| Steel-reinforced concrete(RC)structures served in marine environments or chloride-contaminated environments are facing the risks of deteriorating structurally due to steel reinforcement corrosion,which could have a strong impact on RC structures’safety and usability.The corrosion of steel reinforcements is an electrochemical process,and cathodic protection is the most direct solution as an electrochemical treatement and can stop the corrosion bahaviour essentially,so it has been applied widely around the world.The main idea of cathodic protection is introducing an impressed current or an anode material with more negative potential to make steel reinforcements cathodically polarized and thus protected.Owing to the superior electrically conduction and electrochemical properties,CFRP has become a new group of anodic materials used in the impressed current cathodic protection(ICCP)system.For a corrosion-damaged RC element,it is novel to employ CFRP as a structural strengthener and an anode of an ICCP system.In this way,it is hopeful to improve the load-bearing capacity of RC columns due to CFRP strenghthening,and stop corrosion reactions as well without additional anode material.Funded by Natural Science Foundation of China(No.51578428)“The Mechanics of Cathodic Protection for CFRP Wrapped RC columns”,this paper prepared a conductive adhesive with high strength and superior conductivety using epoxy as matrix and super conductive carbon black as filler,then applied CFRP around the RC columns using the conductive adhesive to achive electrically connection betweetivityn steel reinforcement and CFRP anodes.Based on it,the innovative cathodic protection system was investigated by both non-destructive electrochemical measurements and mechanical tests,and the main works and the results were obtained as follows:(1)Considering the mix amount of carbon black as a variable,the mechanical properties and electrical properties of carbon black/epoxy conductive adhesive were tested.The results showed the incease in the amount of carbon black resulted in decrease of volume resistivity,but also decrease of tensile strength and elongation of conductive adhesive.According to the test results of 153 specimens,the carbon black/epoxy conductive adhesive with good tensile properties and electrical properties was fabricated.Applying the conductive adhesive as the adhesive between CFRP and concrete,a tatal of 33 specimens were fabricated to test the degradation regulation of bond behavior under combined actions of environment conditioning(saline immersion,wet/dry cycling),anodic polarizating(30 m A/m~2、60 m A/m~2、90 m A/m~2).The results showed that along with the increase of aging duration and polarization current density,the failure gradually transferred from debonding at the concrete substrate to the concrete–adhesive interface,and the characteristic values of bond-slip curve(peak shear stress,slip value corresponding to the peak shear stress,fracture energy)also drcreased.The anodic polarization current accerlated the degrations.(2)10 specimens with different initial corrosion levels and different protection methods(non-protection,cathodic protection)were designed to experience saline immersion ageing for120 d.During the ageing,electrochemical noises(EN)were measured periodically.After collecting EN of both potentials and currents of steel reinforcement in concrete matrix,the data was analyzed in time-domain and frequency-domain.The results showed cathodically protected specimen with current density of 30 m A/m~2 exhibited smaller fluctuation ranges and higher noise resistance than control specimen,indicating the effectiveness of cathodic protection in anti-corrosion.In comparison,cathodically protected specimen with current density of 90 m A/m~2 showed adverse results,indicating the current density of 90 m A/m~2 was too large and the steel reinforcement was over protected.Wavelet transform was applied on the time-domain data,and energy distribution plot(EDP)was obtained.The specimens treated with cathodic protection showed higher energy propotion in crystal D1,D2 and D3,which was related to pitting corrosion.With longer time of cathodic protection,the energy percentage of crystal D1,D2 and D3 increased,indicating cathodic protection led the corrosion behavior to be predominated by pitting corrosion.(3)RC columns with different degrees of corrosion(theoretical mass losses of 0,3%,6%and 12%)were prepared and then treated with different protection methods(non-protection,epoxy coating,CFRP strengthening,CFRP strengthening and cathodic protecting)by exposing them to saline imeersion.By measuring the steel potential,linear polarization,and electrochemical impedance spectroscopy(EIS)of all investigated specimens,the efficiency of protection methods in eliminating corrosion had an order of CFRP strengthening and cathodic protecting>CFRP strengthening>epoxy coating.The optimal protection current for specimens with different pre-corrosion degrees were different.The current density of 5m A/m~2 had the best anti-corrosion effect for 3%corroded RC column while the current density of 20 m A/m~2 was the best foor 6%and 12%corroded RC columns.Cathodic protection could improve the charge transfer resistance on steel/concrete surface and also the concrete electrical resistance,indicating cathodic protection can not only improve the corrosion resistance of steel reinforcemnts,but also densify the concrete matrix.(4)A total of 27 specimens were fabricated to investigate the effects of initial corrosion degrees and protection method(non-protection,CFRP strengthening,CFRP strengthening and cathodic protecting)on the axial behavior and eccentric behavior.By measuring and comparing the failure modes,load-longitudinal displacement curves,load-lateral deflection curves,load-strain curves,the following conclusions were drawn:CFRP strengthening and cathodic protecting can transform brittle failure mode to ductile failure mode,significantly improve the deformability of corroded RC columns and show obvious warning before failure.the axial capacity and eccentric capacity increased after CFRP strengthening,while increased further by CFRP strengthening and cathodic protecting simultaneously.The extra increase induced by cathodic protection was more than 10%,and the extra increase closely related to the protection current density.The side effects of the cathodic protection current on adhesives resulted in lower peak deformations and peak strains of cathodic protected and CFRP strengthened specimens than those of CFRP strengthened specimens.But for specimens with higher corrosion level treated with CFRP strengthening and cathodic protecting,the adverse effect on conductive adhesive was offset by the positive effect of cathodic protection,and thus performed much better in deformability. |
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