Understanding the bond performance between BFRP bars and alkali-activated seawater coral aggregate concrete under marine environments

To improve the bond durability of fiber-reinforced polymer (FRP) bars with coral aggregate concrete (CAC), this study employed alkali-activated materials (AAMs) as an alternative to ordinary Portland cement for preparing alkali-activated slag CAC (AACAC) and investigated their bond behavior with FRP bars under seawater corrosion environments. The influences of various exposure times (0, 6, 9, and 12 months) and seawater environments (seawater immersion and drying-wetting cycles) on bond performance were considered. Scanning electron mi-croscopy (SEM) and X-ray diffraction (XRD) were adopted to characterize the microstructural changes and mineralogical characteristics at the cross-section of BFRP bars and at paste matrix-aggregates interfaces of the concrete after seawater environment exposure. The tested results manifested that with the increase in exposure age, the bond strength for AACAC and CAC specimens gradually degraded, but their slope at the ascending stage of bond-stress curves (i.e., bond stiffness) tended to be enhanced. Compared with CAC specimens, AACAC specimens achieved a slightly lower rate of performance degradation. After being suffered from seawater con-ditions for 12 months, the compressive strength and bond strength of CAC specimens decreased by approximately 6.5% and 2.3%, respectively, while those of AACAC specimens only degraded by 2.5% and 1.5%, respectively.