Here's what I did;
Found a scrap piece of MDF shelving that was roughly the size I need. First thing I did, was paint a bit of my "concrete" color to see how it would cover and dry.
Once satisfied, I looked online and found out the distance between expansion joints on the average flight apron. Scaled that down to 1/48 and drew squares.
Taking a small finishing nail, I locked it into a pin vise and scribed my lines using a metal straight edge
Using a paint marker, I filled in the lines. The bleed over is ok, as it will add to the illusion of depth, however it doesn't hurt to lightly sand them so the color isn't quite so sharp.
Then I painted the whole thing a lovely shade of concrete grey and let it cure overnight. This was all day one.
On day two, I lightly dragged my scriber back through my lines. This lifted the grey off the black, but not down to bare wood.
Then I made a mess. Let's face it, equipment leaks, and crews spill things. No flightline is pristine.
Now I have a place to park and can stay off the CSM's grass! (Kind of an inside Army joke)
Be creative. You never know what you can make out of scrap.
Hope you enjoyed, and thanks for looking!
Joe
