A fully coupled viscoelastic continuum damage model for asphalt concrete

Capturing the fatigue-induced evolution of viscoelastic properties of the material is crucial for predicting the fatigue life of asphalt concrete pavements. Current prediction models are often regression-based and lack accuracy, necessitating the adoption of mechanistic models like the Viscoelastic-Continuum Damage (VECD) models. The VECD models often rely on Schapery's work potential theory and elastic-viscoelastic correspondence principles, using pseudo-strain to separate viscoelasticity from damage mechanics. However, this decoupling imposes constraints on how viscoelastic properties can evolve. This study presents a new VECD model that fully couples the viscoelasticity of the material with its damage characteristics. It was developed within a Helmholtz-potential-based thermodynamic framework, ensuring consistency with the laws of thermodynamics. The model could describe the evolution of both the apparent storage modulus and loss modulus during fatigue tests over a wide range of strain levels. It captures the three-stage fatigue behavior of asphalt concrete, allows for unconstrained variations in the apparent phase angle, and provides a clear point of failure. Moreover, it can capture the variation of fatigue life with the applied strain level in a manner similar to the Asphalt Institute fatigue life model.