Study On The Influence Of Environmental Humidity On The Distribution Of Chloride Ion In Concrete

In service reinforced concrete structure will be affected by the natural environment,the influencing factors are mainly divided into two categories: erosion media and climatic and environmental conditions.Chloride ion is the most dangerous corrosive medium in the environment.Its corrosion accelerates the corrosion speed of the reinforcement in the reinforced concrete,resulting in the destruction of the structure and reducing the durability of the structure.The migration of chloride ions in concrete in atmosphere is mainly affected by climatic and environmental conditions.Water is a necessary condition for chloride ion migration in concrete,and it can carry chloride ion migration in pores,thus affecting the distribution of chloride ion in concrete.Carrying out the law and mechanism of chloride ion migration in concrete under different environmental humidity conditions has certain academic and practical engineering significance for the study of concrete durability.In this paper,the effects of different environmental humidity conditions on the internal humidity,moisture and chloride ion transport in concrete are studied by using the environmental humidity simulator,and the chloride ion transport model in concrete under the alternating action of environmental humidity is established,and the numerical analysis is carried out.The influence of environmental humidity on the microstructure of concrete was analyzed by means of microanalysis.Main conclusions include:(1)The humidity response of concrete has hysteresis,and the closer to the concrete surface,the faster the humidity response;It is also related to the mix ratio,the larger the mix ratio,the faster the humidity response.In the process of concrete drying and wetting,the change rule of humidity diffusion coefficient is inconsistent,and the humidity diffusion coefficient Ddry is obviously less than Dwet.The water diffusivity of drying process is obviously smaller than that of wetting process.In the process of drying,the concentration of chloride ions on the surface of concrete increased to a certain extent,while it decreased obviously when wet,and the concentration of chloride ions in the shallow area(about 1-3mm away from thesurface)increased.The wetting process has a great influence on the distribution of chloride ions in concrete.In the whole process of the experiment,the effect on the binding chloride ion was not significant.(2)In different humidity alternating systems,the longer the wetting time is,the higher the saturation value is after reaching the stable state of alternating humidity,the more favorable it is for the migration of chloride ions in concrete.The greater the concentration of chloride ions on the surface of concrete decreases,and the more obvious the concentration of chloride ions in the shallow area(about 2-4mm from the surface)rises.With the accumulation of moisture in alternating cycle,the influence of chloride ion distribution in concrete is more obvious.(3)With the accumulation of alternating periods of humidity,the c-s-h reticulated gel with good crystallization degree began to decrease,the deterioration of pore structure was obvious,and the overall compactness gradually decreased.When the humidity accumulates to a certain extent alternately,the accumulative aperture and maximum pore diameter gradually increase.(4)COMSOL simulation software was used to establish the transmission model of chloride ions in concrete under alternating ambient humidity.By comparison with the test results,it was found that it had a good correlation.