Comparison of CO2 emissions from OPC and recycled cement production

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 degrees 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 degrees C and RC-800 degrees 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 degrees C and RC-800 degrees C were produced through burning waste old OPC pastes at 450 degrees C and 800 degrees C respectively and then grinding into powder through a ball mill. The CO2 emissions from producing OPC, RC-450 degrees C and RC-800 degrees 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 degrees C can reduce 94% of CO2 emission. By mixing with water, an additional 4% CO2 by weight of RC-450 degrees C can be captured in the RC-450 degrees C paste through the formation of calcium carboaluminate and additional calcite. RC-450 degrees C showed lower CO2 emission but a higher strength of paste than RC-800 degrees C. Besides, RC-450 C paste was found to have a similar strength as the OPC paste, and this suggests that the RC-450 degrees C could be used to totally replace OPC. (C) 2019 Elsevier Ltd. All rights reserved.