1452 Weathering Characteristics

Used in an engineering context, a material with good weathering characteristics is one that has an improved resistance to physical breakdown and chemical alteration over time when subjected to normal atmospheric conditions. For steel bridges, corrosion of the load carrying members is a primary cause of structural deterioration. The service life of a bridge can be prolonged if a more corrosion resistant material is used and a more vigorous maintenance program is followed. When compared to conventional high-strength steels, HPS have slightly better corrosion resistance. Corrosion tests conducted in accordance with ASTM G101 have indicated that the atmospheric corrosion resistance index (CI) calculated using the equation

CI = 1.20(%Cr)+ 26.01(%Cu) + 3.88(%Ni) + 17.28(%P) + 1.49(%Si)

is 6.5 for HPS70W steel, as compared to a CI of 6.0 for conventional Grade 70W high-strength steel. A CI of 6.5 means HPS70W possesses the chemical compositions to be classified as a high-performance weathering steel. A bridge designer has the discretion of using HPS70W in an unpainted condition.

The elimination of painting in selected areas may help reduce the life-cycle maintenance cost of the bridge.

Like conventional steels, HPS can also be painted. The paint can act as a protective coat and serve as a barrier to retard atmospheric corrosion. In exposed areas or when used in unpainted conditions, the same guidelines and detailing practice as outlined for conventional weathering grade steels (FHWA 1989) should be followed to assure the successful application and durability of HPS.

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