Researchers at the University of Stuttgart have developed an innovative form of bio-concrete using an unlikely but abundant resource: human urine. This material breakthrough, part of the ongoing SimBioZe project, demonstrates significant potential for sustainable construction and design by applying microbial processes to create a low-impact alternative to traditional cement-based concrete.

Addressing the Environmental Cost of Cement
Concrete is one of the most widely used building materials worldwide, but it comes at a high environmental cost. The production of conventional cement requires firing at temperatures up to 1,450°C, resulting in substantial energy consumption and greenhouse gas emissions. In contrast, the newly developed bio-concrete significantly reduces both energy use and emissions, presenting a viable alternative for eco-conscious architectural and interior applications.

A Microbial Production Process Using Waste
The core innovation lies in a process called biomineralisation, where bacteria induce the formation of calcium carbonate crystals. This is achieved by mixing sand with a bacteria-infused powder, placing the mixture in moulds, and flushing it with calcium-enriched urine over three days. The bacteria break down the urea in the urine, enabling calcium carbonate crystals to form and bind the sand together.

The resulting material resembles natural calcareous sandstone in composition and can be shaped in moulds of various forms up to 15 cm in depth. Current prototypes exhibit compressive strengths ranging from 5 MPa (real urine) to over 50 MPa (synthetic urea), making the material suitable for components in low-rise architecture, interiors, and landscape design.

Optimising for Practical Application
While early results are promising, the research team is now working on increasing the compressive strength when using actual human urine, as bacterial activity tends to decline over the three-day solidification process. Their goal is to achieve at least 30–40 MPa, which would make the bio-concrete suitable for structural use in buildings up to three storeys high.

The project also includes testing the material’s durability, such as freeze-thaw resistance, to determine its feasibility for exterior and landscaping applications.

A Circular System: Bio-concrete and Fertiliser from the Same Waste Stream
One of the most compelling aspects of this project is its circular design approach. Because human urine already contains water and essential nutrients, the process not only reduces water usage but also enables the recovery of valuable by-products for use in agriculture. The research team envisions implementing the system in high-traffic locations such as airports, where separated urine could be processed into both bio-concrete and organic fertiliser.

Next Steps: Real-World Testing
The project, funded under the “Microorganisms as Helpers in Climate Protection” programme by the Baden-Württemberg Ministry of Science, Research and the Arts, has now entered its second phase. This includes optimising the bacterial process and setting up a pilot facility at Stuttgart Airport to demonstrate the dual production system in real-world conditions.

Relevance for Designers
For architects, interior designers, and landscape architects, this innovation offers a concrete example (literally and figuratively) of how biotechnology and waste valorisation can shape future building materials. It illustrates how design can intersect with microbiology to create sustainable solutions that align with circular economy principles. While not yet market-ready, the technology also offers inspiration for product and packaging designers exploring biobased materials and closed-loop systems.

Source: University of Stuttgart
Image: University of Stuttgart / ILEK / IMB / ISWA