Critical Role of Alkali-Metal Ions in a β-Dicalcium Silicate Hydration Reaction: Well-Tempered Metadynamics

β-Dicalcium silicates (β-C2S) exhibit excellent potential for reducing carbon emissions and energy consumption. However, their poor hydration activity leads to low early strength, limiting their large-scale application. Modulation of the hydration medium has been proven to be able to enhance the hydration activity, but the underlying reaction mechanism remains unclear. In this work, the hydration reaction kinetics, atomic structure, and electronic structures in β-C2S/H2O and β-C2S/Na-H2O systems are investigated by well-defined ab initio molecular dynamics and well-tempered metadynamics. The results demonstrate that the sodium ion regulated the interface between the solid and liquid phases, influenced the process of surface hydroxylation, and formed a new dissolution mechanism of calcium. The importance of regulating the interfacial chemistry environment for the hydration reaction was found. This study provides theoretical guidance for further understanding of the early hydration reaction of β-C2S under hydration conditions in the presence of alkali metal ions.