Atomistic Insights into Dual Mechanisms for NaCl-Driven Dissolution and Polymerization of Tricalcium Silicate

In this study, experimental characterization and reactive molecular dynamics simulations were integrated to reveal the effects of NaCl on the early hydration of tricalcium silicate (C 3 S). The results demonstrate that NaCl significantly accelerates the early hydration of C 3 S by promoting Ca dissolution and silicate tetrahedra polymerization. Specifically, Cl – ions coordinate with surface Ca, weakening the Ca–O bonds in C 3 S and reducing the energy barrier for Ca dissolution. Meanwhile, Na + ions compete with Ca 2+ for the O atoms, creating localized charge imbalance and attracting protons, which destabilize Si–O bonds and facilitate the polymerization of silicate tetrahedra. These effects are further amplified at elevated temperatures, which accelerate Ca dissolution and silicate chain formation. For the first time, an atomistic dual-pathway mechanism is proposed in this study, where Cl – facilitates Ca dissolution while Na + drives silicate polymerization during early C 3 S hydration, advancing the molecular-level understanding of ionic effects in cement hydration.