Carbon dioxide equivalent emissions from the manufacture of concrete in South Africa

Abstract

Data was obtained by means of an electronic questionnaire distributed throughout South Africa during 2008 and 2009. Specific activity data was gathered from 130 of the processes and activities contributing to the concrete industry which include admixture, aggregates, cement, fly ash, precast, in-situ concrete, slagment, steel reinforcing and water. The Cement and Concrete Institute initiated this project to develop a model for the quantification of CO2 emissions specific to the concrete industry. The institute’s intention is to determine the emissions resulting from the production of a cubic meter of concrete in South Africa. Depending on the outcome, this will allow the institute to promote the application of concrete over other construction alternatives. The new CO2e model was developed following accepted GHG (Greenhouse Gas) protocol rules. These include relevance, completeness, consistency, transparency and accuracy, when examining direct (scope one), indirect (scope two) and other indirect (scope three) emissions. The emissions associated with each activity are determined by individual process specific questionnaires. The gathered activity data was then consolidated electronically and manipulated to determine the CO2e emissions per ton of product for each process or activity. Emission factors for each activity were determined and inputted into the CO2e model to determine the overall emissions per cubic meter of concrete, province and sector. The final model allows the user to input specific concrete mixes to determine the CO2e emissions resulting from a cubic meter of the specific mix going into roof tiles, bricks, precast concrete slabs or in-situ concrete. It was found that an average cubic meter of in-situ concrete containing a CEM (cement) I 42.5 with extension and admixture with a strength of 30 MPa resulted in a range of between 215 and 240 kg CO2e per cubic meter. In order to compare these emissions to international studies it is only necessary to consider direct emissions. Considering direct emissions, the production of an average South African concrete mix resulted in a range of 142 to 170 kg CO2/m3 compared to Australia with a range of 251 to 273 kg CO2/m3 and the United Kingdom with 266 kg CO2/m3. This equates to between 57 and 62 percent less CO2 emitted from the production of an average South African concrete. The CO2 resulted from direct emissions (67 percent), indirect emissions (23 percent) and the remaining other indirect sources with ten percent.