It’s no one’s fault—for 70 years the state of the art, the best science and the real world experience with zinc was clear—the more zinc on the metal, the longer the corrosion resistance. Most documents go farther and state unequivocally that the relationship is linear—double the zinc and double the life of the material before red rust. Nothing has been available to mitigate or change the rule; until InterCoat®ChemGuard there was no alternative. You could add a bit of life to the galvanized metal with chemtreats and other passivations, but in general you were stuck with simply increased zinc coating weights to gain more corrosion protection.
So to protect manufacturers, to assure end users, to standardize on some reasonable level of uniform conditions, specifications were required. This way the effort is gone; no guessing about what to use where—at least there are standard expectations, standard requirements and standard specs to guide everyone. And there really was no alternative. A spec was not only a guideline, more like an industry minimum, a tiny insurance policy that seemed to mathematically predict an expected life for galvanized product.
If the assumptions are no longer valid, if the linear relationship has been superceded by new technology, the specifiers will have to rethink, recalibrate and write new specs. At a minimum the easiest fix is “or equivalent” as a two word amendment that would cover new discoveries, like InterCoat®ChemGuard. I suppose “unless exceeded dramatically by another form of galvanize” is a bit too much to ask, as realistic as it is. And accurate.
Current specifications will need to be reexamined and rewritten, (think guardrails at G235 and above now only needing G30). If the focus shifts from zinc coating weight to life expectancy of the product, this seems a natural step.
No need to specify more zinc than is required.