Structures and Phase Relations of Aluminum‐Substituted Calcium Silicate Hydrate

Abstract

The structures of aluminum‐substituted calcium silicate hydrate (C‐S‐H) forming in a series of aqueous suspensions formulated with colloidal silica, reactive alumina, and lime and aged for 1 year have been studied using 29 Si and 27 Al magic angle spinning nuclear magnetic resonance spectroscopy (with and without cross polarization (CP)), solution pH, electron microscopy, and X–ray diffraction. As in earlier work dealing with the nature of C‐S‐H in the system CaO‐SiO 2 H 2 O 2 two aluminum‐substituted C‐S‐H phases, having distinctly different anionic structures on the atomic level (Q 2 versus Q 1 Q 2 ), were found to extend into the system CaO‐Al 2 O 3 ‐SiO 2 ‐H 2 O 2 X‐ray diffraction patterns of the two aluminum‐containing C‐S‐H phases are nearly identical, suggesting that their intermediate‐range order is very similar, but MASNMR spectra show that these two phases have markedly different silicate structures on the atomic‐level scale. Both C‐S‐H structures can accommodate approximately 5 mol% of Al 2 O 3 in tetrahedral and possibly octahedral coordination as well.