Experimental And Numerical Simulation Of Chloride Diffusion In Polyurethane Coated Concrete

Chloride ion erosion is one of the main reasons affecting the durability of concrete,and the lack of durability is the main reason for the damage of concrete structure.How to protect concrete from chloride ion erosion has become the focus of concrete protection in the future.Chloride ion erosion damage to concrete is a long-term and slow process.At present,scholars mainly study chloride ion erosion through experiments.The test method can truly simulate the eroded environment of concrete,but it also has the characteristics of low efficiency,long test cycle and easy to be disturbed by the outside world.Numerical simulation has the advantages of simple method,high efficiency and the ability to observe the whole process from the micro level.Because polyurethane coating has the characteristics of excellent performance and high cost performance,taking polyurethane coating as an example,this paper studies the durability of concrete under chloride attack by experimental and numerical simulation.The specific research is as follows:(1)The experimental study on chloride ion transmission in coated concrete was carried out.Considering the influence of coating on chloride ion content in different depths of concrete under different soaking time and different soaking solution concentration,the mechanical properties of concrete under different soaking conditions were tested.(2)Based on Fick’s second diffusion law and considering the comprehensive influence of time and other factors,the chloride ion diffusion model in concrete is modified.Then the chloride diffusion model in the coating is established and modified considering the influence of time.Secondly,through the joint simulation of MATLAB and COMSOL multiphysics software,the three-dimensional random aggregate concrete model is established,and the numerical simulation of chloride ion diffusion process is carried out in COMSOL multiphysics.The results show that under the conditions of different concentration solutions and different soaking days,the fitting degree between the simulation results and the test results is high,and the average correlation coefficient is more than 0.97,indicating that the model has strong applicability.(3)Through the analysis of the protective effect of polyurethane coating,it is found that compared with the concrete without coating,the surface brush coating can hinder the diffusion of chloride ions,the coating can effectively reduce the apparent diffusion coefficient of chloride ions in the coated concrete,so as to improve the ability of concrete to resist chloride ion corrosion,and the chloride ion permeability can be reduced by more than 90%.At the same time,the test shows that the diffusion coefficient of chloride ion in polyurethane coated concrete is 2-3 orders of magnitude lower than that in uncoated concrete,but the protective effect of coating also decreases gradually with time.(4)Based on Fick’s second law,considering the influence of coating on the diffusion coefficient of concrete,and combined with the factors such as chloride ion diffusion coefficient,thickness of concrete protective layer and critical concentration of chloride ion,the life prediction model of concrete under coating protection is deduced.By comparing the results calculated by the coated concrete life prediction model and life-365 life model in this paper,through the life prediction of the same example,it is found that the prediction results of this life prediction model and life-365 model are close without coating,but there is a large difference in the predicted life with coating.In the case of coating protection,the service life of concrete structure is increased by more than 10 times.It shows that the coating can effectively reduce the diffusion of chloride ions in concrete,play a positive role in the protection of concrete structures,and greatly improves the service life of concrete structures in marine and other chloride environments.