In the construction of the weathering steel bridges, it is important to accurately evaluate the environmental characteristics of the local region. It is well-known that the salt accumulation affects corrosion of the weathering steels, because the protective rust layer is difficult to be generated under the high salinity condition. In order to evaluate the corrosion durability for the bridge, the precipitation rate of air-borne salt is investigated monthly for a year prior to construction of bridge. However, climate change makes it difficult for engineer to evaluate the corrosion durability for the weathering steel bridges over 100 years. In this study, the authors focused on the relations between the precipitation rate of air-borne salt and the wind-force energy coefficient. We discuss the estimation feasibility of corrosive environment considering climate change by means of these relations developed in this study.
The purpose of this research is to enhance secureness of weathering steel bridges by preparing contingency plan. So far risk based designing and maintenance system including a computerized corrosion prediction method , visual as well as instrumental rust monitoring methods, etc. has been developed. As the third stage of this project, additional contingency tools and agents were developed for repair painting of anomalously rusted parts. Unlike organic or inorganic materials, weathering steels do not deteriorate internally. Thus life time of weathering steel bridges can be prolonged to a large extent without difficulties, since handling of risk based maintenance system for weathering steel structures has become much easier than ever.
The existing rust with heavy amounts of salinity or anti-freezing agents on the weathering steel bridge surface can lead to serious durability issues. In the event that the anticorrosion functions of weathering steel bridges do not perform satisfactorily, it is necessary to eliminate the cause or to consider the repair coating and the life extension process. In order to achieve the expected life of the repair coating, it is important to perform the correct surface treatment, appropriate surface preparation (near-white blast cleaning, ISO standard Sa2 1/2 equivalent), and the certain removal of rust containing salinity (50 mg/m2 or below). This study provides state-of-the-art techniques on repair method, which is two repair coating methods and one simple repair method for weathering steel bridges. In 2015, some repair methods, with considerable effectiveness, were carried out to actual weathering steel bridges with undesired rust generation. The investigation of three years after repair coating shows that both repair coating film is confirmed to exhibit good corrosion resistance. The weathering steel surface repaired by simple repair method is also in a good state.
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