Controlling workability in alkali-activated Class C fly ash

•Alkali-activated Class C fly ashes have high strength but poor workability.•Retarders, silica modulus, and mixing intensity can change workability.•Workability modification can reduce strength, particularly when retarders are used. Alkali-activation of Class C fly ashes can produce Portland cement-...

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Bibliographic Details
Published in:Construction & building materials 2018-09, Vol.183, p.226-233
Main Authors: Rakngan, Watanyoo, Williamson, Trevor, Ferron, Raissa D., Sant, Gaurav, Juenger, Maria C.G.
Format: Article
Language:English
Subjects:
Alkali metal compounds
Alkali-activated materials
Analysis
Cements (Building materials)
Fly ash
Geopolymer
Retarder
Shear mixing
Slump
Workability
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Summary:•Alkali-activated Class C fly ashes have high strength but poor workability.•Retarders, silica modulus, and mixing intensity can change workability.•Workability modification can reduce strength, particularly when retarders are used. Alkali-activation of Class C fly ashes can produce Portland cement-free binders that take advantage of sodium aluminosilicate hydrate (N-A-S-H) and aluminum-substituted calcium silicate hydrate (C-A-S-H) phases for strength development. However, alkali-activated Class C fly ashes suffer from poor workability and rapid setting; traditional water-reducing admixtures are not effective. In this study, different methods to modify the workability of alkali-activated Class C fly ash mixtures were investigated. Retarders decreased the mixture stiffness and delayed setting, but strength development suffered. Increasing mixing intensity slightly improved workability without significantly impacting strength. Controlling silica modulus significantly improved workability, but the impact on strength was inconsistent.
ISSN:0950-0618
1879-0526
DOI:10.1016/j.conbuildmat.2018.06.174