Time-Varying Law Of Chloride Diffusion Coefficient In Concrete Under Electric Field

In the marine environment,the concrete structure caused by chloride ion erosion is out of service in advance,resulting in a lot of waste of manpower,material and financial resources.However,when the structure subjected to chloride ion erosion is sampled and tested,it often causes damage to the structure in service.Therefore,it is necessary to prepare a test block that is consistent with the chloride ion content of the concrete structure in service in the laboratory.Through the detection of the durability of the test block in the laboratory,the durability of the structure can be mastered without destroying the original structure.In this paper,by applying an electric field to the concrete,the chloride ions in the sodium chloride solution are gradually moved into the concrete under the action of the electric field,so as to achieve a test block with the same chloride ion content and trend in the actual environment in a short time.The main research contents of this paper include:(1)Based on the principle of electromigration,chloride ion migration test under electric field was carried out.Firstly,different current densities and different energization times were designed to conduct directional migration of mortar,ordinary concrete and marine concrete in 10%Na Cl solution to obtain the time variation of chloride ion diffusion coefficient.Secondly,the test block was energized for 3 days,15 days and 30 days,and then the cathode radiation zone and anode radiation zone were taken for RCM test to obtain the spatial variation law of chloride ion diffusion coefficient.(2)Based on the backward difference method of MATLAB,the chloride ion diffusion coefficient under different current densities and different charging time under the action of electric field is obtained by the inversion method using the chloride ion content.The results show that under the action of electric field,the chloride ion diffusion coefficient decreases with the increase of electrification time,and the chloride ion diffusion coefficient increases with the increase of electric field strength.Secondly,the curve of chloride ion diffusion coefficient with time is fitted by CF toolbox,and the age coefficient is obtained,and the formula of chloride ion diffusion coefficient with time under different electric field strength is established.(3)The polygonal random aggregate program is compiled by MATLAB and put into COMSOL software to establish a random polygonal aggregate model.By setting the chloride ion diffusion coefficient under different energization time,the chloride ion content in mortar,ordinary concrete and marine concrete is obtained.By comparing the experimental data with the simulation data,it is concluded that the test block with similar chloride ion content distribution in the actual environment can be obtained by applying different electric fields to the concrete.(4)Comparing the actual chloride ion content data and test data of Hangzhou Bay Bridge exposure test station.The results show that the concrete blocks in the atmospheric zone,splash zone and tidal zone can be made by current density of 0.5A/m~2,1A/m~2and 2A/m~2respectively.In this paper,the experimental study of electric field accelerated chloride ion migration can provide a new method for laboratory preparation of similar specimens to the actual environment.