Strengthening of reinforced concrete structures using alkali-activated materials: A state-of-the-art review

Alkali-activated materials (AAMs), with geopolymers considered herein as a compositional subset, have attracted increasing attention as inorganic matrices for the repair and strengthening of existing reinforced concrete (RC) structures. This review establishes an integrated framework linking constituent selection and reaction products with AAM–concrete and AAM–reinforcement bond behavior, member-level flexural, shear, and confinement performance, and the assumptions underlying analytical and numerical models. Interface test results under tensile, shear, and mixed-mode loading are critically compared by considering variations in specimen geometry, curing conditions, substrate characteristics, and failure mechanisms. The synthesized evidence shows that fly ash- and ground granulated blast-furnace slag-based AAMs activated by sodium-based solutions remain the most extensively investigated systems; however, a universal relationship between constituent composition and strengthening capacity cannot yet be established due to substantial heterogeneity among available datasets. Experimental results demonstrate that a T-sided steel-fiber-reinforced geopolymer composite overlay enhanced the peak flexural load by 124% in tested beams, although the strengthened specimens ultimately exhibited shear-controlled failure. Across the reported AAM overlay and jacketing studies, four-sided strengthening schemes achieved capacity increases of up to 281%, although these values reflect different material systems and strengthening configurations rather than a universal performance limit. The review further highlights key design considerations and research priorities, including standardized testing protocols, interface constitutive modeling, long-term durability, fire and cyclic performance, field implementation, and life-cycle assessment.