For example, the following white and orange striped ramp:
I've seen these at a couple large airports but I've never seen them actually used for anything.
If you've ever watched an aircraft carrier launch a plane, you'll see such a barrier pop up (on hinges) right behind the jet exhaust to deflect it upward and away from other aircraft and deck crew behind the launch catapult.
These things (picture above) look pretty heavy, so they won't be blown over easily. I doubt they would use them to mark a closed runway, unless it's quite long term, as they would be difficult to move around. Does anyone know if they are in fact lightweight, and attach to the runway in some manner?
The following is speculation, as I have no specific knowledge on the matter, but searching a bit it seems that they are needed for deflecting upwards the engine blast
Also, it seems from that website that they also provide a minimum of noise abatement.