Observations on the rheological response of alkali activated fly ash suspensions: the role of activator type and concentration

Kirk Vance, Akash Dakhane, Gaurav Sant, Narayanan Neithalath

Research output: Contribution to journalArticlepeer-review

87 Scopus citations


This paper reports the influence of activator type and concentration on the rheological properties of alkali-activated fly ash suspensions. A thorough investigation of the rheological influences (yield stress and plastic viscosity) of several activator parameters, including: (i) the cation type and concentration of alkali hydroxide and (ii) the alkali-to-binder ratio (n) and silica modulus (Ms), and (iii) the volume of the activation solution, on the suspension rheology is presented. The results indicate a strong dependence on the cation and its concentration in the activation solution. The viscosity of the activation solution and the volumetric solution-to-powder ratio are shown to most strongly influence the plastic viscosity of the suspension. The suspension yield stress is predominantly influenced by the changes in fly ash particle surface charge and the ionic species in the activator. A shift from non-Newtonian to Newtonian flow behavior is noted in the case of silicate-based suspensions for Ms ≤ 1.5. This behavior, which is not observed at higher MS values, or when the fly ash is dispersed in hydroxide solutions or pure water, is hypothesized to be caused by colloidal siliceous species present in this system, or surface charge effects on the fly ash particles. Comparisons of the rheological response of alkali-activated suspensions to that of portland cement-water suspensions are also reported.

Original languageEnglish (US)
Pages (from-to)843-855
Number of pages13
JournalRheologica Acta
Issue number10-11
StatePublished - Nov 2014


  • Fly ash
  • Geopolymer
  • Plastic viscosity
  • Rheology
  • Yield stress

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics


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