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Rheologica Acta

, Volume 53, Issue 10–11, pp 843–855 | Cite as

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 NeithalathEmail author
Original Contribution

Abstract

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.

Keywords

Geopolymer Rheology Fly ash Yield stress Plastic viscosity 

Abbreviations

n

Ratio of Na2O in the activator to the total fly ash content

Ms

Ratio of SiO2-to-Na2O in the activator

(as/p)v

Activation solution-to-powder ratio, by volume (Refer to the definition of activation solution in 2.1

(as/b)v

Activation solution-to-binder ratio, by volume; binder implying fly ash here

(w/s)m

Water-to-solids ratio, mass-based (Refer to the definition of solids in 2.1)

w/c

Water-to-cement ratio, mass-based, for OPC systems

τ

Shear stress, Pa

τy

Yield stress, Pa

ηp

Plastic viscosity, Pa.s

ηa

Apparent viscosity, Pa.s

\( \dot{\gamma} \)

Shear rate, s−1

Notes

Acknowledgments

The authors gratefully acknowledge the National Science Foundation (CMMI 1068985) and Arizona State University for the partial support of this research. The materials for this research were provided by Headwaters Resources and PQ Corporation, and are acknowledged. K.V. also acknowledges the Dean’s Fellowship from the Ira A. Fulton Schools of Engineering at Arizona State University (ASU). This research was conducted in the Laboratory for the Science of Sustainable Infrastructural Materials (LS-SIM) at ASU and the authors gratefully acknowledge the support that has made this laboratory possible. The contents of this paper reflect the views of the authors who are responsible for the facts and accuracy of the data presented herein, and do not necessarily reflect the views and policies of the funding agency, nor do the contents constitute a standard, specification, or a regulation.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • Kirk Vance
    • 1
  • Akash Dakhane
    • 1
  • Gaurav Sant
    • 2
    • 3
  • Narayanan Neithalath
    • 1
    Email author
  1. 1.School of Sustainable Engineering and the Built EnvironmentArizona State UniversityTempeUSA
  2. 2.Department of Civil and Environmental EngineeringUniversity of California Los AngelesLos AngelesUSA
  3. 3.California Nanosystems InstituteUniversity of California Los AngelesLos AngelesUSA

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