Journal of the Korea Concrete Institute (콘크리트학회논문집)

Korea Concrete Institute (한국콘크리트학회)
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Prediction Model for Autogenous Shrinkage of High Strength Fly Ash Concrete

고강도 플라이 애쉬 콘크리트의 자기수축 예측 모델

  • Lee, Hoi-Keun (Dept. of Civil and Environmental, Sungkyunkwan University) ;
  • Lee, Kwang-Myong (Dept. of Civil and Environmental, Sungkyunkwan University) ;
  • Kim, Woo (Dept. of Civil Engineering, Chonnam University)
  • 이회근 (성균관대학교 토목환경공학과) ;
  • 이광명 (성균관대학교 토목환경공학과) ;
  • 김우 (전남대학교 토목공학과)
  • Published : 2003.02.01
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Abstract

Autogenous shrinkage, a significant contributor of early-age cracking of high strength concrete (HSC), must be avoided or minimized from an engineering point of view. Therefore, it is necessary to study how to reduce and to predict autogenous shrinkage with respect to tile control of early-age cracking. In this study, autogenous shrinkage of HSC with various water-binder ratio (W/B) ranging from 0.50 to 0.27 and fly ash content of 0, 10, 20, and 30% were investigated. Based on the test results, thereafter, a prediction model for autogenous shrinkage was proposed. Test results show that autogenous shrinkage increased and more rapidly developed with decreasing the W/B. Also, the higher fly ash contents, the smaller autogenous shrinkage. In particular, even if much autogenous shrinkage occurs at very early-ages, stress may not be developed while the stiffness of concrete is low. In order to consider the change of concrete stiffness, the transition time referred as stiffening threshold, was obtained by monitoring of ultrasonic pulse velocity evolution and considered in the autogenous shrinkage model. From a practical point of view, the proposed model can be effectively used to predict autogenous shrinkage and to estimate stress induced by autogenous shrinkage.

고강도 콘크리트의 초기 균열 제어를 위해서는 균열 발생의 주요 원인인 자기수축에 대한 실험과 예측, 그리고 감소 방안에 대한 연구가 요구된다. 본 연구에서는 물-결합재비가 0.50~0.27이고 플라이 애쉬 대체율이 0, 10, 20, 30%인 콘크리트의 자기수축을 측정하였으며, 실험결과를 토대로 예측 모델을 제안하였다. 실험 결과, 물-결합재비가 낮아짐에 따라 자기수축이 증가하였으며, 재령 초기에서 자기수축 발현률이 크게 증가하였다. 또한, 플라이 애쉬 대체율이 증가할수록 자기수축이 감소하는 결과를 얻었다. 비록 재령 초기에 큰 자기수축이 발생했다 하더라도 콘크리트의 강성(탄성계수)이 낮은 동안에는 응력은 발생하지 않게 된다. 따라서, 본 연구에서는 콘크리트 강성의 변화를 고려하기 위해 초음파 속도 발현 특성으로부터 콘크리트 강성의 발현 시점을 간접적으로 조사하여 이를 자기수축 모델링에 사용하였다. 실용적인 측면에서, 본 연구에서 제안된 모델은 자기수축과 이로 인해 발생한 응력을 예측하는 데에 유효하게 적용될 수 있을 것으로 기대된다.

Keywords

References

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