Regular concrete weighs about 150 lbs/cuft and aluminum weighs about 165 lbs/cuft on earth. (Steel is about 500).
So steel on the moon weighs about 1/2 what aluminum weighs here, and concrete (by volume) would only weigh 25 lbs/cuft. Obviously, you need more volume of concrete to make stuff, and you need a lotta steel in it to get tensile strength, but for compressive qualities and raw sheilding, it's pretty good stuff, right? They're always making canoes out of it at the Universities....!