Closed-loop recycling: Could Denmark produce clinker from end-of-life concrete at scale?

Circular economy (CE), particularly closed-loop recycling, has been identified as a strategy to enhance the sustainability of the cement industry. The chemical composition of the raw meal - the raw materials used to produce cement - is a limiting factor in cement manufacturing, particularly for CE and end-of-life (EOL) concrete recycling. Cement closed-loop recycling entails retrieving ultrafine concrete waste particles (UFCWP, particle fraction between 0 and 0.25 mm) from EOL concrete using advanced recycling technologies that could replace clinker raw meal in cement clinker manufacturing. Utilizing a combined conceptual stoichiometry mass balance model with material flow analysis for the first time, this study demonstrates the chemical limitations of substituting raw materials with ultrafine EOL concrete in a closed-loop recycling process within the Danish clinker production. The main results indicate that a maximum of 11.76% UFCWP can be used to replace conventional raw meal in Danish cement clinker production, resulting in a 10% reduction in global warming potential compared to conventional cement clinker production. For this, we would require three times more EOL CEM I concrete in Denmark than is currently produced (approx 1.2 Mton). This study highlights the mismatch between current cement demand and EOL concrete for closed-loop recycling in Denmark.