Modelling damage and healing of asphalt concrete in a fully-coupled viscoelastic continuum damage framework

Asphalt concrete pavements experience fatigue damage under repeated traffic loading, leading to stiffness reduction and exhibit healing behaviour in the absence of loads, causing an increase in stiffness. In this study, a thermodynamically consistent Viscoelastic Continuum Damage (VECD) framework is developed to describe both the fatigue damage and healing behaviour. Within this framework, a damage parameter is introduced to capture fatigue damage and is split into two additive components – one that completely recovers in the absence of loading and another component that is completely irreversible. By assuming specific functional forms for the Helmholtz potential and the rate of dissipation that depend on these two components, constitutive relations were developed. The resultant constitutive relations consisted of a rate-type viscoelastic model whose model parameters depend on the damage parameter and its components, and an evolution equation for each of the components of the damage parameter. Together, these constitutive relations were shown to capture both fatigue damage during loading and healing during the absence of loads. Moreover, the model is able to characterise the increase in fatigue life with the introduction of rest periods.