Estimation of Service Life of Concrete Pipes in Sewer Networks

The expense of repair and maintenance of private and public sewage systems in Germany runs to about 100 billion US $. This primarily affects concrete pipes and brickwork sewers. Approximately 40 per cent of the damage can be attributed to corrosion by biogenous sulfuric acid attack as a result of long flow periods and insufficient ventilation of waste water. The report deals with investigations into the prediction of concrete corrosion by biogenous sulfuric acid. For testing of service life in cases of dissolute and expansive chemical attack a very simple easily reproducible comparative simulation method has been developed. The specimens are stored in diluted sulfuric acid for 35 days. After 6 days the specimens are removed from the solution, stored under running water for 24 hours and all loose parts removed in an ultrasonic vessel. This procedure corresponds to the practical conditions of cyclic flooding in combined sewers. After the exposure time the undamaged cross-section, the residual weight, the residual compressive strength and the acid penetration depth are determined. The ageing progress of the specimens stored in acid is compared with the observed corrosion of concrete pipes in real sewer systems. The result is a very good correlation between the calculation of corrosion by Pomeroy’s equation and the timeaccelerated laboratory test involving storage in diluted sulfuric acid. The predicted corrosion after laboratory tests in sulfuric acid at pH value 2 corresponds to the average observed corrosion in a 20-years-old combined sewer.