Investigating the shrinkage mechanism, characteristics, and environmental benefits of waste tire rubber-modified cement-stabilized macadam.

Although cement-stabilized macadam (CSM) base is widely used in highway construction for its excellent mechanical properties, but its poor shrinkage resistance leads to thermal and drying shrinkage cracks, which remains a critical challenge. This study used four distinct particle sizes of waste tire rubber particles (RP) to replace fine aggregates through equivalent volumetric and particle size. The strength of rubber cement-stabilized macadam (RCSM) was assessed through unconfined compressive strength (UCS) testing. Following strength validation, systematic investigations into the synergistic effects of RP size (RPS) and RP replacement rate (RPRR) on shrinkage characteristics were conducted through drying shrinkage and thermal shrinkage tests. A dual-index mathematical model (strength retention rate vs. crack resistance coefficient) was established to optimize RCSM mix proportion design, coupled with mechanistic analysis of shrinkage mechanisms and environmental benefits. The results indicate that the shrinkage performance of RCSM exhibits an inverse correlation with RPS and a positive correlation with RPRR. RPRR emerges as the dominant factor governing shrinkage behavior, while RPS predominantly determines the compressive strength. To reconcile mechanical performance with crack resistance, an equilibrium optimization scheme is proposed: RPS = 0.6-1.18 mm and RPRR = 75 %. Mechanism analysis reveals that the high elasticity of RP mitigates shrinkage stresses through energy buffering effects, while its hydrophobic nature contribute to reduced shrinkage coefficients. Notably, the 4.75-RC-100 formulation achieves negative carbon emissions. This research provides methodological references for performance optimization of pavement base materials while establishing an innovative pathway for resource utilization of waste tires.