Study On The Effect Of Chloride Ions On The Corrosion Behavior Of Reinforing Steel And Corrosion Inhibitors

The corrosion of reinforcing steel is the main reason for the premature degradation of reinforced concrete structures,and has been a major disaster in modern society.Whether or not the reinforcing steel in concrete maintains its passivity depends on the physical and chemical conditions at the steel/concrete interface. Carbonation of concrete and ingress of chloride ions are the major reasons which cause the corrosion of reinforcing steel.So far,many investigations have been carried out to study the corrosion and protection of reinforcing steel in concrete,however, there are still a lot of controversy.In the present work,research methods including electrochemical measurements and surface analysis techniques were utilized to study the corrosion inhibitors and the effect of external conditions on corrosion behavior of reinforcing steel.The progress of this work and the main results are as follows:(1) The linear polarization,electrochemical impedance spectroscopy and XPS were used to study the corrosion inhibition of N-lauroyl sarcosine sodium and its mixture containing L-histidine and sodium molybdate for reinforcing steel in simulated concrete pore solutions with chloride ions,and the inhibition mechanism of N-lauroyl sarcosine sodium was primarily analyzed.The results showed that the concentration of 100 mg/L N-lauroyl sarcosine sodium had a best inhibition effect on reinforcing steel in the simulated concrete pore solution with 0.6 mol/L NaCl,its inhibition mechanism may be that the adsorptive and protective film was formed on reinforcing steel surface by the oxygen and nitrogen atoms.The mixed-type inhibitor had a better inhibiting efficiency than the single inhibitor.The admixture of N-lauroyl sarcosine sodium,L-histidine and sodium molybdate had the best inhibiting effect with the concentration of 100mg/L,300mg/L and 500mg/L respectively.(2) The effect of nitrite and chloride ions on the corrosion behavior of reinforcing steel in simulated concrete pore solutions with different pH was studied. The results showed that the corrosion resistance of reinforcing steel is related with the pH of the solution,nitrite ion concentrations and chloride ion concentrations.The drop of pH and the increase of chloride ion concentration would result in the decline of corrosion resistance of reinforcing steel in the solution.The corrosion rate of reinforcing steel decreased with the NO₂^- concentration increasing in the simulated concrete pore solutions with Cl^-.The same result was obtained by electrochemical measurements and SEM technique,the NO₂^- ions have a good inhibiting effect on the steel when the concentration ratio of NO₂^- and Cl^- was 0.4 or higher for the solution pH of 12.50 or 10.50.(3) The method of in-situ measurement of the corrosion parameters for reinforcing steel in concrete by electrochemical and probe techniques has been tentatively established.The results showed that the Cl^- and pH probes can effectively track and monitor Cl^- concentrations and pH values in concrete,respectively.When the concentration of Cl^- added into concrete exceeded 2%(relative to the mass of cement),the corrosion rate of reinforcing steel increased and its corrosion resistance lowered.The reinforced concrete was immerged in a 3.5%NaCl solution,in the early stage,Cl^- concentration at the steel/concrete interface rose sharply,followed by a slow increase,pH value firstly decrease,then increased,and finally had a decreasing trend. After immersion for14 days,the polarization resistance of reinforcing steel decreased and the corrosion rate increased.