Shear performance degradation of basalt fiber-reinforced polymer bars in seawater environments: Coupled effects of seawater sea-sand geopolymer mortar coatings and sustained loading

Geopolymers, as a promising substitute for ordinary cement, exhibit different coating effects with regard to the durability of basalt fiber-reinforced polymer (BFRP) bars. In this study, a comparative investigation was carried out on the shear performance of prestressed BFRP bars coated with seawater sea-sand geopolymer mortar (SSGM). The alkaline content of the SSGM was 4% or 6%. The prestress level was 20% of the ultimate tensile strength at room temperature. The immersion temperatures were room temperature (RT), 40, or 60 degrees C. Interlaminar shear tests and transverse shear tests were conducted at each period (30, 60, 120, and 240 days). The results showed that BFRP bar coated with 6% alkaline content exhibited a slightly higher degradation of shear strength. Furthermore, the prestress developed microcracks in the bars and weakened the interface between the fiber and resin matrix, particular at the elevated temperature. This led to further degradation of the BFRP bars. Additionally, a comparison was made between the shear strength results of BFRP bars coated with SSGM and those coated with ordinary portland concrete or seawater sea-sand concrete, revealing that the long-term shear performance of BFRP bars was less negatively impacted by the SSGM coating. Highlights center dot Coupled effects of SSGM coatings and sustained loading on the degradation of BFRP bars are investigated. center dot SSGM provides better protection for BFRP bars than cement-base concrete. center dot Alkaline content of activator in SSGM has insignificant impact on the BFRP degradation.