IntroductionIn marine environments, the conventional steel reinforcement is prone to corrosion, leading to severe damage to concrete. Additionally, the deficiencies of ordinary concrete in terms of resistance to marine corrosion and impermeability significantly shorten the service life of marine concrete structures, which has attracted widespread attention. To enhance the durability of marine concrete, researchers are actively exploring new solutions. Among these, the use of FRP (Fiber Reinforced Polymer) reinforcement to replace traditional steel bars effectively addresses the issue of steel corrosion. Calcium sulfoaluminate (CSA) cement concrete, with its characteristics of early strength, high strength, corrosion resistance, and excellent impermeability, is particularly suitable for marine concrete structures that require high early-strength and durability. Based on this, the present study investigates the specific impact of different bond lengths of GFRP (Glass Fiber Reinforced Polymer) and BFRP (Basalt Fiber Reinforced Polymer) reinforcement on the bonding performance of the FRP-CSA full-coral aggregate concrete system.MethodsThis study investigated the influence of different bond lengths of FRP bars in full coral aggregate seawater sea-sand sulphoaluminate cement concrete (FCASS-CSAC) on the bond properties. This study used two different types of bars (GFRP and BFRP) and three different bond lengths (5 d, 7.5 d, 10 d, where d represents the diameter of the bars) to cross combine into 6 different types of specimens. All specimens were demolded after 24 h treatment and cured for 28 d in a standard curing chamber (temperature of (20±2) ℃, relative humidity of 95%). Subsequently, compressive strength tests and central pull-out tests were conducted to investigate the bond performance between FCASS-CSAC and FRP bars.Results and discussionWhen the bond length of BFRP and GFRP reinforcement bars is 5 d, the bond stress is generally higher than when the bond length is 7.5 d or 10 d. Specifically, for BFRP bars, the bond strength at a bond length of 5 d is approximately 30% and 60% higher than that at bond lengths of 7.5 d and 10 d, respectively. The bonding performance of BFRP and GFRP reinforcement bars was compared, and the results show that, in the absence of ribbed features, BFRP reinforcement typically exhibits superior bonding performance, with the bond strength generally about 40% higher than that of GFRP bars. This suggests that BFRP reinforcement has a potential advantage in providing stronger bond strength, which may be related to its material properties and the way it interacts with the matrix.ConclusionsThe main conclusions of this study are summarized as follows. The bonding performance of BFRP reinforcement with FCASS-CSAC is generally superior to that of GFRP reinforcement, with an overall bond strength about 40% higher. The bond strength of both types of reinforcement decreases as the bond length increases, with BFRP reinforcement showing a significantly higher bond strength at a bond length of 5 d compared to 7.5 d and 10 d. Based on the experimental results, an empirical formula for predicting bond strength was proposed. Furthermore, finite element simulation analysis was conducted, and the analysis results showed good agreement with the experimental findings.