Bond durability of BFRP bars embedded in concrete with fly ash in aggressive environments

Abstract

Abstract Fiber-reinforced polymer (FRP) bars are an environmentally friendly alternative to steel and are considered ideal substitutes for steel reinforcement in marine concrete structures due to their excellent resistance to chloride ions and mechanical properties. However, the strong alkaline environment in concrete results in the degradation of FRP bars, and the degradation of FRP bars is detrimental to the long-term performance of these structures due to the decrease in interfacial bonding. This study aims to investigate the durability of basalt FRP (BFRP) bar-concrete interfaces in laboratory corrosion environments by pull-out tests. The immersion environments are an alkaline solution (pH 12.8 ± 0.2) and simulated seawater, and the immersion temperatures are set at room temperature (∼ 26 °C), 40 °C, and 60 °C. Furthermore, fly ash is used to improve bond durability. The mechanical properties of the BFRP bars are also determined under the same conditions. Results indicate that the mechanical properties of the BFRP bars and the bond strength decrease as the immersion time increases. The addition of fly ash in concrete can improve the interfacial bond strength. For instance, the bond strength of BFRP-ordinary concrete decreases by 69.0% when immersed in a 60 °C alkaline solution for 6 months, and BFRP-fly ash concrete decreases by 58.1% in the same immersion environment. The same experimental phenomenon can also be obtained in seawater, which can be attributed to fly ash refining the concrete pores and inhibiting the alkaline aggregate reaction of the reactive silica in BFRP. Finally, the retention of bond strength is predicted based on the apparent horizontal shear strength of the BFRP.