Circular economy's potential to reduce AAC carbon emissions

Establishing a circular economy for Xella's building materials – among them Autoclaved Aerated Concrete (AAC) – is and will be one of Xella's key ESG projects for the coming years. In Germany, Xella has made it its goal to duplicate the powder-input in the main AAC-products from annually 60,000 t to 120,000 t by 2030. AAC-powder used today emerges from the processing of AAC production leftovers, cutting residues and leftovers returned from job sites. In order to achieve the 2030 goal, Xella Germany will (1) generate new sinks, and (2) leverage new sources for AAC-powder. Current production recipes are designed to take up emerging powder-quantities, but nothing beyond. The present study describes the inspection and evaluation of current powder input shares per product type and options for their full exploitation by recipe amendments. In 2021, prototypes for Ytong PP2-0,35 and PP4-0,50 containing 20 m.-% powder, and Ytong PP4-0,55 containing 30 m.-% powder were developed by the Xella Technologie- und Forschungsgesellschaft mbH. In order to prospectively supply sufficient quantities of AAC-powder, Xella Germany aims at leveraging waste-AAC from building demolition, so called post-demolition AAC or pd-AAC. We combined the zero burden and the avoided burden methodology to expand the life cycle assessment for the investigated circularity scenarios over the edge of waste generation. Our assessment revealed substitution credits of 0.55 kg CO2e/kg pd-AAC for Ytong PP2-0,35, and 0.43 respectively 0.33 kg CO2e/kg pd-AAC for Ytong PP4-050 and PP4-0,55. The present study illustrates that our ambition to duplicate Xella Germany's powder consumption is achievable, when the new formulations are fully and consequently implemented. The recipe amendments have the potential to reduce expenditures for sand, quicklime, cement and gypsum/anhydrite, thereby reducing Xella Germany's annual (Scope 3) AAC carbon emissions up to 36 kt CO2e. © 2022 Ernst & Sohn GmbH.