Comparative Analysis of Cracking Behavior of Various Asphalt Mixtures under Salt Freeze–Thaw Cycles

To investigate the influence of material performance changes before and after salt freeze–thaw cycles on the cracking behavior of asphalt mixtures, this study prepared four types of asphalt mixtures for comparative cracking behavior analysis. These mixtures utilized two common materials [basalt and styrene-butadiene-styrene (SBS)-modified asphalt] and two solid waste materials (steel slag and crumb rubber–modified asphalt). By combining the semicircular bending test with digital image correlation (DIC) technology, incremental fracture energy and horizontal strain energy were adopted as evaluation metrics to analyze performance evolution from both macroscopic and mesoscopic perspectives. Additionally, asphalt-aggregate adhesion tests were conducted to assess changes in interfacial tensile strength between aggregates and asphalt, revealing the crack resistance of asphalt mixtures at the bonding level. Furthermore, the physicochemical characteristics of steel slag and its interfacial interactions with asphalt were analyzed to elucidate crack formation mechanisms under salt freeze conditions. The research findings indicate that salt freeze–thaw cycles degrade the crack resistance of asphalt mixtures, with Fourier transform infrared (FTIR) spectroscopy analysis showing that physical degradation dominates this process. Increased salt solution concentration exacerbates interfacial bonding damage during freeze–thaw cycles, while thicker asphalt films can partially mitigate this effect. The incorporation of crumb rubber and steel slag significantly improves the deformation characteristics of mixtures, enabling them to maintain excellent low-temperature deformation resistance under freeze–thaw cycles.