The potential of CO2 emission reduction via replacing cement with recyclable wastes in the construction industry sector: the perspective of Iran's international commitments

Given the utmost importance of global climate change as one of the most extensively discussed subjects in environmental engineering along with its growing impact on human life and the environment, numerous studies have been thus far completed on the sources of greenhouse gas (GHG) emissions, particularly carbon dioxide (CO2). In Iran, the construction industry sector is also a major source of GHGs, accounting for 30% of the country's total GHG emissions. In the present study, the contribution of the construction industry sector in fulfilling Iran's obligations was analyzed based on the Paris Agreement within the United Nations Framework Convention on Climate Change to reduce CO2 emissions. Besides, this study aimed to investigate the potential of reducing CO2 emissions through the replacement of 5%, 7.5%, and 10% of cement with marble waste dust (MWD) or 20%, 25%, and 30% of cement with granite waste dust (GWD). For this purpose, firstly, cement production capacity in different Iranian provinces, over a 12-year period, was collected. Then, an economic analysis of transportation, energy consumption, and landfilling costs was conducted based on the data collected by a researcher-made questionnaire, designed to obtain data about cost saving achieved by recycling MWD and GWD instead of landfilling them. As to consider uncertainty in cement production, the lower, middle, and upper boundaries of cement production per capita as feasible scenarios were also estimated, using bootstrapping at a 95% confidence interval for the target year/or 2030. Finally, the potential to reduce CO2 emissions in each Iranian province and the entire country was estimated. According to Iran's commitments under the Paris Agreement, the country is required to moderate its GHG emissions by 4% if there are international sanctions or by 12% provided that such penalties are lifted between 2021 and 2030. The study findings revealed that the partial replacement of cement in concrete with GWD would allow Iran to meet its 2030 GHG emission reduction obligations under the sanction conditions. The results additionally showed that if the concrete production trends in this country, in the past 12 years, continue in the future, the replacement of 20%, 25%, and 30% of cement with GWD will lower the annual CO2 emissions by 54, 67.6, and 81.1 million tons, respectively. Furthermore, it was demonstrated that the only scenario in which Iran could respect its commitments, for the situation where the sanctions are lifted, is the one involving the replacement of 30% of cement with GWD.