Study On Low Cycle Fatigue Properties Of Hydrogen Containing Steel Bars After Electrochemical Repair

The coastal reinforced concrete structure is exposed to the harsh high chloride environment,and the structure is facing serious durability problems.The corrosion of steel bars caused by chloride ion corrosion and the cracking of concrete along the steel bars caused by rust expansion products eventually lead to the failure of the structure in advance.The electrochemical repair technology uses the electric field to remove the chloride ions near the reinforcement and in the concrete protective layer,so as to restore the durability of the structure.However,when the electrochemical parameters are not selected properly,the chemical physical reaction in the process of electrification will lead to the decrease of the bond force between the steel and concrete and the hydrogen embrittlement of the steel bars,which will lead to the deterioration of the mechanical properties and service performance of the whole component.Among them,the hydrogen embrittlement of steel bars will lead to serious degradation of mechanical properties of steel bars,which seriously restricts the application and development of electrochemical repair technology in concrete structures.Through the electrochemical hydrogen charging test,static tensile test and low cycle fatigue test,the paper analyzes the key mechanical indexes such as fatigue life,hysteretic curve,residual strength and energy consumption capacity of the hydrogen containing steel bars after the electrochemical repair,and constructs the hysteretic steel constitutive model of the hydrogen containing steel bars.The main research work is as follows:1)Under different electrochemical parameters,the low cycle fatigue properties of the steel bars after electrochemical repair were analyzed.The results show that the longer the power on time and the higher the current density,the more hydrogen content in the reinforcement,the faster the residual strength degradation,and the more significant the reduction of fatigue life and energy consumption capacity.When the hydrogen content is less than 1.7ppm,the fatigue life is reduced by less than 15%;when the hydrogen content is 4.3ppm,the fatigue life is reduced by about 74%.The results show that there is reversible hydrogen in the steel bar.With the time passing,the hydrogen content in the steel bar decreases,and the fatigue performance recovers to a certain extent.At the same time,the research results can provide a reference for the application of electrochemical repair technology in concrete structures with seismic performance requirements.2)The low-cycle fatigue test was carried out on the hydrogen-containing steel bars after electrochemical repair under different loading amplitudes.The test results showed that with the increase of the loading amplitude,the hysteresis loop area of the steel bar specimen and the peak value of positive load increased.However,the fatigue life of the steel bar specimens is continuously decreasing,and the two have a linear relationship;the loading amplitude is from 1%to 2%,and the fatigue life of the electrochemical group steel bar specimens is reduced from 5%to 54%compared to the blank group.The decrease in capacity is from 8.5%to 51.5%,indicating that the greater the loading amplitude,the more significant the fatigue performance reduction of hydrogen-containing steel bars.3)Considering the effect of hydrogen content on the low-cycle fatigue performance of steel bars and the effect of electrochemical parameters on the effect of electrochemical dechlorination,it is concluded that ELE-3-5(3A/m~2,5d)is the optimal electrochemical parameter group.At the same time,the Reinforcing Steel hysteresis constitutive model of hydrogen-containing steel bars under this energization parameter was constructed,and three fatigue parameters were obtained:_fC=0.136、_dC=0.361 and?=0.410.Comparing the simulation results with the test results,it is found that at low amplitudes,the fatigue life simulation and softening characteristics of the steel bar specimens still have the possibility of further improvement;at high amplitudes,the simulation results are in good agreement with the test results;The simulation result of the pressure peak is almost the same as the test result.The constitutive model laid the foundation for the subsequent finite element simulation of the structure.