Bond durability of BFRP and GFRP bars in sulphoaluminate cement concrete under water immersion environment

To study the durability of bond performance between basalt-/glass-fiber reinforced polymer (BFRP/GFRP) bars and low alkalinity sulphoaluminate cement concrete (SAC), the bond test of 144 specimens were conducted after 30-, 90-, 180- and 360-day water immersion at 20, 40 and 55 °C. The test results indicated that the bond strength between BFRP/GFRP bars and SAC/ordinary Portland cement (OPC) concrete increased in the first 90 days due to the continuous cement hydration, and then decreased due to the long-term degradation. Moreover, the elevated temperature contributed to the more severe deterioration of bond performance. After 360-day aging at 55°C, the bond strength between BFRP (or GFRP) bars and OPC decreased by 24.8% (or 10.4%). Conversely, the FRP-SAC showcased superior durability than FRP-OPC counterpart (26% and 15.9% bond performance enhancement for BFRP- and GFRP-concrete, respectively). To profoundly investigate the inherent degradation mechanism between FRP bars and concrete, scanning electron microscopy (SEM) analysis was conducted. Finally, the long-term bond performance of BFRP/GFRP bars in SAC was comprehensively predicted, remaining a considerable bond strength retention of 92.84∼100% after 75 years of service in moisture saturated environment at 25 °C∼35 °C.