Investigation on degradation of concrete sewer pipes by sulfuric acid attack

The degradation of concrete sewer pipes by sulfuric acid attack is a problem of national importance. The magnitude of the associated costs emphasizes the pressing need to address this issue. In the current thesis, a total of 1120 test specimens were used to investigate the behavior of concrete with different mixture proportions and incorporating various admixtures in sulfuric acid solutions having various concentrations. The mechanical properties, porosity, and microstructure of the different concrete mixtures were measured. Mechanisms underlying the degradation of concrete by sulfuric acid have been investigated, and various approaches of enhancing the resistance of concrete to sulfuric acid attack have been thoroughly examined. Moreover, the feasibility of using artificial neural networks (ANNs) to predict the compressive strength at different ages of the various concrete mixtures and their degradation under sulfuric acid attack was examined. A pilot-scale model consisting of three concrete pipes (75 cm in length and 30 cm in internal diameter) was used to investigate the effect of using various coating films at the internal pipe wall on the generation of biological sulfide in concrete sewer pipes.; Results show that conventional hydration products of portland cement concrete, such as calcium silicate hydrates and calcium hydroxide, are vulnerable in severe sulfuric acid environments. Concrete having non-traditional hydration products (such as that made with geopolymer cement) was found to be more durable in acidic environments. In addition to the nature of hydration products, the concentration of sulfuric acid and time of exposure played key roles in defining the extent and rate of concrete degradation. No clear relationship could however be established between properties of concrete (compressive strength and porosity) and its degradation by sulfuric acid attack. Contrary to the generally accepted view, concrete having a higher w/c ratio and/or lower cement content was more resistant to sulfuric acid attack.; ANN models were developed and proved to be accurate and effective tools for predicting the compressive strength of the different concrete mixtures and their degradation under sulfuric acid exposure. The ANN models were also able to capture the effect of concrete mixture ingredients on compressive strength of concrete and its degradation by sulfuric acid. (Abstract shortened by UMI.)...