Eureka XXL has several 1/35 scale road building concrete panels in the company catalogue. This review covers the Modern Concrete Road Panels (Perforated) (E-018).
Hah! For once I appear to be ahead of the game folks! I’ve had these for a couple of years; I would recommend them as they’re spot on for those dismal tracks built along the Inner German Border - perfect in fact. See here:
This particular project was close to fruition, but I then realized that the spacing was just too compressed for what I wanted to convey, so I’m looking at revising it along these lines: