Experimental Study And Numerical Simulation Of Chloride Ion Diffusion In Concrete

In the strategic development process of China’s “One Belt and One Road” and the development of the western region,the construction of tunnel projects and mine projects in a series of major infrastructure projects under construction is developing in the deep direction,and the problem of high ground temperature is becoming increasingly prominent.The occurrence of high ground temperature not only causes the environmental temperature in the tunnel to rise sharply,which seriously affects the construction safety and the working efficiency of mechanical equipment,and also has a great impact on the support of the tunnel construction process,the stability of the lining structure and the later operational safety.In this high temperature and high heat environment,the durability of concrete structural materials and the service life of engineering structures are also higher.Among them,the erosion of chloride ions is one of the main forms of concrete structure failure.In this paper,the chloride ion diffusion process in intact concrete and concrete structures with cracks is studied,and it is devoted to providing research references for the durability and service life of concrete structures in high temperature environments.In this paper,the effects of water-cement ratio,compressive strength and high temperature on the chloride ion diffusion coefficient of concrete are considered by the combination of laboratory test and numerical simulation.The chloride ion diffusion law of damaged concrete is analyzed and considered.The crack distribution,crack width and crack spacing of the damaged concrete affect the chloride ion diffusion process,and strive to dig deep into the chloride ion diffusion mechanism of concrete.The main research contents of this paper are as follows:(1)Using the electric flux method to test the chloride ion permeability coefficient of concrete,it is found that the chloride ion permeability of concrete decreases with the increase of compressive strength;at a given chloride ion concentration and curing temperature,the chloride ion permeability coefficient of concrete The water-cement ratio increases with increasing water temperature;in a certain temperature range,the temperature rise is beneficial to the chloride ion penetration resistance of concrete;but when the curing temperature is greater than 60 °C,the chloride ion diffusion coefficient of concrete decreases with increasing temperature..(2)Experimental study on artificially prepared cracks by immersion method,using silver nitrate to detect chloride ion penetration depth.In the single-fracture mortar test piece,the diffusion depth of chloride ions increases with the increase of the crack width;the chloride ion diffusion in the 10 mm and 20 mm gap-pitch crack test pieces will have an interaction;the concrete test piece with 20 mm seam spacing The degree of interaction is less than the 10 mm seam spacing.(3)Establish a chloride ion adsorption model and a solid heat transfer constitutive equation model,and couple the two models to calculate the diffusion process of chloride ions in concrete.The temperature of the tunnel lining concrete increases exponentially from the water passing part of the tunnel to the surrounding rock wall.The growth process can be roughly divided into three stages: initial rapid growth,temperature deceleration and temperature balance.After 20 minutes of heat exchange,the temperature of the lining concrete tends to be stable,and the temperature of the concrete from the tunnel to the surrounding rock wall increases linearly with depth.The image describes the diffusion distribution of free chloride ions in the lining concrete at different times.The diffusion of chloride ions in concrete is uneven diffusion.(4)In the direction parallel to the crack,the chloride ion concentration in the crack is significantly larger than the chloride ion concentration in the complete concrete at the same position.The closer the concentration is to the crack,the more obvious the change;the chloride ion concentration decreases in the direction perpendicular to the crack development direction.The greater the distance from the concrete surface,the faster the chloride ion concentration decreases,and the smaller the chloride ion erosion depth.In the crack width calculation range,the chloride ion increases with the increase of the crack width at the same diffusion depth.