Accelerated Biodeterioration Test for the Study of Cementitious Materials in Sewer Networks: Experimental and Modeling

Abstract

Important deteriorations have been observed in concrete sewers, due to hydrogen sulfide (H2S) production. Hydrogen sulfide environment involves the selection of sulfur-oxidizing bacteria (bacteria able to oxidize the reduced sulfur compounds) in contact with the cementitious materials. These biological reactions lead to a local production of sulfuric acid and, as a consequence, to the dissolution of cement matrix and its mineralogical transformations (gypsum and ettringite formation). This phenomenon disturbs the sewer system and leads to expansive works of rehabilitation. As a consequence, a project was initiated in order to propose more efficient solutions. The main objectives of this project are to set up an accelerated test and to develop an associated model. To date, experimental studies and some improvements of the model previously setting up were performed. The first study describes the impact of several parameters, including type of cementitious materials, on hydrogen sulfide adsorption. These abiotic tests involve monitoring hydrogen sulfide concentration as a function of time. This experiment was realized in a hermetic chamber with five types of mortars (cast with calcium aluminate cement (CAC), blended Portland cement (CEM III, CEM IV and CEM V) and super sulfated cement (SSC)) and under different relative humidity. The second study is deterioration state of mortars characterization, thanks to some analyses (SEM – EDX). After three months of exposition, different types of sulphur species are observed on mortar surfaces, which vary with the nature of mortar. All these experiments allow providing improvements to model previously setting up. Abiotic tests measurements are used to determine mathematical law, which modelises hydrogen sulphide adsorption on each type of cementitious material.