Molecular insights into the weakening effect of water on cement/epoxy interface

Abstract The strong interfacial integrity of FRP/concrete bonded system is shown to be significantly weakened in the wet environment, with the interfacial debonding between concrete and epoxy adhesive as major failure mode. However, the fundamental mechanism is still largely unknown. Here the molecular model of calcium silicate hydrate (C-S-H)/epoxy interface is constructed to analyze interfacial deterioration mechanism as affected by water molecules, by relating with the variation in interfacial behavior and failure mode. The simulation results show that water molecules in local C-S-H/epoxy interface degrade the interfacial behavior and lead to the shift in failure mode from cohesive failure of C-S-H gel to interfacial debonding between C-S-H and epoxy, achieving a close agreement with experimental observation. By simultaneously capturing interfacial deterioration and failure mode transition, it is shown that water molecules significantly weaken the interfacial integrity of cement/epoxy interface, and hence the long-term durability of FRP/concrete bonded system.