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Biological decay and its control by biomineralisation in calcareous stones

Üstünkaya, Meltem Cemre
Biodeterioration has an important role in weathering of historical materials. Natural stone materials become vulnerable to physical and chemical changes in outdoor conditions, favouring the biological growth. In this study, biodeterioration on calcareous stones and its control by biomineralisation were studied on limestones from Nemrut Mount Monument and marbles from Pessinous Archaeological Site. For qualitative and quantitative detection of biological activity fluorescein diacetate (FDA) method that was developed for soil microbial activity was applied to stones of historic monuments. Qualitative FDA analysis was used on cross sections of the samples in order to observe the depth of penetration and effects of biomineralisation using a light microscope with fluorescent light source. Quantitative FDA analysis was done by spectrophotometric determination of fluorescence formed by FDA treatment. X-Ray Diffraction (XRD) analyses were used in determining mineralogical structure of patinas and stone base. Light microscopy was used to investigate changes in morphological structure of historic stone in cross and thin sections of the samples. The control of biodeterioration on stone surfaces was studied by biomineralisation treatments using Bacillus cereus. The results of biomineralisation were evaluated by XRD, light microscopy, SEM-EDX and FDA analyses. The results of this study showed that the biodeterioration was an important decay factor in stone materials. It started from the surface and penetrated through the microstructure of the stone up to about four cm depth. Biodeterioration also contributed to the growth of microcracks. Results of biomineralisation using B.cereus to form a protective coating on limestone and marble were also discussed.