Effect of Mixture Design Parameters and Wetting-Drying Cycles on Resistance of Concrete to Sulfuric Acid Attack

Corrosion of concrete sewer pipes by sulfuric acid attack is a problem of global scope, leading to multibillion dollar losses each year. However, research is still needed to better understand the mechanisms of sulfuric acid attack on concrete and the related effects of concrete mixture design parameters. In this paper, the combined effect of wetting-drying cycles and concrete mixture design parameters including cement content, water/cement (w/c) ratio, and coarse aggregate content on the resistance of concrete to sulfuric acid was investigated. Specimens from various concrete mixtures were soaked in sulfuric acid solutions with pH of 0.3, 0.6, 1.0, 1.5, 2.0, 2.5, and 3.0. The mass loss of concrete specimens due to immersion in sulfuric acid and wetting-drying cycles was used as a measure of concrete degradation. For specimens that experienced no mass loss due to low concentration of sulfuric acid, the thickness of the gypsum layer that formed on specimens’ surface was measured on thin sections using transmitted light microscopy. The effect of exposure area/volume ratio of concrete specimens on their mass loss was also investigated. Results show that the mass loss of concrete specimens immersed in sulfuric acid solutions with $\mathrm{pH}<1.5$ increased as the cement content of the mixture increased and as the w/c ratio of the mixture decreased. Moreover, the coarse aggregate content was directly proportional to the mass loss of concrete specimens immersed in sulfuric acid solutions with pH of 0.3 and 0.6, whereas its effect was minor for specimens immersed in the sulfuric acid solution with a pH of 1.0.