Chelation-Orchestrated Hydration Suppression of Tricalcium Silicate: Interfacial Trapping of Calcium Ions by Tannic Acid via Synergistic Experiments and Molecular Dynamics

The hydration of tricalcium silicate (C 3 S), as the dominant process in cement hardening, fundamentally governs concrete strength development and material properties, where organic admixtures serve as critical regulators of its hydration behavior. This study examines tannic acid’s (TA) influence on early cement hydration by elucidating its impact on C 3 S dissolution and adsorption mechanisms through multiple approaches: interfacial adsorption studies, solution complexation analysis, calcium chelation effects, hydration kinetics, and molecular dynamics (MD) simulations. Experimental characterization of TA-C 3 S interactions, including product morphology/composition analysis and ionic behavior during hydration, combined with MD simulations, revealed nanoscale adsorption phenomena between C 3 S, water, and TA. Kinetic analysis using the Krstulović-Dabić model identified a three-stage hydration process (nucleation–growth, phase-boundary reaction, and diffusion), where TA addition reduced both the number of reaction stages and rate constants. MD simulations demonstrated that Ca–O and hydrogen bonding mediate TA-C 3 S connections, while TA’s hydrophilic nature attracts water molecules to its chains, limiting their access to C 3 S surfaces. Additionally, TA sequesters calcium ions released during C 3 S dissolution, promotes surface hydration product accumulation, and ultimately inhibits C 3 S dissolution. These findings collectively demonstrate TA’s multifaceted retardation mechanism governing C 3 S.