不同腐蝕程度之鋼筋在不同介質中之腐蝕電流密度實驗研究

Experimental Investigation for Corrosion Current Density of Corroded Steel Rebars with Different Corrosion Degrees in Different Media

林廣杰(Kuang-Chieh Lin)

指導教授 ： 廖文正

國立臺灣大學/工學院/土木工程學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201903575

摘要

鋼筋混凝土為現今常用的建築結構，外界有害物質侵入鋼筋混凝土中會造成鋼筋腐蝕，而耐震評估中主要以鋼筋的重量損失率來折減鋼筋的性能，故如何有效且準確的得到鋼筋的重量損失率將是一大重要課題。鋼筋的理論重量損失率可以經由量測的腐蝕電流密度再透過法拉第定律計算而得，故影響腐蝕電流密度量測的因子將間接的影響鋼筋理論重量損失率，進而影響耐震評估中對於鋼筋性能的折減。
　　現地在進行腐蝕電流密度量測時尚未考慮到介質電阻對於腐蝕電流密度的影響，因此本實驗以通電腐蝕法將鋼筋腐蝕至不同的重量損失率(1~5%、10%)來模擬鋼筋不同的腐蝕程度，並且觀察鋼筋不同腐蝕程度對於腐蝕電流密度的影響，以及透過此方式來預測無腐蝕鋼筋達到訂定的重量損失率(1~5%、10%)時的腐蝕電流密度值，而後再將鋼筋鑲入不同配比的混凝土以及科技海綿中來觀察不同介質中腐蝕電流密度的發展，並且使用Gecor 8、GalvaPulse及AutoLab量測腐蝕電流密度以及四極式電阻量測儀來追蹤混凝土電阻值的成長，最後再將腐蝕電流密度對應時間的關係積分出鋼筋的理論重量損失率，並在破壞試體後驗證三台腐蝕電流儀對於法拉第定律的適用性。
　　本研究的初步實驗結果顯示，鋼筋表面的鈍化膜破壞前，主要由氯離子的濃度控制鋼筋的腐蝕電流密度，而當鈍化膜破壞後，混凝土的電阻值進一步控制了鋼筋陰陽極間離子與水分的傳輸，對鋼筋腐蝕過程影響較大；不同腐蝕程度的鋼筋於混凝土中所呈現的腐蝕電流密度趨勢皆較為相近，且其初始腐蝕電流密度值的大小沒有明顯的與重量損失率的大小有關；觀察不同配比的混凝土中，當混凝土齡期較短時，不同的水灰比及氯鹽量對於混凝土的電阻值較無影響，而是需要充裕的時間才會開始造成差異。
　　平穩的腐蝕電流密度能夠用來預測無腐蝕鋼筋未來的腐蝕電流密度以及得知在不同混凝土配比中其穩定的腐蝕電流密度，實驗至今所量測的結果尚未得到平穩的腐蝕電流密度值，而後續需要持續進行腐蝕電流密度以及混凝土電阻的量測，觀察後期平穩值的發展趨勢，並對本研究之初步實驗結果進行驗證。

關鍵字

通電腐蝕法 ； 腐蝕 ； 腐蝕電流密度 ； 氯離子 ； 混凝土電阻值 ； 鋼筋重量損失率 ； 法拉第定律

並列摘要

Reinforced concrete is one of the most commonly used construction materials in the civil engineering industry, and reinforcement corrosion is a major problem. The corroded steel rebars will reduce the seismic capacity of reinforced concrete. In the seismic evaluation, the performance of the steel rebars is mainly reduced by its weight loss. Therefore, it is an important issue to obtain effective and accurate weight loss of steel rebars. The theoretical weight loss of steel rebars can be calculated by introducing corrosion current density into Faraday's law. Therefore, the factors affecting corrosion current density will indirectly influence the theoretical weight loss of steel rebars, and further affect the seismic evaluation.
　　The influence of resistance on corrosion current density has not been considered in the corrosion current density measurement. In this study, the steel rebars were badly corroded by electrical corrosion method to simulate different weight loss (1~5%, 10%) of steel rebars, and then the steel rebars were inserted in concrete and sponges. Corrosion current density will be measured by Gecor 8、GalvaPulse and AutoLab, and the resistivity of concrete will be measured by four-point Wenner array probe technique. Observe the influence of different resistivity of concrete on corrosion current density and the effect of different corrosion degrees of steel rebars on corrosion current density. Finally, using the relationship of the corrosion current density to the time to integrate the theoretical weight loss of the steel rebars, and verify the applicability of Faraday's law for each instrument after the expected amount of corrosion is reached.
　　The preliminary results show that when concrete was at an early age, the difference of water-cement ratio and concentrations of chloride ion has no effect on the resistivity of concrete, and it takes plenty of time to make a difference. In addition, before the failure of the passive film on steel rebars, the corrosion current density of the steel rebars is mainly controlled by concentrations of chloride ion. When the passive film is destroyed, the resistivity of concrete controls the transmission of ions and moisture between the cathode and anode in steel rebars, which has significant impacts on the corrosion process. Moreover, the trends of corrosion current density in the steel rebars with different corrosion degrees are similar, and the initial corrosion current density values are not greatly related to the weight loss of steel rebars.
　　The stable corrosion current density can be used to predict the future corrosion current density of non-corrosion steel rebars and to know the stable values in different media. However, the measured values have not reached stable values recently. It requires to measure the corrosion current density and the resistivity of concrete continuously in the future, and observes the trends of the stable values, and then verifies the preliminary experimental results in this study.

並列關鍵字

Electrical corrosion method ； Corrosion ； Corrosion current density ； Chloride ion ； Resistivity of concrete ； Weight loss of steel rebar ； Faraday’s law

參考文獻

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