The physicochemical properties of Portland cement blended with calcium carbonate with different morphologies as a supplementary cementitious material

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.