| Hot Mix Asphalt (HMA), a highway and airfield pavement material, is heterogeneous, granular, and composite. It is traditionally modeled as a homogeneous material using continuum mechanics or semi-empirical methods. As a result, the above models either neglect or over-simply component reactions, failing to predict field performance problems resulting from particle segregation. This research presents micromechanical modeling, a novel approach that accounts for the components.; A micromechanical model is developed for HMA by modeling it as an assembly of asphalt cement coated particles. The asphalt cement is modeled as a viscoelastic material. To represent asphalt cement, several viscoelastic elements (i.e. Maxwell, Kelvin-Voigt, and Burgers' elements) were considered. From these viscoelastic elements the Burgers' element is shown to be most representative of asphalt binder behavior based on mechanical responses and comparisons with physical experimental results.; The model for HMA, ASBAL, is based on the TRUBAL program, a Discrete Element Method (DEM), with Burgers' element. Monotonic and cyclic tests were simulated to observe the ability of the model to predict the mechanical behavior of HMA. During these simulations the physical values of microscopic input parameters were varied to determine how each contributes to the overall behavior of HMA.; Then, the ASBAL model was used to simulate a mechanical test with x-ray tomography to accurately predict residual stresses of the laboratory sample after compaction, the initial modulus, stress levels throughout the test, and number of contacts within HMA matrix.; Using the master curve and the time-temperature superposition theory the input parameters for the Burgers' element at different temperatures were calculated. Using those input parameters, the mechanical responses of HMA at different temperatures were simulated. Results show that at higher temperatures the strength and initial stiffness values are a fraction of those found at lower temperatures. Hence the ASBAL model predicts the temperature softening of HMA that contributes to the rutting of HMA. The micromechanical model simulates the discrete mechanical behavior of HMA and hence can be used to develop performance based tests for HMA. |
