Molecular dynamics simulation of calcium and sodium ion migration in geopolymer formation and mechanical properties

DM Wang and KJ Wang and F Zhang, JOURNAL OF MATERIALS SCIENCE, 60, 22726-22756 (2025).

DOI: 10.1007/s10853-025-11733-5

The optimal exploitation of geopolymers relies on a fundamental understanding of their atomic behavior, and molecular dynamics (MD) simulations provide a robust tool for addressing these issues. In this study, MD simulations are conducted to investigate the distinct behaviors of Ca2+ and Na+ ions during a geopolymer formation process. Simulation reveals that Na+ ions actively participate in polymerization, reacting with the silica-aluminum oxide precursor to form a sodium aluminosilicate hydrate (N-A-S-H) binder (geopolymer). As the Al content increases, more Na+ ions are involved in the chemical reaction. In contrast, the Ca2+ ions exhibit a different behavior, refraining from participating in polymerization and remaining suspended outside the geopolymer surface. The migration processes of Ca2+ and Na+ ions are thoroughly evaluated. Post-polymerization, molecular structure, and mechanical properties of the systems with varying Si/Al ratios are analyzed. The molecular structure analysis confirms the feasibility of this modeling method. Moreover, simulations of mechanical tests are conducted. Tensile test indicates that Na+ ions play a significant role in enhancing the mechanical strength. Shear test demonstrates the torsion and breakage characteristics of the atomic bonds. This study offers a perspective for addressing the conflict between the ease of breaking Al-O bonds and the existence of an optimal Si/Al ratio.

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