KSCE Journal of Civil and Environmental Engineering Research (대한토목학회논문집)

Korean Society of Civil Engeneers (대한토목학회)
권호 표지
DOI QR코드

DOI QR Code

A Study on Moisture Transport of Artificial Lightweight Concrete

인공경량골재 콘크리트의 수분이동 특성에 관한 연구

  • 이창수 (서울시립대학교 토목공학과) ;
  • 최상현 (한국철도대학 철도시설토목과) ;
  • 박종혁 (서울시립대학교 토목공학과) ;
  • 김영욱 (서울시립대학교 토목공학과)
  • Received : 2009.02.18
  • Accepted : 2009.05.15
  • Published : 2009.07.31
Download PDF
⟨ Previous Next ⟩

Abstract

For the first step on the quantitative evaluation of shrinkage reduction and differential shrinkage analysis of lightweight aggregate concrete, this study sets the moisture transport model of concrete by pre-absorbed water of porous lightweight aggregates and measured effective moisture diffusion coefficient, moisture capacity, degree of humidity supply and degree of humidity consumption by water binder ratio and aggregate type. The effective moisture diffusion coefficient in steady state caused by humidity difference between inside and outside of concrete had low value as low water-binder ratio. And in case of same water-binder ratio, effective moisture diffusion of mixtures used normal aggregates were lower than those used lightweight aggregates. To determine moisture store capability of concrete - moisture capacity, moisture contents were measured in 9 humidity conditions. As a result moisture contents of mixtures used lightweight aggregates was higher than mixtures used normal aggregates in all humidity conditions. This study measured lightweight aggregates' degree of humidity supply that applicable to normal atmospheric environment (above RH 50%) and made it quantitatively. Also amount of moisture release was set as a exponential function that represents a clear trend proportion to time and inverse proportion to humidity of the surroundings. As the result of measurement about degree of moisture consumption inside concrete following the internal consumption caused by cement hydration self-drying, it was showed that rapid decrease of humidity, around 10%, at early ages (7~10 days) when water-binder ratio is 0.3 and slow decrease around 5% and 1% when water-binder ratio is 0.4 and 0.5.

다공성 경량골재의 사전흡수수에 따른 콘크리트 수축 저감 효과의 정량적 평가와 부등수축해석모델 상수 제공을 위한 첫번째 단계로서, 수분이동모델을 설정하고 이에 따른 수분이동 특성상수인 유효수분확산계수, 수분용량, 습도공급도, 습도소모도를 물-결합재비, 골재 종류를 변수로 하여 측정하였다. 콘크리트 내, 외부 습도차에 의한 정상상태에서의 유효수분확산계수는 물-결합재비가 낮을수록 낮은 값을 나타내었으며 동일한 물-결합재비인 경우 일반골재를 사용한 배합이 경량골재를 사용한 배합보다 낮은 유효수분확산계수값을 나타내었다. 콘크리트 내 수분의 저장 능력 즉, 수분용량을 산정하기 위해 9가지 습도에서 콘크리트의 수분량을 측정하였으며 경량골재를 사용한 배합이 일반골재를 사용한 배합보다 모든 습도조건에서 수분량이 크게 나타났다. 일반 대기환경 습도 50% 이상 조건에서 적용할 수 있는 경량골재의 습도공급도를 측정하여 정량화 하였으며, 경량골재에서의 수분 방출량은 주변 습도에 반비례하고 시간에 비례하는 뚜렷한 경향을 나타내는 지수함수의 형태로 설정하였다. 시멘트 수화 자기건조에 의한 수분의 내부소모에 따른 콘크리트 내 습도소모도를 측정하였으며, 측정결과 물-결합재비 0.3의 경우 7~10일 이내의 초기재령에서 약 10% 내외의 급격한 습도감소를 나타내었으며 물-결합재비 0.4, 0.5의 경우 완만한 형태로 약 5%, 1% 내외의 습도 감소를 나타내었다.

Keywords

References

  1. 이창수, 박종혁(2006a) 흡착 영역 분리 압력을 고려한 시멘트페이스트의 자기 수축, 한국콘크리트학회 논문집, 한국콘크리트학회, 제18권 2호, pp. 213-218. https://doi.org/10.4334/JKCI.2006.18.2.213
  2. 이창수, 박종혁(2006b) 불포화 공극 보정 수화도 모델을 이용한 콘크리트의 자기수축 예측, 대한토목학회논문집, 대한토목학회, 제26권 제5A호, pp. 909-915.
  3. 이창수, 박종혁(2008) 공극 내 상대습도, 모세관압력, 표면에너지 변화에 따른 콘크리트 자기수축, 한국콘크리트학회 논문집, 한국콘크리트학회, 제20권 2호, pp. 131-138. https://doi.org/10.4334/JKCI.2008.20.2.131
  4. KS A 0078 (1999) 습도-측정방법, 산업자원부 기술표준원
  5. KS B 5344 (1997) 습도계-성능 시험방법, 산업자원부 기술표준원.
  6. ACI Committee 211 (2004) Standard Practice for Selecting Proportions for Structural Lightweight Concrete, American Concrete Institute, pp. 30-34.
  7. ACI Committee 213 (2003) Guide for Structural Lightweight-Aggregate Concrete, American Concrete Institute, pp. 30-34.
  8. Ayano, T. and Wittmann, F.H. (2002) Drying, moisture distribution and shrinkage of cement based materials, Materials and Structures, Vol. 35, pp. 134-140. https://doi.org/10.1007/BF02533581
  9. Bazant, Z.P. and Najjar, L.J. (1971) Drying of concrete as a nonlinear diffusion problem, Cement and Concrete Research, Vol. 1, pp. 461-473. https://doi.org/10.1016/0008-8846(71)90054-8
  10. Bazant, Z.P. and Najjar, L.J. (1972) Nonlinear water diffusion in nonsaturated concrete, materials and structures, Vol. 5, pp. 3-20
  11. Bazant, Z.P. (1982) Mathematical Models for Creep and Shrinkage of Concrete, Creep and Shrinkage in Concrete Structures, edited by Bazant, Z.P., Wittmann, F.H., John Wiley & Sons, pp. 163-256.
  12. Bentur, A., Igarashi, S., and Kovler, K. (2001) Prevention of autogenous shrinkage in hugh-strength concrete by internal curing using wet lightweight aggregate, Cement and Concrete Research, Vol. 31, pp. 1587-1591. https://doi.org/10.1016/S0008-8846(01)00608-1
  13. Bentz, D.P. and Snyder, K.A. (1999) Protected paste volume in concrte extension to internal curing using saturated lightweight fine aggregate, Cement and Concrete Research, Vol. 29, pp. 1863-1867. https://doi.org/10.1016/S0008-8846(99)00178-7
  14. George, C.H. (2002) Guide for the Use of Low-Density Concrete in Civil Works Projects, U.S. Army Corps of Enginners, Report No ERDC/GSL TR 02-13, pp. 26-31.
  15. Gesoglu, M., Ozturan, T., and Guneyisi, E. (2006) Effects of cold-bonded fly ash aggregate properties on the shrinkage cracking of lightweight concretes, Cement and Concrete Composite, Vol. 28, pp. 598-605. https://doi.org/10.1016/j.cemconcomp.2006.04.002
  16. Helland, S. (2000) Lightweight aggregate concrete in norwegian bridges, HPC Bridge Views, Vol. 11, pp. 2-3.
  17. Johannesson, B. and Janz, M. (2002) Test of four different experimental methods to determine sorption isotherms, Journal of Materials in Civil Engineering, Vol. 14, No. 6, pp. 471-477. https://doi.org/10.1061/(ASCE)0899-1561(2002)14:6(471)
  18. Kenneth, W.M. and Nicholas, J.C. (1999) Curing of High Performance Concrete : Report of the State of the art, NIST IR 6295, National Institute of Standard and Technology, Gaithersburg, pp. 17-34.
  19. Kim, J.K. and Lee, C.S. (1999) Moisture diffusion of concrete considering self-desiccation at early ages, Cement and Concrete Research, Vol. 29, pp. 1921-1927. https://doi.org/10.1016/S0008-8846(99)00192-1
  20. Kohno, K., Okamoto, T., Isikawa, Y., Sibata, T., and Mori, H. (1999) Effects of artificial lightweight aggregate on autogenous shrinkage of concrete, Cement and Concrete Research, Vol. 29, pp. 611-614. https://doi.org/10.1016/S0008-8846(98)00202-6
  21. Kovler, K. and Zhutovsky, S. (2006) Overview and future trends of shrinkage research, Materials and Structures, Vol. 39, No. 9, pp. 827-847. https://doi.org/10.1617/s11527-006-9114-z
  22. Lura, P. (2003) Autogenous Deformation and Internal Curing of Concrete, Ph.D thesis, Delft University of Technology.
  23. Lura, P. and Bisschop, J. (2004) On the origin of eigenstresses in lightweight aggregate concrete, Cement and Cocnrete Composite, Vol. 34, pp. 445-452.
  24. Lura, P., Jensen O.M., and Igarashi, S.I. (2006) Experimental observation of internal water curing of concrete, Materials and Structures, Vol. 40, No. 2, pp. 211-220. https://doi.org/10.1617/s11527-006-9132-x
  25. Nevile, A.M. (1998) Properties of Concrete, John Wiley & Sons Inc., 4th Ed.
  26. Ozyildirium, H.C. (2004) Lightweight hpc on poute 106 bridge in virginia, HPC Bridge Views, Vol. 32, pp. 3.
  27. Persson, B. (1998) Experimental studies on shrinkage of high-performance concrete, Cement and Concrete Research, Vol. 28, pp. 1023-1036. https://doi.org/10.1016/S0008-8846(98)00068-4
  28. Rathby, K.D. and Lydon, F.D. (1981) Lightweight concrete in highway bridges, International Journal of Cement Composites and Lightweight Concrete, Vol. 2, pp. 133-146.
  29. Sakata, K. (1983) A study on moisture diffusion in drying and drying shrinkage of concrete, Cement and Concrete Research, Vol. 13, pp. 216-224. https://doi.org/10.1016/0008-8846(83)90104-7
  30. Sideney, M., Francis, J. Young and David, D. (2003) Concrete, 2nd Ed., Prentice Hall, pp. 547-562.
  31. Thomas, A.H. and Theodore, W.B. (2000) State of the Art Report on High-Strength, High-Durability Structural Low-Density Concrete for Applications in Severe Marine Environment, U.S. Army Corps of Enginners, Report No ERDC/SL TR 00-3, pp. 9-52.
  32. Thomas, A.H. and John, P.R. (2001) Benefits of lightweight HPC, HPC Bridge Views, Vol. 17, pp. 3.
  33. Xi, Y., Bazant, Z.P., and Jennings, H.M. (1993) Moisture Diffusion in Cementitious Materials-Adsorption Isotherms, Advanced Cement Based Materials, Vol. 1, pp. 248-257. https://doi.org/10.1016/1065-7355(94)90033-7
  34. Xi, Y., Bazant, Z.P., Molina, L., and Jennings, H.M. (1993) moisture diffusion in cementitious materials-moisture capacity and diffusivity, Advanced Cement Based Materials, Vol. 1, pp. 258-266. https://doi.org/10.1016/1065-7355(94)90034-5
  35. Xin, D., Zollingger, D.G., and Allen, G.D. (1995) An approach to determine diffusity in hardening concrete based on measured humidity profiles, Advanced Cement Based Materials, Vol. 2, pp. 138-144. https://doi.org/10.1016/1065-7355(95)90014-4
  36. Zhutovsky, S., Kovler, K. and Bentur, A. (2002) Efficiency of lightweight aggregates for internal curing of high-strength concrete to eliminate autogenous shrinkage, Materials and Structures, Vol. 35, pp. 97-101. https://doi.org/10.1617/13801
  37. Zhotovsky, S., Kovler, K., and Bentur, A. (2004) Influence of cement paste matrix properties on the autogenous curing of high-performance concrete, Cement and Concrete Composite, Vol. 26, pp. 499-507. https://doi.org/10.1016/S0958-9465(03)00082-9