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 using mineral
carbon capture and utilisation technologies 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 calcium carbonate addition on properties of cement based on
the available 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 study reports the
impact of three different calcium cabronate polymorphs especially that in the
amorphous form. The addition of CaCO3 in Portland cement can increase the compressive strength by about 20%. Examining the hydration shows the possibility 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.