KSCE Journal of Civil and Environmental Engineering Research (대한토목학회논문집)

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

DOI QR Code

An Experimental Study on Electromagnetic Properties in Early-Aged Cement Mortar under Different Curing Conditions

양생조건에 따른 초기재령 시멘트 모르타르의 전자기 특성에 대한 실험적 연구

  • 권성준 (UCI 토목공학과) ;
  • 송하원 (연세대학교 사회환경시스템공학부) ;
  • Received : 2008.03.20
  • Accepted : 2008.08.18
  • Published : 2008.09.30
Download PDF
⟨ Previous Next ⟩

Abstract

Recently, NDTs (Non-Destructive Techniques) using electromagnetic(EM) properties are applied to the performance evaluation for RC (Reinforced Concrete) structures. Since nonmetallic materials which are cement-based system have their unique dielectric constant and conductivity, they can be characterized and changed with different mixture conditions like W/C (water to cement) ratios and unit cement weight. In a room condition, cement mortar is generally dry so that porosity plays a major role in EM properties, which is determined at early-aged stage and also be affected by curing condition. In this paper, EM properties (dielectric constant and conductivity) in cement mortar specimens with 4 different W/C ratios are measured in the wide region of 0.2 GHz~20 GHz. Each specimen has different submerged curing period from 0 to 28 days and then EM measurement is performed after 4 weeks. Furthermore, porosity at the age of 28 days is measured through MIP (Mercury Intrusion Porosimeter) and saturation is also measured through amount of water loss in room condition. In order to evaluate the porosity from the initial curing stage, numerical analysis based on the modeling for the behavior in early-aged concrete is performed and the calculated results of porosity and measured EM properties are analyzed. For the convenient comparison with influencing parameters like W/C ratios and curing period, EM properties from 5 GHz to 15 GHz are averaged as one value. For 4 weeks, the averaged dielectric constant and conductivity in cement mortar are linearly decrease with higher W/C ratios and they increase in proportion to the square root of curing period regardless of W/C ratios.

최근 들어 비파괴기술이 발달함에 따라, 콘크리트 구조물의 건전성 평가에 전자기 특성을 이용한 평가기법이 적용되고 있다. 시멘트 건설재료와 같은 절연성 재료는 고유한 유전상수 또는 전도율을 가지므로 특성화될 수 있는데, 이러한 전자기 특성은 물-시멘트비, 단위 시멘트 량과 같은 배합조건에 따라 변화하게 된다. 실내조건에 노출된 시멘트 모르타르는 일반적으로 수분에 포화되지 않으므로, 공극률이 전자기특성에 큰 영향을 미치는데, 이러한 공극률은 주로 초기재령에서 결정되어지며, 양생조건에 따라 매우 민감하게 변화한다. 본 연구에서는 4가지 종류의 물-시멘트비를 가진 시멘트 모르타르를 대상으로, 전자기 특성(유전상수, 전도율)을 광범위 대역인 0.2 GHz~20 GHz 범위에서 측정하였다. 각 시편은 배합 후 0일에서 28일까지 총 5가지의 다른 수중양생기간을 가지도록 하였으며, 28일 이후, 실내노출상태에서 전자기 특성을 측정하였다. 한편 28일 재령시, 수은압입법을 통하여 공극률을 분석하였으며, 실내상태의 수분손실을 측정하여 포화도를 평가하였다. 양생초기부터 변화하는 공극률을 평가하기 위해, 초기재령 콘크리트의 거동 평가 프로그램을 이용하여 시멘트 모르타르의 공극률 변화를 분석하였으며, 측정된 전자기 특성의 변화를 분석하였다. 전자기 특성을 영향인자(재령, 물-시멘트비)와 쉽게 비교하기 위해서, 5 GHz~20 GHz 영역의 값을 하나의 평균값으로 도출하였다. 초기재령에서 평균화된 유전상수와 전도율은 물-시멘트비의 감소에 따라서 선형으로 증가하였으며, 4주의 양생기간동안 물-시멘트비에 관계없이 양생기간의 제곱근에 비례하여 증가하였다.

Keywords

References

  1. 임홍철, 정성훈(2000) 비파괴 시험을 위한 콘크리트의 전자기 특성의 측정, 한국콘크리트학회 논문집, 한국콘크리트학회, Vol. 12, No. 3, pp. 115-123
  2. Bentur, A. and Mitchell, D. (2008) Material performance lessons, Cement and Concrete Research, Vol. 38, No. 2, pp. 259-272 https://doi.org/10.1016/j.cemconres.2007.09.009
  3. Chrisp, T.M., McCarter, W.J., Starrs, G., and Blewett, J. (2002) Depth-related variation in conductivity to study cover zone concrete during wetting and drying, Cement and Concrete Research, Vol. 24, pp. 415-426 https://doi.org/10.1016/S0958-9465(01)00073-7
  4. Feng, S. and Sen, P.N. (1985) Geometrical model of conductive and dielectric properties of partially saturated rocks, Journal of Applied Physics, Vol. 58, pp. 3236-3243 https://doi.org/10.1063/1.335804
  5. Garboczi, E.J., Schwartz, L.M., and Bentz, D.P. (1995) Modelling the D.C. electrical conductivity of mortar, Material Research Symposium, Proceedings, Vol. 370, pp. 429-436
  6. Glanvile, J. and Nevile, A.M. (1995) Prediction of Concrete Durability, Proceedings of STATS 21 st Anniversary Conference, E&FN SPON, pp. 16-36
  7. Gorur, K., Smit, M.K., and Wittmann, F.H. (1982) Microwave study of hydrating cement paste at early age, Cement and Concrete Research, Vol. 12, pp. 447-454 https://doi.org/10.1016/0008-8846(82)90059-X
  8. Haddad, R.H. and Al-Qadi, I.L. (1998) Characterization of portland cement concrete using electromagnetic waves over the microwave frequencies, Cement and Concrete Research, Vol. 28, No. 10, pp. 1379-1391 https://doi.org/10.1016/S0008-8846(98)00076-3
  9. Halabe, U.B. (2000) Condition Assessment of Reinforced Concrete Structures Using Electromagnetic Waves, Doctoral thesis, Department of Civil Eng. MIT, Cambridge
  10. Halabe, U.B., Sotoodehnia, A. Maser, K.R., and Kausel, E.A. (1993) Modeling the electromagnetic properties of concrete, ACI Material Journal, Vol. 90, pp. 552-563
  11. Ishida, T., Chaube, R.P., and Maekawa, K. (1996) Modeling of pore content in concrete under generic drying wetting conditions, Concrete Library of JSCE, Vol. 18, No. 1, pp. 113-118
  12. Ishida, T. and Maekawa, K. (2003) Modeling of durability performance of cementitious materials and structures based on thermo-hygro physics, Rilem Proceeding PRO 29, Life Prediction and Aging Management of Concrete Structures, pp. 39-49
  13. Ishida, T. Maekawa, K., and Kishi T. (2007) Enhanced modeling of moisture equilibrium and transport in cementitious materials under arbitrary temperature and relative humidity history, Cement and Concrete Research, Vol. 37, No. 4, pp. 565-578 https://doi.org/10.1016/j.cemconres.2006.11.015
  14. Khandaker M. and Anwar H. (2008) Pumice based blended cement concretes exposed to marine environment: effects of mix composition and curing conditions, Cement and Concrete Composites, Vol. 30, No. 2, pp. 97-105 https://doi.org/10.1016/j.cemconcomp.2007.05.013
  15. Korean Standard (2005) Method of Test for Compressive Strength of Concrete: KS F 2405
  16. Mabrouk, R., Ishida, T., and Maekawa, K. (2004) A unified solidification model of hardening concrete composite for predicting the young age behavior of concrete, Cement and Concrete Composites, Vol. 26, No. 5, pp. 453-461 https://doi.org/10.1016/S0958-9465(03)00073-8
  17. Maekawa, K., Chaube, R., and Kishi, T. (1999) Modeling of Concrete Performance: Hydration, Microstructure Formation and Mass Transport, Routledge, London and New York
  18. McCarter, W.J., Starrs, G., and Chrisp, T.M. (2004) The complex impedance response of fly-ash cement revisited, Cement and Concrete Research, Vol. 34, pp. 1837-1843 https://doi.org/10.1016/j.cemconres.2004.01.013
  19. McCarter, W.J., Chrisp, T.M., and Starrs, G. (1999) The early hydration of alkali-activated slag : developments in monitoring techniques, Cement Concrete Composites, Vol. 21, pp. 277-283 https://doi.org/10.1016/S0958-9465(99)00007-4
  20. McCarter, W.J., Starrs, G., and Chrisp, T.M. (2000) Electrical conductivity, diffusion, and permeability of portland cement-based mortar, Cement and Concrete Research, Vol. 30, pp. 1395-1400 https://doi.org/10.1016/S0008-8846(00)00281-7
  21. McCarter, W.J., Chrisp, T.M., Starrs, G., and Blewett, J. (2003) Characterization and monitoring of cement-based systems using intrinsic electrical property measurements, Cement and Concrete Research, Vol. 33, pp. 197-206 https://doi.org/10.1016/S0008-8846(02)00824-4
  22. Nakarai, K., Ishida, T., Kishi, T., and Maekawa, K. (2007) Enhanced thermodynamic analysis coupled with temperature-dependent microstructures of cement hydrates, Cement and Concrete Research, Vol. 37, No. 2, pp. 139-150 https://doi.org/10.1016/j.cemconres.2006.10.006
  23. Neville, A.M. (1998) Properties of Concrete, Longman, 4th Ed. pp. 272-282
  24. Nyshadham, A., Sibbad, C.L., and Stuchly, S.S. (1992) Permittivity measurement using open-ended sensor and reference liquid calibration- an uncertainty analysis, IEEE Transactions on Microwave Theory and Techniques, MTT-40, pp. 305-313
  25. Rhim, H.C. (2001) Condition monitoring of deteriorating concrete dams using radar, Cement and Concrete Research, Vol. 31, pp. 363-373 https://doi.org/10.1016/S0008-8846(00)00496-8
  26. Rhim, H.C. and Buyukozturk,O. (1998) Electromagnetic properties of concrete at microwave frequency range, ACI Material Journal, Vol. 95, pp. 262-271
  27. Rhim, H.C., Kim, Y.J., Feng, M.Q. Woo, S.K., and Song, Y.C. (2004) Measurements of electromagnetic properties of concrete and fiber reinforced polymer for nondestructive testing, US-Korea Joint Seminar/Workshop on Smart Structures Technologies, Sheraton Walker Hill Hotel, Seoul, Korea, September 2
  28. Shi, C., Stegemann, J.A., and Caldwell, E.J. (1998) Effect of supplementary cementing materials on the specific conductivity of pore solution and its implications on the rapid chloride permeability test (AASHTO T277 and ASTM C1202) results, ACI Materials Journal, Vol. 95, pp. 389-394
  29. Song H.-W., Lee, C.-H., and Ann, K.Y. (2008) Factors influencing chloride transport in concrete structures exposed to marine environments, Cement and Concrete Composites, Vol. 30, No. 2, pp. 113-121 https://doi.org/10.1016/j.cemconcomp.2007.09.005
  30. Song, H.W., Cho, H.J., Park, S.S., Byun, K.J., and Maekawa, K. (2001) Early-age cracking resistance evaluation of concrete structure, Concrete Science and Engineering, Vol. 3, pp. 62-72
  31. Soutsos, M.N., Bungey, J.H. Millard, S.G., Shaw, M.R. Patterson, A. (2001) Dielectric properties of concrete and their influence on radar testing, NDT&E International., Vol. 34, pp. 419-425 https://doi.org/10.1016/S0963-8695(01)00009-3
  32. Taylor, M.A. and Arulanandan K. (1974) Relationships between electrical and physical properties of cement pastes, cement and concrete research, Vol. 4, pp. 881-897 https://doi.org/10.1016/0008-8846(74)90023-4
  33. Wittmann, F.H. (1975) Micro wave absorption of hardened cement paste, Cement and Concrete Research, Vol. 5, pp. 63-71 https://doi.org/10.1016/0008-8846(75)90108-8
  34. Zhang, W., Ding, X.Z., Lim, T.H., Ong, C.K., Tan, B.T.G., and Yang, J. (1995) Microwave study of hydration of slag cement blends in early period, Cement and Concrete Research, Vol. 25, No. 5, pp. 1086-1094 https://doi.org/10.1016/0008-8846(95)00103-J