I use a sheet of styrene, and scribe in the expansion panels. Then airbrush a mixture of gray and black to make it look like concrete, and accentuate the panels with black, being a bit sloppy so it looks like the asphault filler (at least I think it's asphault, maybe somebody else out there knows what the black stuff is
). Add some grime with pastel colors, and the occasional oil stain and you're done. I did the tarmac in the diorama below using this technique.