Biogenic sulfuric acid corrosion (BSA)

(finished project, researcher: J. Monteny, for more information contact prof. dr. ir. Nele De Belie)

The state of municipal sewer systems has become a serious concern world-wide, because of the cost of improvements, maintenance and replacement or repair of deteriorated systems. The wastewater collection system is of major importance, since failure can lead to health problems and property damage. The degradation of concrete in sewers is caused by a microbiologically induced type of corrosion and is known as biogenic sulfuric acid attack (BSA).
First, occurrence of BSA in Flanders was investigated through inspection of damage in situ and analysis of wastewater samples. Subsequently, a microbiological test method was designed to monitor the resistance of different types of concrete with regard to BSA. The procedure reflected the worst case conditions by providing H2S, Thiobacilli and nutrients. Furthermore, chemical tests using a 0.5% sulfuric acid solution were performed. Besides the immersion tests, the testing apparatus for accelerated degradation tests was applied. The cylindrical samples were submitted to an alternating immersion in the sulphuric acid solution and drying in the air. After drying, the concrete cylinders were brushed to remove weakly adhering concrete particles. Concrete degradation was quantified by measuring the change of the radius of the cylinders and the surface roughness after each cycle with an automated laser measurement unit. The influence of different parameters such as the type of cement, polymer modification, addition of silica fume and the type of aggregates was explored. 

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Testing apparatus for accelerated degradation tests (left). Concrete cylinders before and after sulfuric acid attack (right).

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Scheme of biogenic sulfuric acid attack.