Healing of marble surfaces by bacterial calcification

ABSTRACT Most of the marble monuments and structures undergo degradation due to the presence of micro and macro cracks that may occur during their service life. These cracks create suitable pathways for harmful substances to enter the marble matrix. Bacterial biocalcification; It is the event that ureolytic bacteria fill and heal the crack by acting as a binder as a result of calcium carbonate precipitation and calcite formation that accumulates in the environment when the necessary environmental conditions and nutrients are provided. When applied to micro/macro cracks, it prevents water infiltration and can increase the durability of the structure. Bacillus subtilis ATCC 6633 was used in this study. Live and dead bacterial cells (107 CFU/mL) were applied to marble samples kept in media containing urea, calcium chloride and calcium acetate. Half of the marble samples used were kept in a CO2 oven for 30 d. The other half is also uncarbonated. Marble samples of 2x2 and 4x4 cm were obtained from the local firm. Stereo microscope/SEM images, EDX-Mapping analysis and XRD analysis were performed. It was observed that B. subtilis had intense CaCO3 precipitation in the medium containing CaCl2. Calcite and aragonite polymorphs were generally found in the medium containing CaCl2. Less CaCO3 precipitation was observed in the medium containing C4H6CaO4. It was determined that calcite, aragonite and vaterite polymorphs were generally found in the medium with C4H6CaO4. It was determined that the macro pores of the marble samples, on which carbonated and live bacterial cells were applied, were partially filled and the micro pores were completely filled. It was seen in the stereo microscope/SEM imaging that the micropores of the marble samples, which were treated with uncarbonated, dead and live bacteria, were also partially filled. Biological healing were achieved in pores with a diameter of 3-5 mm and a diameter of 0.03-0.02 mm. SEM-EDX, mapping and XRD analyzes confirmed that these formations are different from the marble structure and have new CaCO3 crystal structures. In this study, it has been seen that the pores formed in marble as a result of CaCO3 precipitation can be improved and biologically repaired without harming the natural and environment. Keywords: Bacillus subtilis ATCC 6633, biocalcification, biological remediation, Calcium chloride, dead/living bacteria.