Composite Dielectric Model of Asphalt Mixtures Considering Mineral Aggregate Gradation

The composite dielectric model of asphalt mixtures is crucial to the use of the ground-penetrating radar (GPR) for detecting compaction, asphalt content, and other quality-related indexes of asphalt pavements. In this study, the interface transition zone between asphalt and mineral aggregate, as well as the mineral aggregate gradation, are considered based on analyses of the microstructure of the asphalt mixture. The effective medium theory and composite-sphere assemblage method are then combined to develop a microstructure-based physical model of asphalt mixtures. A polarizability equation is formulated for a single-mineral aggregate particle with independent interface behavior in which size effects of the particles are introduced. Based on the physical model of the asphalt mixture and the polarizability equation of the single-mineral aggregate particle, composite dielectric models of the asphalt-mineral skeleton structure (AMSS) and asphalt mixtures considering mineral aggregate gradations are generated. Tests and analyses show that the interface effect has a crucial influence on the polarization of the fine aggregate and filler of the mineral aggregate, which causes increasing polarizability in the fine aggregate and filler, as well as corresponding increases in the effective permittivity of the asphalt mixtures. Compared with classic models, the developed composite dielectric model of asphalt mixtures has higher calculation accuracy, with the prediction results more closely matching the test results of asphalt mixtures.