Corrosion is present in many concrete structures associated with water and wastewater treatment, i.e. in sewer systems. The bacterial activity in the sewers creates a sulphur cycle, which can lead to the bacterial formation of sulphuric acid. The sulphate-reducing bacteria, e.g. Desulfovibrw spp. and sulphur-oxidising bacteria, Acidithiobacilli spp. play very important role in biogenic sulphate attack to the concrete samples. The concrete samples with 10 % of fly ash addition were used for the experiment in both in situ and laboratory model conditions. Experiments proceeded. during 90 days and the corrosion process was demonstrated by the changes of the concrete samples surface detected by SEM/EDX. The chemical composition before and after the experiments was investigated by XRF, FTTR and DTA/TG analyses. The significant changes of surface roughness have been observed for all samples after 90-day exposition to the aggressive environment.
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