“We must finally understand that construction cannot come at the expense of future generations. For years, recycled concrete has shown that quality and sustainability are not mutually exclusive. But as long as we cling to old structures, we are losing valuable time in the fight for resources and climate protection.”
Marlen Luxenhofer, Research & Development Employee, FEESS
Construction demolition waste (CDW) accounts for over half of all waste generated in Germany, making recycling a significant lever for carbon reduction in the built environment. Yet the industry still falls short: mixed CDW, which is more heterogeneous than materials like demolished concrete, is largely landfilled rather than recycled, and the volume generated is growing.
At the recycling center Rabailen in Kirchheim unter Teck, FEESS established a construction waste sorting plant, which is unique in its functionality and set-up and focuses explicitly on the processing of mixed CDW. Through a combination of dry and wet processing and manual sorting, even heterogeneous material can be processed into high-quality recycled construction materials.
Progress is constrained on two fronts. Regulatory frameworks have not kept pace with recycling ambitions: current German regulations do not permit the use of this recycled sand (an unavoidable product of CDW processing) in building construction. The resulting disposal costs for CDW sand represent a significant obstacle for the German recycling industry and lead to mixed CDW being largely landfilled or backfilled. In this project, FEESS is operating beyond the scope of current standards, with results intended to inform future regulatory updates.
Market acceptance is the second barrier. Many customers are sceptical about recycled building materials, yet data shows recycling aggregates performance matches with the primary materials in most application cases.
From demolition waste to new building products: using 100% recycled aggregate for concrete blocks
The life cycle of recycled concrete blocks starts with demolition. Construction and demolition waste is transported to the Rabailen recycling centre in Kirchheim/Teck, where it passes through sorting, screening, flotation, and crushing. The process yields mixed rubble (sand and gravel), used as raw material for new products.
The INBUILT mix combines CDW gravel and CDW sand with cement, water, and plasticiser. What distinguishes it is the use of 100% recycled aggregate across both coarse and fine fractions, sourced entirely from mixed construction waste with no primary aggregates. This deliberately goes well beyond current norms to test a borderline formulation and find the limits of what is technically possible.
The resulting concrete can be cast as in-situ concrete or poured into block formworks. As reuse blocks, they can be stacked dry, without mortar, keeping disassembly and reuse straightforward. Prefabricated applications are equally viable: in the tiny house demonstrator, the concrete was used to cast a steel-reinforced door lintel.
Minimising the extraction of primary materials
An advantage of the new concrete recipe is that it reuses rubble aggregates originating from demolished buildings, thus limiting the construction waste that goes to landfills. At the same time, extraction of primary materials can be minimised, reducing greenhouse gas emissions.
Production of the recycled concrete blocks currently requires significant manual labour, resulting in high costs. Upscaling is therefore scheduled to begin after the INBUILT project is concluded in 2027. Until then, work will be done to optimize production so that competitive cost structures can be offered.
Both concrete products are tested in two demo sites in Germany. The recycling concrete blocks are tested at the tiny house in Pfeffenhausen, through a non-load bearing interior wall at the Leipfinger Bader facility (Demo site 2). The in-situ concrete is tested in an office building in Stuttgart (Demo site 4). The use case at this site is an exterior one as facade elements at an office building on site at the Campus of University of Stuttgart, who will perform the testing of the materials as well.
Prior to application at the demo sites, the recipe went through extensive testing in the labs of the University of Stuttgart. The results will be used to pave the way for future standards towards an improved use of recycling materials.
The company FEESS is a medium-sized family business with over 70 years of experience and know-how. With their headquarters in Kirchheim/Teck, the area of operation covers the greater Stuttgart area in South Germany. The core business is earthworks, demolition and recycling which is practiced at various construction sites and 5 self-owned recycling centres. Today, the range of services comprises a total of eleven segments, through which the company sees themselves as ambassadors for quality recycling in the building industry. Starting out as a small transport company, FEESS evolved to one of the pioneers in the recycling industry and stands for active environmental protection.
This article was written by Marlen Luxenhofer (FEESS) and curated by Giorgio Alessandro (Greenovate! Europe) for the INBUILT project.
