Biogenic corrosion mechanism: study of parameters explaining calcium aluminate cement durability
Résumé
Sewer networks should withstand several aggressions, including biodeterioration processes. This study is focusing on cementitious materials since, depending on their composition, these materials do not display the same behaviour when biogenic sulfuric acid attack occurs. In severe conditions, ordinary Portland cement materials can be deteriorated, while calcium aluminate cement (CAC) materials show good resistance to biogenic corrosion. Results show that this durability difference is due to the difference of cement mineralogy. Firstly, the H2S abiotic oxidation into elemental sulfur is less favourable on CAC. Hence it provides much less nutrients for sulfur-oxidizing microorganisms. Then, the presence of high aluminium content in CAC provides a combination of interesting properties to face biogenic acid attack. The hydrated alumina reacts with acid to create an alumina gel layer, stable up to pH 3-4. The acid attack leads to the release of aluminium ions displaying a bacteriostatic effect on neutrophilic sulfur-oxidizing microorganisms. Finally, an alumina gel precipitates on the surface. This gel has an impact on cement surface porosity which therefore reduces the acid impact and probably limiting biofilm adhesion.