Weathering steel has been widely used in many structures for its good corrosion resistance in unpainted condition, because a dense and tight rust layer naturally formed on the surface exhibits corrosion protectiveness It is, however, known that such a protective rust layer can not be created in the case of usage at seaside area. Thus, a Ca-Ni added weathering steel developed for applications to unpainted steel structures within the coastal area. Two types of outdoor exposure tests were carried out to evaluate its corrosion resistance; one is an ordinary exposure test and another is a sheltered exposure test. The results of these tests show that the amounts of corrosion loss are greater in the case of sheltered exposure tests than for ordinary exposure tests. Furthermore, the difference in the extents of corrosion in two types exposure tests is enhanced, as the amounts of chloride in the atmosphere increased. Larger extents of chloride ions are detected in the samples corroded in the sheltered condition than those in the ordinary test. It was found that Ca-Ni added weathering steel has a better corrosion resistance in such a severe environment, probably because alloying elements such as Ca, Ni contributed to prohibit the penetration of chloride ions to the interface between metal and rust layer.
