Nowadays, numerous concrete structures are urgently needed to be repaired and strengthened for the severe safety and durability of constructions. In this study, a novel type of silane-based interfacial coupling agent (ICA) is prepared by modifying the silane coupling agent (SCA) with a hydrothermally treated nanosilica (HTNS). The effect of ICA on the cement hydration and crystalline form as well as the hydrolysis/condensation extent of siloxanes is illustrated. The bonding strength, morphology and propagation of the interface cracks, and the interfacial ductile fracture characterization are investigated. Besides, the coupling mechanism of ICA in the repaired interface is explored. The results show that HTNS effectively catalyzes SCA hydrolysis and condensation to form Si-O-Si bonding in a neutral environment. The application of ICA on an old cementitious matrix not only significantly improves the bonding strength and toughness of the repair interface, but also mitigates the negative effect of dealcoholization of siloxanes on the hydration of the cement. The repaired interface simultaneously exhibits stiffness, toughness, and multicracking features in the process of straining. On a microlevel, ICA consumes portlandite during cement hydration and finely crystallizes to form a layered plug structure at the repaired interface . With the continuous dissolution of portlandite, the nanosilica in ICA forms a fibrous, stable product with ions and enhances the interfacial pore plug effect.
Keywords: cement; epoxy resin; interface; nanosilica; repair; silane coupling agent; waterborne.