Calcium Oxide–Rich Industrial Waste Ash as a Lime Substitute in Sustainable Metakaolin–Based Binders

Hallsworth, Erik Christopher, Augusthus-Nelson, Levingshan, Teklemariam, Aron ORCID: https://orcid.org/0000-0002-5746-5736, Davis, Sergio, Tosheva, Lubomira and Tedesco, Silvia (2025) Calcium Oxide–Rich Industrial Waste Ash as a Lime Substitute in Sustainable Metakaolin–Based Binders. Waste and Biomass Valorization. ISSN 1877-2641 (In Press)

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Abstract

Corrugated cardboard fly ash (CCFA) is an industrial by-product typically sent to landfill. Unlike conventional coal fly ash, CCFA has limited pozzolanic activity but contains a high amount of calcium oxide (CaO). When hydrated, CaO forms calcium hydroxide (Ca(OH)2), which can react with metakaolin (MK) - a highly reactive aluminosilicate - to promote pozzolanic activation. This makes CCFA a promising material for sustainable cementitious binders. The chemical, physical, and microstructural characteristics of raw and hydrated materials were assessed using mechanical testing, XRF, XRD and BET. Compressive strength development was analysed via response surface methodology across varying water-to-cement ratios. While CCFA alone reduced strength, binary systems 1 replacing 40% of cement with 20% CCFA and 20% MK achieved compressive strengths comparable to mixes with 20% MK alone. These results highlight the potential of CCFA as a sustainable calcium source in low-carbon binder systems, contributing to waste valorisation and cement reduction. Keywords: Calcium oxide-rich waste ash, Characterisation of corrugated cardboard fly ash, Compressive strength, Lime-metakaolin blended mortar.