Solubility and Structure of Calcium Silicate Hydrate

A poorly crystalline class of calcium silicate hydrates known as C–S–H possesses extensive disorder and structural variations at the nanometer scale. The extent of these variations has generally obscured a comprehensive understanding of the C–S–H nanostructure, but new relationships between solubility and structure appear to shed new light on this old problem. These relationships were inspired from the discovery in the CaO–SiO2–H2O system at room temperature of a family of new C–S–H solubility curves: A, C", C', and C (Figure 9). Si magic-angle spinning (MAS) NMR studies and charge balance calculations suggest that these variations in solubility reflect systematic variations in structure of which those in Ca/Si ratio, silicate polymerization, and Ca–OH content appear most important. These findings define more explicit relationships between the nanostructure of C–S–H and the crystal structures of 1.4-nm tobermorite and jennite. C–S–H that equilibrates with aqueous solution