Meso Seepage Simulation Of Autoclaved Aerated Concrete Block With Lattice Boltzmann Method And Its Application In On-Site Detection

Under the vigorous promotion of the ecological civilization construction and the promotion of energy conservation and environmental protection policies,more and more environmentally-friendly building materials have entered the public’s vision,in which aerated concrete blocks have been widely used in construction projects.Aerated concrete blocks are often used in wall masonry of building engineering due to its light weight,good fire resistance,sound insulation,convenient construction and other advantages.According to the previous investigation,it was found that the problems of the aerated concrete block wall leakage caused by the quality of the aerated concrete block,the construction process and the supporting masonry mortar,which were prominent in the actual application process.The phenomenon has become one of the important issues affecting people’s livelihood.Aerated concrete block is a kind of complex porous media material.The impermeability of aerated concrete block wall has a close relationship with its internal pore structure.Aerated concrete block has complex pore structure and the complex connectivity of internal pore channels because of the large porosity.Thus the pore structure and seepage law inside the aerated concrete block based on the mesoscopic level have not been studied.Therefore,this paper combines some of the research team’s research results that participated in the postgraduate study,the article analyzes the internal pore structure characteristic parameters of aerated concrete blocks and masonry mortars based on the meso level.Then it introduces the concept of fractal dimension using the self-programmed MATLAB program.The fractal dimension values of the aerated concrete block internal pore structure are automatically calculated to characterize the complexity of the pore structure.The image processing software was used to realize the aerated concrete block parameter characterization and masonry mortar pore structure slice images.The relationships between the pore structure fractal dimension and the pore structure characteristic parameters were studied.The three-dimensional numerical model seepage simulation of aerated concrete blocks was carried out by the Lattice Boltzmann Method(LBM),in order to give the seepage law inside the aerated concrete block from the meso level.And it can help people to understand the macroscopic aerated concrete block.The internal seepage phenomenon and the macroscopic permeability of the aerated concrete block wall can be realized.It can provide a theoretical basis for testing the permeability of aerated concrete block walls.At the same time,it can combine with analysis of the aerated concrete block’s meso-structure seepage simulation and the aerated concrete block wall’s anti-seepage performance testing instrument developed by the research group,the portable aerated concrete block wall impermeability performance evaluation interface software used in the supporting instrument was developed to quickly determine the aerated concrete building.In the future,the evaluation correction coefficients of theoretical analysis and field tests can be integrated into the interface software of the evaluation of the impermeability of aerated concrete block walls.The impermeability grade of the block wall is used to achieve the purpose of closely combining the research of the subject with the actual engineering application.The main research contents and results of this paper are as follows:(1)Study on the pore structure characteristic parameter inside the aerated concrete block:The pore structure inside the aerated concrete block has obvious fractal features.The aerated concrete block is measured by the third-party toolbox Fraclab in the MATLAB software based on the box-counting dimension method.The fractal dimension of the pore structure images are between 1.775-1.805.The fractal dimension of the aerated concrete block images’ pore structure has a certain relationship with the porosity,pore shape factor,pore surface area and pore size distribution.The pore structural feature parameters of the aerated concrete slice images can be used to predict by the fractal dimension.(2)Study on the pore structure characteristic parameters of different masonry mortars:Through the statistics and analysis of the pore size distribution inside the ordinary masonry mortar samples and the special masonry mortar samples,it can be found that the internal pore structure continuity of the ordinary masonry mortar samples has poor continuity compared with the special masonry mortar samples.The internal pore structure of the masonry mortar sample is one of the main reasons for the new wall impermeability.In the case where the type of masonry mortar is not compulsory currently,it is recommended to use a special masonry mortar to improve the impermeability of the wall.(3)Three-dimensional numerical model seepage simulation of aerated concrete block:The three-dimensional seepage simulation of the aerated concrete block is realized based on the LBM method.The cross-sectional dimensions are 100×100(pixels),200×200(pixels),300×300.(Pixel)CT slice overlay,three-dimensional reconstruction MATLAB program combined with Palabos library program for seepage simulation of three-dimensional numerical model of aerated concrete block.The results show that the three-dimensional reconstruction model in the process of seepage simulation comparing the instantaneous seepage motion cross-sections of the middle and middle parts,it can be seen that the intermediate seepage part forms an obvious "preferred seepage channel";the average seepage velocity of the three-dimensional reconstruction model of the three pixel sizes is the same as the permeability change trend,which is consistent with Darcy’s law,the numerical model permeability ranged from 0.367 to 0.654(lattice units).There was no large fluctuation and the main reason is that the permeability is a property of the porous dielectric material itself,only related to the internal structure of the material.Compared with the two-dimensional seepage simulation of the aerated concrete block before the research team,it can show the three-dimensional dominant seepage channel and study the pore water seepage inside aerated concrete blocks(4)The interface software for evaluating the impermeability of aerated concrete block walls was developed:Based on the structural parameters of aerated concrete block pores and simulation analysis of seepage and in combination with the wall impermeability test instrument developed by the research team,the aerated concrete block was developed through the data measured by the on-site wall impermeability test.The wall anti-seepage performance evaluation interface software can quickly and accurately return the wall anti-seepage performance evaluation level when the project site aerated concrete block wall is tested,which lays a foundation for realizing its engineering inspection application.