Effects of Concrete Composition on Resistance to Microbially Induced Corrosion

Microbially induced corrosion (MIC) is a process that can take place in concrete sewers, septic tanks, and transfer stations and can result in concrete deterioration. MIC is attributable to the microbial oxidation of hydrogen sulfide (H2S) to sulfuric acid (H2SO4) by a biofilm community that is established on a concrete surface. The rate and extent of this process will be influenced by the environment in which it takes place (e.g., temperature, H2S concentration), as well as the composition of the concrete itself. Laboratory experiments were conducted to examine the effect of concrete composition and admixtures on MIC. The experiments were conducted in an isolated chamber where the climate was controlled, including the H2S concentration. Concrete specimens representing 13 mixtures were inoculated with an aqueous suspension containing a mixture of four Acidothiobacillus spp. that have been associated with MIC in sewer systems. Results indicated that calcium aluminate cement (CAC) mortar, blended cement, and incorporation of a silane quaternary amine (SQA) antimicrobial agent can improve resistance to MIC under moderate exposure conditions (i.e., surface pH>2.0). The rapid deterioration of specimens exposed to more aggressive conditions in the chamber indicated that degradation of concrete under the most severe MIC conditions (i.e., concrete surface pH < 2.0) was not prevented by simply manipulating concrete mixture proportions. A second set of experiments was conducted to quantify the effectiveness of SQA for the inactivation of pure cultures of planktonic bacteria. Results indicated that the antimicrobial agent performed well for the inactivation of pure cultures of Acidothiobacillus spp., except A. thiooxidans, which represent bacteria that are likely to be active under the most severe conditions (i.e., surface pH < 2).