Flexural behavior of GFRP reinforced concrete beams with CFRP grid-reinforced ECC stay-in-place formworks

Carbon fiber-reinforced polymer (CFRP) grid-reinforced engineered cementitious composites (ECC) with excellent cracking resistance was used to replace the tension part of concrete beams to improve the beam durability and flexural performance. A new ultradurable hybrid beam type was proposed for marine environments, consisting of a CFRP grid-reinforced ECC layer as a stay-in-place formwork and an overlying concrete part reinforced with glass FRP (GFRP) bars. One reference concrete beam, one hybrid beam using a pure ECC formwork, and eight hybrid beams using CFRP grid-reinforced ECC formworks were tested to evaluate the effects of ECC and CFRP grid presence, grid spacing, CFRP grid cross-sectional area, GFRP bar reinforcement ratio, and ECC strength. Test results revealed that CFRP grid-reinforced ECC formwork substantially improved the cracking load by 53.4%-92.4% and the maximum load by 4.4%-34.4% (except the low-reinforcement-ratio beam) compared with the reference beam. The cracking performance and load-carrying capacity increased with ECC and CFRP grid incorporation, an increasing GFRP bar reinforcement ratio, and a CFRP grid area increase and spacing reduction. The ECC strength had no obvious effect on the cracking performance or load-carrying capacity. No interfacial slippage before ultimate capacity was observed in most beams, demonstrating full composite action.