Tensile properties deterioration of BFRP bars in simulated pore solution and real seawater sea sand concrete environment with varying alkalinities

This study investigates the effectiveness of reducing alkalinity on the durability enhancement of basalt fiber reinforced polymer (BFRP) bars to address their durability in the alkaline environment of seawater sea sand concrete (SWSSC). After accelerated aging at different temperatures and durations, the tensile properties of BFRP bars immersed in simulated SWSSC pore solution and embedded in seawater sea sand mortar (SWSSM) with varying alkalinities were evaluated by tensile testing. In addition, scanning electron microscopy, X-ray micro-computed tomography, and low-field nuclear magnetic resonance were used to examine the microstructure of embedded BFRP bars and SWSSMs. The experimental results indicate that reducing the pH of the solution and SWSSM to around 12 or below can significantly mitigate BFRP bar tensile strength loss. The maximum improvement of tensile strength retention for bare and embedded BFRP bars are 43.52% and 40.27%, respectively. Compared to BFRP bars wrapped in normal SWSSM, the degradation of resin, basalt fiber, and fiber-resin interface of embedded BFRP bars in the low-alkalinity SWSSMs is considerably mitigated due to the reduced alkalinity and porosity. According to the Arrhenius prediction, the tensile strength retention of BFRP bars embedded in normal SWSSM will decrease to 70% within 1.70–5.10 years, but it will be more than 85% for those embedded in low-alkalinity SWSSMs. This study indicates that it is an effective way to mitigate the deterioration of BFRP bars by using low-alkalinity SWSSC when BFRP bars are used as reinforcement in marine SWSSC structures.