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.

Original languageEnglish (US)
Pages (from-to)91-103
Number of pages13
JournalAmerican Concrete Institute, ACI Special Publication
Issue numberSP 312
StatePublished - 2016


  • Alkali activation
  • Cationic type
  • Fly ash
  • NMR spectroscopy
  • Slag

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Building and Construction
  • Materials Science(all)


Dive into the research topics of '29Si NMR investigations on alkali activated fly ash or slag: The role of the alkali cation'. Together they form a unique fingerprint.

Cite this