Metro Stray Current Corrosion Properties Of Steel And The Service Behavior Research

To alleviate the increasingly heavy pressure on urban traffic,subway has been widely used in most cities in China because of the advantages of rapid,large passenger traffic,environmental protection and saving the land resources.It's inevitable that subway stray current will be produced as the subway running.It will lead to a strong electric field around the subway track structure,forcing the chloride ion migrate to the subway reinforced concrete surface rapidly,and it will cause more serious steel corrosion.It will seriously reduce the subway service life.In order to solve the actual problem,this paper based on the national natural science foundation of the underground reinforced concrete interface multi-scale study of corrosion fatigue damage and failure mechanism(51478183),studying the subway electrochemical corrosion of steel in reinforced concrete properties,corrosion mechanics characteristics of interface corrosion features and the service behavior research.The main work and results of the paper are as follows:(1)Simulation experiments were carried out to study the corrosion current density,polarization curve,the influence of polarization resistance and electrochemical corrosion performance characteristics under the influence of intensity of stray current and chloride ion concentration and mixed mineral admixture.The results shows that corrosion time,strength of stray current and chloride ion concentration are the main factors affecting the reinforcement corrosion in reinforced concrete members in subway environment.As the duration of corrosion,stray current and chloride ion increase,the steel corrosion current density measurements also gradually increase,and chloride ion is having a similar effect,but small influence extent than stray current intensity.When the strength of stray current is 40 V,corrosion current density of 57.136 ?A/cm2.In the chloride ion concentration was 5%,the corrosion current density of 49.16 6 ?A/cm2.And the polarization curve and polarization resistance had a similar regularity.And mixed mineral admixture concrete can effectively improve the underground reinforced concrete corrosion resistance,reduce the degree of corrosion,delay the corrosion process.Such as in strength of stray current of 10 v,20 and 40 v,120 v,30 v,mixed mineral admixture of concrete steel corrosion current density within the MAC than ordinary concrete NC was reduced by 20.41%,23.14%,26.37% and 24.93% respectively.(2)Conduct the experiments of Metro stray current corrosion of reinforcement in concrete experiments and corroded reinforced the tense mechanical properties,according to the test results of mechanical property obtaines damage equation.The results show that: with the increasing of strength of the stray current,chloride ion concentration and time,stray current corrosion will cause serious point corrosion phenomenon,leading to the degeneration of elastic modulus,yield strength and degeneration of mechanical properties such as tensile strength,and the higher strength of stray current,chloride ion concentration corrosion time,the more serious corrosion to occur in the steel.steel yield strength,tensile strength,elastic modulus and so on mechanical properties of injury is more serious.When the stray current intensity for maximum 40 V,highest yield strength attenuation rate reached 16.23%.And mixed mineral admixture can reduce the mechanical behavior of corroded reinforced damage.When the stray current of 10 V,20 V,30V and 40 V,mixed mineral admixture of concrete tensile strength attenuation within the MAC compared with ordinary concrete NC was reduced by 20.41%,23.14%,26.37% and 24.93% respectively.Mechanical damage and reinforced the quantitative relation between the stress and strain relations established for subsequent metro stray current corrosion damage of steel research provides the experimental basis and theoretical support.(3)Using a stered microscope observation and X ray diffraction(XRD)observes the corrosion specimen cross section to study the chemical composition in the concrete interface.The results show that the original section gradually evolved into a bar at the interface of reinforced concrete,corrosion products and corrosion of concrete mixing layer.According to elastic mechanics knowledge and deformation compatibility equations,establishes a metro subway the corrosive force of steel time-varying regularity,For the subway protective layer cracking of concrete structures to forecast and assessment of durability..(4)Based on corrosive cracking process of reinforcement corrosion caused by analysis of the concrete cover completely the corrosive cracking of rebar corrosion depth is divided into two parts to calculate;On the basis of the assumption of uniform corrosion,using the theory of elasticity and Faraday's corrosion law calculate the formula of the corrosive cracking time of concrete cover.On the one hand,ignore the influence of the corrosion product on the interface deformation in order to simplify the analysis;On the other hand,consider the corrosive cracking of concrete cover corrosion products into the cracks in the process.And combine the characteristics of the accelerated corrosion and the natural corrosion to the appropriate optimization.Application again early determination of electrochemical parameters of reinforced concrete specimen subway environment,deep underground concrete cover cracking moment rule.