Performance of cement mortars with waste-material addition in microbiological sulphate environment
Keywords:bio-corrosion, sulphate acid attack, concrete, blast furnace slag
Bio-corrosion refers to the corrosion influenced by the presence of microorganisms on the surface of different concrete structures. Sulphate-reducing bacteria (SRB) and sulphur-oxidizing bacteria (SOB) belong to the best studied microorganisms causing bio-corrosion. Concrete sewer pipes, waste water collection systems and treatment plants ensure a suitable environment for the growth and activity of these microorganisms. Sulphur-oxidizing bacteria produce the biogenic sulphuric acid which may cause a significant structural damage to the sewage infrastructure by inducing the deterioration of concrete sewer pipes.This paper discusses the effects of SOB bacterial activity represented by Acidithiobacillus thiooxidans on parameters affecting the durability of cement mortar composites. Two mortar mixtures were used in the experiment: samples with a share of ground granulated blast furnace slag (65 % cement replacement) and the reference samples without any waste addition. The composites were exposed to an aggressive sulphate environment with sulphur-oxidizing bacteria for 60 days. Parameters such as the pH of liquid media and the leachability of the basic inorganic compounds from the cementitious matrix due to the aggressive environment were studied. The better durability of cement mortar samples, based on furnace slag addition, against the biogenic sulphate attack was not confirmed.