A viscoelastic–viscoplastic damage constitutive model for asphalt mixtures based on thermodynamics

Based on irreversible thermodynamics theory, a viscoelastic–viscoplastic damage constitutive model was derived from corresponding functions of free energy and dissipated potential. It characterizes the physical role of internal state variables while being consistent with the fundamental laws of thermodynamics. The developed constitutive model was applied to describe the triaxial creep and triaxial constant strain rate compression tests, and to predict time-dependent response of asphalt mixtures under various compression loading conditions. It shows that the model reasonably characterizes three-stage deformation of creep test, hardening and softening stages of constant strain rate compression test, creep and recovery during loading and unloading, as well as the accumulated permanent deformation after repeated loading–unloading. The predicted volumetric deformation exhibits contraction and dilation, in which viscoelastic component accounts for contraction, while viscoplastic damage component accounts for dilation. The model was also compared against several existing models when representing the permanent deformation behavior of asphalt mixtures to highlight its efficiency and capacity.