The repair and strengthening of deteriorated infrastructure remain challenging, necessitating high-performance repair materials that are durable, compatible, and cost-effective. Fiber-reinforced mortar is considered promising due to its ability to improve durability and bond performance. However, the influence of hybrid fibers on the behaviour of the substrate-repair interface is not fully understood. Hence, the present study aims to develop a composite repair mortar incorporating ultra-fine slag and hybrid fibers, including Alkali-resistant glass fiber (ARGF) and basalt fiber (BF). The objective was to investigate the synergetic effect of these hybrid fibers on the mechanical, bond, and performance characteristics of cementitious composites. A total fiber volume fraction of 0.5% was used across five different hybrid fiber combinations, with 10% of the cement replaced with ultra-fine slag. The experimental program included tests on fresh properties (flowability), physical properties (density), mechanical performance (compressive and flexural strength), durability (capillary water absorption and water absorption), bond strength, and microstructural features using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results revealed that hybrid fiber reinforcement (G50B50) significantly improved the composite performance, increasing compressive strength by 4.63%, flexural strength by 44.6%, bond strength by 10.17% and a notable improvement of 49.83% in energy absorption capacity over mono fibrous mortar (G100B0). Among all mixes, G50B50 exhibited the most favourable synergy, with synergistic coefficient αc1 = 1.023 (compressive strength), αf1 = 1.173 (flexural strength), and αE1 = 1.236 (energy absorption), demonstrating enhanced toughness and post-peak behaviour compared to the mono-fibrous mortar (G100B0). Increasing BF content in hybrid mixes resulted in reduced water absorption by 5.65% and capillary penetration by 41.43%, respectively, accompanied by increased composite density. SEM analysis confirmed strong interfacial bonding between the fiber and matrix and uniform fiber distribution. Overall, the findings established that ARGF-BF hybridization combined with ultra-fine slag produces a high-strength, durable repair mortar with enhanced toughness, bonding performance, and crack resistance, highlighting its strong potential for long-lasting structural rehabilitation and retrofitting applications.
Bhagyasri et al. (Sun,) studied this question.