PSI - Issue 72

Vera Vujović / Procedia Structural Integrity 72 (2025) 5 – 12

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Biodeterioration is defined as the loss of structural capacity over time, as a result of the action of external agents or material leaching (Sanchez-Silva et al. 2008). According to the definition (Rose, 1981): "biodeterioration is the process by which biological agents (living organisms) cause a lowering of constructive quality or value". According to the classification (Allsopp, Seal, 2006 and Gaylarde et al., 2003) biodeterioration is classified into three categories: biophysical, biochemical and aesthetic ("biofilm"). Biochemical biodeterioration is divided into: assimilatory (organisms feed on the component) and dissimilatory (organisms excrete waste products). The biodegradability rating includes: identification; microscopic observation of the biofilm and the layers below; basic and mineral analysis; conclusion about the characteristics of the identified organisms, morphology of decomposition and changed chemical properties of the material. The growth of microorganisms occurs if there is a carbon source, a donor and an acceptor of electrons. Microbes can appear as: heterotrophs when the carbon source is organic, or autotrophs when associated with carbon dioxide. The movement of microorganisms is based on the transfer of electrons from the donor to the acceptor. According to the electron acceptor, microorganisms can be: aerobic (oxygen) or anoxic (no oxygen). The presence of microbial communities depends on the physical and chemical characteristics of the environment. 4.1 Biodeterioration mechanism All over the world, scientists are particularly dedicated to research on the mechanisms of deterioration, where special attention is directed to biodeterioration. NSOB forms colonies on the surface when the pH is slightly alkaline, with a further decrease in pH, ASOB colonies are formed with the oxidation of thiosulphate, elemental sulfur and polythionates present in the environment to sulfuric acid, thus causing deterioration. Sulfuric and nitric acids are the main metabolic products of microorganisms. The conditions for microbial activity and microbial growth depend on favorable environmental conditions such as nutrients (carbon and energy sources), pH, temperature, osmotic pressure, humidity, etc. and the presence of a community of microbes (or a single microbe) suitable for that environment. The intensity and rate of biodeterioration depends on specific material parameters (porosity and permeability, as well as environmental factors). 4.2 Biodeterioration tests and procedures Scientific methods that are most often used for biodeterioration tests are: optical research and microscopy; radiography; molecular spectroscopic techniques; atomic spectroscopic techniques; x-ray spectroscopic methods; mass spectrometry; chromatography; nuclear methods; age determination. There are numerous methods for identifying bacterial activity on surfaces, as well as mineralogical-microbiological methods that are used to describe the topography of the material surface, the morphology of microorganisms, the composition of the material and other properties using electromagnetic radiation or electron diffraction.The most common tests include scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), energy dispersive X/ray spectroscopy (EDAX), X/ray powder diffraction (XRPD). Chemical tests identify and quantify chemical components and reactions within the material (including quantitative (gravimetric and volumetric) and qualitative analysis)). Taxonomic analysis is used to determine: species, genera and families of mosses and algae.

Fig. 6. Graphic time -characteristic