Effects Of Light-transmitting Aggregates And Pores On Light Transmission In Cement-based Materials

Photocatalytic cement-based materials have bright application prospects in the fields of environment and civil engineering,especially the internal doping method has become the main preparation method for such materials due to its excellent photocatalytic durability.However,the lack of knowledge of light transmission in cement-based materials leads to the lack of theoretical guidance for the incorporation of photocatalysts,resulting in low photocatalytic performance or waste of resources.In this paper,the problem of light transport in cement-based materials is studied,and the "three-step method" is used to systematically study the light transport of cement-based materials for light-transmitting aggregates and pores that have a great influence on light transport: In the first step,the light quantity inside the cement-based material is measured experimentally,and the optical parameters are calculated to provide input parameters for simulation and theoretical calculations;The second step is to control the number of pores and light-transmitting aggregates,and build a three-dimensional cement-based structural model.Combined with the optical parameters of the first step,Monte Carlo is used to simulate the light quantity distribution inside the cement-based material.The third step is to couple and modify the transport theories suitable for different optical properties,establish a composite transport equation suitable for cement-based materials,and solve it with the help of the PDE module of COMSOL.The absorption coefficient and scattering coefficient of ordinary Portland cement under the irradiation of 403 nm light were calculated to be 19.36 /cm and 85.27 /cm,respectively using the integrating sphere technique and inverse doubling adding algorithm.And the optical parameters of white cement were calculated to be 1.33 /cm and 217.00 /cm respectively.The radial distribution of light intensity at a specific depth was obtained by means of CCD device and image processing technology.The radial distribution of light intensity at a specific depth was obtained by means of CCD device and image processing technology.It is found that with the increase of the content of light-transmitting aggregate,the total number of radial distributions increases and the slope decreases along the direction of increasing radius,which means that with the increase of aggregate content,the light quantity at the same depth increases and the distribution is more uniform.In the simulation process,a three-dimensional cement-based structural model was built,and the Monte Carlo algorithm was run on the basis of the structural model to obtain the threedimensional distribution of light quantity in the cement-based material.By comparing the simulation results of the same structure,it is found that the mean deviation is 0.0012,and the correlation coefficient is 0.999937.Compared with the experimental data,the axial distribution error is 8.43%,the radial distribution deviation is 0.0372,and the correlation coefficient is0.997133.When the aggregate particle size is small,changing the particle size will not have a greater impact on the light quantity distribution,while larger particle size will affect the light quantity distribution in the middle and deep regions.When the content of aggregate or porosity is small,the light quantity distribution near the source will decrease and the light quantity in the deep will increase with the increase of aggregate content.When the content or porosity exceeds the threshold,the change will significantly affect the distribution of light quantity.In the study of cement matrix material and porosity or light-transmitting aggregate in this paper,the threshold exists between 70% and 80%,which is not related to the specific size of the optical parameters of the cement matrix.In the process of theoretical calculation and simulation,the diffuse approximation equation and the energy transfer equation are simply coupled with the help of boundary conditions,and the composite transport equation is obtained.When the amount of aggregate is small and the influence between aggregates is weak,the mean deviation of the calculation result of the composite equation is reduced from 0.0306 to 0.0116,and the correlation coefficient is also increased from 0.994641 to 0.997819.In view of the more complex situation,the PDE module of COMSOL is used to analyze it,and the influence of point light source and surface light source on the internal light quantity of cement-based materials is studied respectively.The lighttransmitting aggregate not only improves the light transport in the area where the aggregate is located,but also affects the light quantity distribution in the area around the aggregate.Under the same volume fraction,more small aggregates have better improvement effect than less large aggregates.If the power of the incident light source is constant,the axial distribution of the light quantity does not change with the spot size of the incident beam,while the radial distribution becomes more uniform as the spot increases...