Cement Chemical shift

Table 5.4. NMR parameters for calcium aluminates and their hydration products in Portland and high alumina cements, from Skibsted et al. (1993). Chemical shifts relative to Al(H20)e. ...

Si CSA parameters have been reported only for several silicate, calcium silicate and calcium silicate hydrate phases relevant to cement chemistry. These are summarised in Table 6.2 along with Si isotropic chemical shifts reported for structurally well-defined cement constituent phases. 

Table 6.2 isotropic chemical shifts 8, 0) chemical shift anisotropies (6J and CSA asymmetry parameters (qj for structurally well-defined silicate phases common in cement systems... 

Grimmei A.-R., and Zanni, H. 1998. Si NMR study of chemical shift tensor anisotropy of tricalcium silicate. In Nuclear magnetic resonance spectroscopy of cement-based materials, Colombet, R, A.-R. Grimmei H. Zanni and P. Sozzani (eds.). Berlin Springer-Verlag, 57-68. 

Sevelsted, T. E, D. Herfort and J. Skibsted. 2013. chemical shift anisotropies for carbonate ions in cement minerals and the use of Al, and Si MAS NMR in studies of Portland cement including limestone additions. Cem. Conor. Res. 52,100-111. 

Carbon and oxygen isotope analyses of carbonate cements were performed on 20 samples. Each sample was reacted with 100% phosphoric acid at 25 °C for calcite and at 50°C for dolomite. The evolved gas for each carbonate fraction was analysed using a SIRA-12 mass spectrometer. The phosphoric acid fractionation factors used were 1.01025 for calcite (Friedman O Neil, 1977), and 1.01060 for dolomite (Rosenbaum Sheppard, 1986). Oxygen and carbon isotope data are presented in the normal 6 notation relative to pdb (Craig, 1957). Precision (1 o) was monitored through daily analysis of the NBS-20 calcite standard and was better than 0.05%o for both 6 C and 8 0. The isotopic data obtained are for bulk dolomite and calcite separately, and it is uncertain whether or not crystal-chemical zonations are accompanied by strong shifts in isotopic values. 

At that temperature the dissociation pressure is > 1 bar and thus equals the external pressure. The requisite reaction enthalpy AH is 1660kJ/kg. The value of 896°C relates to pure calcite with increasing content of admixtures (e.g., in cement raw meal) the thermal dissociation shifts to lower temperatures. In actual practice it begins between 550° and 600° C. This effect is due to chemical reactions of the CaO with the admixtures Si02, AI2O3 and Fe203, resulting in the formation... 

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