Spectroscopic mapping of biodeterioration products on cementitious materials in sewer networks exposed to low H2S levels

A sewer environment is considered a severe environment, but this severity greatly depends on the effluent's nature, hydro-dynamics, and its structure (length and width, effluent retention time, manholes, etc.). Although cementitious materials were chosen to ensure the durability of the network, alterations in the cement matrix have been observed, primarily attributed to sulfate attack associated with the presence of H2S, which is utilized by micro-organisms in the sewer network. This attack results from two oxidation processes of H2S on the cementitious surface, with the concentration of the sulfuric gas varying significantly along the network. This study investigates the impact of low H2S concentrations on cementitious materials, specifically focusing on two cementitious binders, CEM I and CEM V. The approach aims to understand the biodegradation processes through detailed and localized characterization of the initial and newly formed mineralogical phases. For the first time, micro-Raman spectroscopic mapping, coupled with chemometric tools, has been applied to explore the effects of low levels of HAS and bacterial activity on cementitious matrices. The results indicated the presence of gypsum, ettringite, native sulfur, and CaCO3 polymorphs (calcite, aragonite, and vaterite).