Impact of pore sizes and defects on C-S-H/epoxy bonding in wet conditions: A molecular dynamics analysis

Abstract

Despite the recent advances in understanding the water ingress at the interface of calcium silicate hydrate and epoxy, there are still open questions regarding the pore size and defects' dependence on the structure, dynamic and mechanical properties of the interfaces. In this paper, molecular dynamics simulations are carried out for perfect and defective interface models consisting of C-S-H and epoxy resins, respectively. Gaps of different sizes between epoxy and C-S-H are filled with water molecules, with a maximum spacing of 2.79 nm, to investigate the effect of water ingress on the structural, dynamic, and mechanical properties of the interface. The results indicate that in the interface formed by the defective structure, the calcium ions responsible for providing strength have been transformed into a free state due to the influence of water molecules. Consequently, they lose their ability to bridge between the epoxy and silicate tetrahedra, leading to the inability to establish interfacial strength. The defective structure, with its larger surface area and increased interaction with water, is more susceptible to degradation, especially noticeable in the tensile simulations. Furthermore, the interactions between water and C-S-H are the primary factors influencing the microstructure and dynamic behavior of the interface. As the number of water molecules increases, the interface strength weakens. This work provides new insight into understanding the bonding mechanism of the C-S-H/epoxy interface with water ingress. It contributes to the design and development of FRP reinforced concrete composites.

Keywords

• Calcium silicate hydrate
• Water molecules
• Interface
• Epoxy
• Molecular dynamic simulation