Concrete production accounts for 5–9% of global CO₂ emissions, making it one of the largest industrial sources of carbon dioxide. Approximately 80% of these emissions are attributable to the production of Portland cement clinker, the principal component of cement — the binder in concrete. In light of the associated environmental impacts and growing resource scarcity, the cement and construction industries are compelled to develop more sustainable solutions.

One such solution is the recycling of waste concrete. In particular, it is imperative to advance the recovery of the cement fraction from this material in order to produce a high-quality product within the framework of a circular economy. This is precisely where the research at the Institute of Materials Science, across various projects, comes into play:

The ZABERZEM project is being carried out in collaboration with Hermann Rauen GmbH & Co. of Mülheim an der Ruhr and Vereinigte Schotterwerke GmbH & Co. KG of Stolberg.

The objective of the project is to separate the cement-containing fine fractions from demolition concrete to such an extent that thermal treatment of these fractions yields a high-quality product with the highest achievable strength class and a sufficiently long working time. The addition of slags supports this goal by serving as a grinding aid and as a source of additional strength-forming phases. To this end, it is necessary to investigate which properties of the slags influence the two processes of grinding and rehydration. The aim is to identify the most effective combination of slags, reactivated cement, and, where applicable, additives.

The UpCement project was carried out in collaboration with the Institute for Processing Machinery and Recycling Systems Technology at the Freiberg University of Mining and Technology.

The overarching objective was to develop a process in which the cement paste from waste concrete is separated from the aggregate, followed by a low-energy thermal treatment to produce a reactive cement of near-virgin quality while keeping CO₂ emissions low, ultimately suitable for use in the construction industry.

To obtain scientifically verifiable data while simultaneously establishing practical relevance at an early stage, model cements were produced and analysed under fully controlled conditions, while in parallel, demolition concrete from a real structure dating from the 1970s — the Turmstraße Bridge in Aachen — was investigated. To this end, a total of 40 tonnes of concrete rubble from the bridge were examined at the University of Duisburg-Essen and the Freiberg University of Mining and Technology.

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