Influence of ion concentration in karst water on calcium leaching from cement hydration products: A molecular dynamics and metadynamics study

SJ Guan and XF Zhang and FL Han and T Liang and SY Liu and XG Chen, COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS, 727, 138424 (2025).

DOI: 10.1016/j.colsurfa.2025.138424

The decalcification of calcium silicate hydrate (C-S-H) in karst environments is a key factor that affects the longterm durability of cement-based infrastructure. However, the atomic-scale mechanisms that govern calcium ion desorption and migration from C-S-H under karst water conditions remain poorly understood. In this study, molecular dynamics (MD) and metadynamics simulations were used to systematically investigate the calcium leaching behavior of C-S-H in pure water and representative karst water environments, and for the first time revealed the synergistic promoting effect of multi-ion coupling in karst water on the early-stage decalcification rate of C-S-H. The results revealed that cations in karst water facilitated the leaching of surface calcium (Caw) through an ion exchange mechanism, while anions tended to inhibit sustained leaching by forming ionic associations with surface calcium. In pure water, calcium dissolution proceeded via a relatively straightforward and slower pathway. In contrast, the presence of anions in karst water markedly accelerated the initial decalcification rate by accelerating the desorption of Caw and impacting water molecule diffusion dynamics. Free energy surface analyses further indicated that the promoting effect of anions on Caw leaching diminished over time, suggesting that calcium leaching in karst environments is characterized by greater complexity and activity during the early stages. This study elucidated the atomistic mechanisms of C-S-H dissolution in aggressive aqueous environments to provide a theoretical foundation for the durability design of cement-based materials in karst regions.

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