Experiment And Analysis Of Nano-silica Fume To Improve The Corrosion Resistance Of Reinforced Concrete Against Chloride Salts

The concrete pile foundation and other concrete structures in the coastal environment are corroded by chloride salts and lead to corrosion of internal steel bars,which is the main reason for the lack of structural durability.Incorporation of different types of mineral admixtures can improve the resistance of concrete to chloride erosion to varying degrees.As a nano material,nano SiO₂has extremely high activity and pozzolanic effect,which is conducive to the solidification of chloride ions by the concrete protective layer;it has a very small particle size,so it has a good filling effect and effectively reduces the porosity of concrete.In this paper,through the electrochemical test method,the corrosion test of reinforced concrete with different amounts of nano SiO₂in the chloride ion attack solution was carried out,and the effects of different amounts of nano SiO₂on the reinforced concrete in the chloride salt environment were analyzed.The influence law and micro-mechanism of low durability,the main research content and results are as follows:(1)Make six groups of mortar mechanic test blocks with nano SiO₂content of 0%,2%,2.5%,3%,3.5%and 4%,and perform the bending strength and compressive strength of the mortar test blocks during curing Test to analyze the effect of different amounts of nano SiO₂on the mechanical properties of concrete.The results show that nano SiO₂can effectively increase the flexural strength and compressive strength of concrete in the early stage of curing.However,when the proportion of nano SiO₂is greater than 2%,the mechanical properties of concrete are decreasing with the increase of the amount of nano SiO₂trend.(2)Designed and manufactured a pure paste-reinforced steel specimen with nano SiO₂content of 0%,1%,2%,3%and 4%,using Tafel polarization method and electrochemical impedance spectroscopy method,The open circuit potential,corrosion current density,interface charge transfer resistance and other data of the pure paste-reinforcement specimens with different amounts of nano SiO₂were analyzed.The pure paste-reinforcing steel specimens with nano SiO₂content of 0%?4%were immersed in 1mol/L sodium chloride solution to reach the corrosion state for 240d and 300d respectively.360d,360d,270d.The test results show that adding appropriate amount of nano SiO₂can improve the resistance of concrete to erosion of chloride salts,and the degree of improvement is 3%nano SiO₂?2%nano SiO₂>1%nano SiO₂>4%nano SiO₂.(3)Design six groups of mortar-reinforced steel specimens with nano SiO₂content of 0%,2%,2.5%,3%,3.5%and 4%,and also use Tafel polarization method and electrochemical impedance spectroscopy test Methods:The effect of 2%?4%nano SiO₂on the resistance of reinforced concrete to chloride salt corrosion was analyzed.The results show that the 3%content of nano SiO₂can improve the performance of concrete specimens in the chloride salt environment against chloride ion corrosion.(3)The change rules of porosity,C-S-H gel,Ca/Si and phase composition of each test piece were analyzed by saturated water-dry weighing,SEM/EDS,XRD and other test methods.The porosity test results show that with the incorporation of nano SiO₂,the porosity of the protective layer of the clear slurry has decreased significantly,and the porosity of each specimen has a trend of increasing first and then decreasing with the development of the corrosion process..The analysis of various results can be concluded that the addition of nano SiO₂can effectively reduce the porosity of the concrete protective layer,but the change of the total porosity does not play a major role in improving the resistance of the concrete to chloride salt corrosion;at the same time,an appropriate amount of nano SiO₂The incorporation can increase the formation of C-S-H gel in the cement paste,thereby increasing the cement paste's ability to cure chloride ions,but the incorporation of excess nano SiO₂will make the protective layer of the paste The content of Ca(OH)₂,C-S-H gel and the ratio of calcium to silicon all decreased significantly.