rebarDoubt
To provide you with what you need shed some light on your inquiry, Do you mean slab placed on grade or elevated pier supported by abbutments, walls.. or rigid block foundation or short column pedestals.
Ben537
Probably the remaining perimeter gap (depending on how much depth was removed from the gap)and assuming a depth of 0.25m could be filled with two layers of fill or soil each evenly compacted to a level up to 0.05m lower than the existing concrete slab then either place fresh sand and...