Investigation of the induction period of C ₃ S hydration: A molecular dynamics simulation approach

Abstract Tricalcium silicate (C 3 S) hydration fundamentally determines concrete's mechanical properties and durability. While the induction period of C 3 S hydration has been traditionally attributed to Ca 2+ and OH − ion dissolution dynamics, the atomic‐scale mechanisms governing this critical phase remain incompletely understood. This study employs ReaxFF reactive force field molecular dynamics (MD) simulations to systematically investigate C 3 S dissolution processes, with particular focus on surface structural evolution during initial hydration stages. Accelerated MD simulations at 1300 K revealed unprecedented insights into C 3 S dissolution mechanisms. The 10 ns simulation demonstrated a remarkable six‐order‐of‐magnitude acceleration in dissolution rates compared to room temperature conditions, effectively representing milliseconds of actual hydration time. Notably, hydroxylation increased to approximately 2130% at 1300 K, which is approximately eight times the rate observed at 300 K, confirming that elevated temperatures significantly accelerate initial hydration processes without fundamentally altering the underlying mechanisms. Key findings include extensive binding between Ca‒water and silicon‒water bonds, with hydrogen and water atoms penetrating the solid matrix up to 15 Å. The dissolution process revealed a gradual detachment of silicon from the C 3 S surface, forming silanol groups (potentially H 3 SiO 4 − , H 2 SiO 4 2− , or HSiO 4 3− ). Critically, a double electrical layer formed by silanol groups and calcium ions was observed to cause a progressive slowdown in C 3 S crystal dissolution rates during the 8‒10 ns reaction phase, exhibiting a Ca 2+ /silanol ratio of approximately 3. This research provides atomic‐level confirmation of the double electric layer formation on the C 3 S surface during the induction period and offers a novel mechanistic explanation for the decreased dissolution rate. The findings have significant implications for understanding cement hydration kinetics and potentially optimizing concrete performance at the molecular scale.