Study on the Low-Temperature Cracking Characteristics of Warm-Mix Steel Slag and Rubber Powder–Modified Asphalt Mixtures Using Acoustic Emission Technology

Based on the acoustic emission (AE) dynamic nondestructive testing technology, a semicircular bending test (SCB) was conducted on warm-mix steel slag rubber powder modified asphalt mixture (CR-WSAM) at −10°C and −20°C to monitor its crack evolution behavior throughout the process. The low-temperature cracking resistance of asphalt mixtures was evaluated using the Thermal Stress Restrained Specimen Test (TSRST). By analyzing the fracture energy and AE characteristic parameters (e.g., ring count, amplitude, energy frequency) of SCB, its anticracking performance and damage evolution law were revealed. This study found that the significant increase in the cumulative energy of the acoustic emission signal and the increase in the number of RA signals indicate that the high strength and excellent surface morphology of steel slag enhance the interlocking effect between aggregates inside the mixture and improve the adhesion between asphalt and aggregate interfaces such that the energy release during crack propagation is effectively limited. The addition of SDYK warm-mix agent further improves the viscosity flow characteristics of asphalt, enhances the adhesion between asphalt and aggregate, and reduces the mixing temperature, which is manifested in the delay of the acoustic emission frequency peak and the increase in the proportion of high-frequency signals. In addition, as the temperature decreases, the growth rate in the ringing count in the acoustic emission characteristic parameters accelerates, and the peak amplitude increases significantly, indicating that the material gradually changes from a viscoelastic state to a highly elastic state; the anticracking performance of the four asphalt mixtures is ranked as follows: CR-WSAM > CR-HSAM > CR-WSBAM > CR-HSBAM.