Durability Study Of Concrete Corroded By Chloride Ion In Saline Soil

In Western China,the natural environment is harsh,the climate is dry and less rain,the evaporation is large,and there is a vast saline alkali land.The chloride content in the saline alkali land is very high,and the chloride ion diffuses to the reinforcement surface inside the concrete,resulting in the destruction of the passive film on the reinforcement surface,leading to the corrosion of the reinforcement,which seriously affects the service life of the concrete structure engineering.Therefore,it is of great significance to study the diffusion law of chloride ion in concrete under saline alkali environment to improve the durability of concrete engineering.In view of the Durability Status of concrete highway bridges in the typical saline alkali soil of northwest agricultural irrigation area,many field investigations were carried out.According to the results of many investigations,the chloride ion erosion test of concrete in multi-dimensional space is carried out by using the saline alkali water in the saline alkali soil environment of the investigated area,and the influence of carbonation on the chloride ion diffusion of concrete in saline alkali water is considered.The one-dimensional,two-dimensional and three-dimensional diffusion laws of chloride ion are analyzed respectively.Finally,the chloride diffusion equations of different dimensions derived from Fick’s second law are used to fit the test data,and the durability service life of concrete structure is predicted by combining with the finite element software.The main research contents are as follows:(1)The typical saline alkali land in agricultural irrigation district in Northwest China is selected as the field investigation point to investigate the formation reasons,geological soil conditions,main ion components in saline alkali land and the Durability Status of concrete highway bridges in saline alkali land.The research results show that: the main reason for the formation of saline alkali land in northwest agricultural irrigation area is that the agricultural irrigation uses flood irrigation,the groundwater gradually converges in low-lying flat area,resulting in the groundwater level is raised too high,and the soil salinization occurs after the surface water evaporates;the concrete highway bridge in saline alkali land has been in service for less than 10 years In the case of a,the cement paste on the concrete surface at the contact part of pier column and saline alkali soil has peeled off,resulting in a large amount of aggregate exposure;the chloride ion content of concrete at the junction part of pier column and ground is higher,and with the increase of the height from the ground,the influence of chloride ion in saline alkali soil on the upper structure of bridge gradually decreases;the chloride ion content of soil in saline alkali surface layer is the largest,and the chloride ion content in soil is higher With the deepening of soil depth,the content of chloride ions in the drainage ditch water of saline alkali soil decreased first and then stabilized;the content of chloride ions in the drainage ditch water of saline alkali soil was much higher than that of other harmful ions,and showed a certain seasonal pattern,and the ion content and p H value of saline alkali water in winter and spring were higher than those in summer and autumn;according to the "Code for Durability Design of Concrete Structures of Highway Engineering"(JTG/T 3310-2019),and the environmental conditions are very serious.(2)According to the results of field investigation,the full immersion test of concrete blocks with different dimensions in the salt alkali water environment is conducted to study the erosion mechanism of chloride ions on one-dimensional,two-dimensional and three-dimensional concrete.The results show that the chloride content and chloride diffusion coefficient in concrete increase with the increase of concrete mix ratio;with the increase of diffusion depth,the chloride content shows no difference The trend of breaking down is that when the soaking time of salt alkali water is the same,the erosion degree of three-dimensional concrete is the most serious,followed by two-dimensional,the content of chloride in one-dimensional concrete is the smallest,among which,the content of chloride ions in three-dimensional diffusion can reach 1.59 times and 1.26 times of two-dimensional and one-dimensional diffusion respectively,and the chloride ion content of two-dimensional concrete is the most serious The height is 1.32 times of one dimension,so the influence of dimension on concrete durability cannot be ignored.The actual engineering should be analyzed according to the specific dimension.(3)Through the experiment of chloride ion erosion concrete under the coupling effect of carbonation and saline alkali water environment,the influence of carbonation on chloride ion erosion concrete in saline alkali water under multi-dimensional was studied.The results show that carbonation can accelerate chloride ion diffusion in saline alkali water,and the chloride ion content in one-dimensional,two-dimensional and three-dimensional concrete increased by34.2%,22.9% and 27.5% respectively after accelerated carbonation.(4)Based on the analytical solutions of one-dimensional,two-dimensional and three-dimensional chloride ion diffusion equations derived from Fick’s second law,combined with the finite element software COMSOL multiphysics,the durability of one-dimensional,two-dimensional and three-dimensional concrete structures in saline alkali environment is analyzed.The analysis shows that the service life of concrete pier,pile cap and pile foundation is about 58 years,72 years and 92 years respectively.