Nanoscale insights on the Interface between Passive Film of Steel and Cement Hydrate: Diffusion, Kinetics and Mechanics

Abstract The interfacial region between concrete and steel reinforcement (SCI) determines strength and durability of reinforced concrete structure. In this work, the molecular dynamics simulations were employed for understanding the bonding mechanism of SCI region. In the interfacial region, the calcium ions play the mediation of bonding C-S-H surface and the passivation film by combing the oxygen atoms and hydroxyl groups of C-S-H in the nearest neighbors. The hydroxyl groups in the γ-FeOOH and the unbinding O atom in the C-S-H provide enough oxygen sites to form the hydrogen bonds and hydration, which also improve the bond strength of the interlayer region. Furthermore, introducing single-layer water results in the hydrated Ca2+-water cluster formation, weakening the Ca-O connectivity between C-S-H and passive film. Double-layer water can significantly increase the diffusion of interfacial components and decrease the stability of interfacial bonds. In addition, simulated pull-out test and uniaxial tensile test were performed to evaluate bond strength of C-S-H and γ-FeOOH. Hydrolytic weakening is found due to water ingress in the interfacial region. Double-layer water penetration results in reduction of interfacial shear strength from 0.53 GPa to 0.38 GPa. Also, the Young’s modulus and cohesive strength reduced by more than 50% percentage. This work is expected as an important reference for design and development of reinforced concrete in engineering application.