[kadoban]

There's already other ways to reinforce concrete, one I know of is embedding kind of fiber-glass mesh in it instead of rebar. I quick google suggests that this might be called Fiber Reinforced Polymer (FRP) reinforcing, or possibly that's a different thing I'm not really an expert.

I assume you could use a whole bunch of different materials really, including other metals that don't rust in the same way as steel does.