ᐅ Filling a Basement Excavation – Which Building Material to Use?

Hello!
I need your help. I am having my old house with a basement demolished and backfilled.
My contractor wants to use RC 0/20 for the backfill and compact it layer by layer with moisture. Is this material suitable, or should they use fill sand instead?
I would be very grateful for your advice.
Best regards, Sandro and Merry Christmas

... what should the final result be?

Build a house without a basement, so that the load-bearing capacity is optimal. Or what result do you expect?

Why not build a house with a basement? The excavation is already done. Filling in also costs money, so the final additional costs for the basement should not be that significant.