Effects of biodeterioration on the mechanical properties of concrete

Abstract

Concrete biodeterioration in sewers and structures subjected to environments rich in hydrogen sulfide has been related to the activity of sulfur oxidizing bacteria (SOB). In previous studies, the effect of the activity of SOB on concrete structures has been linked mainly to weight loss. In our work we have investigated, in addition to the weight loss, the variations in porosity and compressive strength. The main objective of this paper is to explore, under controlled conditions, the effect of biodegradation of non-submerged samples, on both the physical properties and the mechanical performance. Towards this aim, cement mortar samples inoculated with pure cultures of Acidithiobacillus thiooxidans, Halothiobacillus neapolitanus, and a consortium containing both strains, were exposed to an H2S-rich environment. Changes in physical properties, including weight and porosity, and compressive strength were measured over 300 days. The results showed that the greatest reduction of weight and compressive strength was observed in samples inoculated with the consortium (7 and 52 %, respectively); while the largest variation in porosity was observed in samples inoculated with A. thiooxidans (27 %). These results were used to obtain relationships between the amount of sulfur available over time with specific physical and mechanical properties; i.e., compressive strength, porosity, weight loss, and physical appearance.