Watashi, I think you're right that only time will tell about the maintenance costs, how those affect cost-of-ownership/lifecycle costs, and how long the bridges made of this stuff will last. Or, for that matter, the pontoons, docks and other structures made of carbon composites. OTOH, it's good to remember that this material is now being used on spacecraft going to Jupiter, space is an extremely hostile environment, and there aren't any repair robots onboard.
However, they may have a good story as far as whole lifecycle cost if their products can last longer with much less maintenance. But only time will tell. Structural plastics in this application are too new to realy know for sure.
Doc K, you'd have to ask the company for customer data. In my experience, manufacturers aren't very forthcoming with that type of info. In addition, because it's plastics, cost comparisons vary widely, being highly dependent on a specific implementation.
Chuck, thanks for the clarification and for pointing out the different sub- and super-structure meanings. As I understood it, the only composites are in the bridge deck and sidewalk. I used the term "substructure" as shorthand to mean everything underneath.
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