Hot Dip Galvanizing for structural washers is no longer a long-term solution due to long declines in service and quality. Many DOTs/FHWA/Owners will reject an entire lot if only a few washers are found with holidays or sticking issues. Recent lots have seen a large increase in the % of parts that are usable making the risks to suppliers for rejection higher.
Another specification ASTM F959 (DTI Washers) specifies "galvanized" is specified, the DTIs shall be zinc coated by the mechanical deposition process or thermal diffusion process. Other coatings are to be used only when approved by the manufacturer.
A task group has been formed to come up with language that would allow for more conducive quality zinc coatings that would not inhibit performance ie thermal diffusion as a substitute for hot dip galvanizing.
Mechanical Galvanzing has shown no real issues with quality or availability.