Hidetoshi NIWA
Study on Relationship between Rust of Weathering Steel and Corrosion Factor in the Outdoor Environment
Eiji IWASAKI, Masatsugu NAGAI
Under the globalization and financial situation in recent years, it is a time to construct bridge not only in domestic but also aboard. It is necessary to maintain enough global competitive power, and one of the most important index is cost. The reduction of life cycle cost (LCC) that contains the cost of maintenance such as painting cost becomes essential condition when steel bridges are constructed. The weathering steel is able to reduce painting cost that increases LCC.
The weathering steel restrains corrosion by generating protective rust on the surface of the steel. Generating of this protective rust is strongly affected by marine salt. The following condition of unpainted weathering steel should be satisfied: maximum amount of marine salts density is less than 0. 05mdd (mg/dm2/day). Moreover, it is known that the estimation amount of plate thickness reduced after 50 years is 0.3mm or less in such a corrosion environment. The corrosion is not same at the actual bridge, and a state of corrosion is different in the part of bridge. However, it is difficult to evaluation for the quantity of marine salt flow into the girder before built the bridge and reduced plate thickness. A system that can estimate marine salt and reduced plate thickness before built the bridge contribute to familiarize the bridge using weathering steel. Accordingly, for the actual bridge using weathering steel, relationship between the quantity of corrosion by measuring corrosion factor such as rust thick and marine salt, adhering salt are discussed.
The results are as follows.
・The marine salt changes by observation time, however the change tends to be similar by a measurement part. Therefore, I seem to be able to express the marine salt of a partial part of the bridge from the marine salt at the remote spot from the actual bridge.
・The monthly average of wind velocity from the excellence direction of the wind and the monthly marine salt are correlative.
・Rust thick of one year exposed test piece is proportional to adhering salt of the piece that is inner surface of girder.
・Rust thick of one year exposed test piece is proportional to yearly averaged airborne salt.
・So that there is correlation between a rust thick and plate thickness, I seem to be able to predict plate thickness by measuring rust thick.
・There is different from the size of the rust thick every part of the actual bridge and the one year exposed piece. It is necessary that test piece is exposed a few years.
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