Discrete element modeling to predict the modulus of asphalt concrete mixtures

The microfabric discrete element modeling (MDEM) approach is used herein to predict the asphalt mixture complex modulus in extension/compression across a range of test temperatures and load frequencies. The method allows various constitutive models to be employed to describe particle and interface properties, such as normal and shear stiffness and strength. An uncalibrated two-dimensional (2-D) model was developed, and complex modulus predictions were compared to theoretical bounds on moduli. As expected, the uncalibrated 2-D model underestimates the significant stiffening effects of the coarse aggregate skeletal structure and predictions are found to be near the lower theoretical bounds, well below experimentally determined moduli. A technique was developed to calibrate the MDEM model to experimental results by dilating aggregates to create additional aggregate contact, which is believed to be more representative of the actual three-dimensional behavior. This method is shown to provide better modulus estimates across a range of test temperatures and load frequencies compared to more traditional calibration methods. As future modeling efforts are extended to three dimensions, the degree of model calibration required should be greatly reduced.