SI-29 NMR-SPECTROSCOPY OF SILICATE ANIONS IN HYDROTHERMALLY FORMED C-S-H

Hydrothermal treatment of lime-silica mixtures under saturated steam p ressures below 200-degrees-C usually gives C-S-H as an initial product , which reacts further to give crystalline calcium silicate hydrates. In this paper, C-S-H was hydrothermally prepared using CaO and silicic acid at Ca/Si ratios of 0.3 to 2.0 and 120-degrees to 180-degrees-C f or 2 h. The C-S-H was examined mainly using Si-29 NMR by the magic ang le spinning gate proton decoupling and cross polarization magic angle spinning methods. XRD for all of the C-S-H showed bands at 0.304, 0.28 0, 0.183, and 0.166 nm. NMR results showed that all of the C-S-H conta ined single chains of silicate anion, which became progressively longe r as the Ca/Si ratio decreased, i.e., as the system became richer in s ilica. This was independent of the preparation temperature. The 0.8 ra tio preparations at 180-degrees-C contained small amounts of double-ch ain structure of 1.1-nm tobermorite. The reaction processing in the li me-silicic acid mixtures is also discussed.