Fatigue damage analysis of modified high-modulus asphalt mixtures based on VECD theory

To investigate the damage characteristics of modified high-modulus asphalt mixtures, four types of asphalt mixtures—a conventional asphalt mixture (AC20) and three high-modulus asphalt mixtures (HMAM, SBS-HMAM, and CR-HMAM)—were subjected to dynamic modulus tests and indirect tensile fatigue tests. Based on the Viscoelastic Continuum Damage (VECD) theory, the viscoelastic properties and damage evolution patterns of different modified high-modulus asphalt mixtures were compared and analyzed. Within this framework, the existing Max W s R failure criterion was adopted to establish a fatigue life prediction equation for high-modulus asphalt mixtures, with model parameters calibrated for each polymer-modified system. The results indicate that the high-modulus additive is the key factor in improving the dynamic modulus of the mixture, while the styrene-butadiene-styrene (SBS) and crumb rubber (CR) polymer modifiers primarily alter the proportion of the viscoelastic components and the damage evolution path of the material. At an identical damage state, the SBS- and CR-modified mixtures maintain a higher level of stiffness integrity. Compared to the mixture with only the high-modulus additive, SBS and CR further enhance the material's resistance to fatigue damage. SBS-HMAM exhibits a higher fatigue life. During loading, the pseudo stiffness of CR-HMAM is lower than that of SBS-HMAM, but its corresponding critical damage level S at fatigue failure is higher. Using the maximum stored pseudo strain energy criterion Max, W s R a probabilistic fatigue equation incorporating failure probability was established based on the Weibull distribution. This approach transforms the deterministic fatigue model into a probabilistic prediction model. This study deepens the understanding of fatigue behavior in high-modulus asphalt mixtures and provides a theoretical basis for their refined design and performance control in long-life pavement structures.