Effect of Crumb Rubber Particle Size on the Rheological Response, Fatigue Response, and Storage Stability of Asphalt Binders: A Review

The use of crumb rubber modifier (CRM) from waste tires can improve asphalt-binder performance, but reported benefits vary with rubber particle size. This review evaluates particle-size effects on CRM-modified asphalt binders, covering production and morphology, swelling and asphalt–rubber interaction, rheology, fatigue, and storage stability. Studies retrieved from Scopus, Web of Science Core Collection and TRID in May 2026 were synthesized thematically. The evidence shows that particle size changes the balance between two mechanisms: coarser, swollen particles provide stronger physical reinforcement, whereas finer particles, because of their greater surface area, interact more rapidly with the asphalt phase. Finer CRM generally improves storage stability and promotes interaction, while coarser CRM can provide stronger high-temperature elastic reinforcement. These competing effects help explain conflicting findings across studies. Study-specific favorable sizes reported on a comparable basis cluster within approximately 40–80 mesh (0.180–0.425 mm, ASTM E11), but the cluster rests on a small and heterogeneous set of studies and reported optima remain dependent on binder type, rubber source, production route, rubber content, processing conditions, and performance criterion. It is therefore reported as a provisional evidence cluster, not as design guidance or a universal optimum. One direct comparison suggests that the multiple stress creep and recovery (MSCR) test may be more sensitive than G*/sinδ to particle-size-dependent high-temperature behavior. Because this rests on a single study, it is advanced here as a testable hypothesis and not as a basis for a size-sensitive specification. More consistent particle-size-appropriate testing and broader mixture- and field-scale validation are needed.