INTERACTIONS OF NUTRIENTS, MOISTURE AND PH ON MICROBIAL CORROSION OF CONCRETE SEWER PIPES

The heaviest corrosion occurred in the area around the sewage level of the concrete sewer pipe. The corrosion rate of this area was 4.3-4.7 mm/yr. The corrosion rates decreased according to the distance from the sewage level. The deterioration at the crown of the sewer pipe was lowest, 1.4 mm/yr. It is concluded that water and nutrients provided by sewage are important factors for microbial corrosion. Two corroded products were mainly produced, depending on pH levels. Gypsum was formed at pH levels less than 3 on the surface of the concrete sewer pipe and mortar specimens. On the other hand, ettringite was produced when pH levels were higher than 3 inside the specimens.