Abstract : Asphalt mixture is the most widely used pavement engineering material. Because the laboratory tests of asphalt mixture are costly, researchers keep searching for a practical numerical simulation approach to facilitate their study on mixture design, compaction process, and service performance. Although the discrete element method (DEM) had been introduced into those research areas for more than three decades and has been proved to be an effective tool, its utilizing is still limited by lacking coarse aggregate morphologies, efficient modeling approaches, and complete mechanical theories. This study aims to extend the application of DEM in asphalt mixture research by 1) establishing a coarse aggregate morphology database. Coarse aggregates were categorized according to shape information and then scanned through a three-dimensional scanner. The essential morphology factors, including grain size, dimensions, surface area, volume, and specific surface area, were collected and analyzed; 2) building the gyratory compaction process. Loose material assembly was precisely generated through the developed algorithm according to the mixture design. The loose material was then compacted through the programed gyration moment. The impacts of contact parameters on compaction were investigated. Speed-up techniques were proposed and verified by analyzing the internal structure of the compacted mixtures; 3) developing a set of modeling procedures with high efficiency, low cost, reliable accuracy, and wide application. The new modeling procedures use coarse aggregate temples from the database to improve simulation accuracy and use geometry information from the gyratory compacted mixtures or random generation method to save laboratory specimens. Hexagonal close-packed (HCP) structure, which has advantages in simulating shear failure and Poisson's ratio, was employed instead of the simple cubic-centered (SCC) structure. The corresponding mechanical calculation for contact micro-parameters was then derived and verify through simple stiffness/bond tests and complete indirect tensile (IDT) tests; 4) applying DEM models to research practice. Based on those improvements, this study involved DEM in the research of the mechanical performance of asphalt mixtures with high contents of ground tire rubber (GTR). Incorporate with laboratory tests, although asphalt mixtures with high contents of GTR have lower IDT strength of was than a conventional mixture, its cracking resistance and fatigue resistance were proved to be higher. By analyzing the contact force distribution in the DEM models, rubber particles with low moduli were found to be the endogenous reason for better performance. By further investigation, the rubber particles functioned as buffers that disperse the loadings. With the above four parts of research, the application of the DEM in asphalt mixture has significant improvement in modeling techniques, mechanical theories, simulation efficiency, and scope of application.

This volume presents selected papers presented during the 4th International Conference on Transportation Geotechnics (ICTG). The papers address the geotechnical challenges in design, construction, maintenance, monitoring, and upgrading of roads, railways, airfields, and harbor facilities and other ground transportation infrastructure with the goal of providing safe, economic, environmental, reliable and sustainable infrastructures. This volume will be of interest to postgraduate students, academics, researchers, and consultants working in the field of civil and transport infrastructure.

In this paper, the shear resistance of asphalt mixtures, which accounts for the permanent deformation characteristics of flexible pavements to a large extent, is analyzed based on the discrete element (DE) method from a microscopic perspective. This study first considered the processes used to obtain the microscopic parameters for the DE model, which typically simulated an asphalt mixture based on its three components. Then the study employed Burger's model to simulate the rheological behavior of asphalt sand mastics (fine aggregates, fines, and asphalt binder). A random generation algorithm was also developed to generate coarse aggregate elements in the DE model complying with the realistic gradations of asphalt mixtures. So as to more precisely model the rheological characteristics of asphalt sand mastics, the microscopic parameters of Burger's model were calibrated via simulations of uniaxial tests in the DE model. Finally, meaningful conclusions were achieved by analyzing the simulation result and the laboratory result. The simulation result was consistent with the laboratory test result, so the use of the established DE model to evaluate the shear resistance property of asphalt mixtures is feasible.