Concrete and Water making paste isn't that strange, what do you get when you mix concrete powder with water? o_O It presumes that powdered concrete isn't the same as its solid form, which is brick in this case after being heated to dry.
If you want special structures, use saltwater or distilled water, they don't react with concrete at all.
I second that. Just because the element's name is "paste" doesn't mean it's the kind of past you get from grinding bugs or something. A good real-world analogue (and, in my opinion, what it's supposed to simulate) is making wet clay. You can then "fire" (heat) the clay to get ceramic, i.e. brick.
As for whether the interaction is good or bad, well...at least it's similar to real life.
And don't jump on my back about a zillion things that aren't like real life, because I didn't make the game.