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  • 學位論文

乾溼循環下氯離子於混凝土中之傳輸行為探討

Discussion of chloride ions in concrete under drying-wetting cycles

指導教授 : 詹穎雯

摘要


台灣位處亞熱帶且四面環海,沿海構造物容易因為海洋鹽分的侵入導致鋼筋受到腐蝕,故了解氯離子侵入混凝土的機理對於混凝土之耐久性設計與鋼筋保護層厚度的選取至為重要。 沿海構造物中,位處潮間帶及浪濺區等有乾溼循環特性的部分經相關研究指出為最容易受氯鹽侵蝕的區域。考量實際海事工程多採用低水膠比之混凝土設計構造物,本研究選擇水膠比0.45的混凝土,搭配不同卜作嵐材料之添加,探討貯鹽試驗(P組)與兩組乾溼循環試驗(C2與C3組)氯離子侵入情形。最後以「氯離子侵入深度」、「氯離子擴散係數」與「氯離子總侵入量」等評估指標來比較貯鹽試驗與乾溼循環試驗氯離子侵入現象的差異。 氯離子於貯鹽試驗下之主要傳輸機制為擴散作用,一般可用擴散方程式來描述氯離子於混凝土中之分布情形;至於乾溼循環試驗,氯離子的侵入主要為表層毛細吸附作用與深層擴散作用聯合貢獻,此部分學者們則採取含表層對流區效應之擴散方程式來描述。 本研究為比較貯鹽試驗與乾溼循環試驗在氯離子侵入深度上的差異,特別針對文獻上之對流區試驗值作迴歸分析,搭配擴散方程式與含表層對流區效應之擴散方程式,可建立貯鹽試驗與乾溼循環試驗氯離子侵入深度模型。由四個試驗齡期的結果可知,試驗值與侵入深度模型高度擬合,顯示此侵入深度模型的良好預測性。 另外由試驗結果可知本研究六個配比中,045S40與045S50兩組不論是在貯鹽試驗或乾溼循環試驗方面,在「氯離子侵入深度」、「氯離子擴散係數」與「氯離子總侵入量」等評估指標上表現最佳。

並列摘要


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".

參考文獻


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