Like the parent said, the ph of concrete become more and more neutral as the years go by. Here in Quebec pretty much all the old bridges, pedestrian bridges, etc built in the 60s-70s need to be teared down because they're basically 100% concrete and the rebars have swollen make them lose chunks all the time. As you can imagine that's not a very positive experience for cars going under those bridges.
As for sacrificial materials, well the whole point is that they get "sacrified" ie: eaten up before the metal you want to protect. At some point depending on conditions, your anode will have been fully corroded, galvanized or whatever the reaction is. So, it's not going to be indefinitely. I had a to swap the anode on a 4 year old water heater for example because of the water composition here.