Can termites eat concrete?
No. Termites cannot gain any nutritional value from concrete. They tend not to bite at it, much like the way you don't try to eat granite.
Termites will sometimes excavate lime mortar and really bad concrete. That is, stuff that's soft enough for their jaws to cut into. Sometimes they can damage bad concrete by pulling individual bits of sand out. If you have autoclaved, aerated concrete (hebel and similar) it is possible, with some difficulty, to get termites to chew into it to make their tunnels.
So, seriously keen termites can open up paths in poor concrete. This is more commonly seen at formwork edges, control joints and cold joints than it is at cracks. These are the places where water accumulates after pouring and makes the concrete much weaker than intended. Still, it is not common.
Termites would much rather walk through a big gap, like a wide crack or hole. They need a hole that's a little wider than their head and just a bit taller. They are much happier if the hole allows for two-way traffic and unless a good number can walk in and out, most subterranean termites will give up on the traffic jam.