(German title: Nachhaltiges Bauen – Biosandstein durch mikrobiologisch induzierte Calciumcarbonatfällung)

At more than 10 km³ per year, concrete is the most widely used building material in the world. One of the main components of concrete is cement, which is produced from limestone at high temperatures. During the so-called burning of cement clinker, the temperatures are around 1450 °C. This manufacturing process results in around 8.6% of global anthropogenic CO2 emissions from the production of cement. For this reason, researchers around the world are trying to find alternatives for the use of cement. One promising approach is microbiologically induced calcium carbonate precipitation (MICP), a process in which calcium carbonate is formed by various microbiological metabolic pathways. If the formation takes place in cavities of mineral particles, calcium carbonate bridges can form between particles and thus hold them together. MICP takes place at temperatures between 20-50 °C. These temperatures are significantly lower than in the production of cement. It therefore has the potential to produce building materials that require less energy than conventional cement. Various studies have shown that MICP has the potential to improve the strength and water permeability of existing building materials such as cement mortar and sandstone, to repair cracks in building materials, and to produce new materials that could be a more sustainable and ecological alternative to conventional building materials such as concrete. The most common mechanism of MICP is the precipitation of calcium carbonate by ureolytic bacteria, such as Sporosarcina pasteurii and Bacillus megaterium. The basic mechanisms of this process are being investigated at the Department of Bioprocess Engineering. So far, there are gaps in the knowledge about the interaction of influences on the MICP such as the ureolytic activity, the microorganism used and the concentrations of the essential raw materials urea and calcium ions during the MICP. These factors partly influence each other and affect the shape and size of the calcium carbonate crystals formed. These in turn significantly influence the strength parameters of the biosandstone formed. The investigation of these influences on a microscopic and macroscopic level is therefore the focus of research at the Bioprocess Engineering department. Another goal is to implement this technology in the field of 3D printing. In cooperation with the Chair of Computional Physics in Engineering, research is being carried out into the possibility of realizing this novel application of MICP. For this purpose, it is not only necessary to optimize the microbiological aspects of MICP, but also to better understand fluid dynamic problems in the distribution and mixing of bacteria and raw materials in the sand bed.