Study on the deterioration mechanism of interfacial bond performance for CFRP reinforced concrete with AAM adhesive under sulfate attack

Alkali-activated materials (AAM) have high mechanical strength, salt corrosion resistance, environmental friendliness, which can be used as an adhesive instead of epoxy resin for CFRP reinforced concrete structures. In this study, the optimum mechanical performance of AAM adhesive was determined through an orthogonal experiment. The appearance, quality, compressive and flexural strength, as well as microstructural changes of AAM adhesive under sulfate attack were investigated. A double shear test investigated the effect of sulfate attack on the interfacial bonding performance of EP and AAM specimens, revealing the deterioration mechanism of the interface. Based on the Popovics model, an interface t-s time-varying model was established for EP and AAM specimens under sulfate attack. The interfacial bonding performance was evaluated using the interfacial fracture energy. The results show that the decrease in bond performance of EP specimens results from the joint deterioration of concrete and epoxy resin, while AAM specimens are only the deterioration of concrete. The maximum shear stress tmax and its corresponding slip value sm of EP and AAM specimens decreased by 36.1% and 28.0%, 27.6% and 27.7%, compared with those before erosion, and the interfacial fracture energy decreased by 59.1% and 50.3% respectively. The model and experimental data shown good agreement and could effectively reflect the variations in interfacial bonding performance. After 103 days of erosion age, the interfacial fracture energy of AAM specimens exceeded that of EP specimens, showing better bonding performance. The study suggests that using AAM instead of epoxy resin as the adhesive for structural reinforcement under sulfate attack is a better choice, and its results can promote AAM's application in the CFRP reinforced concrete field.