Chlorides Diffusion for Concrete Bridge Decks Due to De-icing Salts

摘要

De-icing salts are regarded as one of the major causes of deterioration of concrete bridge decks in metropolitan area. In this study, 180 samples from concrete decks in Seoul, South Korea, were examined from which concrete powders were extracted using a special driller at certain depths from the surface. The purpose of this study was to get adequate data of the surface chloride content to determine how severe the environmental condition were to which the concrete had been exposed, how rapidly de-icing salts penetrate into the internal concrete, and to characterize the distribution of the chloride profiles. Generally, the compressive strength of concrete decks in Seoul is 21 MPa to 24 MPa. It has been considered to depict de-icing salt penetration into concrete as pure diffusion. However, this approach has serious limitations because the exposure conditions are significantly complex and concrete properties change with time. Hence, the analysis of chloride diffusion is based on Fick's 2nd law containing a power law function of the chloride diffusion coefficient and on probabilistic analysis to depict the uncertainty in environmental conditions, such as the dispersion of de-icing salts. In order to depict the time dependent chloride diffusion coefficient, a Gaussian distribution of the Cl~- diffusion coefficient over time was considered. The rank correlation coefficient test and turning point test were used for examining the randomness of the surface chloride content and the chloride diffusion coefficient. Based on items described above, the required cover depth for getting 15 years of targeted service life of bridge decks is calculated as a function of probability of corrosion.