Study On Ion Transport And Performance Degradation In Concrete Under Strong Corrosive Environment

There are large area of salt lakes and saline-alkali land in China,especially in the northwest.The durability of concrete structures in these areas has been seriously threatened for a long time.Sulfate erosion is the main reason for the decline of durability of concrete structures in these areas.The ion transport into the interior of the concrete,a series of physical and chemical changes occur in the concrete,causing cracking of the concrete,and the mechanical properties and durability of the concrete are seriously damaged.Concrete sulfate attack damage is affected by many factors.Its own performance and external environmental factors are the main factors affecting the resistance of concrete to sulfate attack.For different influencing factors,domestic and foreign scholars have carried out a series of experiments and theoretical studies,but different test environment and test methods have different results,and different with actual erosion.Therefore,the field test is carried out in this paper,and the indoor simulation field test and the control group test are conducted to study the concrete sulfate attack under different factors.Influences of performance and ion transport,and the establishment of concrete ion transport model and damage model under different factors provide an important theoretical basis for concrete sulfate erosion.The main research contents and results of this paper are as follows:?1?Investigating corrosive environments investigation on some typical areas of Lake Tema Lake passing through the Geku Railway before conducting indoor and outdoor tests.The concrete structure in this area is seriously eroded,and the soil and lake water in the area are tested for sulfate concentration.It is found that the soil and lake water in this area are rich in high concentration of sulfate,which is extremely corrosive.Therefore,it is of great significance to carry out research on concrete sulfate erosion in the background of this project.?2?In order to reduce the difference between the corrosive environment of the indoor test and the actual corrosive environment at the site,the indoor test design has two kinds of erosion environments.First,the saline soil is retrieved in the Tema Lake and the concrete specimen is buried in the salt.Erosion in the soil and adding a certain concentration of the etching solution.During the test,it is found that the etching solution will evaporate periodically,and the period is two months.Therefore,the Na₂SO₄ solution with a concentration of 3%is added in a period of once every two months;In a constant temperature and humidity environment,the concrete specimens were fully immersed in 3%Na₂SO₄ solution,and the erosion solution was replaced at a cycle of Once a month.The indoor test results were compared with the field test results,and the concrete specimens were buried.It is feasible to add an erosion solution to the saline soil for erosion test.?3?This paper studied the effects of different water-to-binder ratios,different mineral admixtures,different erosion systems,different curing time and different test piece sizes on the performance degradation of concrete subjected to sulfate attack.Under different factors,concrete is eroded.There are certain differences in the deterioration law Under different factors,Reduces the Water to glue ratio and addition of fly ash can improve the sulfate resistance of concrete.The Water to glue ratio ratio mainly changes the compactness of concrete,and the mineral admixture replaces the cementitious material.The dual role of filling concrete pores,curing time mainly affects the degree of cement hydration and the formation of concrete internal structure.The test piece size is different,the specific surface area is different,the contact area of concrete test piece per unit volume and erosion environment is different,the erosion rate of concrete sulfate is different.?4?The concentration of sulfate ion at different depths in concrete subjected to sulfate attack under different influencing factors was titrated by barium sulfate gravimetric method.The ion transport and diffusion laws of concrete specimens subjected to sulfate attack were basically the same under different factors.However,the influencing factors are different,the ion transport diffusion rate in concrete is different,and the faster the ion transport diffusion speed,the faster the concrete performance deteriorates.?5?Based on the theory of damage mechanics and Fick's second law,combined with the experimental results of this study,the ion diffusion model and concrete damage model of concrete subjected to sulfate corrosion are presented,and the field test and laboratory test are compared and analyzed.Concrete provides a more accurate model for the performance degradation process during sulfate corrosion.?6?Comprehensive comparison and analysis of the effects of water to glue ratio,external admixture,erosion system,conservation time and test piece size on compressive strength,elastic Modulus,mass change and ion transport diffusion law of concrete subjected to sulfate attack The lower water to glue ratio,the concrete exhibits good resistance to sulfate attack;the fly ash and ore fines can refine the pore structure of the concrete,and the incorporation of the mineral powder improves the early corrosion resistance of the concrete,but with the age of erosion the increase of the period,the mineral powder is not conducive to the resistance of concrete to sulfate attack.During the age of erosion,the concrete mixed with fly ash shows good corrosion resistance;when the curing time is too short,it suffers from sulfate attack,and the concrete is difficultthe to reached design strength,and the performance degradation rate is faster.the specimen size smaller,the specific surface area is large,the larger of contact area between the unit volume concrete and the corrosive environment,and the faster the erosion rate;it can be found from the above research results that in the corrosion under the same environment,reducing the transmission and diffusion rate of aggressive ions inside the concrete is the most effective measures of concrete.