Mineralogical Characterization of the Biodegradation of Sewage Cementitious Materials in the Presence of H2S

Abstract

The biodegradation of cementitious materials in sewage systems is mainly due to the biotic oxidation of hydrogen sulfide (H2S) into sulfuric acid. It leads to a local and progressive dissolution of the cementitious matrix as well as the precipitation of some expansive products such as gypsum and ettringite. In such a context, this paper focuses on the characterization of the altered layers present on several types of cementitious materials (CEM I ordinary Portland cement, CEM III blast furnace cement, CEM V composite cement, and CAC: calcium aluminate cement). The studied samples are mortars exposed, to different H2S concentrations, for several years in a local sewage plant managed by the Interdepartmental Syndicate for the Sanitation of the Paris Agglomeration (SIAAP). Transversal crosssections of these mortars were first chemically characterized by energy dispersive spectroscopy (EDS) in order to obtain elemental mapping. Additionally, to better understand the surface degradation and the appearance of mineral phases revealing the process, µ-Raman mappings were performed on the deteriorated zones at different time scales. Gypsum was observed on all samples. The analysis confirmed the greater resistance of CAC materials in such an environment than that of Portland cement-based materials.

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