Abiotic interaction between hydrogen sulphide and cementitious materials

Abstract

Concrete deterioration is extensively observed due to hydrogen sulphide emission in sewerage networks. The presence of this gas leads to the development of sulphur-oxidizing bacteria which produce sulphuric acid. Local deterioration of concrete sewer pipes, based on dissolution-precipitation mechanisms and the formation of ettringite and gypsum, degrades their mechanical properties and prevents optimum waste water collection. Due to expensive rehabilitation works, innovative sewerage network construction or repair approaches must be established and evaluated. The main final objective of this study is to put forward a representative, quick and standardized test and to develop a predictive model for the service life of different types of concrete in the environment of sewer pipes. This study focuses on interaction between cementitious materials and hydrogen sulphide (H 2 S) which is the first step of the degradation mechanism. Mortars based on different types of cement (CEM I, CEM IV and CAC) were exposed to H 2 S under various conditions (relative humidity, pre-exposure to H 2 S or otherwise). Changes in the H 2 S concentration were monitored as a function of time and the H 2 S adsorption rate was calculated. After 6 months of exposure, the state of deterioration of mortars was assessed. Some gypsum crystals on mortar surfaces based on CEM I and CAC cements and a mix of elemental sulphur and gypsum crystals on mortar surfaces based on CEM IV cement were observed by SEM-EDS. The decrease in the H 2 S adsorption rate, highlighted when the relative humidity decreased and when gypsum was present, must be taken into account in the modelling process.