC). The graphic segregation index (GPSI) is employed to assess the mixing degree of coarse aggregate and asphalt mortar within spatially variable specimens [i.e., Superpave-13, stone mastic asphalt (SMA-13), and open-graded asphalt friction course (OGFC-13) mixtures]. The results reveal that asphalt mixtures with different aggregate gradations have different compaction characteristics. For example, the increase of fine aggregates may reduce the strain energy and the average contact force during compaction. The compaction curves of the three gradation types were very different, which is attributed to different packing states and gyratory numbers. Aggregate segregation has a significant effect on micromechanical behavior. Specifically, the contact number and the proportion of strong contact force change considerably with height. In terms of segregation degree, the GPSI of OGFC-13 specimens was the highest, and the volume change of its fine particles created a leakage zone after the compaction. Additionally, this segregation had an increasing tendency with gyration numbers, and it was influenced by gradation types. Furthermore, the uniaxial compressive strength and cohesion of the Superpave-13 specimen decreased, whereas the friction angle increased with the increase of GPSI.