SIMULATION OF THE MICROMECHANICAL BEHAVIOR OF ASPHALT MIXTURES USING THE DISCRETE ELEMENT METHOD

The members of the Committee appointed to examine the dissertation of ALA R. ABBAS find it satisfactory and recommend that it be accepted. __________________________ Chair __________________________ __________________________ __________________________ ii ACKNOWLEDGEMENT I would like to thank Dr. Tom Papagiannakis for serving as the chairman of my committee and for his great support throughout my graduate study. I would like also to express my deepest gratitude to my co-advisor Dr. Eyad Masad for his valuable input and continuous encouragement. I wish to extend my sincere thanks to Dr. Chair: Tom Papagiannakis This study describes a methodology for characterizing the micromechanical behavior of asphalt mastics and asphalt mixtures using the discrete element method. Asphalt mastics are defined as dispersions of aggregate fines within a medium of asphalt binder, while asphalt mixtures are defined as agglomerates of aggregate particles of various sizes combined with asphalt binder and air voids. The stress-strain behavior of these composites is highly dependent on temperature and loading rate. The effect of the aggregate fines on the macromechanical behavior of asphalt mastics is studied through the generation of discrete element models that contain different percentages of soft and stiff particles. The temperature dependency of the asphalt binder is included in the analysis through the modification of the stiffness of the soft particles. The numerical results are compared with experimental measurements on mastics using different fine aggregate types, and volumetric concentrations. The viscoelastic response of asphalt mixtures at high temperatures and the fracture mechanism at low temperatures are also investigated. The discrete element models of the microstructure are analyzed under dynamic loading conditions similar to that in the simple performance test in order to study the relationship between the behavior of the binder and that of the asphalt mixture. Aggregates are assumed to be rigid and the iv viscoelastic interaction among the mix constituents is described using a viscoelastic model. The DEM results are compared to experimental measurements of viscoelastic properties on materials of one aggregate source and nine different binders. In addition, the indirect tension test is simulated and the effect of the asphalt binder film thickness on the tensile strength and the failure strain is examined. Three types of bonds are incorporated in the analysis in order to describe the cohesion within the asphalt binder, the cohesion within the aggregate particle, and the adhesion between the aggregate and the binder.

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