SummaryTobermorite minerals vary in some proper lies, notably in whether or not unidimensional lattice shrinkage occurs by about 300 °C to give a 9·3 form; specimens that do this are called normal, and ones that do not, anomalous. Data are compared for thirteen natural tobermorites and the extent to which normal or anomalous character is related to other properties is examined. The most definite correlations found are with chemical composition and morphology. The conditions of formation of normal and anomalous tobermorites are discussed in the light of synthetic evidence.

The reactions were investigated that occur when lime, cement, and quartz sand are mixed together and molded, then treated at 180°C under saturated steam pressures to produce autoclaved aerated concrete. The hydrothermal treatment of mixtures gives Ca-rich C-S-H with varying Ca/Si ratios as an initial product, which reacts further with silica dissolved from quartz to form 1.1-nm tobermorite with increase of curing time. During autoclaving, the composition of C-S-H and tobermorite as a binder continues to change until after 8 h, when the Ca/(AI + Si) ratio becomes constant at 0.8. As the reaction proceeds, the number of micropores increases, and the strength also increases due to the binder effect of the tobermorite. However, the total pore volume does not change, remaining constant values. [

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Hydrothermal treatment of lime-silica mixtures under saturated steam pressures below 200°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 CdSi ratios of 0.3 to 2.0 and 120" to 180°C for 2 h. The C-S-H was examined mainly using 29Si NMR by the magic angle spinning gate proton decoupling and cross polarization magic angle spinning methods. XRD for all of the C-S-H showed bands at 0.304, 0.280, 0.183, and 0.166 nm. NMR results showed that all of the C-S-H contained single chains of silicate anion, which became progressively longer as the CdSi ratio decreased, i.e., as the system became richer in silica. This was independent of the preparation temperature. The 0.8 ratio preparations at 180°C contained small amounts of double-chain structure of 1.1-nm tobermorite. The reaction processing in the lime-silicic acid mixtures is also discussed.