Debonding mechanisms of epoxy from calcium silicate hydrate surface under the conditions of saline solution at elevated temperature

Abstract

Interface bonding between calcium silicate hydrate (C–S–H) and epoxy is of critical importance for C–S–H/epoxy composites that are extensively utilized in the civil engineering, and yet it is susceptible to saline solution or elevated temperature. Herein, molecular dynamics is applied to explore the debonding mechanisms of epoxy from C–S–H surface under the coupling effect of water, ions, and temperature. Aqueous environment is the prerequisite for temperature and ions to influence interface bonding. At dry state, temperature elevation promotes the structure relaxation of C–S–H/epoxy interface, which optimizes the coordination structure at interface and increases interface energy. At wet state, on the contrary, temperature elevation aggravates the weakened effect of water molecules on interface bonding. The dynamics of epoxy molecules changes from the feature of solid state into fluid state. Water molecules and Na+ act in the same way at the interface. Both compete for active sites of epoxy molecules and C–S–H surface, which interferes the formation and stability of the bonds between C–S–H and epoxy molecules. As compared with water molecules, ions play larger roles in weakening interface bonding.