Nature of Interatomic Bonding in Controlling the Mechanical Properties of Calcium Silicate Hydrates

Calcium silicate hydrate ( C-S-H) is the most important phase of hydrated cement gel which is the key material in construction industry. It is well accepted that hardened cement paste consists of either poorly crystalline or completely disordered phases. Although a myriad of speculative atomistic models of disordered C-S-H have been proposed, the fundamental basis of structure-property relationships remain elusive. This study focuses upon the correlations between mechanical properties and electronic structure based on well-defined quantum mechanical parameters. We use 20 CSH minerals with known structure to gain fundamental understanding of structure-property relationship. The results indicate Si-O bond order density, which represents the cumulative bond strength of SiO bonds, has no direct correlation with bulk mechanical properties which is counterintuitive and against conventional wisdom. The variations are determined more precisely by the overall atomic and electronic structure dictated by bond order density of the Ca-O and hydrogen bonds ( HB). Most importantly, there is a multifaceted balance between different types of interatomic bonds including the HBs in controlling mechanical properties. HBs categorized in relation to next nearest neighbor ( NNN) enable us to identify specific types of HBs that are prevalent in CSH. In certain crystals such as suolunite, the HB network is organized in such a unique way that enhances its mechanical properties. The approach and findings presented in this paper points to a broad roadmap for the developing next-generation cements.