Numerical Simulation Research On The Microstructure Heterogeneity And Transmission Performance Of Cement Paste

At present,our country is vigorously carrying out marine strategies,and more and more marine projects are being put into construction.However,the harsh marine service conditions make the reinforced concrete structures in marine engineering face serious durability problems,the chloride ion from seawater leading to the corrosion of reinforced steel which seriously affects the service life of reinforced concrete.The macro-mechanical behavior and durability of cement-based materials are closely related to their micro-scale characteristics.In the durability research of cement-based materials,the influence of pore structure on permeability has always been the focus of in-depth research carried out by scientists at present.However,the existing test methods can only describe the common variables of pore macroscopic parameters,and can't reveal the deeper distribution of pore structure at the micro level.Therefore,a method for characterizing the pore structure of cement-based materials is proposed by useing fractal theory,and on this basis,a finite element calculation model for the three-dimensional reconstruction of cement paste is established.It is found that the spatial distribution of the internal pore-solid structure of cement-based materials has a certain influence on the chloride ion diffusion coefficient.Finally,based on the multifractal theory,the change law of the heterogeneity of cement-based materials is discussed.Based on the study of the full text,the following main conclusions are obtained:(1)Through the MIP experiment,it is concluded that the most suitable fractal type in cement-based materials is solid phase volume fractal,which satisfies the relationship:??d^(3-D_SM).The solid mass fractal parameters of the pore structure of the cement paste with different conditions are obtained by the method of linear fitting.Simulate the iterative generation of the corresponding pore-solid structure model.The results show that the pore size distribution of the model can reproduce the experimental results of MIP very well.(2)The imidazole cationic corrosion inhibitor has excellent corrosion resistance in simulated concrete pore solution.Based on the solid phase volume fractal theory,a finite element calculation model for the chloride ion diffusion coefficient of cement-based materials is established.Using MATLAB program to reconstruct the three-dimensional structure of cement paste,and each voxel(with a size of 1?m)is considered as a separate fractal and conforms the solid-phase volume fractal model.According to the general diffusion equation of ion transport in porous media,comprehensively considering the steric hindrance effect and preferential path effect in the actual ion transport process,the effective chloride ion diffusion coefficient calculation model of each element is given.Comparison of finite element simulation and experimental results show that the spatial distribution of the internal pore-solid structure of cement-based materials has a certain influence on the chloride ion diffusion coefficient,but in general,the chloride ion diffusion coefficient of cement paste can be predicted more accurately.Comparison of finite element simulation and experimental results show that the spatial distribution of the internal pore-solid structure of cement-based materials has a certain influence on the chloride ion diffusion coefficient,but in general,the chloride ion diffusion coefficient of cement paste can be predicted more accurately.(3)The multifractal properties of cement paste are investigated based on two local measures of relative density and relative porosity.The changes of ln?(q,?)and ln(?)of the two show a good linear relationship,which satisfies the necessary premise of multifractal analysis;The results show that the multifractal spectrum f(?)and the generalized dimension Dq calculated based on the relative density are very close to the Euclidean geometric dimension 3,and do not converge within the given value range of q.Therefore,we suggest that multifractals are not suitable for describing the distribution of relative density.Compared with the relative density,the multifractal spectrum f(?)calculated by the relative porosity and the generalized dimension Dq have more obvious differences,which are well distinguished from the Euclidean geometric dimension,and convergent.The multifractal spectrum width??can quantitatively characterize the degree of clustering of the internal structure distribution of cement-based materials,Heterogeneit,i.e.In summary,based on the theory of fractal and multifractal,a quantitative characterization method suitable for cement-based materials,which can accurately describe the heterogeneity of the pore structure of cement paste is proposed.Therefore,it is meaningful for exploring the relationship between chloride ion diffusion coefficient and pore structure of cement-based materials.