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This dissertation presents the development of an anisotropic viscoplastic continuum damage model to describe the permanent deformation of asphalt pavements . The model is developed to account for several phenomena that influence the permanent deformation of Asphalt Concrete (AC ) at high temperatures . These phenomena include strain rate dependency , confining pressure dependency , dilation , aggregate friction , anisotropy , and damage . The model is based on Perzyna's theory of viscoplasticity with Drucker -Prager yield function modified to account for the microstructure anisotropy and damage . A parametric study was conducted to study the effect of key factors such as inherent anisotropy and damage on the model response . A preliminary investigation was conducted to demonstrate the capabilities of the model and its sensitivity to changes in the microstructure distribution and loading conditions . The model was used to describe laboratory experimental measurements obtained from the Federal Highway Administration (FHWA ) Accelerated Loading Facility (ALF ) . The model had a good match with these experimental measurements . In particular , using the damage parameter , the model was able to capture the point at which AC experienced tertiary creep in a static creep test . A comprehensive experiment was conducted to systematically determine the model parameters and the evolution laws that describe AC hardening , anisotropy , and damage . The experiment consisted of a set of compressive triaxial strength tests conducted at three confining pressures and five strain rates . Based on these experimental measurements , the model was modified to include a nonassociated flow rule . The model was shown to capture the experimental measurements very well . Furthermore , an experiment was conducted to capture and characterize damage evolution in AC due to permanent deformation . AC specimens were loaded using a triaxial compression setup to four predefined strain levels at three confining pressures . X -Ray computed tomography and image analysis techniques were used to capture and characterize the evolution of cracks and air voids in the deformed specimens . Damage was found to be a localized phenomenon in the sense that there exists a critical section in an AC specimen that is mainly responsible for failure . The results of the damage experiment supported the damage evolution function proposed in the viscoplastic model . |
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