The main reason for molding them in resin is the amount of flexibility it allows you, the individual modeler. There are printed cardboard options out there. But you're limited to how that manufacturer thinks they should be colored and weathered.
With a base from MaxModels, you can choose what shade to you want the concrete to be. I've seen concrete in shades ranging from a darkish gray through light gray, as well as various shades of tan, even tending towards a pinkish hue. What color concrete you want to replicate is entirely up to you.
You can choose how prominantly you want the crack and joints to show. A light, or no wash to keep them subtle, or some preshading and a heavy wash to really make them pop. Or anywhere in between. Like panel lines on models, the texture, joint lines, and cracks on my bases are a bit overscale. But if they weren't, they wouldn't show up. If you want to tone them down, they can easily be filled in as much as you want. Additional craking and pitting can also be incorporated with simple modeling tools.
Oil and other fluid stains? Again, all up to you. Add some oil and fuel stains with artist's oils. Want to model a scene right after a rain shower? Easy to do with some future or clear casting resin. Want to add some ground work where I didn't? Just build the area up with some epoxy putty, acrylic gel medium, plaster, celluclay or anything else you want; and finish as you like.
The possibilities are almost endless. I provide a relatively blank canvas for you to finish as your imagination sees it.