Transmission Behavior of Chloride Ion in Concrete under Different Hydrostatic Pressures
Date Issued
2016
Date
2016
Author(s)
Jheng, Cheng-Jyun
Abstract
Salt ponding test is a common method for evaluating the durability of concrete. Due to that chloride ion requires considerable time to penetrate the concrete specimen（e.g., 90-day Salt ponding test）, the salt ponding test is regarded to be a long-term test. In order to shorten the process of evaluating the durability of concrete, this study adopts hydrostatic pressure to accelerate the movement of chloride ion, and this method is defined as “Seepage pressure test”. To know the transmission behavior of chloride ion, the influences caused by hydrostatic pressures, pozzolanic material types, replacement rates and compressive strengths under the same duration of testing time are discussed in this study. Two hydrostatic pressures 3 and 5 kgf/cm2 and water-cement ratio of 0.55 are adopted in the experiments. By quantifying the influences, the seepage pressure test can be proved to be an accelerated test and able to substitute salt ponding test with the indexes like the depth of chloride ion penetration and the accumulation rate of chloride ion concentration. In order to simplify the analysis of the transmission behavior of chloride ion under hydrostatic pressures, it is supposed that the transmission behavior is contributed by the diffusion. Therefore, the diffusion equation is fitted to the chloride concentration data from seepage pressure test to obtain equivalent chloride transmission coefficient Deq. However, the curved shape of diffusion equation and convection-diffusion equation are not the same. With the testing time increasing, the greater the difference between the two curved shape will be, and the correlation coefficient R2 will decrease. In this study, the correlation coefficient R2, higher than 0.900, is taken as a baseline, to make sure Deq can be applied to substitute convection-diffusion equation and describe the transmission behavior of chloride ion under hydrostatic pressures. Moreover, the 7 days experimental results show that diffusion coefficient D and equivalent chloride transmission coefficient Deq have a good linear relationship. Therefore, it is expected that D and Deq can be used to establish the relation between salt ponding test and seepage pressure test. In addition, Deq can also be applied to determine the durability of concrete. By taking the depth of chloride ion penetration as the index, experimental results show that 21-day seepage pressure test, with 5 kgf/cm2 hydrostatic pressure, can be used to substitute 90-day salt ponding test. Similarly, by taking the accumulation rate of chloride ion concentration as the index, the experimental results show the same as above.
Subjects
concrete
chloride
pozzolanic material
salt ponding test
seepage pressure test
diffusion coefficient
equivalent chloride transmission coefficient
Type
thesis
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