sorta the same issue I had
This is what I did about it:
I did do some cork, but I mainly grabbed some bits of sprue, a few paperclips, some left over cogs I had from another project, some textured plasticard (textured with a template I made out of hobby aluminum) and a rubble paste mix (made from other left over small sprue bits,
misc pieces of stuff, and various size rocks).
I would have liked to use more bits from actual
40k buildings but I don't really have any.
Basically I used the pieces of plasticard to show different metal textures, the sprue generally I cut into shapes to be support beams that had fallen, some I drilled a couple holes and put paperclip wire in then painted to look like rebar. I also took a rectangle paper cutter (another of my scrapbooking tools) and made some 'bricks' out of funfoam.
Then I just tried to paint everything realistic colours, with several washes to help tie it together and make it look gritty. I didn't weather anything because it was meant to look newly destroyed.
Anyway, hope this gives you some ideas at least!