This study is aimed at determining the suitability of joining sections of weathering steel guiderail with galvanized fasteners. Concerns included the possibility of an adverse galvanic reaction between the zinc and steel that might either reduce the life of the galvanized coating, or interfere with the development of protective rust on weathering steel, To address these issues, a study was conducted which included atmospheric tests, metallographic examination of galvanized bolts taken from guiderail exposed at eight locations along the Garden State Parkway for up to 15
years, electrochemical measurements of galvanic effects, and Raman analyses of the guiderail rust. Overall, this work indicates that there are few, if any, adverse effects resulting from use of galvanized fasteners with weathering steel. Specifically, it was observed that the iife of a galvanized fastener coating is only slightly reduced by coupling to weathering steel, provided the initial coating is thick enough (50 micrometers or more) to endure a limited, initial period of galvanic attack prior to the development of a protective rust layer on the steel. Long-term tests are underway to confirm this conclusion, Also, discoloration on the surface of weathering steel exposed to drainage from galvanized fasteners decreases with time of exposure. Raman spectroscopy indicates that the discoloration is associated with a surface enrichment in lepidocrocite (y-FeOOH), one of the usual components of weathering steel rust.
Keywords atmospheric, galvanic, guiderail, galvanized, rust, weathering steel