University of Stuttgart researchers are developing a cement-free "bioconcrete" that uses bacteria and human urine to produce a calcium carbonate binder. Campers at the CMT fair donated about 100 litres to the project led by Professor Lucio Blandini. Test samples reached roughly 60 MPa and could be used for blocks, columns and paving stones, but scaling is challenging: an estimated 26,000 litres of urine would be needed for one cubic metre. Researchers are partnering with airports and festivals and will study effects of medication residues and donor variability.
Researchers Turn Urine Into Cement-Free 'Bioconcrete' — Campers Donate 100 L at Travel Fair
Professor Lucio Blandini, head of the Institute for Lightweight Structures and Conceptual Design (ILEK), holds a piece of concrete made from urine. Katharina Kausche/dpa
Concrete made with human urine may sound surprising, but researchers at the University of Stuttgart are testing a cement-free alternative that could cut the construction industry’s climate impact. At the CMT travel trade fair, campers contributed roughly 100 litres of urine to help develop a bacteria-driven binder the team calls "bioconcrete."
Donating, Not Flushing
Professor Lucio Blandini and his team from the Institute of Lightweight Structures and Conceptual Design (ILEK) invited fair visitors to pour samples into collection containers under the slogan "We build on urine." The researchers collected about 100 litres by the end of the event and thanked several regular donors who returned multiple times.
How Bioconcrete Works
The process mixes sand with a bacterial powder, packs the blend into moulds and repeatedly rinses it with urine over several days. Bacteria break down urea in the urine and trigger precipitation of calcium carbonate crystals, which act as the binder and harden the material. The team reports test specimens can reach compressive strengths near 60 megapascals — strong enough for blocks, columns and paving stones — and in some cases the curing can be faster than ordinary cement.
Industry Context and Advantages
Cement production is responsible for a large share of global CO2 emissions (roughly 6–7%), so alternatives that avoid cement could significantly reduce the carbon footprint of concrete. Stuttgart’s bioconcrete uses inexpensive, widely available raw inputs and is developed with support from sustainable-toilet firms Arwinger and Kompotoi.
Scaling Challenges
Scaling remains a major obstacle. Small test pieces require hundreds of litres of urine, but the researchers estimate that producing one cubic metre of bioconcrete would require on the order of 26,000 litres of urine — a volume that demands dedicated collection infrastructure and logistics. The team is exploring partnerships with airports, festivals and other high-traffic sites to source larger quantities.
Open Questions and Next Steps
Further research will examine how contaminants in urine — such as medications, hormones or recreational drugs — affect the bacterial process and final material properties. To date, trials have primarily used urine donated by men, so the researchers plan to test a broader range of samples. Future goals include producing larger structural elements, refining collection systems and assessing life-cycle environmental benefits versus traditional cement concrete.
Outlook: The project has drawn strong public interest and curiosity. While promising in the lab, bioconcrete must overcome supply, regulatory and consistency challenges before it can be adopted at scale.
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