Walkley, B. orcid.org/0000-0003-1069-1362, Ke, X., Provis, J.L. orcid.org/0000-0003-3372-8922 et al. (1 more author) (2021) Activator anion influences the nanostructure of alkali-activated slag cements. The Journal of Physical Chemistry C, 125 (37). pp. 20727-20739. ISSN 1932-7447
Abstract
Alkali-activated materials are promising low-carbon alternatives to Portland cement; however, there remains an absence of a fundamental understanding of the effect of different activator types on their reaction products at the atomic scale. Solid-state 27Al and 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and 1H–29Si cross-polarization MAS NMR spectroscopy are used to reveal the effect of the activator anion on the nanostructure, cross-linking, and local hydration of aged alkali-activated slag cements. The main reaction product identified is a mixed cross-linked/non-cross-linked sodium-substituted calcium aluminosilicate hydrate (C–(N)–A–S–H) gel with a structure comparable to tobermorite 11 Å. Analysis of cross-polarization kinetics revealed that a higher content of soluble silicate in the activator promoted the incorporation of Al into the aluminosilicate chains of C–(N)–A–S–H gels, charge-balanced preferentially by protons within the gel interlayer. In sodium carbonate-activated slag cements, aluminosilicate chains of C–(N)–A–S–H gels are instead charge-balanced preferentially by Ca2+ or AlV ions. Hydrotalcite was observed as a secondary reaction product independent of the activator used and in higher quantities as the content of sodium carbonate in the activator increases. The presence of soluble silicates in the activator promotes the formation of an Al-rich sodium aluminosilicate hydrate (N–A–S–H) gel which was not identified when using sodium carbonate as the activator. These results demonstrate that the anion type in the activator promotes significant differences in the nanostructure and local hydration of the main binding phases forming in alkali-activated slag cements. This explains the significant differences in properties identified when using these different activators.
Metadata
Item Type: | Article |
---|---|
Authors/Creators: |
|
Copyright, Publisher and Additional Information: | © 2021 The Authors. Published under a CC BY licence (https://creativecommons.org/licenses/by/4.0/). |
Dates: |
|
Institution: | The University of Sheffield |
Academic Units: | The University of Sheffield > Faculty of Engineering (Sheffield) > Department of Chemical and Biological Engineering (Sheffield) The University of Sheffield > Faculty of Engineering (Sheffield) > Department of Materials Science and Engineering (Sheffield) |
Funding Information: | Funder Grant number Engineering and Physical Sciences Research Council EP/M003272/1 |
Depositing User: | Symplectic Sheffield |
Date Deposited: | 11 Oct 2021 13:38 |
Last Modified: | 11 Oct 2021 13:38 |
Status: | Published |
Publisher: | American Chemical Society (ACS) |
Refereed: | Yes |
Identification Number: | 10.1021/acs.jpcc.1c07328 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:178969 |