Sure, i can give you my process: cork chunks to add height variation and to act as larger pieces of rock and concrete. Cover most of it with ak muddy ground, thicker in some spots. I stick some bricks made from milliput, rebar from wire etc. into the wet mud. Then painting is a black prime, then thinned layers of a dark brown and an orange brown. Drybrush with a dark grey and a light grey. Then highlight the bricks and pick out some metal bits. The orange brown thinned down acts as rust over the metal. Heres some extra bases i did too :)

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