Analysis of concrete from corroded sewer pipe

The microbial populations in the loose outer corrosion layer (OCL) and the bound inner corrosion layer (ICL) of concrete from a corroded sewage collection system were enumerated. Chemical and physical studies were performed to determine the mineralogical composition strength of the samples. The average number of acidophilic sulphur-oxidizing microorganisms (ASOM) found were 14,500 and 16,000 MPN/g (OCL) and 12,500 and 100 MPN/g (ICL) at the crown and springline. The average numbers of neutrophilic sulfur-oxidizing microorganisms (NSOM) found were 108,000 and 114,000 MPN/g (OCL), and 5 and 300 MPN/g (ICL) at the crown and the springline. The average compressive strength of the concrete undergoing corrosion was reduced by 20%. The results suggest that an initial ecological succession occurred on the concrete surface and that the progression of the corroding front into the concrete was controlled by the penetration of acid produced by ASOM followed by the ASOM themselves. NSOM did not appear to penetrate the concrete.