Biodeterioration (disintegration of stone surfaces due to organism activity) in modern structures and cultural heritage is a problem that does not only affect the aesthetic appearance of stone elements but also changes their functionality (e.g. building protection) and indirectly influences the economy (e.g. cleaning costs, costs of impregnation agents protection, costs of renewal). Bioreceptivity is a material's susceptibility for the population of living organisms. Methods for bioreceptivity determination are usually based on a quantification of a grown microbiological mass on an exposed stone surface in a determined time. In this thesis a method for bioreceptivity determination is implemented based on an image analysis of autofluorescing pioneer organisms with a fluorescent microscope. The method is primarily meant for assessing the direct influence of a rock's own intrinsic features (e.g. mineral agents, porosity, etc.) on its sensitivity for organism growth. Bioreceptivity has been determined on fifteen frequently used commercial types of natural stone for construction purposes in Slovenia. Mineral composition, petrographic and microstructural features were determined with the help of optical microscopy and other complementary methods (water absorption due to capillary rise, porosimetry with mercury). The rock samples were inoculated (spread) with the following phototrophic organisms: Chlorella vulgaris, Chroococcus minutus and Pseudococcomyxa sp. and exposed to a growth chamber for four weeks. Due to the fastest growth and for counting cells of a proper form and size, the most appropriate microorganism for the laboratory experiment of bioreceptivity proved to be Chlorella vulgaris. It was established that different rocks have a different bioreceptivity which depends on their mineral composition, roughness and physical features, e.g. porosity, and can be assessed in laboratory conditions. In case of dry surface samples, it is important to have a permanent water supply which is provided by the water absorption through the capillary pore system (pores which are less than 0,1 micrometer in diameter). The largest cell growth was registered on sandstone and tuff which are more porous and where the capillary rise is the strongest. It has been established that in case of dry surface samples a) the soaking of the surface, which depends directly on surface roughness and chemical composition, and b) the pore type (rocks with capillary pores prevent drainage and enable a longer water presence on the rock's surface) have the greatest influence. The results of bioreceptivity analysis examinations of water saturated samples show the prevalence of a rock's mineral composition. The growth results are higher in water saturated samples. It can be concluded that water availability is the key factor for cell growth.
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