Plastic Worker,
I don't know whether "flashing" would significantly modify the surface energy of aggregate or not. It would probably help to drive off water and other molecules of crap stuck to the aggregate however.
My intuition is that since plastic bottles are composed from hydocarbon molecules that quickly "flashing" them will modify the chemistry at the surface of the plastic perhaps oxidizing it ever so slightly. I've read about using corona discharge and plasma treatments to get things to stick to difficult plastics which uses a similar principles.
Most aggregates like Quartz, Sand, Alumina, etc. are composed of relatively chemically inert oxides close to what they line furnaces with. I'd suspect without proof or reference that it might be difficult to get aggregates hot enough to see any effect whatsoever in permanent surface energy modification.
OT: I learned about the plasma etch stuff when I was busy trying to figure out how to get epoxy to stick to teflon. It turns out that for that problem there is some stuff called fluoro-etch which modifies the surface chemistry a few atoms deep in a block of teflon and renders it epoxiable. There's also an older formulation called tetra-etch which sounded so nasty I'd avoid touching the ten foot pole that touched the ten foot pole that touched the stuff.
Thanks for the post and if you think of anything else, enquiring minds want to know.
--Cameron