コンクリート模擬環境における鋼材表面の電気化学的特性

抄録

A sodium chloride aqueous solution saturated with calcium hydroxide and its gel solution were used as simulated concretes for investigating electrochemical behavior of corroded steel in concrete. Results obtained are as follows:
(1) From cathodic polarization measurements of platinum in the gel solution, the gel solution was considered to act as an uniform diffusion layer for dissolved oxygen. The effect of concrete cover is evaluated experimentally by changing the thickness of the gel solution and theoretically by applying the finite element method.
(2) The polarization resistance of steel increased with decreasing cathodic potential until it reached its maximum at a specific potential, showing that the anodic resistance increases and the effect of cathodic protection can be estimated by this value.
(3) The changes of pH and chloride-ion concentration on the surface of steel were investigated after the polarization current had been applied on the steel. In the gel solution pH decreased with anodic polarization and increased with cathodic polarization, but in the aqueous solution pH was independent of polarization. In both the aqueous and gel solutions chloride-ion concentration was independent of polarization under the experimental conditions investigated. This phenomenon was explained by considering mass balance of chemical species in the solution close to the surface of steel.
Above results show that the gel solution is more adequate as an simulated concrete than the conventional simulated solutions.