Suitability of Basic Oxygen Furnace Slag as a Coarse Aggregate in Concrete Made with Supplementary Cementitious Materials
Tsematse TSEMATSE, Lewis PARSONS, Sunday NWAUBANI
Abstract. Basic Oxygen Furnace Slag (BOFS), a by-product of steelmaking, offers an environmentally friendly alternative to natural coarse aggregates (NCA) in concrete. In South Africa alone, over a million tons of BOFS is produced annually, however, the low utilisation rate of the by-product often leads to growing landfills of the material. The low utilisation rate is primarily due to the free lime content of BOFS, which causes volume instability of the BOFS due to the larger calcium hydroxide crystal which forms during the hydration process and thus limits the potential applications for use. This study explores whether the incorporation of supplementary cementitious materials (SCMs), namely ground granulated blast furnace slag (GGBS) and Metakaolin (MK), may improve the volume stability of concrete made with BOFS as an aggregate but reacting with the BOFS hydration products. Concrete mixes were prepared with 0%, 50%, and 100% volumetric replacement of NCA by BOFS. Furthermore, ordinary portland cement was partially replaced with 60% GGBS in some mixes and 15% MK in others. The compressive strength test was used to assess potential reactivity between BOFS and SCMs, while prism expansion tests evaluated the impact on volume stability and the concrete microstructure was assessed by microcrack analysis method. Results show that BOFS aggregates react with SCMs, due to the difference in the rate of compressive strength gain of the BOFS mixes, relative to those with NCA. Furthermore, including SCMs improved the overall volume stability of concrete made with BOFS, though microcracks were more prevalent. This suggests that while macro-scale stability improved, microstructural issues remain.
Keywords
Concrete, Aggregate, Supplementary Cementitious Material, Pozzolanic Reaction, Basic Oxygen Furnace Slag
Published online 4/2/2026, 7 pages
Copyright © 2026 by the author(s)
Published under license by Materials Research Forum LLC., Millersville PA, USA
Citation: Tsematse TSEMATSE, Lewis PARSONS, Sunday NWAUBANI, Suitability of Basic Oxygen Furnace Slag as a Coarse Aggregate in Concrete Made with Supplementary Cementitious Materials, Materials Research Proceedings, Vol. 63, pp 168-174, 2026
DOI: https://doi.org/10.21741/9781644904053-19
The article was published as article 19 of the book Advances in Cement and Concrete Research
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 license. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
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