Influence of chloride ion penetrated into concrete on the destruction of passivation film of steel bar

摘要

Steel bars in concrete structure maintain a passivation state due to the high pH of the pore solution of the concrete. However, in a space where many chloride ions are present such as a marine environment, the chloride ions permeate the concrete, destroying the passive film of steel bars. It is known that destruction of the passive film of steel bars in concrete is less severe than destruction in aqueous solution, even in the presence of the same total chloride ion concentration. According to a previous study in the field of cement chemistry, chloride ions in concrete are present as "binding chloride ions" fixed to the hardened cement body, and "free chloride ions" which continue to exist in the pore solution. Further, it is believed that only free chloride ions affect the steel bar corrosion. However, there are no previous studies in which the concentration of free chloride ions in the pore solution was estimated from the electrochemical point of view. In this study, the free chloride ions in concrete were estimated using the "Deduction method", which is a method of measuring the in-current of the anode proposed by the authors. First, the oxygen reduction equilibrium potential in concrete were compared with the oxygen reduction equilibrium potential in a solution adjusted to various pH, and pH in concrete pore solution was obtained based on the electrochemical measurement results. Further, it is possible to obtain critical film breakdown potential of steel bars in concrete by using the proposed "deduction method". As a result, critical film breakdown potential in concrete at various chloride ion concentrations were compared with critical film breakdown potential in a solution simulating the pore solution in concrete, and the concentration of free chloride ion in concrete pore solution was obtained based on the electrochemical measurement results.