Monitoring carbon steel behavior under biotic and abiotic conditions

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Monitoring carbon steel behavior under biotic and abiotic conditions E.J. León1, D.A. Koleva1, H.M. Jonkers1, J.M.C. Mol2, H. Terryn2,3, K. van Breugel1 1 Civil Engineering and Geosciences, Department Materials & Environment, 2 Faculty 3mE, Department Surfaces & Interfaces, Delft University of Technology, Delft, The Netherlands. 3 Vrije Universiteit Brussel, Dept. Electrochemical and Surface Engineering, Brussels, Belgium ABSTRACT Deterioration of concrete structures, together with corrosion of reinforcing steel due to the action of microorganisms, is known as Microbiologically Induced Corrosion of Concrete (MICC). The activity of microorganisms can initiate and further accelerate both steel corrosion and cementbased matrix degradation in reinforced concrete structures. The mechanism is related to initial surface colonization and further bio-products (and aggressive substance respectively) penetration into the bulk concrete matrix, reaching the reinforcement level. Common knowledge is that biodeterioration-related infrastructure degradation, maintenance and repair have a significant economic impact worldwide. However, due to the complexity of all related mechanisms, a durable and feasible solution is still to be achieved for the engineering practice. This paper briefly points out main bio-degradation related mechanisms for concrete, steel and reinforced concrete structures and presents results on the electrochemical response of carbon steel in simulated environment under biotic and abiotic conditions. INTRODUCTION Reinforced concrete (RC) is the most used material in construction. The pH of the concrete pore solution is typically in the range of 12.7 – 13.4, allowing the passivation of reinforcing steel. However, premature failure of RC worldwide results from reinforcement corrosion due to aggressive substances penetration, including bio-degradation, and since it is related to an increasing socio-economic impact has already become a serious challenge [1, 2]. For main structural materials as steel, concrete and RC, three main types of degradation mechanisms are related to the presence of microorganisms and sulfate ions (SO42+) respectively. For concrete, “sulfate attack” is a result of chemical reactions between the hydrated cement phases and sulfate ions. The sulfate source for this deterioration process can vary, but also includes products from bacterial activity e.g. Sulfate Reducing Bacteria (SRB) reduce sulfate to produce hydrogen sulfide (H2S); Sulfur Oxidizing Bacteria (SOB) oxidize sulfur compounds producing sulfuric acid (H2SO4). The chemical reaction of these acidic substances with cement hydration products results in concrete degradation [3]. For steel structures only, SRB are responsible for biogenic sulfide steel corrosion, also known as Microbiologically Induced Corrosion (MIC) [4]. If both steel and concrete are considered e.g. RC structures, bacterial activity will lead to degradation of concrete, enabling MIC to occur on the surface of the exposed reinforcing steel. The combined action of these two m

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