Can you effectively run lower power 5V TTL signals through a large piece of metal?
Rebar conducts but is also inductive ~ 0.5uH/m so if you have any grid transients nearby, you should add RF caps. It will also pickup AM signals.

I suggest 100kHZ LPF.

ESD and EMI ingress needs to be suppressed , otherwise no problem.

Contact corrosion must be avoided.