Influence Mechanism of the Interfacial Water Content on Adhesive Behavior in Calcium Silicate Hydrate−Silicon Dioxide Systems: Molecular Dynamics Simulations

The performance indicators of concrete are mainly determined by the interface characteristics between cement hydration slurry and aggregates. In this study, molecular dynamics technology was used to evaluate the effect of the interfacial water content on the evolution of the interface structure, interaction energy, and mechanical properties of calcium silicate hydrate (C-S-H) and silicon dioxide (SiO2) systems, and the weakening mechanism of the C-S-H/SiO2 interface in a humid environment was revealed. The results showed that all stress–strain curves of C-S-H/SiO2 were divided into the elastic stage and the failure stage. As the interfacial water layer thickened, the molecular weight of the water invading the C-S-H gradually increased, and the desorption of Ca2+ ions in the surface region became significant, while the amount of Ca2+ ions entering the water-layer region increased. The interaction energy of the C-S-H/SiO2 progressively became larger, and the energy ratio (ER) significantly decreased; the tensile strength σc and residual strength σr of C-S-H/SiO2 both showed a downward trend. In summary, a lower water content had a limited impact on the interfacial bonding strength, while the weakening effect enhanced with an increase in the interfacial water content. This phenomenon was also demonstrated in concrete interfacial bond strength experiments.