Molecular insights into structural and dynamic properties of water molecules in calcium silicate hydrate nanopores: The roles of pore size and temperature

Calcium silicate hydrate is the primary hydration product of Portland cement and plays a crucial role in determining the strength of cement-based materials. The structural and dynamic properties of water molecules within calcium silicate hydrate nanopores have significant implications for the mechanical and durability performance of these materials. However, the influences of pore size and temperature on the properties of water molecules have not been fully explored. In this work, using molecular dynamics simulations and theoretical analysis, the evolution and mechanisms of the structural and dynamic properties of water molecules in different scenarios with various pore sizes and temperatures are systematically investigated. It is shown that the diffusion coefficients of water molecules increase with both pore size and temperature. Moreover, water molecules have a tendency to adsorb onto calcium silicate hydrate substrates, forming a distinct layered structure. As a result, the water molecules near the surfaces of calcium silicate hydrate substrates exhibit limited mobility, leading to smaller diffusion coefficients compared to those in other regions. Additionally, the distinctions in properties between water molecules and Ca2+ ions are elucidated and the underlying mechanisms behind these differences are also unveiled. The results and findings in this work deepen the understanding of structural and dynamic properties of water molecules within calcium silicate hydrate nanopores, providing valuable insights for improving the mechanical and durability performance of cement-based materials.Document Type: Original articleCited as: Liu, S., A, H., Tang, S., Kai, M., Yang, Z. Molecular insights into structural and dynamic properties of water molecules in Calcium silicate hydrate nanopores: The roles of pore size and temperature. Capillarity, 2023, 8(2): 23-33. https://doi.org/10.46690/capi.2023.08.0

Structure, Fractality, Mechanics and Durability of Calcium Silicate Hydrates

Cement-based materials are widely utilized in infrastructure. The main product of hydrated products of cement-based materials is calcium silicate hydrate (C-S-H) gels that are considered as the binding phase of cement paste. C-S-H gels in Portland cement paste account for 60–70% of hydrated products by volume, which has profound influence on the mechanical properties and durability of cement-based materials. The preparation method of C-S-H gels has been well documented, but the quality of the prepared C-S-H affects experimental results; therefore, this review studies the preparation method of C-S-H under different conditions and materials. The progress related to C-S-H microstructure is explored from the theoretical and computational point of view. The fractality of C-S-H is discussed. An evaluation of the mechanical properties of C-S-H has also been included in this review. Finally, there is a discussion of the durability of C-S-H, with special reference to the carbonization and chloride/sulfate attacks