Discussion of chloride ions in concrete under drying-wetting cycles

• Main Authors: Chia-Chen Hsu, 許家禎
• Other Authors: Yin-Wen Chan
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/rup3u9

碩士 === 國立臺灣大學 === 土木工程學研究所 === 105 === Taiwan is located in the subtropical and surrounded by the sea. Due to the invasion of salt, it may lead to corrosion of steel in the coastal structures. As a result, understanding the mechanism of chloride intrusion into the concrete for the durability of concrete design and thickness of the protective layer is important. Coastal structures situated in the tidal zone and splash zone have been identified as being the most susceptible to salt erosion. Considering the practical marine engineering, it often uses low water-cement ratio of concrete to design structures. This study selected concrete with a water-cement ratio of 0.45 and with the addition of different pozzolan materials to explore the transmission behavior of chloride ions in salt ponding test(P group) and drying-wetting cycle test(C2 and C3 groups). Finally, using the evaluation index of "chloride ion invasion depth", "chloride ion diffusion coefficient" and "total amount of chloride ion invasion" to judge the difference of chloride ion invasion. The main transport mechanism of chloride ion under salt ponding test is diffusion. Generally, it can use the diffusion equation to describe the distribution of chloride ions in concrete. As for the drying-wetting cycle test, The invasion of chloride ions is mainly due to the contribution of capillary adsorption and diffusion. Some scholars use the modified diffusion equation taking into account the convection zone to describe the transmission of chloride ion under drying-wetting cycle test. In order to compare the difference between the salt ponding test and the drying-wetting cycle test on the invasion depth of chloride ions, the regression analysis was carried out for the experimental values of the convection zone in the literature. By using the diffusion equation with the modified diffusion equation, we can establish the model of the chloride ion invasion for both salt ponding test and drying-wetting cycle test. It can be seen that the experimental data from the four test ages is highly fitted with the invasive depth model. In other words, it shows good predictability in this invasive depth model. In addition, the experimental results show that in the six mixes, 045S40 and 045S50 perform well in some index of evaluation such as "depth of chloride ion invasion", "chloride ion diffusion coefficient" and "total amount of chloride ion".