Fibrous things like fiberglass and carbon fiber get their strength from the length of the fibers distributing force across the assembly. Ground fiberglass is b

Fibrous things like fiberglass and carbon fiber get their strength from the length of the fibers distributing force across the assembly. Ground fiberglass is basically worthless after you account for supply compared to demand. It would be better to cut them up into strips/sheets and use them to build retaining walls or something (using them whole is not practical because they are big enough to make transport expensive). The inertness of fiberglass in the presence of most common things makes it an attractive building material for things that are expose to the weather but it is expensive when new and until now there has never been much supply of used fiberglass in any consistent form factors so it is rarely used and construction techniques are not very mature (read: common enough to be cost competitive). Honestly we can probably just let old turbine blades pile up. If there's one thing the free market is good at it's finding creative uses for expensive materials that are waste products as far as their original use is concerned.