Corrosion resistance and deterioration mechanism of coral concrete reinforced with steel-FRP composite bars

Abstract

The corrosion behavior of steel-FRP composite bars (SFCB) in coral concrete under harsh environmental conditions, as well as the mechanisms of deterioration, remain inadequately understood. This research gap impedes the accurate assessment of long-term this structural durability and stress analysis. In this study, corrosion testing, bond strength testing, and scanning electron microscopy (SEM) analysis were performed on SFCB immersed in seawater at varying temperatures, as well as on SFCB embedded in both coral concrete and sea sand concrete. The results indicate that, for the center pull-out test, the coral concrete with ordinary tertiary rebar (OTR) exhibit pull-out damage, whereas the specimens with SFCB show splitting damage, with cracks typically propagating in three directions. The bond strength retention between SFCB and coral concrete is lower than that between SFCB and sea sand concrete, largely due to the higher porosity and permeability of coral concrete. Additionally, the tensile strength of SFCB shows a slight decline over time when immersed. After soaking at room temperature 20 ± 2 °C for 180 days, the retention rates of bond strength between SFCB and coral concrete, SFCB and sea sand concrete are 93.90 % and 98.03 %, respectively, as well as 80.76 % and 93.89 % at 50 ± 2 °C, respectively. SFCB is corroded to a decreasing extent by alkaline solution, salt solution, and free water, in that order. The corrosion damage in SFCB initiates with the degradation of the outer resin due to water absorption and expansion, eventually causing the breakdown of the inner fiber matrix. Furthermore, this resin degradation significantly affects the bond strength between SFCB and coral concrete, while its impact on the tensile strength of SFCB is relatively minor. The average tensile strength of concrete-wrapped and directly immersed specimens decreased by 4.39 % and 6.97 % when immersed in seawater at 50 ± 2 °C for 180 days, respectively, and only decreased by 1.8 % at 20 ± 2 °C. Therefore, this study enhances the understanding of corrosion damage and mechanisms of deterioration in coral concrete structures containing SFCB, providing valuable data to improve their durability.