Numerical Simulation Of Chloride Diffusion In Concrete Considering Load Effect

In the marine environment,the load will accelerate the diffusion of chloride ions in the concrete and promote the corrosion of the steel bars inside,which will eventually lead to the decline or even damage of the concrete structure.The problem of diffusion of chloride ions in concrete under load has become a hot spot in the study of durability of concrete structures.How to consider the effect of load on chloride ion corrosion in concrete is the difficulty in studying the above problems.The diffusion of chloride ions in concrete is a natural and long-term process.At present,the methods for studying the diffusion of chloride ions in concrete are mainly composed of physical tests and numerical simulations.The physical test implementation period is long,the labor,material and financial resources are large,and the research efficiency is relatively low.Compared with physical experiments,it is an efficient and fast research method to study the effect of load on the diffusion behavior of chloride ions in concrete by numerical simulation.In this paper,by establishing the quantitative relationship between the volumetric strain,porosity and other parameters of the concrete under the load and the internal chloride ion diffusion coefficient,a macroscopic and mesoscopic numerical simulation method for the diffusion of chloride ions in the loaded concrete is proposed,and different load levels are calculated.The concentration distribution of chloride ion diffusion in the numerical model of concrete.Based on Fick’s second law,a prediction model of chloride ion diffusion in concrete considering the influence of load is established to further predict the durability service life of the loaded concrete structure.The main research contents of this paper are as follows:(1)The load will cause changes in the microstructure of the concrete.When the load level is low(that is,the concrete structure is not cracked),it can be considered that the load mainly causes the volumetric strain and porosity of the concrete to change,affecting the internal chloride ion.Diffusion characteristics.In this paper,the quantitative relationship between the volumetric strain,porosity and other parameters of the unexpanded concrete under the load and the chloride ion diffusion coefficient is established,which lays a foundation for the numerical simulation of chloride ion diffusion in the loaded concrete.(2)At the macro level,the concrete can be generalized into a uniform and isotropic medium.According to the quantitative relationship between external load,porosity and chloride diffusion coefficient,the concrete is proposed under external load.A macroscopic numerical simulation method for chloride ion diffusion.By establishing a three-dimensional macroscopic numerical model of the loaded concrete beam in COMSOL Multiphysics,the multiphysics coupling algorithm and the numerical simulation method of chloride ion diffusion in the loaded concrete are combined to calculate the concrete beam in the macroscopic model under different load levels.The concentration value of chloride ion diffusion.The correctness of the results of the macroscopic numerical simulation was verified by physical test data.(3)From a mesoscopic level,concrete can be considered as a composite material composed of a three-phase medium composed of cement base,aggregate and interface transition zone.Based on the external load,the quantitative relationship between the porosity of each constituent phase in the concrete and its internal chloride diffusion coefficient,a mesoscopic numerical simulation method for the diffusion of chloride ions in concrete under external load is proposed.Based on the stochastic generation and random placement algorithm of three-dimensional spherical coarse aggregate,a threedimensional three-dimensional mesoscopic numerical model of the loaded concrete beam is established in COMSOL Multiphysics.Finally,the chloride ion in the mesomodel of concrete beam under different load levels is calculated.The concentration value of the diffusion.The mesoscopic numerical simulation calculated values agree well with the experimental measured values,which verifies the correctness of the mesoscopic numerical simulation evaluation method.(4)According to the concentration distribution of chloride ion diffusion in the concrete numerical model of concrete beam under different load levels,combined with Fick’s second law,the prediction model of chloride ion diffusion in concrete considering the influence of load is established.On this basis,the durability service life of the concrete structure is predicted under different load levels,different critical chloride ion concentrations and different concrete protective layer thicknesses.