Enhancing structural integrity and crack resistance of rubberized concrete using aqua-thermally treated rubber aggregates and recycled tire steel fibers for structural applications

Incorporating waste tire-derived rubber into concrete often results in significant strength reductions, primarily due to weak bonding at the rubber-cement interface. Despite various surface treatment methods for enhancing rubber adhesion, the mechanical performance of rubberized concrete remains inferior to conventional concrete. Reinforcing rubberized concrete with industrial steel fibers mitigates this limitation through the fiber-bridging mechanism. However, their high cost and environmental footprint restrict broader applicability. Although steel fiber recovered from waste tires offers a sustainable alternative, their incorporation remains challenging for fully restoring the mechanical performance of rubberized concrete. Employing rubber in its as-received condition intensifies this phenomenon, impairing the efficacy of fiber-bridging action. Consequently, this study assessed the synergistic effect of recycled tire steel fibers and rubber particles subjected to a novel aqua-thermal treatment. Both rheological and mechanical performances, including short-term and long-term strengths, were assessed across varying rubber and steel fiber contents. This combination restored compressive strength with rubber contents up to 12.5 %, surpassing previously reported performance levels. The flexural strength exceeded control values at rubber contents up to 15 %, further validating the efficacy of the proposed approach. Microstructural characterization techniques revealed enhanced synergy between aqua-thermally treated rubber and steel fibers within the concrete, explaining the underlying mechanism for observed performance gain. Additionally, the high-tensile strength of recycled tire steel fibers controlled both micro- and macro-crack propagation, enabling efficient stress transfer across the matrix. This mechanism transformed the brittle failure mode of concrete into a more ductile response, enhancing damage tolerance at failure. This dual-recycled material approach enables the production of high-performance rubberized concrete for structural applications, promoting sustainable construction well aligned with global low-carbon and waste reduction targets, while comprehensive durability testing continues.