I’ve had pretty good success with 1/16" basswood and 1/32" plywood. This is not cheap in quantity, but worked well for my limited needs.There is some texture on its surface that represents the roughness of concrete better than styrene does for me (although I have used styrene, too, just find the wood easier to use for this purpose in most cases.)
I usually cut a cardboard template, then cut the wood if there are any complex shapes. You can spray paint both, then weather, and the basswood is good if you need to taper or thin the edges to get clearance near the rail. I’ve used Aleene’s and CA to hold it in certain spots, but in some places it just sits in place nicely.
Here’s a pic of what passes for an intermodal facility on my layout when I had things pulled off to paint track. It’s more of a NG-to-SG transfer in my case, plus the road that serves it and the area around the station.
On the station platform with passengers awaiting a train and - a burger.
