Abstract
The deterioration of reinforced concrete structure due to the corrosion of steel bar is caused by the penetration of chloride ion into concrete, particularly in marine environment. In order to estimate the lifetime of concrete structure located close to such as marine environment, it is very important to predict the penetration behavior of chloride ion, and Fick’s law theory with diffusion coefficient of chloride ion is generally used. So the diffusion coefficient has to be calculated theoretically and exactly.
In this paper, calculating apparent diffusion coefficient (Da) of concrete under a non-steady state has been considered theoretically and as a consequence, it was cleared that the solution formula of Fick’s second low can be used calculate Da only if the chloride biding isotherm is linear. In addition, the accuracy of Da obtained by calculation has been studied. The measurement of chloride ion concentration profile, which causes the error of Da, is influenced by the thickness of sampled layers. Electron probe microscopy analysis (EPMA), can measure a large number of chloride concentrations with thin layer thickness, resulting in an accurate profile, and consequently and accurate calculation of diffusion coefficient. The measurement method using EPMA is excellent especially in the cases of high resistance concrete to chloride penetration containing mineral admixtures. The resistance properties of blast furnace slag and meta-kaolin were evaluated quantitatively using Da determined by EPMA. Consequently, it became clear that the chloride penetration resistance of meta-kaolin is about three times higher compared to that of blast furnace slag, and the type of cement does not have any influence on the resistance properties.
