Modeling fracture evolution of crumb rubber asphalt concrete under long-term vapor exposure: A coupled moisture-mechanical approach

Crumb rubber asphalt mixture, recognized as a cleaner paving material due to its recycling of waste tires and carbon reduction potential, is widely used for its environmental benefits. However, the coupled effects of moisture and fracture significantly undermine the durability of crumb rubber asphalt concrete (CRAC), especially under long-term vapor exposure. Few studies have systematically addressed this coupling, which involves complex interactions between diffusion and cracking processes occurring at varying intensities and rates. To bridge this gap, this study proposes a sequentially coupled framework and develops a Moisture-Mechanical Evolution Model (MMEM) that expresses mechanical properties as a function of moisture content. The model was calibrated using moisture sorption tests (MST) and semi-circular bending (SCB) tests. Results indicate that prolonged vapor exposure accelerates micro-crack formation and widens macro-crack propagation paths under mechanical loading. Furthermore, over 30% reduction in functional performance is predicted for crumb rubber asphalt pavement after three years of service in moist environments. This study not only elucidates the coupled moisture-fracture mechanism in CRAC but also provides a practical modeling approach for assessing durability, thereby supporting the development of more sustainable and cleaner pavement materials.