Industrial production of recycled cement: energy consumption and carbon dioxide emission estimation

The urge to reduce greenhouse gas emissions, in particular carbon dioxide, is a global problem, not only in spatial terms but also in terms of the scope of activities and sectors involved. Nevertheless, some sectors/industries are more critical due to their overall contribution to the problem, which is the case of the Portland cement industry. The present research estimates the energy consumption and carbon emissions associated with a novel process for producing cement by recycling used concrete and mortars. The novel process assessed resorts to the magnetic separation of the cement paste from the aggregates, followed by the thermal reactivation of the cement paste. Comparing the recycled cement production with the clinker production, higher energy consumption (over 9000 MJ/t compared with roughly 4000 MJ/t for Portland cement) and lower carbon dioxide emissions (average 730 kg CO₂/t compared with more than 800 kg CO₂/t for Portland cement) were estimated. However, the potential benefits in an industrial application are potentially much higher with the optimization of the production process. In particular, improvements in the washing and drying of the material prior to the magnetic separation will be critical since most of the energy is consumed in the process of drying.