Reactive molecular dynamics study of CO2-induced debonding at the steel- concrete interface: Influence of Ca/Si ratio and Al incorporation in C-S-H

WZ Sun and YH Wang and P Wang and Y Zhang and DS Hou and MH Wang and XM Zhou, CONSTRUCTION AND BUILDING MATERIALS, 492, 142626 (2025).

DOI: 10.1016/j.conbuildmat.2025.142626

Reinforced concrete is widely used in modern structural engineering, with its performance largely dependent on the bond strength at the steel-concrete interface. Carbonation is a key factor contributing to interface debonding and steel reinforcement corrosion. This study employs reactive force field molecular dynamics simulations to investigate the impact of carbon dioxide (CO2) on interfacial bond strength. By constructing models of calciumsilicate-hydrate (C-S-H) with varying Ca/Si ratios and bridged oxygen-modified structures, as along with passivation film models, we examined CO2 diffusion, adsorption, and their effects on interfacial friction and film stability. The results reveal that CO2 significantly decreases interfacial friction (up to 27.4 %), disrupts the ordered arrangement of water molecules, weakens the hydrogen bond network, and consequently diminishes bond strength at the interface and the corrosion protection for steel. Notably, the interfacial system with a lower Ca/Si ratio exhibits higher sensitivity to CO2, resulting in more severe degradation of the passive film. In contrast, incorporating aluminium oxide as a replacement for bridged oxygen in C-S-H effectively enhanced the matrix's CO2 adsorption and immobilization capacity, mitigated CO2-induced damage to the passivation film, and improved interfacial stability and carbonation resistance. Significantly, this system exhibited the smallest reduction in interfacial friction, with a decrease of only 19.8 %. These findings provide a theoretical basis for developing high-performance anti- corrosion materials and offer new insights into designing more durable reinforced concrete structures.

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