Saving natural resources has become increasingly important. In construction, research has been done on alternative methods to replace conventional building materials. One of those novel methods is MICP (microbial induced calcium carbonate precipitation). In this process, calcium carbonate crystals are precipitated with the help of ureolytic bacteria. A cementation solution consisting of urea and calcium salt is used. This precipitation can be used for solidification. In the field of MICP research, there exist multiple publications with several kinds of tests, but no verifiable compressive strength test. However, most researchers are concerned with soil improvement or self-healing methods, to fill cracks in concrete. Similarly, column tests are mainly conducted to investigate the strength. This study presents, a new method of strength assay that uses hardened sand samples of 3 cm edge length. This allows for an accurate compressive strength verification and thus the effect of the biocementation treatment. In addition, this method applies a single treatment method with a novel type of formulation of the MICP components. The results show that a single MICP treatment is sufficient for the consolidation of various sands. Compressive strength of up to 1.8 N/mm2 was achieved in the process tests in the uniaxial strength test.

Microbial-induced calcium carbonate precipitation (MICP) is a novel approach that is already being applied in various areas of construction. The precipitated calcium carbonate can be used to reduce porosity and thus increase the durability of deteriorated building components. This study investigates whether MICP injections are suitable for building rehabilitation. Porous mortar test samples of recycled aggregate and parts of deteriorated masonry were prepared. The MICP injections were performed without pressure and with an injection pump. The treatment effect was investigated after MICP injection by testing the porosity, strength and microscopic evaluation. It can be observed that multiple MICP injections under pressure result in a reduction of the pore volume of porous mortar samples. The produced calcium carbonate precipitates in the pore space of the samples and increases the density by 1.59% and the weight by 7.56%, which also results in a 48.3% reduction of the capillary water absorption. The results of strength tests show an increase of 45.16% in flexural strength and 35.64% in compressive strength compared with the untreated mortar samples. In addition, the MICP process was investigated and the precipitation was characterised. The X-ray diffraction (XRD) of the precipitated calcium carbonate confirms that mainly calcite was formed, which was also found in the pore structure of the MICP-injected masonry after the microscopic analysis. Precipitated calcium carbonate could be detected especially near the injection spots.