Investigation of Protective Rust Formation on Unpainted Steel Bridge Girders and Exposure Test Panels of Weathering Steels after 12-Year-Construction

摘要

Twelve years after it was built on a highway in the mountainous Tohoku area, an unpainted weathering steel bridge and the exposure panels installed on it were studied in order to determine the condition of the rust layers on their surfaces. The rust on the bridge was deep reddish brown, and protective rust seemed to have formed steadily, but the resistance of the ion properties was, on average, as low as 0.34 k#OMEGA#. The rust layers on the exposure test panels, in contrast, were almost uniformly non-polarizing and contained condensed Cr and Cu. The many cracks in the rust layers were lined by condensed Cl, and presumably this was what lowered the resistance of the ion properties. The Cl was produced from de-icing agents spread on the roadway in the wintertime; its mist must have accumulated and penetrated into the rust layers. Studies of the effect of Cl on the formation of protective rust are needed.