Micromechanical modeling of constitutive and damage behavior of heterogeneous asphalt materials

A computational and analytical study has been conducted to develop micromechanical models for heterogeneous particulate asphalt materials. Inelastic, softening and damage-coupled viscoelastic behaviors of the matrix material were considered in studying the micro-structural response of these asphalt composites. Asphalt concrete is composed of aggregates, mastic cement and air voids. The load carrying behavior of such a material is strongly related to the local load transfer between aggregate particles, and this is taken as the microstructural response. The first microstructural model incorporated a network of special frame elements with a stiffness matrix developed to predict the load transfer between cemented particles. The second approach incorporates the ABAQUS user material subroutine with continuum elements for asphalt mastic and rigid body defined with rigid elements for each aggregate. A comparative study is given for micromechanical modeling of asphalt materials by using micro-frame elements and doublet mechanics. Continuum damage mechanics was incorporated within micro-frame element network model to predict typical global inelastic/softening behavior found in asphalt materials. Using image processing and aggregate fitting techniques, simulation models of indirect tension and compression samples were generated from surface photographic data of actual laboratory specimens. Model simulation results of the overall sample behavior and evolving micro-failure/fracture patterns compared favorably with experimental data collected on these samples. A series of model asphalt samples have been generated and simulated with controllable microstructure variation in an effort to determine the effects of particular microstructural variables on the material response. These simulations explored the relationship between microstructure parameters and damage behavior of particular asphalt samples. A finite element micromechanical modeling approach was proposed by using the Schapery nonlinear viscoelastic model for the brittle failure and rate-dependent damage behavior. Cyclic loading responses of linear and damage-coupled viscoelastic materials were compared. Using numerical simulations of model asphalt samples, the effect of loading rate on the material viscoelastic damage behavior was also investigated