Experiment and LSTM-driven tensile strength retention prediction of B-SFCBs: Multi-parameter coupling under chloride and alkaline solution attacks

Steel-FRP composite bars (SFCBs) were developed to synergize the advantages of steel and fiber-reinforced polymer (FRP), demonstrating significant potential for marine infrastructure applications. Among these, basalt FRP (BFRP) wrapped SFCBs (B-SFCBs) offer optimal economic and serviceability performance. This paper investigated the tensile behavior of B-SFCBs following 180-day exposure to water, chloride, and alkaline solutions. Mass variation and tensile properties were systematically monitored throughout the exposure period. Microscopic testing was also supplemented with scanning electron microscopy (SEM) to characterize micro-damage progression. Results demonstrated that 180-day corrosive exposure reduced tensile strength by 14.5 % and 29.7 % in chloride and alkaline respectively. Notably, microscopic examination confirmed no significant interfacial damage between the steel core and FRP sheath. A comprehensive database of 79 experimental data points was assembled to analyze post-exposure strength. A long short-term memory (LSTM) model with optimized hyperparameters was subsequently developed. The trained LSTM identified four critical input parameters: pH, temperature, stress level, and chloride concentration. Subsequently, an explicit moisture absorption model was formulated to predict tensile strength retention, integrating damage contributions from the identified parameters to achieve significantly enhanced prediction accuracy.