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Coal gasification and composite ashes as partial replacements for Portland cement in concrete – strength and selected durability performance

Published online by Cambridge University Press:  16 November 2020

Mike Otieno Open the ORCID record for Mike Otieno [Opens in a new window]  and
Dikeledi Maboea
Mike Otieno*
Affiliation:
School of Civil and Environmental Engineering, University of the Witwatersrand, Johannesburg
Dikeledi Maboea
Affiliation:
School of Civil and Environmental Engineering, University of the Witwatersrand, Johannesburg
*
Corresponding author: Mike Otieno (Mike.Otieno@wits.ac.za)
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Abstract

This study investigated the use of mixed weathered coal fine ash (MWA) and coal gasification ash (CGA), sourced from Sasol® Ltd, South Africa, as partial replacements (10%, 15% and 30% by mass) of Portland Cement (PC) in concrete. The objective was to assess the feasibility of using the ashes, which are generally of lower quality than FA, in concrete in order to avert their negative environmental impact i.e. disposal in heaps and landfills. Companion reference concretes were made using conventional fly ash (FA). Two water-to-binder (w/b) ratios (0.50 and 0.60) were used. The concretes were tested for compressive strength (7, 28 and 56 days) and durability (gas permeability and chloride resistance at 28 and 56 days). In general, the results strongly suggest that the ashes can be used in conventional structural concrete – both from strength and durability viewpoints. Aspects that require attention when they are used include decrease in both workability and rate of strength gain. The gas permeability of the CGA and MWA concretes were similar to those for FA at all replacement levels but a 15% replacement level gave higher chloride resistance.

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Articles
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MRS Advances , Volume 5 , Issue 54-55: Nanoscale and Quantum Materials , 2020 , pp. 2807 - 2816
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Copyright
Copyright © The Author(s), 2020, published on behalf of Materials Research Society by Cambridge University Press

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