Atomic-Level Simulation of Sulfate Attack Effects on Interfacial Shear Behavior of Concrete Cold Joints

Abstract

In saline-alkali or coastal regions, sulfate attack is a primary factor causing performance deterioration of concrete structures. Hence, concrete cold joints, being weak interfaces of structures, warrant attention regarding their shear deterioration performance in sulfate attack environments. This study employed molecular dynamics simulations to establish models characterizing concrete cold joints, specifically a CSH-a-to-CSH-b (CC) interface and a CSH - a - to - SiO 2 (CS) interface. The influence of different Na 2 SO 4 solution concentrations (0%, 5%, and 10%) on the shear deterioration behavior of these interfaces was investigated. The results indicated that as the Na 2 SO 4 concentration increased, the degree of interfacial erosion damage became more pronounced. The penetration of Na 2 SO 4 solution altered the interfacial ionic interactions, making the substrate ions more likely to bond with the solution ions, thereby further deteriorating the shear performance of the interface. When the Na 2 SO 4 concentration increased from 0% to 5% and then from 5% to 10%, the maximum shear stress of the CC interface decreased by 68.8% and 31.0%, respectively, whereas that of the CS interface decreased by 62.5% and 39.4%, respectively. Additionally, Na 2 SO 4 solution significantly influenced the shear failure mode of the model. In the absence of Na 2 SO 4 erosion, shear failure occurred within the CSH-a substrate with lower strength and unstable bond energy. However, as the Na 2 SO 4 concentration increased, the failure mode shifted to distinct interfacial shear failure. This study reveals the influence of sulfate concentration at the nanoscale on the shear behavior of concrete cold joints, providing a new perspective for understanding their deterioration mechanisms in sulfate attack environments.