They are pretty much interchangeable. There are going to be cases where one is more appropriate, but the distinction between the three words is very subtle. Some examples off the top of my head (the last one answers your question about "concrete"): "Yes, I'm sure there are problems, but what problems, specifically?" "Animals in general, and dogs in particular." "After we've seen enough concrete examples, we'll be able to understand the abstract principle."

"concrete" is very close in meaning to "specific". It has more the sense of "real", as opposed to theoretical. e.g. to give a concrete example (of the theory I have just discussed) .... "specific" is much more common than "concrete". I see students use "concrete" much more commonly that native speakers do.