Slightly of topic, but in a similar vein, I have just put together a dio base for my Ar555, which features a concrete runway. I cut the slabs individually from a sheet or picture framers mounting board, bought from a local art shop.
This comes in lots of colours, inluding several which are close to concrete, which I bought, and tarmac, so well worth a look.
The mounting baord is great because it possess a slight surface texture and is easily cut. I sprayed mine with a base coat of Tamiya Deck Tan, followed by low lighting the edges with a thin spray of RLM79, to simulate old and discoloured concrete.
I then sprayed the whole runway section lenghtways with a light streaks of RLM66 to simulate tire scrub, and general dirt.
It really was very simple.
I'll try and post some pictures next time.
Karl