Effect of alkalinity and pre-cracks of seawater sea-sand concrete on the deterioration of BFRP bars in marine environment

The durability of basalt fiber-reinforced polymer (BFRP) bars in seawater sea-sand concrete (SWSSC) is a major problem due to their susceptibility to corrosion in alkaline environments. Moreover, the corrosion development in BFRP bars can be affected by micro/macro cracks within the SWSSC. In this study, normal seawater sea-sand concrete (NA-SWSSC) and low alkalinity seawater sea-sand concrete (LA-SWSSC) specimens with different prefabricated crack widths were prepared to study the long-term performance of embedded BFRP bars. The degradation on surface morphology, tensile properties, and microstructures of samples were characterized after accelerated aging in a seawater erosion environment. Results demonstrated that reducing the alkalinity of SWSSC could effectively mitigate the decomposition of resin and deterioration in mechanical properties. The residual tensile strength of BFRP bars in low alkalinity environment (L-O group) is about 26.8 % higher than that of NASWSSC group (N-O group). The increasing crack width benefits corrosion resistance of BFRP bars, especially in the high alkalinity group. The increasing crack width can enhance the long-term tensile strength of BFRP bars due to reduced pore solution alkalinity through ion exchange with external environment. Meanwhile, these aging resistance enhancements are less pronounced in LA-SWSSC than that in NA-SWSSC due to low ion concentration difference. The deterioration of embedded BFRP bars is primarily attributed to the hydrolysis of the epoxy resin matrix. The research outcomes could provide valuable insights into extending the serviceability of BFRP bars in SWSSC.