An overview of nitrates-induced corrosion of reinforced concrete structures: case studies, laboratory investigations and corrosion mechanisms

Abstract

The paper presents the results of the research on the long-term corrosion behaviour in service of the reinforced concrete structures located in nitrates-based industrial environments. Two representative types of reinforced concrete structures were investigated: industrial multi-storied buildings of fabrication and granulation towers of nitrates-based products. The case studies revealed the existence of severe nitrates-induced corrosion damage affecting the resistance, stability and durability of structures in these aggressive environments. Laboratory investigations performed on a large number of concrete and steel reinforcement samples, which were extracted from the corrosion affected elements, underlined the complexity of the corrosion process of reinforced concrete in nitrates-based environments affecting concrete and steel reinforcement by different mechanisms. The degradation of concrete consists in some decalcification and expansion phenomena which lead to cracking and, finally, to a rapid concrete destruction. The stress corrosion cracking represents the specific type of reinforcement corrosion in such aggressive environments. This phenomenon, similar with those observed at some steel tendons for prestressed concrete structures, is characterized by the cracking and brittle fracture of the steel reinforcement, without loss of steel cross-section and without visible loss of metal. The generalized and localized corrosion of steel were also identified. The possibility of apparition and development of stress corrosion cracking phenomenon of steel reinforcements, associated with the non-controlled reduction of the physical and mechanical characteristics of concrete by corrosion, lead, in the end, to a significant reduction or even to a loss of bearing capacity and sudden collapse of reinforced concrete structures, with no apparent premonitory signals.