The rebar (in the manner you are using it and the way we typically use it in slabs) does nothing for the "strength" of the concrete and its ability to withstand loads of vehicles. As brownbagg points out, that strength comes from the soil underneath. The slab is just a cap that distributes the load evenly over the ground.
A 4" slab is a very effective thickness and just fine for a RV or heavy truck. (BTW - The loads your RV puts on the slab are not fully dependent on the weight of the vehicle. The tire size, tire pressure, and tire profile all part of the equation.)
The rebar is used for crack control. All concrete cracks and your cut/control joints and the rebar will work together to control how frequently those cracks occur and where they occur. (Hopefully in the saw cuts and out of plain sight.)
For a quality slab, you'll want a balance of a number of factors:
- quality of base material under slab (including compaction)
- cement ratio (typically aligned to the psi rating)
- water content
- slab thickness
- cross section of steel in the slab (amount of rebar)
- frequency/spacing of saw cut joints
- proper placement of expansion joints (if needed)
- management of re-entrant corners (if you have any)
- admixtures
- quality of workmanship/finish
- probably other attributes, I'm forgetting...
#4 rebar on 16 centers, 4000-4500psi concrete and planing to up fiber in.
This should give you fine crack control if you have normal saw cut spacing of 10-12'. If it isn't very hot right now, you may be able to skip the fiber but I'd check for a local recommendation. That product only helps with plastic shrinkage cracking, (from rapid evaporation of the water in the concrete) which is more of a concern in your part of the world than many of ours'.
My question is as I measure pad thickness, there are a few areas that will only be 4 inches thick, the rest is around 5.5-6.5inches.
Is this from the grading, or by design? Having inconsistencies in the thickness of the slab is more likely to lead to cracking. (You'll get higher/differential shrinkage stresses building up in the thicker sections.) If you have thicker edges, that's less of a concern.
