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 29Si and 27Al 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‐SiO2H2O2 two aluminum‐substituted C‐S‐H phases, having distinctly different anionic structures on the atomic level (Q2 versus Q1Q2), were found to extend into the system CaO‐Al2O3‐SiO2‐H2O2 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 Al2O3 in tetrahedral and possibly octahedral coordination as well.

Characterization by Multinuclear High‐Resolution NMR of Hydration Products in Activated Blast‐Furnace Slag Pastes

“…Measurements were conducted under magic angle sample spinning (MAS) up to 5 kHz in zirconia rotors with a Varian 7 mm probe. 12 The Hartmann-Hahn match condition for 1 H- 27 Al CP was adjusted with a sample of kaolinite. Kaolinite was used as a secondary standard for chemical shift (Ϫ91.2 ppm with respect to TMS).…”

“…(3) 27 Al NMR Spectroscopy 27 Al NMR spectra were measured from SP experiments in the four kinds of pastes as a function of time. Results only for N and NS samples are shown in Figs.…”

“…10 Optimal mechanical strength and workability were obtained with activations containing around 7% of silicate. The high-resolution nuclear magnetic resonance (NMR) technique in solid state was applied to characterize the local structure and bonding around 29 Si, 27 Al, and 23 Na ions in hydration products. The aim of this work is the characterization of the structure of hydration products obtained from a set of selected activations producing gbfs cements with extremely different mechanical properties.…”

Silicon Substitution for Aluminum in Calcium Silicate Hydrates

“…However, no correlations between aluminum substitution in C-S-H and the chemical composition of the solution were established. A pH dependence was clearly demonstrated by Kwan et al 16 Our purpose in this article was to correlate the concentrations in solution with aluminum substitution in C-S-H, using MASNMR and MQ MASNMR. 27 Al has 2I observable transitions that can be separated into two groups: the central transition (1/2 ↔ −1/2) and the other transitions, often called the external transitions.…”

Immobilisation of heavy metal in cement-based solidification/stabilisation: A review

“…C-S-H gel may contain Al, Fe and Mg due to sorption or co-precipitation (Taylor, 1993;Andersen et al, 2003). It is reported that minor components can modify the crystal growth by substitution in the lattice of the calcium silicate hydrates (Kwan et al, 1996;Kulik and Kersten, 2001). Almost all calcium in natural crystalline phases of calcium silicate hydrate such as tobermorite (C 5 S 6 H 5 ) and xonotlite (C 5 S 5 H) can be replaced with heavy metals, for example, cobalt or nickel (Viehland et al, , 1997.…”