So, I found a bug/dupe/gitch yesterday.

What you need:

8 high rebar frames placed down
1 claw hammer
Wood

So since your rebar frames are 8 high you need to jump to hit the last rebar frame.
you jump up and you MIGHT hit the first one twice but the block under it will upgrade to wood rebar frame.
Then do the same thing again and the block under will upgrade to concrete
Then you do it again and the block under will upgrade to reinforced concrete block, even though you did not have any concrete mix or steel ingots.

There is a small chance of actually succeeding doing it but its still there.