Pore Characteristics Analysis And Seepage Simulation Of Cast-in-situ Frost-resistant Vegetation Concrete

Frost-resistant vegetation concrete is a patented products developed on the basis of the vegetation porous concrete,which solves the problems of low strength,insufficient antifreeze performance,poor planting effect and complex construction technology existing in the engineering application of ordinary vegetation concrete.With the country's vigorous promotion of ecological civilization construction,frost-resistant vegetation concrete is widely used in ecological engineering construction in northern cold regions,organically combining engineering slope protection with green ecology.The complex pore structure in cast-in-situ frost-resistant vegetation concrete directly determines its mechanical properties,durability and planting properties.At present,there are few studies on pore structure characteristics and seepage mechanism of the cast-in-situ frost-resistant vegetation concrete from a meso-scale perspective.Based on the previous research results of the research group,takes the CT sequence images of cast-in-situ frost-resistant vegetation concrete as the research object,the characteristics of two-dimensional plane pores are analyzed,the pore space distribution is analyzed by three-dimensional reconstruction pore meso-scale model,and ignoring the influence of vegetation,the single-phase seepage simulation of the cast-in-place frost resistant vegetation concrete structure is carried out to reveal the seepage mechanism inside the specimens,the main conclusions are as follows:(1)The sequence images of cast-in-situ frost-resistant vegetation concrete are obtained by CT scanning technology,and the two-dimensional plane pore characteristic parameters are extracted and analyzed by ImageJ software using digital image processing technology.The results show that the pore diameter and pore area are distributed in a single peak,which indicates that the pore has good homogeneity and the pore size is relatively uniform;the gap between the long axis and the short axis of the pore is small,the roundness of pores is close to1,the shape of the pore is close to a perfect circle;the difference between the average value of plane porosity and the measured total porosity is small,which shows that the combination ofCT scanning technology and digital image processing is feasible for pore structure analysis;fractal dimension is used to characterize the irregularity and complexity of pore structure,the measured values show that pores have good fractal characteristics;the regression analysis of the relationship between the plane porosity and the fractal dimension shows that the linear fitting effect is better.(2)Based on CT images,three-dimensional visualization software Avizo is used to reconstruct the pore meso model of cast-in-place frost-resistant vegetation concrete,and the pore model was labeled to analyze the pore space distribution characteristics quantitatively.The statistic of pore shape factor distribution shows that the pore shape is mostly circular;the distribution of pore diameter and pore surface area are similar to those of 2D,which shows that the pore distribution results obtained by 3D modeling are consistent with those of 2D quantitative analysis.(3)The equivalent pore network model is constructed to characterize the geometric characteristics and topological structure of pores of cast-in-situ frost-resistant vegetation concrete,through the analysis of pore throat size,it is found that the throat radius and length are normal distribution,which indicates that throat homogeneity is good;the distribution of pore radius is continuous and in a single peak,which indicates that the pore homogeneity is good;the average pore throat ratio is relatively small,indicating that the degree of uniformity of pore throat connection is relatively high;the statistical results of coordination number distribution shows that the connectivity of pore topological structure of cast-in-situ frost-resistant vegetation concrete specimens is good.(4)Based on the constructed real meso-scale model of cast-in-situ frost-resistant vegetation concrete,the single-phase seepage simulation is carried out,the results show that seepage simulation results are in good agreement with the results of physical experiments,which verifies the reliability of the three-dimensional reconstruction model and the feasibility of the single-phase seepage simulation method;along the direction of fluid flow,the pressure on pores gradually decreases,and the maximum pressure appears near the entrance;the seepage path in the middle part of the concrete specimen is relatively complete,and the number of seepage lines is large,which is conducive to water seepage and the relative velocity of fluid is relatively fast.The research results in this paper can accurately describe and evaluate the meso-scale pore characteristics and permeability of the cast-in-place frost-resistant vegetation concrete,provide data support for the popularization and application of cast-in-place frost-resistant vegetation concrete,and better guide the engineering practice.