Molecular elucidation of cement hydration inhibition by silane coupling agents.

Silane coupling agents are widely recognized to retard early hydration when incorporated into fresh cement paste, yet the atomic-level mechanisms underlying their effects on clinker dissolution, such as adsorption of silane monomer onto reactive surface sites and modification of ion detachment pathways, remain unexplored. Here we show dissolution behavior of tricalcium silicate (CaSiO) under 3-aminopropyl triethoxysilane impact using ab initio metadynamics, with experimental validation of the retardation effects in silane-treated pastes. The shielding effect of silane induces shifts in free energy changes of stepwise calcium dissolution from negative to positive and alters the most stable Ca coordination state during dissolution, resulting in the transition of dissolution from spontaneous to non-spontaneous. Specifically, hydrolyzed silane adsorbs dissociatively onto the CaSiO surface by forming ionic Ca-O bonds, thereby occupying reactive sites and introducing steric hindrance. This, in turn, impedes coordination interactions between calcium ions and water molecules. Experimental results further corroborate these interactions, as evidenced by reduced calcium concentrations in silane-treated pastes, which in turn slowed the hydration process. These findings offer nanoscale insights into the role of SCAs in cement hydration and provide a foundation for future research into the complex interactions within organic/cement systems.