The Creep Model In Early Age Of Sealed Concrete

Abstract:As an important indexes of concrete, creep has long attracted the attention of scholars and engineering. In practical engineering, considering the factor of economy and duration, many concrete structures bear the load earlier, while for steel concrete structures, the core concrete shares the force with the steel when it just beginning to develop strength, therefore, the concrete creep features of these structures which loaded in early age should be stressed. And in the National Natural Science Foundation of China (51278037) funded, this paper studied the early age creep behavior of sealed concrete and established predictive model relevantlyIn order to study the behavior of sealed concrete at early age, this paper combines the theoretical analysis with experiment. To carry out the early age creep test of sealed concrete, the loading age of specimens for testing are1day,3days,7days and28days respectively, and access to creep test curves and the corresponding age of concrete strength values,and to obtain the curve of loading-unloading,there have some specimens on sustained load. The test results showed that:the creep of concrete which at a constant load increases with age load-decreases and the development of strength and degree of hydration are rapid growth in the first and then gradually slow with the increase of age, and the rate of C70is greater than C50In the theoretical analysis, we establish the creep model of core concrete in early age, which is based on the cluster model theory and hydration dynamics theory. The concrete be seen as two-phase mixture of aggregate and cement in Cluster model theory and expresses the creep deformation under load stress of cement paste through Nishihara model or Burgers model which those are come from visco-elastic mechanics; taking into account the effects of humidity on hydration of concrete cement,this paper corrects the theory of hydration dynamics on the basis of the original one and use it to describe the degree of hydration of cement in different age, and then we can get the degree of hydration in different ages which were fitted by the modified model and compared with the experimental data. To describe the creep properties of early age concrete,this paper combines the degree of hydration in different age with rheological models and we can get the parameters through fitting on experimental dataThen, according to the result of test,we can get the values of creep of sealed concrete in different instars which under axial compression loads And we can obtain the creep deformation values of plain concrete under the same conditions with value based on the theory of difference of creep and both the fitted and experimental data are in good agreementFinally, we compare the predict creep strain results which obtained from the model like the core concrete early age creep model, ACI model, B3model, BP2model, CEB-FIP (90) model, CEB-FIP (2010) model and GL2000models to experimental data and do some analysis.