Numerical Studies on Asphalt Concretes

Abstract

Computational modeling of asphalt mixtures is discussed in this chapter using different methods of DEM (discrete element method), FEM (finite element method) and XFEM (extended finite element method). In the DEM, particles are bonded together at contact points and are separated by external forces. Two homogenous and heterogeneous discrete element models have been generally developed to model crack growth behavior of asphalt concretes. In the homogenous models, behavior of material is considered cohesive at the crack trajectory whilst elastic behavior is assumed at other regions. In the heterogeneous discrete element models, an image processing technique is employed to capture the microstructure of materials. The digital images of specimens having different aggregate sizes are obtained by scanning laboratory asphalt specimens. In the subsequent section, the effects of various parameters including vehicle wheel position, horizontal load, elasticity and thickness of the road layers on the crack tip parameters (i.e. stress intensity factors) are investigated using two-dimensional (2D) and three-dimensional (3D) FEM. For this purpose, a four-layer road structure including asphalt concrete, base, sub-base and sub-grade layers is modeled in ABAQUS. Meanwhile, a top-down crack is regarded within the asphalt concrete layer. Furthermore, extended finite element method (XFEM) has been proved to be a very efficient computational method to characterize the discontinuous mechanical problems such as crack extensions. In the XFEM, the numerical model is divided into two regions. In the first region, the classical finite element meshes are generated for the un-cracked part of geometry; while, in the second region, the meshes defined in the cracked part of geometry are enriched by appropriate functions. Thus, the XFEM incorporates enrichment functions to solve fracture problems. In the last section of this chapter, the simulation of crack propagation using cohesive zone model (CZM) is described. Four material properties including fracture energy, tensile strength (for the cohesive elements), Young’s modulus and Poisson’s ratio (for the bulk material) together with the load-CMOD curve should be experimentally determined.