Experiment And Numerical Simulation Of Chloride Transport In Concrete Under Hydraulic Gradient Reverse Osmosis

The chloride ion in marine environment is the most important factor leading to the corrosion of marine concrete structures.The study on the law of chloride ion transport is one of the hotspots in the durability study of marine concrete structures.Based on the migration mechanism and transmission model of chloride ion in concrete,put forward the active reverse osmosis anti-corrosion technology.In order to verify the feasibility of active reverse osmosis anti-corrosion technology,on the macro level,experiment on one-dimensional reverse osmosis diffusion was carried out to explore the law of chloride ion migration in concrete under different hydraulic gradient reverse osmosis,different time of water pressure action and different surface environments.On the microscopic level,the time-varying law of pore structure parameters of concrete specimens under different hydraulic gradients is explored through mercury injection test,and the spatial difference of pores in concrete under the action of water pressure is analyzed.The influence of reverse seepage on mass transfer capacity of concrete such as seepage structure is analyzed.Further,the mathematical model is proposed.According to macro/micro test parameters(the spatial and temporal distribution of chloride ion in concrete;time-varying law of pore structure parameters)model parameters are proposed.The model is solved by numerical methods and mutually verified with the test results,and the revised mathematical model is used for long-term prediction of chloride ion transport law in concrete.Combined with the principle of seepage in porous media and mass transfer,this paper provides a new idea for anti-corrosion design of concrete structure.The main research works and results are as follows:(1)One-dimensional concrete reverse osmosis diffusion test was carried out through the concrete permeameter.The accelerated test was conducted out the concrete columns with large water cement ratio and chloride salt immersion solution with high concentration,to explore the space-time distribution of chloride ions under different hydraulic gradient reverse osmosis,and to explore the feasibility of this method by comparing it with specimens subjected to free diffusion and dry-wet cycles.The analysis shows that under the action of hydraulic gradient reverse osmosis,the chloride ion in concrete decreases significantly,and the reverse osmosis force gradient increases,the more significantly the chloride ion decreases.(2)Through the mercury injection test,the change law of the pore structure parameter of concrete specimens under different hydraulic gradient and water pressure in different time is researched,and the influence of the pore structure on different location of concrete is further analyzed.Mercury injection test results show that the different hydraulic gradient(pressure)lasted 90 days,most probable aperture and total porosity and critical aperture of the different position of concrete changed are not apparent,it demonstrates that different water pressure in the specimen(length 15 cm)of hydraulic gradient has little effect on pore structure of concrete,and the allowable hydraulic gradient of the test concrete is greater than 600.And after 90 days of seepage under the action of different water pressures,the proportion of each pore level in the same position of concrete is almost equal.Therefore,it can be considered that the distribution of pore structure in concrete is stable,which is also the premise for chloride ion to achieve balance.(3)According to the relation of mass conservation of chloride ion in concrete,the mathematical model of reverse osmosis diffusion test was proposed,and the parameters of the mathematical model were modified according to the data obtained from the the concrete reverse osmosis diffusion test and the pressure mercury test,and the numerical simulation results are compared with the test results.The numerical simulation shows that the numerical simulation is in good agreement with the experimental results,which indicates that the chloride ion transport can be predicted according to the revised mathematical model.Furthermore,according to the parameters and theoretical model related to the properties of concrete,and the steady time and chloride ion concentration of chloride ion movement inside concrete under different water pressure can be predicted.The reasonable value of water seepage pressure can be calculated through this model,which make the concentration of chloride ion in the concrete cover keep a lower value than the critical chloride ion concentration,and thus achieve the effect of the resistance to chloride ion corrosion.