Study On The Effect Of Compressive Stress On Chloride Transport And Corrosion Rate Of Steel Bar In Concrete Under High Water Pressure

With the continuous advancement of the process of urban modernization in China,urban engineering construction is gradually changing from the ground to the underground.The underground engineering needs to serve in the complex environment of high water pressure,high stress and high corrosion for a long time,which is different from the above-ground engineering.Its durability should not be underestimated.Based on this,this thesis studies the transmission of chloride ion in concrete and chloride corrosion of steel bar in underground structure under the coupling action of high water pressure and compressive stress.In this thesis,by using the method of combining experiment with theoretical model,the impermeable instrument is used to simulate the coupling environment of underground high water pressure and pressure stress,the high water pressure permeability test is carried out,and the natural chlorine salt immersion control group is set up.The influencing factors are as follows: water pressure grade(1.2MPa,2.4MPa,3.6MPa),internal compressive stress of concrete(11.4MPa,22.8MPa,34.2MPa),cover thickness(35mm,75 mm,115mm)and infiltration time(1.5d,8.5d,15.5d).The chloride ion concentration at different heights in concrete is measured by direct potential method,and the effect of concrete internal pressure stress on chloride ion transport in reinforced concrete under high water pressure is obtained.based on the reverse osmosis principle,the transport process of chloride ion is theoretically analyzed,and the infiltration theoretical model is established,which is simulated by finite element software.The transport model of chloride ion in plain concrete under high water pressure and the transport model of chloride ion in reinforced concrete under the coupling action of high water pressure and internal pressure and stress in concrete are established.Through the 120-day electrochemical non-destructive testing test of reinforced concrete specimens infiltrated by chloride under the coupling action of high water pressure and compressive stress and natural immersion environment,the polarization curve and electrochemical parameters were measured based on linear polarization method.including corrosion potential,corrosion current density,polarization resistance,corrosion rate,etc.,summarize the time-history variation of chloride corrosion rate of steel bar.The changing rules of deblunt corrosion time and corrosion state of steel bar are obtained.According to the time-varying model of steel bar corrosion rate in the whole process,the time-varying mechanism of steel bar corrosion rate in concrete under high water pressure and high stress chloride environment is analyzed,and the factors of water head pressure,concrete internal pressure stress,infiltration time and cover thickness are taken into account.a time-varying model of chloride corrosion rate of steel bar under the coupling action of high water pressure and compressive stress is established.This thesis makes an in-depth study on the chloride corrosion of steel bars in concrete under the coupling action of high water pressure and internal pressure and stress in concrete,and analyzes the different corrosion phenomena on the back surface and the facing surface,as well as the morphology characteristics of corrosion pits.The corrosion characteristics of chloride corrosion of steel bar under the coupling action of high water pressure and compressive stress are obtained.The corrosion amount per unit length of steel bar is calculated according to the conversion relationship between corrosion current density and corrosion weight.Based on the micro-cell and macro-cell mechanism of steel bar chloride corrosion,the chloride corrosion mechanism of reinforced concrete under the coupling action of high water pressure and concrete internal pressure stress is explored.It is found that the concrete internal pressure stress squeezes the connecting hole and compresses the transmission channel.Hinder the transport of ion,water and oxygen,and delay the deblunt time of steel bar.Finally,combined with the service life principle of reinforced concrete structure,the cracking service life of concrete cover 35 mm under different grades of hydraulic pressure and concrete internal pressure-stress coupling condition is predicted.There are 76 pictures,51 tables and 92 references in this thesis.