Iron in the CaO-SiO2-H2O System

Abstract

FIG. 2. 298i MAS NMR spectra of the serie A. properties constitutes a major challenge of cement chemistry. Their characterization is difficult beacause of their variable stoichiometry and their low crystallinity make difficult. In this work, we focused on the effect of Fe 3+ incorporation on the tobermorite-like structure of low Ca/Si ratio (initial value 0.8: Fig. 1) by using the fellowing complementary techniques 298i MAS NMR, 57Fe M6ssbauer spectroscopy and Transmission Electronic Microscopy (TEM). Fe 3+ was introduced as a notrate either initialy with CaO, SiO2 and H20 (series A samples) or after precipitation of the C-S-H (series B samples). For low Fe/Si ratios, Fe 3+ substitutes Ca 2+ in the CaO sheets and in the interlayer space of the Te-OcTe structure of the C-S-H. Because of the charge compensation needed in such a mechanism, the maximum Fe/Si ratio is of about 0.3 At Fe/Si higher than 0.33, no more Fe 3§ atoms can be incorporated into the C-S-H structure and different neoformed iron hydrates precipitate according to the two reaction routes.