The article considers the change in the physical and mechanical characteristics of cement stone made of the CEM I 42,5 N Portland cement in the process of bacterial and fungal corrosion for 6 months in the air and moisture conditions. It is established that the density of concrete during microbiological corrosion increases under constant moistening of the sample. However, after drying, a decrease in the density of concrete is recorded by 10 % under the influence of Bacillus subtilis bacteria and by 14 % under the influence of black mold. The degree of influence of microorganisms on the amount of water absorption of cement stone is established experimentally. Bacteria increases water absorption by 7 %, black mold increases water absorption by 10 %. Within 6 months, water absorption increased from 21 to 24,5 % for bacterial corrosion in indoor conditions, and from 24 to 29 % for fungal corrosion. When exposed to capillary moisture for 6 months, the water absorption of concrete increased to 30,4 % under the influence of Bacillus subtilis bacteria and to 37,3% under the influence of Aspergillus niger van Tieghem fungi. An increase in the water absorption of concrete is associated with an increase in porosity due to biodegradation. Under room conditions of exposure to bacteria, the porosity increases from 14,1 to 15,3 %, and from 14,3 to 17,9 % after exposure to black mold. With constant moistening, the porosity of cement concrete increases to 19,1 and 25,6 % with bacterial and fungal corrosion, respectively. The loss of compressive strength of cement stone is 13 % under the influence of bacteria and 15 % under the influence of fungi in the air for 6 months. In case of microbiological corrosion of concrete under conditions of constant wetting, the strength decreases by about 35 % in 6 months

The article presents data on the study of the kinetics of liquid corrosion of cement concrete infected with microorganisms Bacillus subtilis and Aspergillus niger. The equilibrium concentrations of calcium cations during fungal and bacterial corrosion of cement concrete in an aqueous medium are established. According to the profiles of calcium hydroxide concentrations in the thickness of cement concrete during fungal and bacterial corrosion, it was found that during fungal corrosion of concrete, the intensity of interaction of calcium hydroxide with the products of the vital activity of microorganisms is higher than during bacterial corrosion. In case of fungal corrosion under conditions of Aspergillus niger infection, citric acid has the greatest impact on concrete since its amount in the products of the vital activity of microorganisms is maximum. Profiles of concentrations of aggressive substances by the thickness of the concrete sample show that bacterial corrosion proceeds more slowly than fungal corrosion and allow us to calculate the time to reach the maximum concentration of aggressive substances at the surface of steel reinforcement in concrete. Corrosion of reinforcement in concrete with fungal corrosion will begin in 2.5 years after infection, with bacterial corrosion after 5.5 years.

The article considers the change in the structural and phase composition of cement stone made of Portland cement of the CEM I 42.5 N brand in the process of bacterial and fungal corrosion during 6 months when humidified. The X-ray images of cement stone show peaks that characterize the non-hydrated components of Portland cement alite, belite, tricalcium aluminate, four-calcium aluminoferrite and gypsum. By the method of X-ray phase analysis, it is found that during microbiological corrosion, the content of all phases of cement stone decreases. The aspergillus niger van Tieghem fungi have a stronger effect on the structural and phase composition of cement stone. Fungal microorganisms destroy the crystalline phases and absorb amorphous phases – calcium hydrosilicates C-S-H (I) and C-S-H (II) and tobermorite. When bacteria Bacillus subtilis affects the cement stone, the content of the calcite phase increases, which is a product of corrosion, while the action of black mold reduces the intensity of CaCO3 peaks. A decrease in the content of low-base calcium hydrosilicates and ettringite, as well as other crystalline phases, leads to a decrease in the compressive strength of the cement stone. During 6 months of microbiological corrosion of cement concrete under conditions of constant wetting, the compressive strength decreases by about 35 %.

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The degree of corrosion damage by microorganisms to the concrete wall of the basement is investigated. The biofilm on the surface of the concrete wall under study is formed by micromycetes Aspergillus niger, bacteria Bacillus subtilis, Actinomycetes, nitrifying bacteria Nitrosomonas, lactic acid bacteria Lactobacillus and sulfate-reducing bacteria Desulfovibrio. The waste products of microorganisms consist of organic acids secreted by micromycetes of Aspergillus niger, ammonium ions, carbonate-, nitrate-, sulfide-ions secreted by bacteria. To establish the corrosion state of steel reinforcement in biodegradable concrete, the electrode potential was measured. The established values of the surface potential of steel reinforcement are in the range -351 ÷ -376 mV. This suggests that the probability of local corrosion of steel reinforcement in a biodegradable concrete wall is strong. It will take about 20 years to achieve an aggressive concentration of organic acids at the surface of steel reinforcement in biodegradable concrete with a layer thickness of 5 cm. However, in conditions of constant moistening of the concrete surface, this period is reduced to 10-11 years. The predicted rate of local corrosion of steel reinforcement in concrete exposed to microorganisms is at least 0.2 mm/year. It was found that the depth of concrete destruction under the influence of microorganisms, mainly micromycetes Aspergillus niger, for 20 years is 1.3 cm; for 50 years is 2.1 cm.