Atomic-scale insights into mechanical properties of calcium silicate hydrates: role of hydrogen bond networks and bond order distributions

Calcium silicate hydrate (CSH) serves a critical role in maintaining the structural integrity of buildings. However, the relationships between its mechanical properties and crystal structures remain unclear. In this study, density functional theory (DFT) was used to systematically analyze the mechanical properties of 33 CSH phases. The findings demonstrate a linear correlation between elastic modulus and crystal density. In addition, the partial bond order (PBO) of Ca-O bonds significantly affects the crystal density. This effect, together with the water content, determines the mechanical properties of CSH. Notably, the unique cage-like hydrogen bond network present in kenotobermorite-4O markedly enhances the interlayer cohesion, giving it superior mechanical properties to those of conventional CSH. Additionally, the study elucidates the anisotropic characteristics of CSH materials, revealing that mechanical anisotropy is strongly correlated with the enhancement of PBO(Ca-O). These findings offer a theoretical framework for comprehending the mechanical behavior of CSH and establishing essential connections between its microstructure and mechanical properties.