Decreasing concrete sewer pipe degradation using admixtures

Concrete sewer pipes are exposed to sulfur-oxidizing bacteria that produce sulfuric acid resulting in a gradual reduction in surface pH. The reaction between sulfuric acid (H 2 SO 4 ) and calcium hydroxide (Ca(OH) 2 ) is the main cause of sewer pipe degradation with sulfate attack playing a secondary role in this corrosion process. Several experiments were conducted in which concrete samples, containing various admixtures, were soaked in H 2 SO 4 solutions to simulate accelerated microbiologically influenced corrosion within concrete sewer pipes. Several test series were performed, each at a different pH. Length, mass, and pH changes were recorded from the specimens over time. Concretes containing no admixture, metakaolin, silica fume, or an organic corrosion-inhibiting admixture were evaluated. Results from the tests showed that there were significant benefits to adding silica fume or the organic corrosion-inhibiting admixture to concrete in this environment.