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Constitutive Relations for Asphalt Concrete Under High Rates of Loading

A main characteristic of asphalt concrete (AC) is its tendency to behave elastically and viscoplastically during cold and hot seasons, respectively. An understanding of the mechanical behavior of AC under various loading conditions is crucial to a more rational design of flexible pavements and requires more elaborate and comprehensive constitutive relations for AC. AC behavior under high rates of loading was experimentally studied using uniaxial, triaxial compression, and pavement simulation tests. The loading matrix followed in the testing program consisted of 0.05-, 0.1-, and 0.2-s loading durations; three stress levels of 207, 414, and 827 kPa; and three temperatures of 24°C, 35°C, and 41°C. The experimental results indicated that AC materials display an elastic-viscoplastic response under uniaxial stress pulses. The viscoplastic response was characterized by the rate dependency of the plastic response and was found to be linearly strain hardening. The results revealed that the yielding point is dependent on the strain rate and temperature and increases as both variables increase. The developed model uses a yield criterion based on the loading function defined by Drucker-Prager. The uniaxial material properties were calibrated to field conditions from the pavement simulation test data through an optimization process that involved iterative calls between finite element results and the optimum parameters, which were obtained using ABAQUS and CONMIN, respectively. This analysis resulted in the development of a generalized elastic-viscoplastic constitutive relation for AC.