QUANTIFICATION OF CALCIUM SILICATE PHASES IN PORTLAND CEMENTS BY SI-29 MAS NMR-SPECTROSCOPY

Si-29 magic-angle spinning (MAS) NMR spectroscopy is shown to be a val uable tool for quantifying two calcium silicates, alite (Ca3SiO5) and belite (Ca2SiO4), in Portland cements. Determination of these minerals involves computer deconvolution of the Si-29 MAS NMR spectra combined with elemental analysis of the bulk SiO2 content. The applicability o f the method is demonstrated for various types of Portland cements and it is shown that the monoclinic M(I) and M(III) forms of alite can be distinguished by Si-29 MAS NMR. Inversion-recovery Si-29 spin-lattice relaxation MAS NMR allows quantification of the relative content of a lite and belite in an independent way and the results of the deconvolu tion for two of the cements have been tested and confirmed using this technique. Comparison of the Si-29 MAS NMR results for the alite and b elite contents with the traditional Bogue calculation demonstrates tha t this calculation strongly overestimates the belite content at the ex pense of alite in Portland cements. Improved correlations are observed when the NMR data are compared with the alite and belite quantities d etermined from a Taylor-modified Bogue calculation.