Concrete resistance to sulfuric acid immersion: The influence of testing details and mixture design on performance as it relates to microbially induced corrosion

Sulfuric acid immersion tests are often used as a surrogate test for assessing concrete resistance to microbially induced corrosion (MIC). Although sulfuric acid immersion cannot mimic the complex nature of MIC in the field, these studies may be useful in assessing material resistance to a late stage of MIC (during microbial production of sulfuric acid). This article investigates the sulfuric acid resistance of a wide variety of concrete mixture designs exposed to a range of sulfuric acid concentrations. Specimens were constructed from twelve mixture designs with varying water to cementitious materials ratio (w/cm), cement type, supplementary cementitious material replacement, aggregate type and content, and air content. The specimens were exposed to sulfuric acid solutions with pH values of 0.5, 0.8, 1.1, 1.5, and 2.0 and monitored for changes in appearance, mass, cross section, and dynamic elastic modulus. Specimens of different mixture designs were isolated in separate containers to assess acid consumption over time. Results show that as the w/cm was decreased, acid consumption increased and physical degradation increased. A thicker layer of corrosion products developed on specimens of higher w/cm. The partial replacement of ordinary portland cement with fly ash, silica fume, ground granulated blast furnace, or finely ground limestone, the use of Type V cement, the use of limestone coarse aggregate, and the increase of coarse aggregate all resulted in improved resistance to sulfuric acid compared to concrete made with ordinary portland cement at an equivalent water w/cm. The magnitude of the improved performance was not always substantial and varied between mixtures. Material responses appeared to differ over the range of acid concentrations used; however, as expected, the most severe degradation for every mixture was observed in the most concentrated acid. The authors provide guidance as to when acid immersion tests are appropriate as well as potential improvements for the acid immersion test.