Study On Transport Behavior Of Chloride In Concrete Cracks

The corrosion of steel bars caused by chloride ingress is one of the most important reasons for the destruction of concrete structures.The concrete structures usually serve with cracks,and the cracks provide rapid transport channels for chloride,which will affect the service life of the concrete structures.In theory,the transport process of chloride in concrete cracks is mainly affected by the crack morphology and the solution composition in the crack.Therefore,this thesis studied the effect of crack morphology and crack solution composition on the chloride transport process in the crack,and simulated the chloride ion transport process in the crack based on Fick's second law.The main conclusions of this thesis are as follows:(1)The crack width has a great influence on the chloride diffusion coefficient of straight cracks.When all the conditions were the same,the chloride diffusion coefficient in the crack increased with the increase of crack width.When the crack width was lower than 317 ?m,the chloride ion diffusion coefficient increased rapidly as the crack width increased;when the crack width was higher than 317 ?m,the chloride diffusion coefficient in the crack also increased with the crack width,but the increase rate slowed down.(2)When the crack width were the same,the chloride ion diffusion coefficient in the crack gradually increased with higher concentration of Na Cl solution.There is little difference between the ion composition in artificial seawater and real seawater,but the solution composition had little effect on the chloride diffusion coefficient in straight cracks.(3)The material for the crack wall had a little influence on chloride diffusion coefficient in cracks.There is a slight difference between the chloride diffusion coefficients in the straight cement paste cracks and Plexiglass cracks.When the crack width was smaller than 300 ?m,the chloride diffusion coefficient in the paste cracks was slightly lower than that in the Plexiglass cracks;when the crack was higher than 300 ?m,the chloride diffusion coefficients in two types of cracks were almost the same.(4)When the crack width was smaller than 150 ?m,,the diffusion coefficient of chloride ions in real concrete cracks increased as the crack width increased,and when the crack width was higher than 150 ?m,the diffusion coefficient of chloride ions in real cracks tended to be stable.Provided with the similar crack width,the diffusion coefficient of chloride ion in C30 crack was the lowest,C50 was the moderate,C80 was the highest.This is because that: the tortuosity of the concrete cracks of the C30 specimens was the highest,the tortuosity of the concrete cracks of the C80 specimen was the smallest,and the tortuosity of the cracks of the C50 specimen was somewhere in between.(5)The results of the numerical study showed that the crack width had no effect on the chloride diffusion coefficient in straight cracks without considering the effect of convection.Crack width has an effect on the diffusion of chloride ions in broken-line cracks.If keeping the crack tortuosity constant,the chloride ion diffusion coefficient increased with the increased crack width.If the crack width was kept the same,the higher the tortuosity of the broken-line crack,the smaller the chloride diffusion coefficient.By comparing the experimental and numerical results on the chloride diffusion coefficients in straight cracks,the effect of convection on the chloride transport in crack was deduced.When the crack width was smaller than 100 ?m,the effect of convention was is minor;when the crack width was higher than 100 ?m,the impact of convection was gradually increasing as the crack width increased.When numerical simulating chloride ion transport in real concrete cracks,broken-line cracks can better characterize real cracks,and the numerical simulation results taking consideration of the effect of convection were in good agreement with the experimental results.