混凝土中鋼筋腐蝕之臨界氯離子濃度探討

Abstract

由於台灣屬於腐蝕性侵蝕的環境。而當氯離子侵入混凝土中累積到一定的含量時，鋼筋表面的鈍化層會被破壞，進而使鋼筋開始腐蝕，降低結構物的強度與耐久性，對結構物造成極大威脅。因此，鋼筋腐蝕已成為影響結構物使用壽命和安全性的主要因素之一。 本研究藉由在混凝土拌合時，添加不同濃度的氯鹽，來模擬鋼筋在不同氯鹽濃度下的腐蝕情況，希望能藉此找出誘發鋼筋腐蝕之臨界氯離子濃度。另外藉由量測腐蝕電流（為非破壞性檢測），與直接取出鋼筋，藉由觀察其表面腐蝕情形與重量損失來審視實際的腐蝕情況（破壞性檢測）。另外再做初始酸鹼值試驗和酸中和試驗，藉由不同的表達方式來縮小臨界氯離子濃度的範圍。 在量測混凝土中氯離子時，水溶法約可溶出5∼6成的氯離子，而酸溶法可溶出約8成。 水灰比的差別與氯離子鍵結率並無直接相關，爐石可有效的提高提高氯離子的鍵結率，飛灰則恰巧相反；在混凝土中的鋼筋腐蝕情形的部分，水灰比亦無直接相關，而爐石取代可提高臨界氯離子濃度，飛灰的表現則沒有爐石那樣的優異。同時，鋼筋實際的腐蝕情形皆與腐蝕電流密度呈線性正相關。

Taiwan is surrounded by sea, so the reinforced concrete structures are exposed to corrosive environments. When chloride ions penetrated into the concrete, to reach a certain concentration, the reinforcing steel surface passive layer will be destroyed and cause the steel corrosion, it will reduce structure strength and stiffness. Therefore, the reinforcing steel corrosion is the main factors to structures life and security. This study added different concentrations of chloride salts via the mixing water to simulate the reinforcing steel corrosion situation at different chloride concentrations, And we identified the critical chloride ion concentration. We also used non-destructive testing to determine the corrosion situation of reinforcing steel, destruct the specimen and remove the reinforcing steel to observe actual corrosion in the end. The other tests like initial pH value and acid neutralization tests were used to narrow the critical range of chloride ion concentration. When measuring chloride ion in concrete, there is about 50%~60% leachable via water soluble, and about 80% chlorine ions via acid solution method. The difference between W/B is not directly related to the bonding rate of chloride ion or the corrosion of reinforcement in concrete. Slag can improve the bonding rate instead of flyash. Slag can also increase the critical chloride ion concentration. However, flyash can’t increace it as good as slag. It is positively linear correlation between the corrosion of reinforcement and the corrosion current density.