Development of a micromechanical modeling approach to predict asphalt mixture stiffness using the discrete element method

Micromechanical modeling has tremendous potential benefits in the field of asphalt technology, for reducing or eliminating costly tests to characterize asphalt-aggregate mixtures for the design and control of flexible pavement structures and materials. A microfabric discrete element modeling (MDEM) approach is presented for modeling asphalt concrete microstructure. The technique is a straightforward extension of a traditional discrete element methods (DEM) analysis, where various material phases (e.g., aggregates, mastic) are modeled with clusters of very small discrete elements.; High resolution optical images were obtained in order to study the microstructure of asphalt mixture and to prepare geometry input for the MDEM model. The MDEM approach is used herein to predict asphalt mixture complex modulus in extension/compression across a range of loading times and frequencies. The method allows various constitutive models to be employed to describe particle and interface properties, such as normal and shear stiffness of the elements and cohesive and adhesive strength. Biaxial (or uniaxial) compressive test and hollow cylinder tensile tests were employed in this study for the stiffness (complex modulus) prediction. For the coarse HMA mixture studied, the uncalibrated MDEM models gave excellent predictions for both uniaxial compressive test and hollow cylinder tensile test simulations. For the fine mixtures studied, there were insufficient numbers of coarse aggregate contacts captured by the image technique and the uncalibrated 2D model underpredicted the significant stiffening effects of the coarse aggregate skeletal structure. Various techniques were developed to calibrate the 2D MDEM model to experimental results. The MDEM model calibrated to experimental results on a single material at a single frequency and temperature closely match measured moduli across a range of test temperatures and load frequencies. As future modeling efforts are extended to three-dimensions, the degree of model calibration required should be greatly reduced.; The MDEM approach was also utilized in the design and optimization of physical test equipment such as hollow cylinder tensile tester. In addition, tensile strength simulations and creep stiffness prediction are also very promising by using the MDEM approach.