Comparison of CO2 emissions from OPC and recycled cement production

Abstract

Abstract The production of ordinary Portland cement (OPC) is responsible for a significant part of global CO2 emission. For decades, the raw material and high burn temperature (up to 1500 °C) for OPC production have not been changed to reduce the CO2 emission significantly. In order to reduce the CO2 emission for cement production, two types of recycled cements (RC-450 °C and RC-800 °C) were produced in this study. It is hoped that the potential application of recycled cement could help to mitigate the CO2 emission in cement production. The application of recycled cement could significantly reduce the environmental impacts caused by the landfills of demolished waste concretes. The recycled cements RC-450 °C and RC-800 °C were produced through burning waste old OPC pastes at 450 °C and 800 °C respectively and then grinding into powder through a ball mill. The CO2 emissions from producing OPC, RC-450 °C and RC-800 °C were calculated and compared through considering the CO2 emissions from both fuel burning and the clinker materials. Compared to the production process of OPC, the production of RC-450 °C can reduce 94% of CO2 emission. By mixing with water, an additional 4% CO2 by weight of RC-450 °C can be captured in the RC-450 °C paste through the formation of calcium carboaluminate and additional calcite. RC-450 °C showed lower CO2 emission but a higher strength of paste than RC-800 °C. Besides, RC-450 °C paste was found to have a similar strength as the OPC paste, and this suggests that the RC-450 °C could be used to totally replace OPC.