Enhancement of Structural Stability and Mechanical Properties of Rubberized Asphalt Mixtures in Dry and Cold Processes Using Pre-Swollen Waste Crumb Rubber

Incorporating waste crumb rubber (WCR) as a flexible aggregate in asphalt mixtures enables large-scale recycling of end-of-life tires (ELTs) and improves urban sidewalk safety. However, such dry processes are often constrained by the intrinsic swelling of WCR and its poor compatibility with bitumen. This study introduces a pre-swelling treatment on WCR by using epoxidized soybean oil (ESO) to simultaneously enhance interfacial bonding and volumetric stability in rubberized asphalt mixtures. Disk-shaped pre-swollen WCR samples were prepared and tested using a dynamic shear rheometer (DSR). In addition, cold mixtures were produced by combining 1–4 mm pre-swollen WCR with reclaimed asphalt pavement (RAP) materials at different ratios through the dry process, and the volumetric parameters, cross-sectional distribution, air voids, indirect tensile strength (ITS), and indirect tensile stiffness modulus (ITSM) were evaluated. Results indicate that the pre-swelling treatment shifted the WCR surface behavior from predominantly elastic to more viscous, reducing its sensitivity to secondary swelling. Consequently, the mixtures exhibited 36% higher volumetric stability, 23% higher ITS at 25 °C, and 62% higher ITSM at 5 °C than those prepared with untreated WCR. However, ESO serves as a rejuvenator for RAP, requiring control and further investigation. Overall, this study provides a strategy for high-value WCR recycling in safer urban slow-mobility infrastructures.