2000 Volume 49 Issue 2 Pages 88-95
Non-painted bridge were weathering steel was built and exposure test panels were installed on it on the highway of the Tohoku mountainous area. Twelve years having passed since then, investigations were made on conditions of rust layers formed on those surfaces.
It was found that rust on the bridge was deep reddish brown in general and protective rust seemed to have been formed steadily but ion properties resistance value was so low as 0.34 kΩ on average. On the other hand, in the investigations of rust layers of exposure test pieces, it was recognized there were almost uniform non-polarizing layers containing condensed Cr and Cu.
But many cracks were found on those rust layers and condensed Cl existed along them. It is supposed this may be the cause which made the ion properties resistance value low.
This Cl was supposedly produced from antifreeze agent spread on the road in winter time, and its mist may have accumulated and penetrated into the rust layers. In the future, it must be studied what effect this Cl will give to formation protective rust.
