Interfacial strengthening and mechanical enhancement of rubberised concrete: approaches, mechanisms, and sustainability perspective

Incorporating rubber particles as aggregate replacement in concrete is a sustainable strategy to mitigate end-of-life tire accumulation and natural aggregate depletion. However, the inherent polarity incompatibility between the hydrophobic rubber particles and the hydrophilic surrounding concrete matrix leads to the formation of a porous, weak interfacial transition zone (ITZ), resulting in insufficient stress transfer across the rubber-cement paste interface, consequently reducing mechanical strength and limiting the structural feasibility of rubber concrete. This review presents a systematic, mechanism-oriented synthesis of recent advances in interfacial strengthening strategies for rubberised concrete, with emphasis on ITZ enhancement and recovery of mechanical performance. Chemical treatment, physical activation methods and pre-coating strategies were critically evaluated. Microstructural evidence from SEM, FTIR, EDS, XRD and contact-angle analyses was integrated to explain the governing mechanisms, including surface cleaning, functional group grafting, chemical bridge formation (Si–O–Ca, Si–O–Si), oxidation-induced surface texturing, and the formation of mechanically compatible cementitious shells that reduce stiffness disparity and enhance stress transfer. Surface modifications are comparatively assessed and ranked by their efficiency in strength recovery and ITZ strengthening, as reported in existing studies. Hybrid and cementitious pre-coating approaches demonstrate that the highest ITZ densification and strength recovery can be achieved by silane coupling agents and KMnO₄ oxidation. Thermal and plasma treatments offer moderate improvement, whereas NaOH and water washing exhibit comparatively limited enhancement. Although treated rubber concrete consistently exhibits higher strength than untreated rubber concrete, its mechanical performance remains lower than that of conventional concrete. Nevertheless, optimised interfacial strengthening significantly enhances strength and supports structural applicability at low-to-moderate levels of rubber replacement.