Effects of surface characteristics and alkalinity on the deterioration of BFRP bars and BFRP-SSC interface in seawater environment

This study investigated the surface characteristics and concrete alkalinity on the deterioration of basalt fiber reinforced polymer (BFRP) bars and the interface between BFRP bars and seawater sea-sand concrete (SSC) in a seawater environment. The degradation of BFRP bars with three surface characteristics (sand coating, helically-wound, and helically-wrapped) embedded in two alkalinities of SSCs and BFRP-SSC interface were studied by shear, tensile, and pull-out tests, respectively. Additionally, the microstructure of the BFRP and BFRP-SSC interface was characterized by Fourier transforms infrared spectroscopy (FTIR), X-ray computed tomography (X-CT), and scanning electron microscope (SEM). The experimental results showed that sand-coated BFRP bars exhibit the best durability performance among the three types of BFRP bars due to forming a protective layer of sand and the helically-wound BFRP bars degrade from the groove (rich fiber and less resin protection zone). The degradation of BFRP bars in low alkalinity (LA) SSC is significantly mitigated owing to the reduced alkalinity. Furthermore, the hindering effect of the sand layer also enhances the bond durability between bars and SSCs compared with the other two types of BFRP bars. The bond strength between BFRP bars and LA-SSC is slightly reduced after 180 days of seawater immersion, while that in ordinary (O) SSC decreases significantly. The pull-out failure of sand-coated BFRP bars in LA-SSC is wearing out of the sand layer and surface resin after environmental conditions, while that of helically-wound BFRP bars in LA-SSC are peeling off ribs. The research outcomes can serve as solid base for employing BFRP bars in the marine environment.