Micro-scale studies of microbialinduced carbonate precipitation for the application of biocementation
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- Institutt for fysikk 
Cement, which is used as a binding material in conventional concrete, is the second most consumed material by humans, after water. The production process of cement, however, causes a high emission of CO2 and contributes in total with up to 5% to the human-caused CO2 emissions. To slow down global warming, the global greenhouse gas emissions need to be reduced and therefore there is a need for construction materials with lower greenhouse gas emissions. A biological approach to produce a solid, concrete-like material is microbial-induced carbonate precipitation. The precipitated calcium carbonate crystals can bind a granular medium, such as sand, together to form a stable material. This process is called biocementation. The stability of the material is dependent on the microscopic properties of the crystals, such as size, amount, and distribution of the crystals in the granular medium and the crystal structure. This thesis aims to provide an experimental framework for the investigation of micro-scale processes in biocementation to get a better understanding of the biocementation process. The pH was used as a parameter to monitor the progress of the reaction. Two methods are presented to follow pH changes and precipitation kinetics during the process at the micro-scale. The first method uses UV/VIS spectroscopy to monitor the average pH evolution in real time in small volumes. In the second method, confocal laser scanning microscopy is used to monitor local pH changes at the grain scale in situ and in real time. For that method, a microscope sample cell is presented, which allows the monitoring of local pH changes for different crystallization conditions. With the developed methods microbial-induced carbonate precipitation was investigated in the presence of calcite seeds and sand grains to get a better understanding of biocementation. The obtained results can be used for benchmarking pore-scale simulations of the process and will contribute to the knowledge-based improvement of the material for large-scale construction applications.