Firstly, concrete isn't a weapon, it is a defensive utility, not an offensive one (weapon).
Correcting that, the best defense is people. More specifically, "civilians".
You can now easily defend yourself if you surround yourself with civilians like ISIS has done. Without civilians, no-doubt the US will "precision bomb" your entire stronghold to dust.
That's the whole reason the US spend trillions of $ on precision weaponry and surveillance now. The US is trying to develop weapon systems that, even when defending oneself with civilians, when you walk outside your civilian-filled afghan hut alone to go to the outhouse, a tiny precision bullet from the sky assassinates you in an instant. They are getting there, and it's ever closer to fruition, regardless of how disturbing it all is.
EDIT: I mean, why do you think they are pouring money into drones that can stay in the air for ages, path-changing (steerable) "smart" bullets, face recog AI, flight stablisation, etc.. It's ALL an effort to create the aforementioned precision assassination system.