Something I'm curious about - there seems to be some sort of maintenance of reinforced concrete, where people periodically jackhammer a small patch and expose s

Something I'm curious about - there seems to be some sort of maintenance of reinforced concrete, where people periodically jackhammer a small patch and expose some rebar, and then cover it up again. Anybody know what they are doing? I used to park in a garage where it seemed like they were always doing it.