Bond durability between geopolymer-based CFRP composite and OPC concrete substrate in seawater environments

Geopolymer binders are regarded as promising environmentally-friendly approaches for repairing damaged structures because of their excellent bonding and durability. The interfacial bonding properties between the geopolymer and the damaged structures are critical to the effectiveness of the repair, however, the durability of this interfacial bonding in complex environments remains poorly understood, impeding the application of the aforementioned repair methods. Therefore, this study investigates the durability of the interfacial bond between geopolymer and ordinary Portland cement (OPC) concrete in seawater environments, providing valuable insights for engineering applications of geopolymer-based repair techniques. The adoption of OPC concrete as the substrate was based on its widespread use as a cementitious material in existing structures. Additionally, geopolymer repair mortars and epoxy resin were utilized as the bonding matrix adhered to the OPC concrete substrates, while small-diameter carbon fiber-reinforced polymer (CFRP) bars served as reinforcement for the bonding matrix. Single-shear tests were conducted to investigate the bond strength and failure modes between the geopolymer mortar/epoxy resin and OPC concrete substrates after 90, 180, and 360 days of exposure to a seawater environment. The interfacial degradation mechanisms were captured using scanning electron microscopy (SEM) techniques. The results showed that the interface between the geopolymer repair mortar and the OPC concrete was identified as the most vulnerable component, which dominated the failure of the geopolymer-bonded OPC concrete. SEM analysis revealed an increase in the microcrack width at this interface, resulting in a 2.86-times increase in slip between the geopolymer repair mortar and the OPC concrete after 360 days. Due to the degradation of epoxy caused by seawater exposure, the failure modes of the epoxy-bonded OPC concrete transformed from OPC concrete cracking to epoxy rapture with increasing exposure time. The bond strength of post-exposure epoxy-bonded OPC concrete was higher than that of the geopolymer–bonded OPC concrete, but the former exhibited a more brittle failure behavior. •The deterioration of the interface between geopolymers and OPC concrete exposed to seawater was investigated.•The bonding properties of geopolymers (inorganic) and epoxy resins (organic) on OPC concrete are compared.•The microstructures at the interface of geopolymer and OPC concrete were