A mill scale may form on the steel surface during hot rolling process,which exhibits a cer-tain degree of anti-corrosion effect.When a large number of steel bars are used in a construction project,most of them may be naturally exposed to atmosphere for a long time,and thus the mill scale will turn in-to a loose and porous yellow-brown rust scale due to atmospheric corrosion.In order to understand the nature of the passivation behavior of pre-corroded steel rebars with mill scale during the concrete curing process,the electrochemical behavior of HRB400 rebars with mill scale before(bare bar)and after being atmospherically pre-corroded for 3 months(pre-corroded bar)was comparatively assessed in simulated concrete pore solution by means of open-circuit potential measurement,electrochemical impedance spec-troscopy,dynamic potential polarization curve,Mott-Schottky curve and XPS.The results show that the type of rebars can be completely passivated in the simulated concrete pore solution,whilst their surface all reached stability within 5 d.But the passivation effect and corrosion resistance of pre-corroded rebars are slightly worse than those of the bare rebars.The changes in surface composition of the two kind re-bars before and after passivation are mainly due to the significant decrease in Fe(Ⅱ)oxides,while signifi-cant increase in Fe(Ⅲ)oxides and hydroxyl oxides,and the excellent passivation effect and corrosion re-sistance of the bare rebars compared with the pre-corroded rebars are due to the lower Fe(Ⅱ)oxide con-tent and higher Fe(Ⅲ)compound content after passivation.
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