Erosion experiments and molecular dynamics simulations of hydrated calcium silicate under the action of sulfate

Abstract

The ion transport process between the C-S-H and corrosive ions was simulated using the molecular dynamics method. High-purity C-S-H gels were prepared using the solution method and were subjected to different durations of magnesium sulfate erosion. The microscopic morphology of the eroded samples was studied using X-ray diffraction (XRD), scanning electron microscopy (SEM). By analyzing the experimental and simulation results, it was determined that the main erosion mechanism of the magnesium ions was to generate weak hydrated magnesium silicate or sphalerite, while the sulfate ions caused decalcification of the C-S-H, producing gypsum and thaumasite with swelling. Further, the addition of sulfate ions increased the diffusion coefficients of the magnesium and calcium ions, thus leading to enhanced erosion, and the erosion caused by the sulfate ions was the main cause of the ordinary Portland cement (OPC) mechanical and durability performance problems.