Effect of shrinkage-mitigating materials, fiber type, and repair thickness on flexural behavior of beams repaired with fiber-reinforced self-consolidating concrete

Abstract

While self-consolidating concrete (SCC) has emerged as a highly effective approach for the repair of concrete structures, there have been few investigations regarding the effect of the combination of different fiber and shrinkage-mitigating material types (shrinkage-reducing admixture, SRA; superabsorbent polymer, SAP; and expansive agent, EA) on the flexural behavior of repaired structures. This study aims to explore the influence of three different shrinkage-mitigating materials (1.25%–2.5 % SRA, 4%–8% EA, and 0.2%–0.4 % SAP), four fiber types (two macro synthetic fibers, MSF_A and MSF_B; 5D hooked steel fibers, 5D; a combination of 80 % 3D hooked steel +20 % short steel fibers STST) on fresh and hardened properties, cement hydration, and drying shrinkage of fiber-reinforced self-consolidating concrete (FR-SCC). Specifically, the effect of different shrinkage-mitigating materials, fiber types, and two repair thicknesses corresponding to 1/3 and 2/3 of the total height of prismatic element on the flexural performance of composite specimens repaired using FR-SCC was studied. The bond strength between existing concrete and FR-SCC was also investigated to reveal the flexural behavior of the composite beams. The results indicate that prismatic specimens repaired with FR-SCC made with 1.25 % SRA showed excellent flexural performance compared to those repaired using FR-SCC made with 4%–8% EA and 0.2%-0.4%SAP. The adverse effect of the incorporation of 4%–8% EA and 0.2%–0.4 % SAP on flexural behavior of repair specimens can be attributed to a lower existing concrete-FR-SCC interfacial and fiber-matrix bond strengths. Using SRA, EA, or SAP in FR-SCC improved bond strength with substrate by 10%–60 % compared to FR-SCC without any shrinkage-mitigating materials. The use of 1.25 % SRA showed the highest bond strength, which increased by 10%–37 % and 33%–44 %, respectively, compared to that made with SAP and EA. As the increase in the repair thickness of specimens, the incorporation of SRA, EA, or SAP had different efficiencies to enhance the flexural toughness and residual strength of the repair specimens. Furthermore, the incorporation of 5D fiber and 1.25 % SRA in SCC showed excellent flexural performance, followed by MSF_A, STST, and MSF_B fibers. The increase in the repair thickness from 1/3 to 2/3 of the total height of the composite beam enhanced the flexural toughness and residual strength by a maximum of 133 % and 160 %, respectively, attributing to fiber type and the increase in fiber volume at the cross-section of specimens.