Advances in Discrete Element Modeling of Asphalt Mixture: A Literature Review

The complicated composition structure of the asphalt mixture makes it difficult to determine its multi-scale performance. It is impossible to understand the internal interaction mechanism of asphalt mixture only through laboratory tests, especially under complex conditions at the microscale, which can be effectively solved by the discrete element method (DEM). This paper summarized the progress and advances in DEM modeling of asphalt mixture mainly consisting of the principle of DEM, DEM simulation for asphalt mixture, asphalt mixture compaction and mechanical behavior based on the DEM. The basis of DEM modeling is the well-known Newton's second law, through which the discrete elements are determined primarily according to the motion equation and force–displacement law. The DEM modeling of asphalt mixture often includes the simulation of coarse aggregates, asphalt mortar and air voids regardless of two-dimensional (2D) and three-dimensional (3D) DEM. The morphological characteristics of coarse aggregates and spatial distribution of air voids are essential to the simulation results of asphalt mixtures. In addition, the commonly used DEM contact models in asphalt mixture, including the linear model, Burgers model and linear parallel bond model, are introduced and analyzed. The main micro-parameters of various contact models are usually obtained through laboratory test results by trial and error. And the selection of contact modeling and determination of macro-parameters are discussed. Then, asphalt mixture compaction based on DEM, mainly containing Superpave gyratory compaction (SGC) and Marshall impact compaction (MIC), is estimated in this paper. It is concluded that displacement, rotation and contact stress of aggregate particles can be accurately captured similar to SmartRock. Moreover, varying mechanical behavior and the significant influencing factors based on DEM are evaluated comprehensively. Finally, further prospects in DEM modeling of asphalt mixture are proposed to promote the development and application of numerical simulation in pavement engineering.