PERFORMANCE OF WEATHERING STEEL IN HIGHWAY BRIDGES
A Third Phase Report

VI. MARINE AND INDUSTRIAL ENVIRONMENTS

Weathering steel appears to be performing satisfactory in marine environments. This finding is based on the study of two bridges included in this survey.

Figures 9 and 10 are illustrations of Bridge #50, located in the southern portion of Louisiana, immediately adjacent to the Gulf of Mexico. This bridge is partially painted due to an early concern for excessive corrosion; the remaining sections of the bridge are unpainted. Both the painted and unpainted portions of this weathering steel construction appear to be performing well. However, an additional investigation is being initiated at this site to quantify the performance of the unpaintedweathering steel, and to compare the performance of the bridge members to test samples at the bridge site. Once completed, this study will provide additional guidance for this type of environmental exposure.

The Antioch River Bridge in California crosses a river that also has a high salt content. Shortly after the 39-span bridge was constructed in 1977, CALTRANS reported "severe" corrosion on some sections of this 8,640 foot long bridge. However, the 1993 inspections did not reveal any evidence of severe corrosion, or any other concerns regarding the performance of weathering steel. It is believed that the corrosion that appeared earlier in several bridge members was a result of direct exposure to sea water spray that occurred during transportation from Japan on the open deck of a cargo ship. No problems have been reported in this structure since the initial concerns emerged.

The FHWA TA recommends the use of "wet candle" equipment in accordance with ASTM Test Method G 92 "Characterization of Atmospheric Test Method Sites," Method B, to determine the suitability of the application of weathering steel in marine environments. An upper limit of 0.5 mg chloried/100 cm2/day, average, is recommended for areas where marine salts may be present in the atmosphere. Unfortunately, this test takes many months to complete. A more practical means of assessing site corrosion potentials, appears to be a "corrosion monitor" developed by the ATLSS Center at Lehigh University.

For bridges that are located in an industrial area and subjected to the effects of air borne sulphur trioxides, an upper limit of 2.1 mg/100 cm2/day (average) is recommended by the FHWA TA for use of weathering steels. None of the bridges inspected as part of this project are in areas with such exposure limits, so an evaluation of this criterion was not possible. However, as a result of the ever-increasing emphasis throughout the United States on clean air standards, it is anticipated that sulphur trioxide levels will rarely, if ever, influence future decisions for using weathering steel in industrial areas.

Figure 10 – LA Route 23 over
Doullut Canal – Built 1975