This study proposes the addition of calcium carbonate produced from flue-gas carbon dioxide to reduce carbon emissions of Portland cement manufacturing from 0.96 kgCO2/kg of Portland cement to 0.33 kgCO2/kg of Portland cement with comparable strengths. This study reviews the impact of calcite addition on properties of cement based on the literature. Experimental findings are presented on how the addition of different polymorphs of calcium carbonate influence physicochemical behaviour of Portland cement in terms of hydration chemistry, compressive and flexural strength and thermal analysis. Three polymorphs of calcium carbonate (amorphous, micro calcite and nano calcite) are studied. This is the first study to report the impact of three different calcium carbonate polymorphs especially that in the amorphous form. The addition of CaCO3 in Portland cement can increase the compressive strength by about 20% when compared to the benchmark. Examining the hydration shows the formation of scawtite and tilleyite with competing effect on the product strength during hydration. Formation of 8 mass% of combined scawtite–tilleyite phases at ambient conditions using CaCO3 is a new discovery; it results first in an increase in compressive strength and then, above 8 mass% it negatively impacts compressive strength. This study also provides avenues to use calcite as a sustainable supplementary cementitious material to reduce carbon emissions as well as improve early strengths. These characteristics are evidence that calcium carbonates provide a new regime of carbonate activity, modified hydration reactions, and can be used as a step towards the next generation of low-carbon Portland cements utilising mineral carbon capture technologies.
The authors wish to acknowledge Dr Mohammed Imbabi (late) and Prof Fred Glasser for their contributions to the early discussions regarding mineral carbon capture and utilization and to Prof Fred Glasser for fruitful discussions regarding mineralogy and cement chemistry. We also thank Dr Wanawan Pragot for sharing her experience especially related to LCA. We acknowledge ACEMAC Facility at the University of Aberdeen for their support for electron microscopy.
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
- mineral CCU
- calcium carbonate
- portland cement