does anyone know what the actual size of the concret squares on a tarmack is? If I can get the size then I can scale it down to the proper scale needed.

I'm looking for the same info Jody, so if I find anything I'll be sure to post it here.

In the meantime, here is a link from my model club showing a neat way to replicate the concrete if you're interested.

Concrete Runway

Cheers, D

Having built a couple of airports in my time I can tell you that the size of the concrete blocks depends on the geotechnical properties of the ground upon which it is built.

Hard ground means you can have thinner broader blocks, soft ground needs deeper and smaller ones.

So I'd reckon you should try drawing a grid pattern and see what gives the best look?

that's certainly useful information, allows for some flexibility.
Ive been researching the same question for a specific air field I want to model.
Using images and tools on Google Earth, and various photos, I've settled on 15 feet.

http://www.wiehes.com/kwajair/air05.html

In Belgium it is 3 meter by 6 meter