Concrete Modulus Of Elasticity Prediction Based On Nanoindentation Technology And Homogenization Theory

Concrete material is consisted of aggregate,cement matrix,interfacial transition zone and pore in mesoscale level.Considering that in practical engineering applications,the mechanical properties and component ratios of each phase will vary with time and environmental conditions.Meanwhile,because of the heterogeneity of concrete meso-structure,it is difficult to evaluate the durability of concrete structures by only studying its macroscopic mechanical properties.As a result,scholars all over the world are increasingly enthusiastic about the research on meso-and macroscale mechanical properties of concrete materials.In this context,the paper analyzes degradation mechanism of concrete material under freeze-thaw cycles,and focuses on the effect of pores on mechanical properties evaluation.At the same time,the mechanical properties of concrete with different freeze-thaw cycles are analyzed by nanoindentation technique.The main work in this thesis are as follows:1.The indentation tests are carried out on the aggregate,matrix and interface with the different indentation grids respectively.Using Gauss mixed model to process the experimental data,the modulus of elasticity of each component is obtained.The results show that the modulus of elasticity of aggregate varies little,and the modulus of elasticity of matrix and interface decreases greatly with the increase of freeze-thaw cycles.2.A prediction cell model of concrete with low-degradation aggregates and pores is proposed,and aggregates and pores are generated with the random locations using Monte Carlo method and abidirectional walk method.3.The influences of pores and the mechanical properties of each component on the macroscopic mechanical behavior of concrete are considered under the effect of freeze-thaw cycles.Based on asymptotic homogenization theory,the periodic boundary conditions are applied on the cell model,and the obtained results are compared the results of Abaqus software simulation.It turns out that the effective modulus of elasticity degrades obviously with the increase of freezing and thawing cycles.Neglecting the pores effect have a great impact on the results.The theoretical calculation results are in good agreement with these of Abaqus simulation.In conclude,this paper summarizes the multiscale method for studying the mechanical properties of concrete,proposes a cell model of concrete with pores and carries out the mesoscopic experiment and homogenization method simulation.New ideas and methods for analyzing the aging mechanism of concrete under the freeze-thaw cycles are provided in this work.