Now, if we go completely theoretical, assuming this is a simply supported slab,
concrete below the reinforcing steel bars only functions to protect the steel rebar from corrosion and from softening immediately in case of fire. So, only the top half of concrete in this slab is actively working to prevent collapse.
Funga kitabu sasa, now since the entire depth of concrete is cast in one go, if the lower half is performing this badly in protecting the rebar from corrosion (pervious concrete, allows moisture and oxygen to go work on the steel), the upper half is definately not to spec (its extremely hard for pervious concrete to meet strength specs).
So, whats the way forward;
No. 1 is to determine the extent of steel corrosion and depending on slab span, concrete quality and expected loads, engineer apatiane opinion on whether its salvageable.
No. 2, kwa soko kuna companies e.g BASF, Sika, Dr. Fixit, Fosroc..... that sell special construction products to fix such a mess. If the slab is very pervious, kuna products that if applied on all slab surfaces will bring that to an end. Below pia kuna products that can protect the steel from further rusting and bond to the existing concrete kabisa.
No. 3 monitoring, just incase uuziwe products bonoko hapo no. 2, or your assumptions in no. 1 came short, early warning signs za further deteroriation wil give the investor ample time to plan his next step