The Numerical Simulation Of Concrete Compressive Strength Based On The Test Of The Initial Imperfection

As a quasi-brittle material,it has the initial imperfection in concrete before under the loading,such as microcrack patterns and pores.the existence of the initial microcracks has a great influence on the mechanical properties and failure of the concrete.At present,In order to study the effect of concrete initial imperfection on the strength of concrete,the academics are always based on numerical simulations,and The structural parameters of the initial imperfection in the numerical model are always based on the qualitative hypothesis.Therefore,this paper establishes the concrete numerical model based on the structure parameters of initial imperfection which are got from microstructure test.The main work and conclusions are as follows:(1)The concrete test scheme and mix ratio is determined.The concrete mix ratio is determined based on the slump of mixing property and the strength of concrete,studied the effects of water-cement ratio and aggregate type on the initial defects and strength of concrete.The initial imperfection test mainly includes two parts: the vacuum-epoxy-impregnation method and the digital-Image-processing(DIP)technique.(2)The test studies the concrete micro-structure,and the initial defect distribution of concrete is analyzed quantitatively.Quantitative analysis of concrete initial defect by the digital-Image-processing technique obtaining the microcrack characteristics(such as area,legth,width,etc)of the initial microcrack of concrete.The results show : with the decrease of water-cement ratio,the percentage of the area of the initial microcrack in the concrete interface in the total area of the initial microcreck in the concrete and the average width of the initial microcracks decrease,and the total area and total length of the initial microcracks increase.(3)The influence of initial defects on the strength of concrete is analyzed.The relationship between initial defects and concrete strength is analyzed by the micro-structure test of concrete and the macroscopic strength test: With the decrease of the average width,the pore content,the percentage of the area of the initial microcrack in the concrete interface in the total area of the initial microcreck in the concrete,total defect content,the compressive strength and the tensile strength of the concrete show an increasing trend.Obtained by analysis,the mechanical properties of the interface have a great influence on the mechanical properties of concrete.(4)A numerical model of concrete consisting of coarse aggregates,mortar,ITZ and initial defects is established.We simulate the uniaxial compression test,and make a comparison between the simulation results and the macroscopic experiments results.The results show: the mesoscopic numerical model can simulate the compression strength of concrete and the failure process well.(5)The influence of aggregate content on the strength of concrete is analyzed by the model has been established.The different numerical model with 40%,35% and 25% of coarse aggregate volume was used to simulate the uniaxial compressive strength of concrete.The simulation results show :the maximum compressive strength of the numerical model on the volume of coarse aggregate is 35%.