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Study on Volume Deformation Distribution of Concrete with One Surface Exposed to Dry Condition

Author: ZuoXueFeng
Tutor: GaoXiaoJian
School: Harbin Institute of Technology
Course: Geotechnical Engineering
Keywords: one surface exposed to dry condition volume deformation relative humidity distribution characteristics
CLC: TU528.0
Type: Master's thesis
Year: 2008
Downloads: 16
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Abstract

Shrinkage and cracking were the primary factors influencing the durability of modern concrete, and the drying shrinkage is the common and primary reason of concrete cracking. The drying shrinkage will present obvious non-uniform distribution and deformation gradient with leaving various depths from the exposed surface in practical engineering. The self-restraint shrinkage stress produced by the deformation gradient can aggregate the cracking of concrete. It is important to study the volume deformation distribution of concrete under dry condition.A new apparatus for measuring drying shrinkage deformation gradient of concrete was developed in this paper. Shrinkage strain of concrete with different mix proportion was measured during 3d to 28d after the concrete specimen was shaped in various depths from the exposed surface by using this new apparatus, and only one surface of the concrete specimen was exposed to dry condition during the experiment on the condition of RH35﹪,RH55﹪and RH75﹪. Relative humidity change of concrete in various depths from the exposed surface was also studied by using embedded humidity sensors. However, in practical engineering concrete structures are always reinforced. The shrinkage deformation distribution of reinforced concrete was also studied in this paper.The experimental results have been found as follow: the drying shrinkage process extended gradually from the exposed surface to the internal of the concrete, but the speed is very slow. Because the water escapes from the near surface layer of concrete, the humidity is markedly lower in the internal layer than in the near surface layer of concrete, accordingly the humidity gradient formation in the concrete. So the shrinkage is markedly lower in the internal layer than in the near surface layer of concrete, and the shrinkage gradient exists between the internal layer to the near surface layer of concrete. The water to cement ratio of concrete has different influence on deformation gradient of concrete specimen, such differential distributions of shrinkage strain and relative humidity according to depths from the exposed concrete surface get worse by decreasing water to cement ratio. This is the reason low water to cement ratio of concrete specimen is easy to crack in practical engineering. The mineral admixtures of flay ash, silica fume and slag can lower deformation gradient of concrete in a certain extent, consequently that can restrain the cracks leaded by the drying shrinkage deformation gradient.The drying shrinkage is markedly influenced by humidity condition, the lower of the relative humidity and the larger of the humidity gradient, the larger of the drying shrinkage deformation gradient. There is a good linear relationship between shrinkage strain and relative humidity reduction in different depths of concrete. However, the surface layer concrete has a lower shrinkage than the internal layer concrete when they reach the same relative humidity. The shrinkage strain of reinforced concrete is significantly less than the plain concrete. It was showed that constraint degree of reinforced concrete increased with increase of reinforcement ratio.

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