Microbial deterioration of concrete infrastructure

Scope and Method of Study. Experiments were conducted to characterize and identify acid producing microorganisms that may be responsible for the deterioration of concrete bridges in Texas. Culture-based and culture independent methods were used to identify and characterize the microorganisms. Analysis of ions present in the microbial medium due to acid production and the dissolution of calcium were detected by ion chromatography and inductively coupled plasma spectroscopy.;Findings and Conclusions. Samples obtained from Texas Department of Transportation (TxDOT) were used to isolate the microorganisms present on the deteriorating bridge columns. A mixed culture of microorganisms was isolated by growing them in media specific for acid producers.;Ion chromatography analysis detected sulfates and nitrates present in the medium, indicating the presence of acid producers. Dissolution of calcium from the concrete due to the acid production by these microorganisms was detected by inductively coupled plasma spectroscopy (ICP), further indicating the role of the acids.;Agar plates with a pH-sensitive indicator were used to isolate the true acid producers from the mixed culture of microorganisms. The acid producers were sequenced and a Streptomyces species capable of oxidizing thiosulfate to sulfate was identified. Therefore, it was concluded that the deterioration occurring on Texas bridge sites may result from a microbial-induced deterioration. This occurrence may result due to the presence of sulfur oxidizers, oxidizing sulfur sources and nitrifying bacteria oxidizing nitrogen sources. The strong acids produced by these microorganisms may result in severe corrosion of the concrete cover.