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Rebar in concrete is protected against corrosion by a passive film that is stable
due to the high alkalinity of the pore solution. Corrosion may start once the
protective passive film on the rebar surface breaks down (depassivation) due to
the ingress of external ions such as chlorides or processes such as carbonation.
The main goal of this investigation is to characterize the effect of surface
conditions, specifically the presence of mill scale, on chloride-induced
depassivation of rebar in concrete pore solution using electrochemical and
microscopy techniques. To achieve this goal, linear polarization tests were
conducted on black steel rebar with and without mill scale in a special corrosion
cell that is designed to simulate in-service conditions. Both electrochemical and
microscopic observations suggest that enhanced corrosion of as-received rebar in
concrete occurs in crevices at the interface between the underlying steel surface
and the mill scale which are linked to the free surface.