Sporosarcina pasteurii induced carbonate formation for repairing and preventing damage in existing stone masonry structures

Natural stone is one of the most widely used geological construction materials. Although stone masonry structures have the potential to survive over centuries, they may be subject to significant damage and deterioration. Various conservation treatments have been explored for modifying the characteristics of stone, often in the layer closer to the surface. However, treatments may limit the breathability of the material triggering further damage. This work studies microbially induced carbonate precipitation by bacteria as a breathable alternative for the protection of building stone from deterioration. The mineralogical composition and pore structure of most stone types used in construction are favourable for the growth of bacterial communities, while calcium carbonate as the healing product is highly compatible with the substrate. A protocol for the application and assessment of biological healing was determined, taking into consideration the specific needs of bulk materials and existing structures. Sporosarcina pasteurii, an aerobic, ureolytic bacterium, was applied to two different types of stone: i) a massive calcitic chalk from Cyprus, popularly called Lympia stone, ii) a dolomitic limestone from Italy, popularly known as Pietra d'Angera. The healing effect of the newly formed minerals was determined and compared to reference samples by recording changes in water absorption and drilling resistance, as well as by means of SEM/EDS and confocal microscopy on calcein stained samples. The results demonstrated that Sporosarcina pasteurii induced sufficient cementation in the near surface region of the specimens to an extent that could be considered protective, yet compatible with the natural properties of the materials