The industrial building in the industrial park in Puchheim, a small town near Munich, Germany, had been a commercial building for more than 50 years. Even after all these years, it was still in good condition, built with autoclaved aerated concrete wall panels. After the previous tenant moved out and the requirements of a new interested party changed, the owner decided to demolish the old hall and build a bigger, wider and higher hall. The planning and design of the new hall was entrusted to the Munich-based architectural firm b_arch.

New hall built with autoclaved aerated concrete

A similar supporting structure with reinforced concrete columns and autoclaved aerated concrete (AAC) wall panels was chosen. AAC is particularly suitable because of its positive properties: It is made of mineral raw materials, offers excellent thermal insulation, is very durable, easy to repair, and the building only needs an exterior coating to protect it from the elements. At a time of climate change, the efficient use of resources is crucial. The owner explains his decision: "As a house builder, I want to create a durable and resilient building fabric that can be flexibly adapted to changing uses."

Urban mining: how an old building becomes a new one

Since the AAC of the old hall was in very good condition and the client was committed to sustainable construction, the material should be reused as much as possible in the new hall. In order to make this possible, Xella Technologie und Forschungsgesellschaft mbH was contacted, whose task is to continuously improve the products of the Xella Group and to research new processes. For years, there have been numerous projects in which the return of autoclaved aerated concrete from building demolition into AAC production was investigated.

Xella regards any form of AAC as a valuable material, which helps to reduce the use of valuable primary raw materials. Since 2015, Xella Germany and other national companies have had a return system for AAC offcuts on construction sites in the form of big bags: instead of handing off the offcuts to disposal companies for high fees, they can be collected at the construction site and returned to the plant. At the plant, the returned unmixed off-cuts are then processes by grinding and milling and returned into the ongoing production of AAC.

Circularity: demolition material gets back to the plant

Back to Puchheim: in fall 2022, the deconstruction of the old industrial building began, during which the AAC was strictly separated from other materials in order to obtain unmixed material. The demolition company involved in this project – namely Osterried Entsorgung GmbH – crushed, sorted and screened the old material, and the powder obtained was then transported to the Xella plant in Schrobenhausen for the production of new AAC. The construction work was recently completed.

The project shows: the closed raw material cycle at Xella works and puts Xella in a pioneering role.  It shows the importance of urban mining. "We benefit in two ways: on the one hand, we can reduce the proportion of valuable raw materials and the CO2 emissions of our products, and on the other, we meet the demands of our customers, who are specifically looking for sustainable products," explains Oliver Kreft, responsible for circular economy at Xella Technologie- und Forschungsgesellschaft mbH.