Viscoelastoplastic continuum damage model for asphalt concrete in tension

A viscoelastoplastic continuum damage model has been derived and characterized for describing the behavior of asphalt concrete subject to an all-around confining pressure and deviatoric tension loading. The primary application of this model is to better understand the fatigue damage process in asphalt concrete pavements. As a result of this application and because of the bimodal behavior of this material outside the linear viscoelastic range, the modeling effort has focused primarily on the tensile characteristics. The developed model uses the elastic-viscoelastic correspondence principle, work-potential theory with damage mechanics, time-temperature superposition with growing damage, and strain-hardening viscoplasticity to arrive at a constitutive relationship. This relationship considers the experimentally observed transformation of asphalt concrete from an initially isotropic material to a transversely isotropic one by using a single-state parameter and three different damage functions. The relationship between these damage functions and the more conventional values of the modulus and Poisson's ratio is shown to gain further physical insight into the material. Characterization of the model is performed by using constant crosshead rate monotonic tension tests with and without confinement and low strain temperature and frequency sweep complex modulus tests. The model is found to adequately describe the response of asphalt concrete under constant crosshead rate tension tests at various rates and two temperatures, the conditions that are not used in characterization.