考量鋼筋不同腐蝕型態及混凝土內氯離子濃度之長期腐蝕電流模型建立實驗設計

Experimental Design for Long-Term Corrosion Current Models Considering the Different Corrosion Types of Steel Bars and Chloride Ion Concentration in Concrete

黃大展(Da-Zhan Huang)

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(2018年)

https://doi.org/10.6342/NTU201803342

摘要

現行耐震評估程序尚未考慮材料老劣化所造成之影響，可能在進行耐震評估時過於高估受劣化結構物之殘餘耐震能力，然而要進行材料老劣化後之耐震評估，鋼筋腐蝕後有效截面積之折減量是一重要參數，但目前於實務應用上，因受量測儀器不同、鋼筋腐蝕型式差異及長時間腐蝕電流發展等複雜因子影響，如何利用非破壞性檢測求得鋼筋腐蝕量進而推算鋼筋截面折減量，亦是尚待解決之課題。
本研究第一部分實驗藉由在裸鋼筋上採用不同防鏽塗裝形式，後插入海綿並添加鹽水加速腐蝕，以模擬不同腐蝕型態下之鋼筋，並持續進行腐蝕電流量測試驗，實驗參數選用3號及7號鋼筋，搭配紅丹漆及Epoxy兩種不同防鏽塗裝，並利用Gecor 8、GalvaPulse及AutoLab三種不同儀器持續進行腐蝕電流量測，在達預期之腐蝕量時破壞試體，比較透過法拉第定律計算之理論重量損失與實際鋼筋重量損失之關係，期望能確認鋼筋在不同腐蝕形態下，常用於現地之非破壞性檢測儀其量測值法拉第定律的適用性。
　　　第二部分之實驗藉由採用在混凝土內添加氯離子之方式，並分別以不同氯離子濃度、混凝土強度、有無添加鋼纖維及有無箍筋作為參數，再利用Gecor 8及GalvaPulse兩種儀器持續進行腐蝕電流量測，建立混凝土內不同氯離子濃度下，鋼筋腐蝕電流與時間之關係圖，預計在達預期之腐蝕量時破壞試體，比較理論與實際鋼筋重量損失之關係，以確認上述儀器用於RC構件中法拉第定律之適用性，期望透過上述兩實驗能提出在不同腐蝕情況下適合的腐蝕電流量測技術及分析方法，並建立預測鋼筋混凝土材料老劣化之模式。
　　第一部分之初步實驗結果顯示，量測較鈍態區之鋼筋時，Gecor 8之量測值有較佳之準確度。此外不論內部鋼筋是否為均勻腐蝕，局部腐蝕，或點狀腐蝕，量測值將會顯示此量測範圍內之總腐蝕貢獻量。而較小號鋼筋，有量測出較高腐蝕電流值之趨勢。紅丹漆較Epoxy有更好之腐蝕電流抑制效率。
第二部分之初步實驗結果顯示，GalvaPulse有較Gecor 8量測值高3~5倍之趨勢，此外箍筋之存在，並不會對腐蝕電流之量測值有顯著的影響。鋼纖維之添加，因做為犧牲陽極之效果，能使主筋之腐蝕電流下降60~75%左右。
目前研究中各試體皆尚未達到預期之腐蝕量，後續仍須持續進行實驗，待試體達到明顯腐蝕前後差異時再破壞試體，比較理論與實際重量損失兩者間關係，以驗證各儀器，在不同鋼筋腐蝕情況下法拉第定律之適用性。

關鍵字

腐蝕 ； 腐蝕電流 ； 氯離子 ； 劣化 ； 鋼筋重量損失

並列摘要

The influences of material ageing and deterioration have not yet been considered in the current seismic evaluation; thus, the residual seismic capacity of the deteriorated structure could be overestimated. The reduction of the steel bar’s cross-sectional area after corrosion is a major parameter to carry out the seismic evaluation for deteriorated materials. However, in current practics, how to use non-destructive measurement to obtain the key parameter still remains unsolved.
The first part of this experimental design is to confirm the applicability of the Faraday’s law under different corrosion conditions. By using two different corrosion inhibitors, Red lacqnuer and Epoxy, coated on size #3 and #7 bare steel bars, then simulate the steel bars under different corrosion patterns and insert them into sponges soaked with salt water to accelerate the corrosion. In this phase, three different instruments Gecor 8, GalvaPulse and AutoLab, are used to constantly measure the corrosion current. When the expected amount of corrosion is reached, the corroded rebars will be taken out to for further measurement and the validity of the Faraday’s law can be confirmed by comparing between the theoretical weight loss calculated and the actual weight loss of the steel bar measured.
The second part of thise experimental design will establish the relationship between time and the concrete’s corrosion current measurement, while adding different concentrations of chloride ion, and using concrete strength, with or without steel fiber and stirrups as parameters. Gecor 8 and GlavaPulse will be used to constantly measure the corrosion current. The corroded rebars embedded in the concrete cube specimens will be taken out by demolishing the concrete at the time of reaching target amount of corrosion, and by comparing the theoretical and actual weight loss of the steel bar, the applicability of Faraday’s law for the above instruments in RC components will be confirmed.
These two experiments are expected to propose a suitable corrosion current measurement technique and an analysis method for different corrosion conditions, furthermore establish a model for reflecting the ageing and deterioration of concrete materials.
The preliminary results of the first experiment show when measuring passive rebars, Gecor 8 is more accurate. In addition, regardless of the corrosion types, the total corrosion is close to that obtained from Faraday’s law by the corrosion current within the measured area of the steel bar. Aside from that, compared with Epoxy, Red Lacquer is more efficient for corrosion inhibition and smaller steel bars trend to have higher corrosion current values.
The second part’s preliminary result of the experiment shows that GalvaPluse’s measured value is 3-5 times higher than Gecor 8 and the stirrup does not have significant effects to the measured value of the corrosion current. It is also noted that steel fiber can reduce 60%-75% corrosion current of the main bar.
Currently, the experiment is still in process as none of the specimens has reached the target corrosion amount. Once the specimens reach a specific amount of corrosion, the relationship between theoretical and actual weight loss will be compared to verify the applicability of Faraday’s law for each instrument under different corrosion conditions.

並列關鍵字

Corrosion ； Corrosion Current ； Chloride ion ； Deterioration ； Weight loss of reinforcement

參考文獻

[1] ASTM C1202-12, “Standard Test Method for Electrical Indication of Concrete's Ability to Resist Chloride Ion Penetration.”

[2] A. Djerbi, S. Bonnet, A. Khelidj & V. Baroghel-bouny, “Influence of Traversing Cracks on Chloride Diffusion into Concrete.” Cement and Concrete Research, 38, 877-883, 2008.

[3] ACI Committee 318, “Building Code Requirements for Structural Concrete (ACI 318M-14) and Commentary (ACI 318RM-14),” Ameriacn Concrete Institute (ACI), Farmington Hills, MI, 2014.

[4] ACI Committee 222, “Protection of Metals in Concrete Against Corrosion (ACI 222R-01),” Ameriacn Concrete Institute (ACI), Farmington Hills, MI, pp.11, 2001.

[5] ASTM C876-15, “Standard Test Method for Corrosion Potentials of Uncoated Reinforcing Steel in Concrete.”