Microbial mediated deterioration of reinforced concrete structures

Biogenic sulfuric acid corrosion is often a problem in sewer pipelines, compromising the structural integrity by degrading the pipeline’s concrete components. We investigated the microbial populations in deteriorated bridge concrete, with samples taken from bridge concrete both above the water level and in adjacent soils. Total counts of microbial cells indicated a range of 5.3 ± 0.9 × 10 6 to 3.6 ± 0.3 × 10 7 per gram of concrete. These values represent the range from slightly to severely deteriorated concrete. From severely deteriorated concrete samples, we successfully enriched and isolated one sulfur-oxidizing bacterium, designated strain CBC3. This strain exhibited strong acid-producing properties. The pH of the pure culture of CBC3 reached as low as 2.0 when thiosulfate was used as the sole energy source. 16S rDNA sequence analysis revealed that the isolated strain CBC3 was close to members of Thiomonas perometablis with 99.3% identity. Fluorescent In Situ Hybridization (FISH) analysis of significant numbers of sulfur-oxidizing bacteria from deteriorated concrete indicated that T. perometablis was the dominant acidophilic bacterium, comprising 32.0% of the total active bacteria in the severely deteriorated concrete. Semi-continuous cultures of T. perometablis CBC3 and Thiomonas intermedia were used to evaluate the biodegradation of cement samples. A weight loss of up to 5.7% was observed after 3 months, compared with a weight loss of 0.3% in non-inoculated control.