Woodland Scenics actually has a concrete looking mold material. Woodland Scenics is a popular train scenery company with great products. I've used their stuff to create a diorama for my rally Subaru and it looks very realistic in the 1:24 scale.
You need three products to create the concrete road, well two mainly, the third is kindof optional. You will need:
ST1452 - Smooth-It (1 qt.) = $4.98
ST1454 - Concrete Top Coat (4 oz.) = $4.29
ST1455 - Paving Tape = $6.49 *OPTIONAL*
While it may seem expensive, the results are stunning, very realistic and customizable, you could even use some of your old wheels and make burnout marks on it with black paint.
If you want some pictures of what I've made with some of their other products let me know and I'll get some pictures.
Here is their site if you're interested in their products, should be able to find them at any local hobby train store.
http://www.woodlandscenics.com/