Assessment of the effect of concrete properties on service life of concrete sewer pipes subjected to hydrogen sulphide attack

Corrosion of concrete sewer pipes due to hydrogen sulphide attack decreases the service life of sewer systems and results in significant economic losses each year. The reaction between sulphuric acid and calcium hydroxide is the main cause of sewer pipe degradation. In this paper a technical discussion about the corrosion mechanism and the effective parameters in corrosion rate of concrete in sewer systems are presented. The generic formula for calculation of corrosion rate indicates that the mix design with higher alkalinity (expressed as the proportion of equivalent calcium carbonate) will lead to lower corrosion rate. Therefore using concrete mixes with higher alkalinity increases service life of sewer pipes. Reliability analysis is then applied in a concrete sewer system to accurately predict service life of the pipeline and to assess the effect of alkalinity of concrete on service life. For this purpose and to consider all uncertainties about input data, a reliability method (Monte Carlo) is implemented. The results from Monte Carlo simulation method showed the degree of sensitivity of service life of the pipeline to change in the level of alkalinity. The results of this study can be used by engineers and designers of concrete sewers, with focus on the properties of concrete mixture that can affect the service life of the system