DETERIORATION OF CONCRETE COMPOSITES PLACED IN SEWER PIPELINES EVALUATED BY CALCIUM AND SILICON IONS CHANGES

The corrosion of concrete in sewers poses a major problem in the modem world. There are two major causes of internal corrosion in a sanitary sewer. The first is conventional acid attack caused by low pH industrial waste discharged directly into the sewer system. The second cause is grouped together as sulphide corrosion, hydrogen sulphide (H2S) corrosion or sulphide attack. This paper is aimed at the presentation of the results of the experiments proceeded in real environment in sewage system during 0.5 year, 1 year and 1.5 year. The sulphur-oxidising and sulphate reducing bacteria present in the waste water was considered to be the main corrosion factor of concrete samples. The concrete matrix deterioration was evaluated by study of Si/Ca, Si/Al and Si/Fe ratios changes after the experiment. The concentrations of Si, Ca, Al and Fe ions were measured at the beginning of experiments and then at the end of every period by XRF method. The ratios of Si/Ca, Si/Al and Si/Fe measured in concrete samples have been changed during the various time of concrete samples exposition (0, 6, 12 and 18 months) to the waste water. In addition the concrete samples were evaluated by thermal analysis DTA/TG. The shift of peak temperatures of 18 months exposed samples was observed.