Journal of the Korea Concrete Institute (콘크리트학회논문집)

Korea Concrete Institute (한국콘크리트학회)
권호 표지
DOI QR코드

DOI QR Code

Damage of Overlaid Concrete Structures Subjected to Humidity Changes in the Atmosphere

습도 변화에 따른 콘크리트 덧씌우기 보수체의 손상분석

  • 윤우현 (경원대학교 환경정보대학원)
  • Published : 2002.10.01
Download PDF
⟨ Previous Next ⟩

Abstract

The failure phenomenon of overlaid concrete structures, such as surface crack, and peel-off failure, shear bond failure in the end contact zone, was investigated due to humidity changes. To investigate this failure phenomenon, the surface tensile stress, and the shear stress, the vertical tensile stress in the contact zone were analysed using the non-linear stress-strain relationship of material such as strain-hardening- and strain-softening diagrams. Overlay thickness and overlay material were the main variables in the analyses. It is assumed that the initial surface humidity of overlaid concrete structures was 100％ r.H. With a atmospheric humidity of 55％ r.H. and two load cases for drying(LCI), curing and drying(LC2), the stress states of overlaid concrete structures were calculated. The result shows that only fictitious cracks occurred in the overlay surface of CM2O, ECM25, and no shear bond failure occurred in the contact zone without CM2O. The peel-off failure was proved to be the main cause of the damage in the overlaid concrete structures. Only for overlay thickness of 1cm occurred no peel-off failure in the case of drying after a long-term public use(LC1). In the case of curing and drying during overlay work(LC2) occurred the peel-off failure within 1.5days for all the overlaid concrete structures.

본 연구에서는 습도 변화와 같은 물리적인 원인으로 보수체의 손상(표면 균열, 경계면 파괴)을 유발하는 표면 인장 응력과 기층과 보수층 단부 경계변의 연직 인장 응력 및 전단 응력이 해석적으로 조사되었다. 응력 계산 시에는 사용 재료의 비선형응력-변형률 곡선이 사용되었고, 특히 변형률 경화, 변형률 연화 특성이 고려되었다. 응력 계산은 보수층의 두께와 보수 재료를 변수로 하였다. 습도 변화에 의한 영향은 보수체가 장기간 공용된 후 수위 하강으로 인해 나타나는 현상(콘크리트 댐)과 보수 후 일정한 양생 기간 후에 거푸집을 제거했을 때 나타나는 현상의 두 가지 경우에 대해서 조사되었다 건조되기 전 보수체 표변의 초기 습도는 100%, 대기 습도는 55%로 가정하였고, 계산기간(양생＋건조기간)은 30일간으로 하였다. 상기 두 가지 경우에 대해서 응력을 계산한 결과, 보수체 표면에서는 일부 보수체(CM20, ECM25)에서 단지 변형률 연화 단계의 가상 균열이 발생되었다. 한편 단부 경계면에서는 양생 중에 부착 강도를 약간 상회하는 일부 보수체(CM20)를 제외하고는 부착 전단 파괴는 발생치 않았다. 습도 변화에서도 단부 경계면의 들뜸현상(Peel-Off)이 보수체 손상의 주요원인으로 나타났고, 이를 유발하는 연직 인장 응력은 공용 중에 건조되는 경우에는 보수층 두께 dO=1cm에서만 부착 강도보다 낮은 값을 유지하고, 보수 작업시 양생 후 대기에 노출되는 경우에는 1.5일 이내에 발현된 부착 강도를 초과하였다.

Keywords

References

  1. Yoon, W. H., "Damage of Overlaid Concrete Structures Subjected to Thermally Transient Condition by Rainfall," Journal of the Korea Concrete Institute, Vol. 13, No. 5, pp.491-498, October 2001.
  2. Sim, J. S., Oh, H. S., and Yu, J. M., "A Study on the Prediction Model of Shear Strength of RC Beams Strengthened for Shear by FRP," Journal of the Korea Concrete Institute, Vol. 12, No. 5, pp.35-46, October 2000.
  3. Park, T. H., Bu, J. S., and Cho, B. S., "Flexural Behavior of Dual Concrete Beams Using Fiber Reinforced Concrete at Tensile Parts," Journal of the Korea Concrete Institute, Vol. 13, No. 6, pp.584-592, December 2001.
  4. Chung, Y. S., Park, J. H., Park, H. S., and Cho, C. B., "Pseudo Dynamic Test for the Seismic Performance Enhancement of Circular RC Bridge Piers Retrofitted with Fibers," Journal of the Korea Concrete Institute, Vol. 14, No. 2, pp.180-189, April 2000. https://doi.org/10.4334/JKCI.2002.14.2.180
  5. Sim, J. S. and Oh, H. S., "Semi-Empirical Prediction of Crack Width of the Strengthened Bridge Deck with External Bonding Plastic," Journal of the Korea Concrete Institute, Vol.14, No. 2, pp.231 -238, April 2000. https://doi.org/10.4334/JKCI.2002.14.2.231
  6. Klopfer, H., "Wassertransport Durch Diffusion in Feststoffen." Bauverlag GmbH Wiesbaden und Berlin, 1974.
  7. Yoon, W. H., "Untersuchung der Temperaturund Feuchtebedingten Spannungsverhaltnisse im Bereich von Instandsetzungen bei Massiven Betonbauten," Dissertation der RWTH Aachen, 8. 1989.
  8. Bazant, Z. P. and Najjar, L. J., "Nonlinear Water Diffusion in Non Saturated Concrete," Materials and Structures, Vol. 5, No. 25, pp.1 - 20, 1972. https://doi.org/10.1007/BF02479073
  9. Argyris, J. H., Warnke, E. P., and Willam, K. J., "Berechnungen von Temperaturund Feuchtefeldern in Massivbauten Nach der Methode der Finiten Elemente," DAfStb Heft 279, 1977, pp.1 -42.
  10. Weber, J. W., "Empirischer Formeln zur Beschreibung der Festigkeitsentwicklung und der Entwicklung des E-Moduls von Betons," Betoruverk+Fertigteil-Technik, 1979, pp.753 - 756.
  11. Bruhwiler, E., "Bruchmechanik von Staumauerbeton Unter Quasi-Statischer und Erdbebendynamischer Belastung," Dissertation EPF Lausanne, July,1988.
  12. Ferraris, C. F., "Mechanismes du Retrait de Lapate de Ciment Durcie," Dissertation der EPFL, These No. 621, 1986.
  13. Mears, A. R. and Hobbs, D. W., "The Effect of Mix Proportions Upon the Ultimate Air-Drying Shrinkage of Mortars," Magazine of Concrete Research, Vol. 24, No. 79, pp.7784, 1972. https://doi.org/10.1680/macr.1972.24.79.77
  14. Hillerborg, A., "Analysis of one Simple Crack, Fracture Mechanics of Concrete, " Elsevier Science Publishers, Amsterdam, 1983, pp.223-249.
  15. Bruhwiler, E. and Wittmann, F. H., "The Wedge Splitting Test, a Method of Performing Stable Fracture Mechanics Tests," Proceedings of the International Conference on Fracture and Damage of Concrete and Rock, Contribution VIII-5, Vienna, July, 1988.
  16. Huges, B. P. and Chapman, G. P., "The Complete Stress-Strain Curve for Concrete in Direct Tension," RILEM Bulletin No.30, 1966, pp.95-97.
  17. Cleland, D. J., Naderi, M., and Long, A. E., "Bond Strength of Patch Repair Concrete," Adhesion between Polymers and Concrete (ISAP), 1986, pp.235-244.
  18. Hilsdorf, H. K. and Belli, H. W., "Einflu$\beta$ der Haft-brucken auf die Haltbarkeit von Ausbesserungen mit Zementmortel," Forschung Stra$\beta$enbau und Stra$\beta$enverkehrstechnik, Heft 342, 1981, pp.45-90.
  19. Judge, A. I., Cheriton, L. W., and Lambe, R.W., "Bonding Systems for Concrete Repair-An Assessment of Commonly Used Materials," Adhesion Between Polymers and Concrete (ISAP), 1986, pp.661-681.
  20. Peier, W. H., "Adhesion Testing of Polymer Modified Cement Mortars," Adhesion Between Polymers and Concrete(ISAP), 1986, pp.730-740.