Flexural behaviour of seawater–sea sand concrete beams reinforced with GFRP bars: Effects of the reinforcement ratio, stirrup ratio, shear span ratio and prestress level

Glass fibre-reinforced polymer (GFRP) bar-reinforced seawater–sea sand concrete (SWSSC) has been widely regarded as a new structural material with great potential due to its environmental friendliness. To safely and economically utilize seawater and sea sand to cast GFRP bar-reinforced flexural members in coastal areas, an experimental study was conducted to investigate the flexural behaviour of 12 GFRP bar-reinforced SWSSC beams. The various considered parameters included the (1) reinforcement ratio, (2) stirrup ratio, (3) prestress level, and (4) shear span ratio. The experimental results for the GFRP bar-reinforced SWSSC beams were verified via a comparison to the calculation models of GB 50608-20 and ACI 440.1R-15 for FRP bar-reinforced normal concrete (NC) beams. The results indicated that the prestress level is the main factor controlling the cracking load of the GFRP bar-reinforced SWSSC beams, and the cracking load of prestressed beams was 81% higher than that of nonprestressed beams. The ultimate load of the GFRP bar-reinforced SWSSC beams was strongly correlated with the reinforcement and shear span ratios (the higher the reinforcement ratio or the lower the shear span ratio was, the higher the ultimate load). Under the influence of the reinforcement and stirrup ratios, the failure mode of the GFRP bar-reinforced SWSSC beams could be transformed from GFRP bar rupturing into concrete crushing. Moreover, the calculation model of ACI 440.1R-15 overestimated the ultimate flexural capacity of the nonprestressed beams, while the calculation model of GB 50608-20 yielded conservative estimation values for the nonprestressed specimens and overestimated values for the prestressed beams. To ensure safety, the calculation model of GB 50608-20 for FRP bar-reinforced NC beams can be adopted when designing nonprestressed GFRP bar-reinforced SWSSC beams. In contrast, a prediction model for prestressed GFRP bar-reinforced SWSSC beams should be further investigated.