A Study on Correction Method of Exposure Time in Exposure Examination of Weathering Steel

In recent years, public investment in Japan is reduced, and low-cost and durable structures are used intensively. The number of bridge using unpainted weathering steel has been increasing. Weathering steel generates a precise protection rust on the surface, and controls invasion of corrosion factors. Thus, by using the weathering steel, it is possible to omit the painting. It is important to use weathering steel in consideration of environmental conditions of a construction site. At the moment, local exposure examination is known as one method to evaluate the application of weathering steel. In case of local exposure of 30 µm or less in the amount of corrosion for one year, application of weathering steel is possible in area of Japan. However, in the short-term exposure examination, there is no index for exposure time, and the influence of observed time is not considered.

The purpose of this study is to clarify the influence of the observed time at which a piece of weathering steel is installed in a weathering steel exposure examination. And, we aimed to correct the effect of the observed time. Specifically, we investigated by shifting the starting time of airborne salt investigation, and an exposure examination for several months.

From the results, the relations between the change of the amount of corrosion and other corrosion factors and exposure time were considered. Moreover, the relation of each corrosion factor in the corrosion environment of a researched bridge was grasped. And the correction method for the influence of exposure time on the exposure examination by exposure time is proposed. From wind speed of AMeDAS station, correction method for the effects were examined. As a result, it was possible from the value of the wind speed, to represents the tendency of the effects of installation time.