以貯鹽試驗探討鋼筋混凝土之氯離子擴散及鋼筋腐蝕

Evaluation of the Chloride Diffusion and the Corrosion of Reinforced Concrete with Salt Ponding Test

陳泰誠(Tai-Chen Chen)

指導教授 ： 詹穎雯

國立臺灣大學/工學院/土木工程學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201602397

摘要

台灣處於亞熱帶與熱帶地區且四面環海，沿岸地區鋼筋混凝土受到海洋氯鹽的侵襲，屬於易腐蝕環境。當氯離子含量在鋼筋表層累積至一定量時，鋼筋表層的鈍化膜（passive film）會被破壞，導致鋼筋被腐蝕，降低結構物的強度與勁度，大幅縮短建物使用年限，因此在鋼筋混凝土普及的時代，氯離子對鋼筋的腐蝕行為已成為一重要課題。
　　本研究以貯鹽試驗將氯離子擴散進入鋼筋混凝土內，以爐石、飛灰取代部分水泥，了解卜作嵐材料對混凝土緻密程度的影響。氯離子在鋼筋表層逐漸累積，利用腐蝕電流密度量測鋼筋腐蝕情形，希望能夠得到誘發鋼筋腐蝕之臨界氯離子濃度。本研究探討影響混凝土緻密程度之參數包含擴散係數、總入滲量、固結能力，鋼筋腐蝕趨勢則是以腐蝕電流密度作為判斷依據。
　　擴散係數隨著水膠比增加而提高，而在早齡期爐石能夠有效降低擴散係數，但飛灰混凝土早期滲透性較高，擴散係數較大。影響鋼筋開始腐蝕時間的主要因素為緻密程度，緻密程度越佳鋼筋開始腐蝕時間越晚，pH值為影響的次要因素，酸鹼值降低使鋼筋能夠容許的氯離子濃度降低。
　　當腐蝕電流密度為0.1μA/cm2比起0.5μA/cm2更能作為達到臨界氯離子濃度的指標，以總氯離子及自由氯離子濃度分析卜作嵐取代之混凝土會產生較大的誤差，其值分別介於0.604~1.833%和0.517~1.588%佔膠結材重量，以[Cl-]/[OH-]分析臨界氯離子濃度有效地縮小臨界值的範圍，其值介於1.351~1.807。

關鍵字

耐久性 ； 貯鹽試驗 ； 擴散係數 ； 腐蝕電流密度 ； 臨界氯離子濃度

並列摘要

Due to the climate and geographic location, coastal reinforced concrete buildings in Taiwan are attacked by chloride ion and exposed to corrosive environments. When the chloride content on the surface of rebar reaches the limit, the passive film would be destroyed so that the rebar could be corroded. This result would reduce the strength and stiffness of structure and significantly shorten service life of buildings. Therefore, the issue of chloride-induced corrosion becomes important in this age.
　　In this study, chloride ions are accumulated on the surface of rebar and diffuse into the reinforced concrete through salt ponding test. Moreover, parts of cement of the specimens are replaced by slag and fly ash to clarify the influence of the density with different pozzolanic materials. In this study, the value of chloride threshold, which makes rebar start to corrode, is determined by measuring the corrosion current density, and the studied influenced factors are diffusion coefficient, total ingressive chloride amount, chloride binding capacity on density of concrete and corrosion current density on corrosion of rebar.
　　The results show that diffusion coefficients increase with the increase of water-binder ratio. At early age, the diffusion coefficient is decreased effectively by adding slag. On the other hand, adding fly ash makes higher diffusion coefficient because of the lower permeability. Also, it is discovered that the main factor influencing the initial time of corrosion is the density of concrete. The higher density takes more time corroding. The secondary factor is the pH value. The lower pH value makes the rebar corrode faster.
　　From the experimental results, the chloride threshold value is better defined as 0.1μA/cm2 of corrosion current density instead of 0.5μA/cm2. Additionally, it is noted that the chloride threshold value defined by [Cl-]/[OH-] is of accurate range as 1.351~1.807% of binder mass, while the chloride threshold values defined by total chloride content and free chloride content are of wider ranges as 0.604~1.833% and 0.517~1.588% of binder mass.

並列關鍵字

Durability ； Salt ponding test ； Diffusion coefficient ； Corrosion current density ； Chloride threshold value

參考文獻

[11] 蔡旻廷，「使用壓力滲透試驗探討混凝土中氯離子之滲透行為」，碩士論文，國立臺灣大學土木工程研究所

[12] 何季軒，「以貯鹽試驗探討鋼筋混凝土之臨界氯離子濃度」，碩士論文，國立臺灣大學土木工程研究所

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