Hi all, I'm currently building in Melbourne. We specified a raft slab and the builders plans and engineering specified 25 mpa concrete, however they have poured the slab using 20 mpa concrete (i.e. a weaker mix).
I'm still waiting for a response but where do I stand on this matter and what would be an appropriate course of action?
Is the 20 mpa likely to be a problem with the same slab design (i.e. pier spacings, 120mm thickness, etc)?