Bond durability of FRP bars and seawater–sea sand–geopolymer concrete: Coupled effects of seawater immersion and sustained load

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Fibre reinforced polymer (FRP)-reinforced seawater–sea sand–geopolymer concrete (SSGC) structures combine the advantages of corrosion-free FRP bars in marine environments and the direct utilization of seawater and sea sand, fly ash, and ground granulated blast furnace slag (GGBS), which can lead to a reduction in carbon emissions and promote sustainable development in civil engineering. This study explores the combined effects of seawater immersion (laboratory condition, ∼26 °C) and sustained load (60% ultimate interface bond strength) on the durability of the interface between FRP bars and SSGC by pull-out tests. The test parameters included FRP bar type and immersion duration (60 and 180 days). River sand and freshwater geopolymer concrete (RSGC) were used for comparison. The properties of the SSGC were also studied to reveal the impact on the interface performance. The results showed that the increase in GGBS content reduced the setting time but was beneficial for improving the compressive strength of the concretes at 28 d due to the large amount of calcium ions contained in the GGBS. The increase in Na2SiO3 content increased N-A-S-H, resulting in a dense cementitious material; compressive strength increased, and the axial ultimate strain of concrete decreased. The long-term performances of SSGC and RSGC in a seawater immersion environment were similar and characterized by reduced strength and enhanced brittleness. The bonding strength between the FRP bar–concrete interface decreased due to the decreased concrete strength under seawater immersion. As the immersion time increased, the fibre fractured under the effects of sustained load, leading to an increase in the bond strength degradation. The bond–slip constitutive model was analysed based on existing models.