Factors involved in the long term corrosion of concrete sewers

Microbial induced corrosion (MIC) of reinforced concrete sewers and manholes is a significant problem in sewage systems with global repair costs estimated to be in the order of billions of dollars per year. When the corrosion is sufficiently advanced it can lead to structural failures with potentially serious longer-term operational consequences. While the fundamentals involved in concrete sewer deterioration are reasonably well-understood, the prediction of the rate of deterioration and the quantitative effects of various influencing factors are not well developed. This paper outlines the basic mechanisms involved in deterioration of concrete sewers and the likely effects of various influencing factors, based on currently available information. A brief description of the current knowledge gaps is also provided. A new ARC and industry funded research project is discussed that combines industry and multi-disciplinary university research with the aim of determining the relationship between sewer environmental parameters such as H₂S level, temperature and humidity and the instantaneous corrosion rate of concrete using in situ field observations and extensive laboratory testing. Investigations into the molecular, chemical and material dynamics of the corrosion process will enable an accurate picture of the various underlying processes to be constructed. This data along with historical records and the experience of the industry participants will enable a phenomenological model of the corrosion process to be constructed. It will enable industry to estimate the reliability and the expected remaining physical life of concrete sewers.