United States Department of Transportation
i
Analysis and assessment of microbial biofilm-mediated concrete deterioration.
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2008-10-01
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[PDF-1.63 MB]
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Edition:Technical report; Sept. 2007-Aug. 2008.
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Abstract:Inspections of bridge substructures in Texas identified surface deterioration of reinforced concrete columns on
bridges continuously exposed water. Initial hypothesis were that the surface deterioration was a result of the
acidity of the water in which the columns were exposed. However, evaluation of the water acidity indicated that
the surrounding waters were only very slightly acidic and near neutral. Discussions between engineers from the
Texas Department of Transportation (TxDOT) and researchers at Texas A&M University and the Texas
Transportation Institute (TTI) hypothesized that the damage could be a result of microbial attack. Microbial
attack is often identified as an acid attack because some microbes can produce sulfuric acid. This research
investigated whether microbes were present at areas on the bridge that were exhibiting attack, determined if
there was a correlation between degree of damage and number of microbes present, determined if these microbes
were acid producing microbes, and identified the microbes present at the field sites. Results indicate that
microbes are present at the bridge columns experiencing surface deterioration, that the number of microbes
present is directly correlated with the degree of damage, and that these microbes are acid producing. The
research identified five genera: these included Bacillus, Brachybacterium, Flavobacterium, Lysinibacillus and
Thiomonas. The group with the largest numbers of representatives was Bacillus, which was composed of 17
strains. The second largest group was identified as Thiomonas perometabolis, which consisted of seven strains.
The researchers concluded that the damage to the concrete bridge columns is microbial attack. Because some
bridge structures are exhibiting significant microbial attack of the concrete cover and because the long-term
performance of the columns (and hence bridges) are most sensitive to concrete cover, further research is needed
on how to prevent and mitigate this attack.
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