I used yellow wood glue on my Verlinden bunker, worked great. Some folks like to use epoxy, but that's too much work for me.
Here's an answer to a question I know you didn't ask, but a caveat: that plaster soaks paint up like a sponge! It'll suck a loaded brush dry just like that, before you even have time to move the paint around. Some folks like to seal the plaster with a spray lacquer or something similar before painting plaster, but that's too much work for me if the plaster is to represent plain ol' concrete. I recommend mixing a very thin wash (probably oil or enamel paint thinned with turpentine) in a nice concrety color (dirty gray with some yellowish/brownish tint) and giving the whole structure a heavy wash BEFORE the glue gets anywhere near it (any errant glue spots with resist the wash and it won't soak in and it'll be the first thing you notice any time you look at the dio and you'll have to hide it with some improbably-placed bit of equipment or such like and the nice folks at the model show will ask all sorts of awkward questions-- ask me how I know!
) As a plus, the wash acts as its own wash, so you won't have to go through the usual paint-wash-drybrush drill. Plaster is a very similar material to concrete, so you can just let it be itself and it will represent quite nicely.