Abstract
It is commonly considered that the corrosion of steel in concrete is controlled by the oxygen content of the pore solution and there are service life models that relate the corrosion rate to the amount of oxygen. It is also commonly believed that in water saturated conditions the oxygen content in the pores is negligible and that underwater there is no risk of depassivation and the corrosion rate is very low. However, the available data on corrosion rates in immersed conditions do not indicate such performance; on the contrary corrosion develops when sufficient chloride reaches the reinforcement. In the present paper, results are presented for tests performed in alkaline chloride solutions that were purged with nitrogen to reduce the oxygen content. The results indicate that at very low oxygen concentrations, corrosion may develop in the presence of chlorides. The presence or absence of corrosion is influenced by the amount of chloride, the corrosion potential and the steel surface condition.
Highlights
The cathodic corrosion reaction in concrete is believed to be the reduction of oxygen that penetrates through the concrete pores in the presence of water, according to the reaction 1 : O2 + 2 H2O + 4 e- 4 OH- (1)Owing to the high alkalinity of the pore solution, the steel bars embedded in concrete will remain passive unless a decrease of the pH of the electrolyte in contact with the metal occurs
It is commonly considered that the corrosion of steel in concrete is controlled by the oxygen content of the pore solution and there are service life models that relate the corrosion rate to the amount of oxygen
Results are presented for tests performed in alkaline chloride solutions that were purged with nitrogen to reduce the oxygen content
Summary
Owing to the high alkalinity of the pore solution, the steel bars embedded in concrete will remain passive unless a decrease of the pH of the electrolyte in contact with the metal occurs. This decrease can be induced by neutralization of the alkalinity by carbon dioxide (i.e. carbonation) or by the chlorides whose presence induce metal dissolution and further hydrolysis of the water by the metal ions, which are able to decrease the pH and result in the production of local corrosion and pits 2. By bubbling nitrogen the dissolved oxygen content was reduced, less than 1 ppm remained
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