We are on black clay here.
I am using #4 rebar and 2-1/4" chairs and currently have it planned for 18" grid but the more I research the more I am inclined to go to 20"-24".
I am definitely dowling into the old slab using adhesive and will just direct pour up to it.
I have asked 1 of the readimix companies I got initial quotes from, what additives they have, Water reducer/superplasticizer, fibers, etc. Seems those can really strengthen the slab and make it a lot easy to pour and finish from all the videos I've watched. I just don't know what's available here.
Didn't plan to use plastic since it won't be fully enclosed, more of a lean to carport.
The term groundbeam I think is being used for footer here by the building official since they said if a structure was going on the slab they are required.
I was planning to excavate the area down some and pack in some sand and gravel but I believe when they did my shop, they just dug the groundbeam/footers around the perimeter and then through the center both directions, spread that dirt over the floor area, packed it and poured right over that. Picture below.
It's been 16 years and its had a 10K RV trailer parked in the center bay and no cracks so far.
That kind of matched up with some saying the best base is one that's been undisturbed for years and mother nature has compacted.