Crumb Rubber Asphalt: A Systematic Review of Performance, Durability and Sustainability

Crumb Rubber Asphalt (CRA) is among the most established high-value pathways for recycling end-of-life tires in transport infrastructure. However, despite decades of research and field application, the literature remains dispersed across binder modification, mixture performance, incorporation technologies, long-term durability, environmental implications and circularity. This study presents a systematic review of peer-reviewed journal articles indexed in Scopus and Web of Science (WoS) that address the use of crumb rubber in asphalt binders and mixtures. The review is structured around four interrelated questions: how incorporation route governs rubber-bitumen interaction; how crumb rubber affects rutting, fatigue, low-temperature cracking and moisture susceptibility; how aging, emissions and life-cycle impacts shape the sustainability case for CRA; and which unresolved methodological limitations still restrict broader implementation. The evidence shows that crumb rubber generally improves rutting resistance, elastic recovery, fracture tolerance, and, in several surface applications, acoustic performance. These benefits, however, are not intrinsic to rubber addition alone. They depend on a process-sensitive design window involving rubber gradation, rubber content, base-binder chemistry, digestion temperature, interaction time, blending energy, storage conditions, and the use of complementary technologies such as warm-mix additives, rejuvenators, pre-swelling treatments or hybrid modifiers. Wet-process systems remain the most mature and technically reliable route, whereas dry-process technologies offer implementation simplicity but exhibit greater variability in material response. Terminal-blend technologies improve workability and storage stability, although, in some cases, they partially reduce the elastomeric contribution associated with intact rubber particles. From a sustainability perspective, CRA clearly contributes to waste-tire valorization and may reduce life-cycle burdens when durability gains are realized and production conditions are optimized. Nevertheless, these environmental advantages are conditional rather than universal. Future research should prioritize standardized reporting, multi-scale mechanism-to-performance integration, realistic weathering and aging protocols, harmonized life-cycle assessment and credible end-of-life recycling pathways for rubberized asphalt systems.