Modelling concrete deterioration in sewers using theory and field observations

Samples of new and 70year old pre-corroded OPC concrete were exposed for up to 48months in 6 sewers throughout Australia. Corrosion losses at each site followed the bi-linear trend originally proposed by Wells and Melchers [1]. During an initial phase (lasting <2years) negligible loss of material occurs however once the surface pH=6 losses commence and accumulate linearly at a rate that is likely to remain constant over time. Corrosion rates were found to be sensitive to humidity but insensitive to concrete alkalinity. A first pass model which predicts the rate of concrete sewer pipe corrosion from a knowledge of local average sewer gas temperature, humidity and H2S concentrations was also developed. The equation predictions were in good agreement with rates determined from field observation and historical data.