Study of the corrosion of reinforcement in concrete elements used for the repair of monuments

The conservation of cultural heritage is a demanding and imperative task. Of particular interest is the prevention of damage in monuments in load bearing elements made of reinforced concrete. In this case, the remediative intervention should be done with special caution, especially in places of the structure where earthquakes pose immediate threat for the integrity of historical monuments. The present work focuses on the problems associated with corrosion of steel in reinforced concrete, considered as a composite material consisting of steel and inorganic constituents. The study is concerned with S500s Tempcore® steel and the associated corrosion phenomena, responsible for the degradation of the mechanical properties of the reinforced concrete. Corrosion of steel bars in reinforced concrete is attenuated due to either of the incomplete coverages of the metal with concrete, leaving it exposed to the aggressive marine environment or from galvanic corrosion. The latter is due to the presence of different types of metallic elements introduced by the welding process employed often in pre-earthquake and post-earthquake repairs in order to strengthen load bearing elements. In a microscopic scale the development of special conditions may lead to major damages of the structures. In the present work, we report on the results of mechanical stress measurements done on S500s Tempcore® steel bar specimens. Prior to the stress measurements, the specimens were subjected to accelerated corrosion by exposure in salt spray chamber for time periods up to 90 days. Specimens in which welding side-by-side was applied were also exposed at the same conditions and the respective mechanical stresses were measured. The effect of increasing corrosion damage on the strength properties of the steel S500s Tempcore® was moderate. The effect of salt spray exposure on the tensile ductility however was appreciable. All measurements have shown that corrosion had an adverse effect on the materials strength, while the ductility of the specimens was drastically reduced. The embrittlement of reinforcing steel due to corrosion was confirmed both by the gradual decrease of the specimens’ ductility and the examination of the morphology of the cross-section of the respective specimens by scanning electron microscopy.