[abduhl]

As an aside, fiberglass (similar to carbon fiber) is used frequently (but still not much, relative to steel) in many applications. We use it extensively in underground applications.

The problem with fiberglass reinforcement is that it does not undergo ductile failure like steel does. Steel will yield and, in addition, has strain hardening behavior. Fiberglass just fractures and that's that. Extra precautions must be taken when using fiberglass in failure critical members.

[brudgers]

Steel and concrete also have similar moduli of thermal expansion. This means that as the temperature fluctuates, there is minimal internal stress owing to the similar strains.