乾溼循環下氯離子於混凝土中之對流區探討

台灣位處於亞熱帶地區，四面環海且氣候高溫潮濕，使沿海之鋼筋混凝土結構物容易受到氯鹽侵蝕而造成鋼筋腐蝕。一般而言，多數人認為在海底下之鋼筋腐蝕情形最為嚴重，但其實多數研究顯示在潮間帶及浪濺區等有乾溼循環效應之地區，鋼筋腐蝕最為嚴重。故應該針對此區域進行混凝土之耐久性設計與鋼筋保護層厚度之選取。氯離子於貯鹽試驗下，主要傳輸行為為擴散作用。而在乾溼循環試驗下，氯離子傳輸行為為表層毛細作用與較深層之擴散作用聯合貢獻。因此在乾溼循環作用下，氯離子表層因有濃度累積之現象而產生對流區。且研究顯示產生對流區過後之氯離子侵入深度與總侵入量皆會提升。故本研究希望藉著「氯離子擴散係數」、「對流區深度」、「氯離子侵入深度」與「氯離子總侵入量」等指標對混凝土之耐久性能進行評估。本研究為比較不同對流區深度對氯離子入侵行為之影響，故設計了三種水膠比（0.45、0.55、0.65）、兩種卜作嵐材料取代率（無取代、爐灰取代50%）與三種乾溼循環機制（貯鹽、14天一循環、28天一循環）。探討上述變因對對流區深度之影響。本研究利用水溶法氯離子滴定求出各深度之氯離子濃度與對流區深度，並配合所蒐集之文獻進行迴歸分析，求出對流區深度之迴歸式。且由迴歸式搭配含對流區效應之擴散方程式，可建立乾溼循環試驗之氯離子侵入深度模型，並由比色法所求出之氯離子侵入深度進行驗證。由本研究之試驗結果得知乾溼循環試驗之氯離子侵入深度等於貯鹽試驗之氯離子侵入深度加上對流區深度。且乾溼循環週期越長，確實會加深對流區深度。而對流區深度迴歸式與侵入深度模型，由文獻與本研究之試驗結果驗證下顯示高度擬合，故相當具有參考價值。

關鍵字

氯離子；貯鹽試驗；乾溼循環試驗；對流區；擴散係數；侵入深度模型

並列摘要

Taiwan is located in the subtropical, surrounded by the sea and the weather is not only humid but also high tempature. Due to the invasion of salt, it could casue corrosion of steel in coastal concrete structures. Normally, most of the people believe corrosion of steel under the sea is most severe, in fact many researches shows that area situated in the tidal zone and splash zone where having drying-wetting cycle effect has the most severe corrosion of steel. Therefore, it should conduct the durability of concrete design and the selection of thickness of protective layer. The main transport behavior of chloride ion under salt ponding test is diffusion. As for the drying-wetting cycle test, the transport behavior of chloride ions is mainly due to the contribution of capillary adsorption and diffusion. Thus, under the effect of drying-wetting cycle, chloride ions surface layer has accumulation of concentration and casue convection zone. Researches indicate after the produce of convection zone, both the invasion depth of chloride ions and total amount of chloride ion increase. In order to carry out the evaluation of concrete durability, “chloride ion diffusion coefficient”, “convection zone depth”, “chloride ion invasion depth” and “total amount of chloride ion invasion” these indexes are being used. In order to compare different convection zone depth influences on chloride ion invasion behavior, designing three types of water-colloid ratio (0.45, 0.55, 0.65), two types of pozzolan material replacement (OPC, SF50) and three types of drying-wetting cycle mechanism (ponding test, cycle of 14 days, cycle of 28 days). To dicuss above variables effect on convection zone depth. This study used water-soluble chloride ion titration to get chloride ion concentration for each depth and convection zone depth, the regression analysis was carried out for the literatures collected, and then get the regression equation of convection zone depth. By using the regression equation with the modified diffusion equation, we can establish model of the chloride ion invasion depth for drying-wetting test and verify the model by the chloride ion depth produced from colorimetric method. According to the test result, the chloride ion invasion depth of drying-wetting cycle test is equal to the chloride ion invasion depth of ponding test plus convection zone depth. The longer the period of drying-wetting cycle, the deeper the convection zone depth. As for the regression equation of convection zone depth and model of invasion depth, the literature and test results of this study indicate that they are highly fitted, therefore it has high level of reference value.