| Summary: | 碩士 === 國立中央大學 === 土木工程研究所 === 99 === The structure of low-level radioactive waste disposal sites is mainly made of concrete. Different from the general purpose of concrete structures, the service life of the disposal sites is expected to be hundreds of years. In addition, Taiwan is surrounded by ocean, which suggests the disposal sites may be subject, therefore vulnerable, to the environment. When the disposal sites are exposed to such a condition in a long term, it may cause concrete deterioration and reduces its durability.
This study focuses on the effect of chloride on concrete, and uses the chloride threshold to predict the time to initial corrosion of steel in concrete. Test and analysis include: 1) high integrity container of H mixture, 2) traditional ACI mixture and 3) denser mixture designs.
The results show concrete internal structures with a low water-binder ratio are more compact, resulting in a lower chloride ion diffusion coefficient. However, chloride continuously accumulates, which causes a higher concentration on the surface. Based on the diffusion coefficient, H mixture is better than ACI mixture. To estimate the time to initial corrosion caused by chloride, two main factors are taken into consideration: the diffusion coefficient and time - m factor. Concentration profiles of chloride at different times are used for residual analysis. To define the acceptable range of the diffusion coefficient, we look into the threshold of the chloride concentration and the thickness of concrete, and further estimate the time to initial corrosion of steel in concrete.
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