Molecular mechanisms of typical chelating agents influencing the early hydration of C3S: a combined MD and DFT study.

Abstract

Organic chelating agents are widely used to regulate cement hydration, yet the molecular relationship between ligand structure, interfacial adsorption, and mineral dissolution remains unclear. To overcome the limitations of single-scale approaches, this study employs a comprehensive synergistic framework combining density functional theory (DFT), well-tempered metadynamics, and unbiased molecular dynamics (MD). This framework investigates four typical chelating agents-acetic acid (AA), citric acid (CA), EDTA, and sodium gluconate (SG)-specifically selected for their distinct and representative arrangements of carboxylate, hydroxyl, and amine groups, evaluating their effects on C3S dissolution. This multiscale strategy successfully bridges precise electronic structures with dynamic hydration kinetics. Static DFT calculations show that multidentate ligands establish strong interactions with surface Ca sites via Na+-mediated ternary anchoring, whereas flexible ligands like SG exhibit weaker static adsorption. Metadynamics further reveals distinct retardation mechanisms by mapping the free-energy landscape: CA and EDTA operate via an inductive-trapping mechanism, stabilizing departing Ca in high-coordination free-energy minima to increase the barrier for further detachment, whereas SG elevates the dissolution barrier primarily through a steric-hindrance mechanism. Unbiased MD simulations demonstrate that chelator adsorption delays the complete surface decoordination of Ca, reorganizes the local water structure, and competitively restricts interfacial ion transport. Ultimately, the intrinsic capability to inhibit Ca release follows the sequence of EDTA > CA > SG > AA. These results link molecular coordination, interfacial adsorption, and dissolution energetics, providing a robust mechanistic basis for understanding chelator-induced retardation of C3S hydration.