Temperature-Driven Degradation Mechanisms of Steel–Concrete Interfaces in NaCl Solution Environments: Nanoscale Insights from Molecular Dynamics Simulations

This study aims to clarify the temperature-dependent degradation mechanisms of the steel–concrete interface in NaCl solution environments at the nanoscale, focusing on the key components of calcium silicate hydrate (C-S-H, the primary hydration product of cement) and iron oxyhydroxide (γ-FeOOH, a critical component of steel passive films in highly alkaline environments). Using Materials Studio software (2023) and molecular dynamics simulations, the evolution of the interface’s performance under temperatures ranging from 300 K to 390 K (corresponding to 27 °C to 117 °C) is systematically investigated. The results reveal that elevated temperatures degrade the performance of C-S-H/γ-FeOOH interfaces through three main mechanisms: (1) The stability of the hydration shell around aggressive ions is weakened, enabling these ions to occupy the coordination positions of calcium ions on the interface and form stable ion pairs with surface calcium ions, thereby weakening interfacial bonding. (2) The mobility of surface calcium ions is enhanced, reducing the strength of the interaction of ion pairs and diminishing the mediating role of calcium ions in connecting the C-S-H and γ-FeOOH phases. (3) Hydrogen bond stability at the interface decreases, as indicated by reduced hydrogen bond angles and numbers, coupled with increased hydrogen bond lengths. The above three reasons lead to a decrease in adsorption energy in the C-S-H/γ-FeOOH interface, which degrades the interface bond’s performance.