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This research has been selected for a presentation at of the , the world’s largest conference in geosciences. was chosen from more than 20,000 submissions.

Every year, Luxembourg generates large volumes of construction and demolition waste as buildings are renovated, replaced and rebuilt. At the same time, the country relies heavily on imported natural aggregates for concrete production. 

New research by Dr. Natascha Kuhlmann and Prof. Dr. Markus Schäfer explores how materials from demolished buildings can be identified, classified and reused by tracing their geological origins.

Giving old buildings a second life

Concrete is everywhere: in homes, schools, bridges and roads. But producing it requires enormous amounts of natural raw materials such as sand and gravel. In Luxembourg, these resources are limited. At the same time, construction activity continues to generate large quantities of waste.  

Reusing materials from demolished buildings could help reduce waste and lower dependence on imported materials. In this context, existing buildings can be seen as a valuable source of future raw materials. This idea was first explored within the European Interreg project ����ͷ��GR-CIRKLA and served as the starting point for this research.

The challenge, however, is consistency. Materials recovered from old buildings are often mixed and can behave very differently once reused in new concrete, impacting its quality and reliability. “Therefore, knowledge about their properties is essential. Especially for buildings constructed with rubble stone masonry, this can significantly increase the potential for reuse.” explains Prof. Dr. Schäfer.

For Dr. Natascha Kuhlmann, geology offers part of the answer. “Before the 1940s, many buildings in Luxembourg were constructed using locally sourced stones such as sandstone, limestone, dolomite and slate” explains Natascha. “These materials all have different properties, which affect how they react when recycled.”

From an engineering perspective, Prof. Schäfer highlights that some stones absorb more water than others. Some are more resistant to frost or mechanical stress. Understanding where these materials originally came from can therefore help predict whether they are suitable for reuse in concrete production.

‟ With its high construction activity, limited natural resources and diverse geology, Luxembourg offers a particularly valuable real-world setting for this type of research”

Dr. Natascha Kuhlmann

Postdoctoral researcher

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Not all stones behave the same way

Despite these differences, many recycling facilities still treat recycled mineral-based construction materials in the same way.

Dr. Natascha Kuhlmann and Prof. Markus Schäfer aim to change that by developing a classification approach that links different local rock types to the way they react in concrete. This could help recycling facilities to sort and process materials more precisely before they reuse them in future construction projects.

‟ By linking demolition materials to their geological origins and historical quarry locations, we aim to improve the classification of recycled aggregates and strengthen their future use in concrete production for more resource efficiency and a circular economy in construction”

Prof. Dr. Markus Schäfer

Full professor in Structural engineering and composite structures

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But how does this actually work? Recycling construction materials starts on the demolition site itself. Materials such as metal, wood, glass and plastics are first separated from concrete and masonry. The remaining mineral materials are then crushed, cleaned and sorted before they can be reused as recycled aggregates for new concrete production.

But recycling is only part of the process. An important step is assessing whether the recovered materials are suitable for reuse. Before recycled aggregates can be incorporated into new concrete, they must meet strict quality requirements regarding their composition, strength, durability, frost resistance, and potential contamination. 

European and national regulations therefore limit how and where recycled aggregates can be used, depending on their quality. This is where the researchers’ approach becomes particularly relevant. By improving the identification and classification of recycled materials, they hope to support more reliable quality assessment and increase confidence in their use in future construction projects.

The researchers are currently developing a geological-engineering approach for recycled mineral construction materials with the support of the Master Thesis project of ����ͷ��.lu student Nicola Simoes and the . The project combines geological maps, historical quarry locations, local building traditions, and material testing. In parallel, a database of local rock types and their engineering properties is being established to support future reuse strategies in construction.

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This project brings together universities, research institutions, and public authorities. Markus Schäfer and Natascha Kuhlmann (����ͷ��, Department of Engineering) initiated the study and served as the main authors.

Other contributors:

• Tom Berna and Stefan Maas (Department of Engineering)
• (Trier ����ͷ��versity of Applied Sciences)
• (Service Géologique de l’État, Luxembourg)
• (Institute of Geosciences, ����ͷ��versity of Bonn)
• (Ministère de l’Économie, Cellule de la construction durable)

• ����ͷ��GR-CIRKLA