Chemical and mechanical activation of hybrid fly ash cement

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Du Toit, Grizelda
Kearsley, Elsabe P.
Mc Donald, James M.
Kruger, Richard A.
Van der Merwe, Elizabet Margaretha

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Thomas Telford

Abstract

Hybrid fly ash cement is a binder with a composition between that of pozzolanic fly ash cement and alkali-activated fly ash cement. Its production requires less cement clinker than ordinary Portland cement, facilitating a much-needed reduction in the carbon dioxide footprint related to the production of high-clinker-containing cement. Research on activation methods is required to overcome the low early age strength and slow strength development in hybrid fly ash cements. In this study the activation of a South African siliceous fly ash (70%) for use along with Portland cement (30%) in a hybrid alkaline binder was investigated. Both chemical (the addition of sodium sulfate) and mechanical (milling) activation of fly ash was studied. The aim of this work was to develop a better understanding of the characteristics of compressive strength development of hybrid fly ash cement mortars over an extended curing period of up to a year. The results indicated that the combination of mechanical and chemical activation (sodium sulfate) can be considered a viable solution to improving early strength and slow strength development, so that hybrid cements are able to comply with the strength requirements of the BS EN 197 cement specification.

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Keywords

Blended cements, Compressive strength, Chemical activation, Strength development, Mechanical activation, Early age strengths, Cement specification, Alkali-activated fly ashes, Activation method, Sulfur compounds, Sodium sulfate, Portland cement, Fly ash (FA), Compressive strength, Carbon dioxide, Binders, Alkalinity

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Citation

Du Toit G, Kearsley EP, Mc Donald JM, Kruger RA and Van der Merwe EM (2018) Chemical and mechanical activation of hybrid fly ash cement. Advances in Cement Research 30(9): 399–412, https://DOI.org/ 10.1680/jadcr.17.00156.