Application of 29Si Homonuclear and 1H−29Si Heteronuclear NMR Correlation to Structural Studies of Calcium Silicate Hydrates

Structural characterization of calcium silicate hydrate (C-S-H) is of major importance, as it is the main constituent of Portland cement and is responsible for its principal cohesion and durability properties. In this paper we apply homonuclear and heteronuclear solid-state NMR methods for the investigation of C-S-H. We use double quantum homonuclear 29Si−29Si correlation using the BAck to BAck recoupling scheme to gain information about connectivity between silicates and 2D 1H−29Si HETeronuclear chemical shift CORelation (HETCOR) to characterize the proton environment of the silicate chains. Our observations are in agreement with the tobermorite model and with previous results, but we get evidence of a continuous decrease of the silicate chain length with increasing Ca/Si ratio rather than a bimodal distribution of chain length.