Utilization and Sustainability Evaluation of Steel Slag and RAP in Hot Recycled Asphalt Mixtures-Case Study

To address natural aggregate scarcity and improve the high-value utilization of Reclaimed Asphalt Pavement (RAP), this study proposes a steel slag-RAP hot recycled asphalt mixture (SSRM) as a sustainable alternative to conventional limestone-RAP mixtures (RM). Unlike previous studies mainly focusing on performance verification, an integrated environmental-economic evaluation framework was developed based on real highway expansion project data under a "cradle-to-gate" boundary and incorporating transportation distance thresholds. SSRM containing 50% RAP and 23% steel slag as coarse aggregate replacement was evaluated through rutting, semi-circular bending (SCB), freeze-thaw splitting (TSR), and skid resistance tests. Compared with RM, SSRM exhibited 14-16% higher dynamic stability and 20-25% higher fracture energy at -10 °C, along with improved moisture stability and skid resistance, mainly attributed to the rough and alkaline characteristics of steel slag enhancing adhesion and aggregate interlocking. Life-cycle assessment (GWP100) and cost analysis indicate that SSRM reduces carbon emissions by 10-11% relative to RM and about 40% compared with conventional virgin mixtures, while initial construction costs decrease by 9-10%. Transportation sensitivity analysis identifies equal-emission and equal-cost thresholds of approximately 590 km and 380 km, respectively. Within typical material supply radii (300-400 km), SSRM demonstrates both environmental and economic advantages, providing a practical framework for low-carbon material selection in highway construction.