Fracture modeling of steel slag asphalt mixtures considering moisture-induced slag expansion under long-term vapor exposure

Incorporating steel slag as the dominant aggregate in asphalt mixtures has garnered increasing attention for its both mechanical and environmental benefits. However, the moisture-induced expansion of steel slag under long-term vapor exposure degrades the integrity of asphalt mixtures. The steel slag asphalt mixture exhibits crack propagation during its service life. To address this issue, we developed a fracture modeling framework that incorporates a moisture-cohesive zone model (M-CZM) and a moisture-induced slag expansion equation (M-SE) within a finite element (FE) model of asphalt mixtures. This framework simultaneously defines the decrease in adhesion/cohesion and steel slag expansion as a function of moisture content. We conducted a semi-circular bending test on asphalt mortar specimens with different vapor exposure time to validate the fracture modeling framework. The results showed that the simulation results had little difference with the measured ones. Based on the framework, we simulated the fracture process of steel slag asphalt mixtures under long-term vapor exposure. The coupled damages of moisture-induced adhesion/cohesion reduction and slag expansion were quantified. The results indicated that adhesive damage precedes cohesive damage under moisture-induced slag expansion. After 100 days of vapor exposure, the asphalt mixture's peak force decreases by 35 %. The coupled effects of moisture-induced adhesion/cohesion reduction and steel slag expansion shift the crack initiation point from the middle toward the edges of the specimen. This work provides insight into the fracture evolution of steel slag asphalt mixtures under long-term vapor exposure, offering evidence for assessing the durability of such mixture design.