Insights into bio-deterioration of concrete exposed to sewer environment: A case study

Abstract

Microbial corrosion induced is considered to be the main cause of concrete deterioration in sewer systems. In this study, the corrosion depths and rates of concrete cores sampled from different sections of concrete sewer pipes exposed to real sewer environments were measured. The pH profile, phase assemblage, and microstructure of corroded concrete relative to depth were also determined. Results showed that after 32 years of exposure, the concrete sewer pipe suffered severe corrosion. Under the influence of water flow fluctuations, the concrete in the waterline region presented more serious thickness loss (up to 23.85mm) compared to the crown region, and the average corrosion rate of concrete in the waterline region and crown region was 0.71mm∙a−1 and 0.20mm∙a−1, respectively. The lowest pH level of concrete pore solution in the sewer was 5.74, observed in the layer close to the surface in the waterline region. The correlation and functional relation between the depth from the concrete surface, pH level, ions, and elemental concentrations in the concrete pore solution was obtain by Spearman correlation test and multivariate function nonlinear fitting. The presence of calcium carbonate behind gypsum and ettringite in inner concrete suggested potential carbonation due to the CO2 produced by heterotrophic bacteria in sewer environment. The results of this study suggest the contributions of flowing water and carbonation in the bio-deterioration of concrete under real sewer environment are non-negligible.