Concrete is booming. Around 4 billion tons of cement are processed into concrete and used worldwide every year. With serious consequences for the environment. conventional cement is fired at around 1,450 degrees Celsius. This consumes a lot of energy and releases large quantities of greenhouse gases," says Lucio Blandini , Head of the Institute of Lightweight Structures and Conceptual Design (ILEK) at the University of Stuttgart.
Researchers from three institutes at the University of Stuttgart are developing a new type of building material - bioconcrete. Thanks to its high compressive strength, it can not only replace traditional sandstone and, in some cases, cement-based concrete. It can also potentially be produced entirely from waste materials and therefore has a significantly lower ecological footprint. The researchers are using an abundant but previously underestimated raw material for production: human urine. They have successfully tested their process in a feasibility study funded by the Baden-Württemberg Ministry of Science, Research and the Arts.
"Bioconcrete is produced through biomineralization. This is a biotechnological process in which living organisms produce inorganic material using chemical reactions," explains Maiia Smirnova, research associate at ILEK. we add a powder containing bacteria to the basic ingredient sand, fill the mixture into a mold and rinse it with urine enriched with calcium for three days in an automated process. The decomposition of urea by the bacteria with the addition of calcium to the urine causes crystals of calcium carbonate to grow. This solidifies the sand mixture into bioconcrete. At the end of the process, a solid is obtained that is chemically similar to natural sand-lime brick." Depending on the formwork, elements of different shapes and sizes can be produced, currently with a depth of up to 15 centimetres.
The first samples produced show promising material properties. Using technical urea, the team has achieved a compressive strength of over 50 megapascals - significantly more than previously available building materials based on biomineralization. With urea in synthetically stabilized urine, the mark of 20 megapascals was achieved. With real human urine, the value was five megapascals, as bacteria do not remain active for the full biomineralization period of three days. This now needs to be improved. The scientists calculate that a strength of the biomineralized material in the range of 30 to 40 megapascals would be sufficient for the masonry of two to three-storey buildings. They are currently carrying out freeze-thaw tests to determine whether the material can be used outdoors.
"The production process for our bioconcrete consumes considerably less energy and causes fewer emissions than conventional cement production. Our approach is also sustainable because we embed the product in a circular value chain," says Blandini. The researchers have developed a concept that shows how urine could be separated and processed from the partial wastewater flow in places with a high volume of people, such as an airport, in order to use it as a raw material for the production of bioconcrete. At the same time, this process could recover secondary valuable materials from the wastewater to produce fertilizer for agriculture. "By producing two products at the same time, we achieve an even better environmental balance," says Smirnova.
Following a successful evaluation, the project has now been extended for three years by the Baden-Württemberg Ministry of Science, Research and the Arts. In further laboratory tests, the researchers want to identify impurities in human urine that have a negative impact on the activity of the bacteria and therefore the quality of the bioconcrete. Based on this, the manufacturing process is to be optimized. The team, together with the Centre for Organic Farming at the University of Hohenheim, is also focusing on simultaneous fertilizer production.
As soon as the laboratory tests have been completed, the concept will be tested under real conditions: The plan is to create a test environment at Stuttgart Airport in which urine is collected and processed into bioconcrete and fertilizer.
The "SimBioZe" project: Simultaneous biocement and fertilizer production from wastewater
The "SimBioZe" project is being funded as part of the "Microorganisms as helpers in climate protection - using microbial processes for a climate-neutral future with innovative methods" funding line. The Baden-Württemberg Ministry of Science, Research and the Arts supported nine projects for one year as part of this program. Four of them have now been extended for a further three years, including "SimBioZe".Three institutes at the University of Stuttgart are pooling their expertise in the interdisciplinary project "SimBioZe": The Institute of Lightweight Engineering, Design and Construction (ILEK) , the Institute of Microbiology (IMB) and the Institute of Sanitary Engineering, Water Quality and Waste Management (ISWA) . In the second project phase, the Center for Organic Farming at the University of Hohenheim will come on board as a new partner. Cooperation with industrial partners, including Stuttgart Airport, is also planned
