Research On Constitutive Relation And Microstructure On Porous Concrete With Silica Fume

Porous concrete is a kind of concrete with perforated pores.Because of its permeability and permeability,it is called"breathing concrete",which brings good ecological effect to the environment and is one of the important bases for maintaining a benign cycle of ecological environment.It has the characteristics of high porosity and low strength.Adding appropriate amount of silica fume to porous concrete can effectively improve its strength,but the existing research results mainly focus on the macroscopic properties such as compressive strength,flexural strength and frost resistance of porous concrete,and little research on its constitutive relation and microstructure.Therefore,the constitutive relationship and microstructure of silica fume reinforced porous concrete are studied in this paper.With reference to the constitutive model proposed by Zhenhai Professor,and using the nlinfit function in MATLAB software to fit the nonlinear least square method,the constitutive relation of porous concrete mixed with silica fume is fitted.In the microcosmic aspect,the internal microstructure of porous concrete mixed with silica fume is introduced by scanning electron microscope and X ray energy spectrometer.The main results obtained in this paper are as follows:(1)The mix design,preparation process and main physical and mechanical properties of porous concrete are studied.The design porosity of the porous concrete is close to the effective porosity,and the difference of the numerical value is within 1%.It shows that the absolute volume method can effectively control the porosity of the porous concrete.However,the plane porosity is slightly different from the effective porosity.There is a good positive proportional relationship between the effective porosity and the permeability coefficient,but it is basically in inverse proportion to the compressive strength,and the corresponding relation and correlation coefficient are obtained respectively.(2)The constitutive relationship of porous concrete mixed with silica fume is fitted through the uniaxial compression test of 12 groups of porous concrete specimens with 36sizes of 100×100×300mm~3.According to the characteristics of stress strain curve obtained by the test,the constitutive relation of porous concrete containing parameters a and B is proposed,and the constitutive parameters a and B of porous concrete with different design porosity under different silica fume content are obtained.Finally,the fitting results are compared with the test results,and the fitting results are better.(3)The action mechanism of silica fume and the effect on the hydration reaction of cement are further analyzed by observing the microstructure of cement stone and ITZ.It is concluded that when the amount of silica fume is less than 10%,under the silica fume filling effect and the volcanic ash effect,the cracks and pores in the specimen are reduced,and the microstructural density is greatly improved.Because the silica fume can weaken the water film on the surface of coarse aggregate,the thickness of the interface transition zone is thinner.But when the amount of silica fume is more than 10%,excessive silica fume produces clusters,which makes the structure of cement paste uneven and has a bad effect on the strength.