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EIS monitoring on corroded reinforcing steel in cement mortar after calcium electro-deposition treatment

칼슘 전착처리 후, 시멘트 모르타르 속 철근의 부식속도에 대한 EIS 모니터링

  • 김제경 (동아대학교 해양도시건설.방재연구소 (교육부지정 대학중점연구소)) ;
  • 기성훈 (동아대학교 건축공학과) ;
  • 이정재 (동아대학교 건축공학과)
  • Received : 2019.09.09
  • Accepted : 2019.12.30
  • Published : 2019.12.01

Abstract

The primary purposes of this study are to understand a fundamental effects of electro-deposition on reinforcing steel in saturated Ca(OH)2 electrolyte, and evaluate the corrosion rates of rebars under cyclic 3wt.%NaCl immersion and dry corrosion environment. The three cement mortar specimens with cover thickness 5, 10 and 30mm, were prepared in the experiment. To monitor the corrosion rates of rebars in mortar, the three cement mortar specimens were exposed to 110 wet-drying cycles(8-hour-immersion in 3wt.%NaCl and 16-hour-drying in a room temperature) in the laboratory. During the wet-dry cycles, the polarization resistance, Rp, and solution resistance, Rs, were continuously measured. The instantaneous corrosion rates of rebars on the effect of electro-depositing with sat. Ca(OH)2 electrolyte were estimated from obtained R-1p and degrees of wetness were estimated from Rs values. From the experimental results, the corrosion rates of rebars were greatly accelerated by wet/dry cycles. During the mortars exposed to drying condition, the large increases in the corrosion rates were showed at all rebar surfaces in three mortar specimen, attributed from the accelerated reduction rates of dissolved oxygen in drying process. However, the corrosion rates on rebar surface electrochemically deposited with sat. Ca(OH)2 electrolyte showed the clear decreases, caused by calcium deposits in the porous rust layer.

본 연구는 시멘트 모르타르 속에 매입된 철근이 3wt.% NaCl 전해질 수용액에 8시간 침지 및 대기 중에서 16시간 건조가 반복되는 환경에 있을 때 교류 임피던스법을 이용하여, 10kHz에서 용액저항, 10mHz에서 전하이동저항을 측정하여, 그 값의 차이로부터 분극저항을 계산하여 부식속도를 측정하였다. 부식속도를 제어하기 위해 포화 Ca(OH)2 용액에서 일정시간 전착하여, 그 효과를 관찰하였다. 철근의 부식속도는 용존산소의 확산속도 증가에 의해, 침지보다는 건조 환경에서 가속되었으며, 이것은 모르타르 두께가 얇을수록 명확히 측정되었다. 침지 및 건조 반복횟수가 증가함에 따로, 철근의 부식속도는 부동태에서 Low-middle 상태로 가속되었으며, 그 기준은 다수의 연구자들이 사용한 기준을 사용하였다. 이 기준에 의해 철근의 부식속도가 Low-middle 상태가 되면, 포화 Ca(OH)2 용액에서 -10 uA/㎠ 전류밀도를 사용하여 철근에 전착을 진행하고, 5일간 건조시킨 후, 3wt.% NaCl 용액에서 침지-건조 반복실험을 다시 진행하면서, 부식속도를 측정하였다. 측정결과, 모르타르의 두께가 얇은 경우, 부식속도의 감소를 명확히 관찰하였다. 또한, 전착에 의한 철근의 부식속도 감소는 침지상태에서 보다 철근이 건조과정에 놓일 때, 더욱 크게 측정되었다. 전착처리에 따라 칼슘은 철근표면과 모르타르 계면에 존재하는 Porous rust layer의 void를 메우는 것으로 보인다. 시험체가 건조과정에 놓일 때, 철근표면에 형성된 다공질의 녹층속에 농축된 Ca2+가 침지과정보다 쉽게 CO32-와 결합되어, CaCO3가 형성됨으로서 철근의 부식속도를 더욱 감소시킨 것으로 생각된다.

Keywords

References

  1. So, H. S. (2006), Environmental Influences and Assessment of Corrosion Rate of Reinforcing Bars using the Linear Polarization Resistance Technique, Journal of Korean Society of Civil Engineering, 22(2), 107-114.
  2. Kim, K. J., Lee, M. H., Moon K. M. (2006), Principle and Application of Cathodic Protection for Concrete structures, Journal of the Korea Concrete Institute, 18(5), 23-33
  3. Lee, S. T., Moon, D. J., Kim, W. J., Moon, J. H. and Kim, H. S. (2010), Application of Macrocell Sensor System for Monitoring of Steel Corrosion in Concrete Structure Exposed to Marine Environment, Korean Society of Coastal and Ocean Engineers, 22(4), 241-247.
  4. Kwon, S. J., Lee, M. H., Park, S. S. (2012), Development and Application of Anti-Corrosive Steel Using Electro-Deposition of Sea Water (1) - Development of Electro-Deposition System Using Sea Water, Journal of Korea Institute for Structural Matenance and Inspection, 16(5), 78-87. https://doi.org/10.11112/jksmi.2012.16.5.078
  5. Kyung J. W., Tae S. H. and Jang S. Y. (2006), Application of Electrodeposition Method, Journal of the Korea Concrete Institute, 18(5), 41-46.
  6. Lee, C. H., Song, H. W. (2009), Experimental Study on Artificial Crack Healing for Concrete Using Electrochemical Deposition Method, Journal of the Korea Concrete Institute, 21(4), 409-417. https://doi.org/10.4334/JKCI.2009.21.4.409
  7. Kho, Y. T., (1999), The fundamentals of Corrosion and Anti-corrosion. The Corrosion Science Society of Korea, 3-14.
  8. Kim, J. K., Kee S. H., Yee J. J. (2018), Corrosion Monitoring of Reinforcing Bars in Cement Mortar Exposed to Seawater Immersion-and-dry Cycles, Journal of the Korea Institute for Structural Maintenance and Inspection, 22(4), 10-18. https://doi.org/10.11112/JKSMI.2018.22.4.010
  9. A. Nishikata, Qingjun Zhu, and E. Tada (2014), Long-term monitoring of atmospheric corrosion at weathering steel bridges by an electrochemical impedance method, Corrosion Science, 87, 80-88. https://doi.org/10.1016/j.corsci.2014.06.007
  10. Denny A. Jones (1996), Principles and Prevention of Corrosion 2nd Edition, Prentice-Hall, Inc., New Jersey, USA, 61.
  11. Ryu J. S. and N. Otsuki (2001), Crack closure of reinforced concrete by electrodeposition technique, Cement and Concrete Research, 32, 159-164. https://doi.org/10.1016/S0008-8846(01)00650-0
  12. Building Research Establishment (2001), Corrosion of steel in concrete: In Investigation and assessment Digest 444, Part2, BRE, London, UK.
  13. Joh, S. H., Lim, Y. C., Mohamed Ismail, Lee, and Han Seung (2010), Fundamental Study on Developing Embedded Miini-Sensor for Nondestructive Diagnosis Corrosion of Rebar, Journal of the Korea Institute for Structural Maintenance and Inspection, 14(6), 179-186. https://doi.org/10.11112/jksmi.2010.14.6.179
  14. Kim, J. N., Jee, N. Y. (2007), A Study on the Distribution of Stern-Geary Constant for Calculating the Corrosion Current Density of Steel Reinforcement in Concrete by means of the Polarization Resistance Method, Fall Conference of Korea Concrete Institute, 577-580.
  15. A.P. Yadav, A. Nishikata, and T. Tsuru (2004), Electrochemical impedance study on galvanized steel corrosion under cyclic wet-dry conditions-influence of time of wetness, Corrosion Science, 46, 169-181. https://doi.org/10.1016/S0010-938X(03)00130-6
  16. A. Nishikata, Y. Ichihara, and T. Tsuru (1995), An Application of Electrochemical Impedance Spectroscopy to Atmospheric Corrosion Study, Corrosion Science, 37(6), 897-911. https://doi.org/10.1016/0010-938X(95)00002-2
  17. Kwon S. J., Lee S. M., and Park S. S. (2012), Development and Application of Anti-Corrosive Steel Using Electro-Deposition of Sea Water(2) - Evaluation of Application Rebar with Electro-Deposition Using Sea Water, Journal of the Korea Institute for Structural Maintenance and Inspection, 16(6), 155-162. https://doi.org/10.11112/jksmi.2012.16.6.155
  18. Lee C. H., Kim T. S., and Song H. W. (2009), Corrosion Resistance of Blended Concrete and Its Application to Crack Healing, Journal of the Korea Concrete Institute, 21(6), 689-696. https://doi.org/10.4334/JKCI.2009.21.6.689