Enhancement of Bond Performance of FRP Bars with Seawater Coral Aggregate Concrete by Utilizing Ecoefficient Slag-Based Alkali-Activated Materials

Abstract

To effectively utilize marine resources on reefs or islands and to improve the bearing capacity and serviceability of fiber-reinforced polymer (FRP) reinforced seawater coral aggregate concrete (CAC) structures in marine environments, this paper investigates the applicability of using alkali-activated materials (AAMs) as substitutes for ordinary Portland cement (OPC) in FRP reinforced CAC structures. Three types of FRP bars, i.e., carbon-FRP (CFRP), glass-FRP (GFRP), and basalt-FRP (BFRP) bars, with different bond lengths (L = 50, 70, and 100 mm) were selected to determine the bond characteristics of FRP bars in alkali-activated seawater coral aggregate concrete (AACAC), as well as in cement-based CAC, which was chosen as the reference. Moreover, a scanning electron microscope (SEM) was employed to detect the microstructure characteristic at the interfacial transition zone (ITZ) between the coral aggregates and the paste matrix. The results indicated that the AACAC specimens contained a stronger mechanical bite force at the paste–aggregate interface and exhibited a higher splitting tensile strength (approximately 6.7% improvement) than those of the CAC specimens. Additionally, the ultimate bond strength and the initial slope of the bond–slip curves at the ascending branch (i.e., initial bond stiffness) were significantly improved by utilizing AAMs. Improvements of approximately 26.6%, 26.8%, and 16.9% were achieved in the bond strength for the specimens with CFRP, GFRP, and BFRP bars, respectively. It was concluded that the utilization of AAMs as alternatives for OPC was an effective method in improving the mechanical interaction at the paste–aggregate interface and promoting the anchorage capacity of FRP bars in CAC, which may represent a promising approach for applying AAMs in FRP reinforced CAC structures or members.