Meso-structure Numerical Simulation Analysis Of Concrete Permeability Based On CT Technology

As a heterogeneous complex multiphase material,the flow of concrete is very complex.In order to investigate the fluid seepage law in the concrete,by means of CT faultage technology,digital image processing,statistics,test method,this paper quantitative researches the characteristics of pore structure,analyzes statistical rules of concrete pore structure,and establishes the numerical model of real concrete seepage at the nanoscale and micronscale,which can provide some direction and reference for the study of fluid seepage law in concrete.The main contents of this paper are as follows:(1)Through scanning the concrete specimen by CT,757 CT faultage images are obtained.By analyzing preliminarily,it was found that the scanning images appear insufficient contrast,and have the background that from the center to the edge gradually become bright.Aiming at this problem,the strong contrast images are obtained by using the image processing method of background subtraction.While,this method still can't resolve the problem that aggregates are non-sticky.Thus,the method of image segmentation based on circular partition and region growth is used to segment the aggregates and the morphological operations are used to divide the pores.Then the two-value images of aggregate and the pore are obtained respectively.(2)Based on the 2D images,the 3D pore structure and the mercury intrusion porosimetry,the characteristics of pore structure under the multi-scale concrete are calculated.(1)14 typical faultage images of CT images are selected as the analysis objects.Based on the 2D images,the pores' area in each fault is did statistical analysis and the porosity is calculated.Then,the distribution of the pore area of the concrete is well reflected by the mid-value of pore area which is calculated in the previous step.The frequency of porosity and the cumulative frequency curve indicate that the probability of small porosity is the largest,and the frequency decreases with the increase of porosity.The fractal dimension program is calculated by Matlab box counting method.The Sierpinski triangles are used to verify the reliability of program.The fractal dimension of the concrete pores in each fault is calculated by this program,and the relationship graph between porosity and fractal dimension is drawn.From the relationship graph,it is find that the bigger the porosity is,the larger the fractal dimension is.(2)Using the Mimics software to reconstruct the 3D pore structure of concrete,the porosity of the concrete under 3D state is calculated.Extracting the coordinates of the focal point of the pore center and the coordinates of the furthest point of the pore,the pore diameter is calculated.Then,the density probability function of pore diameter and the pore spacing probability density function are drawed and the targets that the functions reflect are used to characterize the pore structure of concrete.(3)Ultizing the pore structure of the concrete under the nanometer scale which is obtained?The pore size and pore size distribution were analyzed statistically.(3)By using the method of adding pictures,the meso-penetration model of concrete which contains aggregate,mortar and pore are established,and the image type is converted into vector type by using vector software.Importing vectorial data in the finite element analysis software COMSOL Multiphysics,using porous media seepage module,the 2D meso-seepage of concrete is analyzed,pressure-velocity distribution diagram in flow field is exported,and the coefficient of model is calculated.Compared with the results of mercury intrusion test,the rationality of the model and the reliability of the calculation is verified.