I used glass fibre reinforced concrete stock troughs in Kentucky...

I used glass fibre reinforced concrete stock troughs in Kentucky nearly 30 years ago , they were a complete failure when the troughs froze solid in winter the expanded ice cracked the troughs .
I doubt CNTs would have made any difference , rebar rods banded around either inside or outside the troughs would have prevented the troughs cracking I am guessing
CNTs are useful but have their limits maybe for holding together 30 cms of concrete they would work , and they definitely reduce surface wear but for something like a concrete beam more than say 70cm in length with a static or live load , I can not conceptualise how they could replace steel rods or tensioned steel rods in concrete, as the CNTs are not bound together like a steel rope spanning a distance - maybe if a carbon fibre rope was available they would work then