Research On Meso-pore Structure And Clogging Laws Of Ceramic Permeable Pavement Brick

The construction of permeable road by utilizing permeable pavement materials plays an important role in the construction of sponge city.However,permeable pavement materials often have clogging problems in the practical applications,which adversely affect their functions and service life.The essence of the clogging problem is that the clogging substances enter the pores of the permeable pavement materials,which reduces the connectivity of pores and the permeability coefficient of permeable pavement materials.Therefore,the analysis of the meso-pore structure of permeable pavement materials is an important basis for the study of its clogging laws.By reading domestic and foreign literature,it is found that the existing researches on the meso-pore structure and clogging laws of permeable pavement materials are mostly based on permeable asphalt mixture and permeable concrete,while there are few studies on ceramic permeable pavement brick composed of waste ceramic particles.In addition,the raw materials and production process of ceramic permeable pavement brick are different from other permeable pavement materials,which makes that the meso-pore structure and clogging laws of ceramic permeable pavement brick are different from those of other permeable pavement materials.Therefore,it is of great significance to study the meso-pore structure and clogging laws of ceramic permeable pavement brick,and the research results can promote its application in the construction of sponge city.In this study,the meso-pore structure and clogging laws of ceramic permeable pavement brick were studied by XCT scanning experiment,image processing and analysis,permeability experiment,clogging experiment and seepage calculation.The main conclusions obtained are as follows:(1)The two-dimensional and three-dimensional characteristics of the pores in the upper structure and the lower structure of the cylindrical specimen of ceramic permeable pavement brick were analyzed.As for the analysis of the two-dimensional characteristics of the pores,it was found that the porosity and the two-dimensional fractal of the pores of the upper structure of the cylindrical specimen were larger than those of the lower structure.As for the analysis of the three-dimensional characteristics of the pores,it could be seen that the equivalent diameter of the connected pores of the upper structure and the lower structure of the cylindrical specimen were larger than that of the isolated pores.The three-dimensional shape factor of the isolated pores in the upper structure and the lower structure was larger than that of the connected pores,which indicated that the three-dimensional shape of the isolated pores was more regular.(2)Based on the test device,the penetrating experiment and the clogging experiment of brick were carried out.The results showed that the permeability coefficient of ceramic permeable pavement brick during the clogging process gradually decreased with the increase of the clogging time.The process of the decreasing of permeability coefficient could be divided into the rapid decreasing stage,the slow decreasing stage and the stable stage.The normalized clogging experiment results could be better fitted with an exponential function.After the clogging experiment,the mass analysis and the particle size analysis of the clogging particles staying at different locations were carried out,and it was found that the mass of the particles deposited on the surface of specimen accounted for the largest proportion.For the particles entering the specimen,the proportion of the particles which could be washed reversely out from the specimen was relatively small.For different clogged specimens,the characteristics of particle size distribution of the clogging particles deposited on the surface were similar.The characteristics of particle size distribution of the clogging particles washed reversely out from the specimen and the clogging particles entering the specimen were also similar.Moreover,the proportion of particles with a particle size of 0.005 to 0.075 mm was the largest,and the proportion of particles with a particle size of 1 to 2 mm was the smallest.(3)A calculation model with appropriate size was taken out from the upper structure and the lower structure of the cylindrical specimen,and the seepage calculation was carried out using Avizo software.It could be seen that although the internal connective pore-structure was same for the same seepage calculation model,the number distribution of streamlines was difference when the fluid flowed in different main flow directions under the same pressure condition,because there was a "dominant path phenomenon" in the process of flowing.In addition,when the fluid flowed in the connective pores of the seepage calculation model,the location where the flow velocity was largest mainly occurred at the location of the pore throat.(4)The research also analyzed the relationship between the permeability coefficient and the characteristic parameters of the pore-structure.It was found that for the upper structure and the lower structure of the cylindrical specimen,the permeability coefficient was positively correlated with the effective porosity and the connectivity index,and negatively correlated with the tortuosity.But the scatter diagrams were relatively scattered,because the permeability coefficient was affected by many characteristic parameters of the pore-structure.