Long-term shear performance of bare and cement mortar-coated BFRP bars in corrosive environments

Abstract

For the safe design of a basalt fibre-reinforced polymer (BFRP) bar for use as a reinforcement in concrete structures, it is essential to investigate the durability of the BFRP bars. This work focuses on the physicochemical properties of BFRP bars coated with cement mortar after immersion in distilled water, alkaline solution and seawater. The effects of the immersion medium, cement mortar coating size, immersion time and immersion temperature on the shear resistance of the BFRP bar as well as the microstructure and chemical composition of the interface between the basalt fibre and concrete substrate were examined. The cross-linking density of the resin matrix was used to illustrate the decomposition of BFRP bars. Then, the degradation evolution and mechanism of cement mortar-coated BFRP under various immersion environments were revealed. The results show that all the immersions have a negative influence on the shear performance of BFRP bars, and the effect of the alkaline solution is the most significant. The alkalinity played an important role for the BFRP bars immersed in distilled water and seawater, and the apparent shear strengths of the specimens coated with 0, 10, and 20 mm cement mortar immersed in 40 °C distilled water decreased by 27%, 32% and 57%, respectively, after one year. The alkali-silica reaction (ASR) of the SiO2 in basalt fibre was found at the cement mortar-BFRP interface, and the ASR contributed to this coating size effect.