<sup>29</sup>Si NMR Investigations on Alkali Activated Fly Ash or Slag: The Role of The Alkali Cation

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Title: 29Si NMR Investigations on Alkali Activated Fly Ash or Slag: The Role of The Alkali Cation

Author(s): Akash Dakhane, Zihui Peng, Robert Marzke, and Narayanan Neithalath

Publication: Special Publication

Volume: 312

Issue:

Appears on pages(s): 1-14

Keywords: Fly ash; Slag; Alkali activation; Cationic type; NMR spectroscopy

Date: 10/1/2016

Abstract:
The influence of alkali cation (M = Na or K) on the alkaline activation of fly ash and slag are evaluated. NaOH, KOH (4M and 8M), or Na or K silicates (SiO2/M2O = 2.0) are used as the activators for fly ash systems which are then heat-cured, while Na or K silicates (SiO2/M2O = 1.5 and 2.5) are used to activate slag systems, which are then cured in ambient conditions. For alkali activated systems proportioned using Na-based activators, the compressive strengths were found to be higher for both the source materials. For the fly ash based systems, 29Si MAS NMR spectroscopy identifies abundance of Q4 structures with Al incorporation (N-A-S-H gel). An increase in gel structural order and the presence of higher amounts of Si-rich units as the activator alkalinity increases are noted, along with a higher degree of disorder for the K-based systems. The reaction product signature for the activated slag systems, dominated by the Q2 species are consistent with Al-substituted C-S-H (C-A-S-H) gel.