Experimental Research And Umerical Simulation On Shrinkage Of Concrete

With the development of construction technique, various large-scale structures are appearing. It is well known that restraining the volume change of concrete due to its shrinkage can led to its cracking in over-long concrete structures. Because expansion joints are not set, avoidance of cracking damage due to shrinkage is an important objective in the design of over-long structures. It is necessary to conduct research on shrinkage of concrete. Specific work is as follows.Eleven groups of concrete shrinkage strain are measured. In this paper, the effect of mineral admixtures (fly ash and slag), polypropylene fiber, and UEA expansive agent on the shrinkage is analyzed. It is shown that fly ash, polypropylene fiber and UEA expansive agent can effectively inhibited shrinkage. With the increase of slag proportion,the shrinkage of concrete increases within the range of certain proportion. Specimens are under the nature condition, thus the influence of relative humidity and temperature on shrinkage is very definite.In order to estimate the shrinkage deformation of concrete, various predicting models have been established to predict the shrinkage of concrete. These models are quite different in many aspects and considerations. Common models are briefly introduced and analyzed. The comparison and analysis of these models are carried out with shrinkage experiments. It is shown that CEB-FIP(90), RILEM B3 and GL2000 Model have a better predicting precision than ASRI(86)and Wang tie-meng model. So these models are firstly recommended in case of lack test data.Based on FICK diffusion law and mass conservation law, a theoretical model of concrete moisture field is established. Then mathematical equation based on the finite element method (FEM) is suggested to solve the nonlinear partial differential equations about moisture diffusion. The similarity between moisture field and temperature filed of concrete is applied to digitally solve the moisture filed problems with converted temperature filed. It is shown that this approach is feasible by comparing previous experiments results.The parameter selection during the simulation of the moisture filed is discussed. According to beginning and boundary condition, various factors of influences moisture diffusion are considered. The distribution of humidity field in concrete at variable moisture condition is studied by using FEM. It can be found that the shrinkage humidity gradient is mainly concentrate in the surface. There is a significant difference of moisture diffusion with different region, which affects the progress of shrinkage. Finite element simulation of drying shrinkage is carried out by cooping analysis of moisture and strain filed. The calculated results are in good agreement with the experimental results.