Predicting life expectancy of concrete septic tanks exposed to sulfuric acid attack

The attack of concrete owing to sulfate present in sewage is a major problem, both in Australia and worldwide. The prediction of the expected long-term performance of concrete exposed to sewerage and similar environments can be difficult as it is affected by a large number of parameters. In addition the deterioration process in concrete takes a long time to reach a significant level. Whereas considerable research has been undertaken in flowing sewage systems in pipes, little research has been undertaken on static systems contained in septic tanks. A research project conducted at RMIT University has investigated the deterioration of concrete septic tanks located in rural Victoria. A comprehensive set of laboratory experiments was established to measure the accelerated deterioration of concrete under exposure to sulfuric acid. The specimens were manufactured using the same mix design and ingredients used in septic tank production in rural Victoria prior to 1990. The mass changes in the concrete specimens have been recorded and based on the data, a statistical model has been developed to predict the mass change of concrete with time as a function of the cement content and acid concentration observed in sewage.