A coupled aging–viscoelastic–viscodamage model for predicting fatigue behavior in aged asphalt pavements

Oxidative aging increases the stiffness and brittleness of asphalt pavements, reducing resistance to fracture and fatigue cracking. This study introduces a coupled aging–viscoelastic–viscodamage constitutive model to capture the effects of oxidative aging on the mechanical behavior of asphalt pavements. The model integrates oxygen diffusion, aging time, and temperature into a state variable that modifies viscoelastic compliance, relaxation times, and damage properties. Using a continuum damage mechanics framework, the model effectively couples aging, fatigue damage, and viscoelastic behavior. The proposed model was implemented in a finite-element framework to simulate a 2D axisymmetric asphalt pavement subjected to mechanical pulse loading and oxygen diffusion over ten years. Results show that the simulated unaged pavement exhibits a bottom-to-top cracking pattern, while surface-down cracking dominates in the aged pavement due to oxygen-induced material degradation. Validation against laboratory data demonstrates the model’s ability to predict fatigue life, stiffness evolution, and damage density under various aging conditions. The findings highlight the importance of incorporating oxidative aging effects in pavement performance models to improve design and maintenance strategies for long-term durability.