In order to acquire the critical chloride ion concentration for the break-down of passivation film in the initial carbonization environment of concrete.According to the basic principle of electrochemi-cal reaction,the anodic polarization characteristics of rebar steel HRB400 in a simulated initial carbon-ized concrete solution were studied by means of open-circuit potential-and anode polarization curve-measurement.Results showed that there was a linear relationship between the breakdown potential and the chloride ion concentration in logarithmic plots,and the rationality of passivation potential and tranpas-sivation potential as the key parameters of the breakdown potential was analyzed.Based on this,the up-per limit[Cl-]u and lower limit[Cl-],of critical chloride ion concentration for rebar steel HRB400 are ob-tained.Accordingly,the relationship between pH value and chloride concentration of pitting corrosion sen-sitivity of the rebar steel was drawn.The service status of rebar steel HRB400 in the pH range of 12.5-11.0 is evaluated,and the expressions of the upper limit[Cl-]u and lower limit[Cl-],of the critical chloride ion concentration and pH value are given.
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