I'm remodeling a large commercial building, +/- 100k s.f.. I'm attempting to provide a drive-thru into the existing facility by opening up the existing masonry walls to allow vehicles access pick up area and drive out with merchandise
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The interior concrete slab on grade is 4-5" thk. which will now be subject to exterior temperatures. If vehicular loads warrant a thicker slab, can an additional slab be poured over the existing? If so what are pro's and con's.

Its always so tempting to re pour over a existing slab. The only correct way that can be done is the original slab needs to have proper drainage slope and then be able to put 4" crushed stone over that then the 6" of required concrete to support a car with min 6x6 10 gage wire in the concrete.


If that area doesn't get rain then you can add new concrete over old and it needs to be 6" thick with wire int it. If heaver vehicles may use it at times then 3/8 rebar is in order.
If you have the elevations there to accomplish this then fine, If not don't Simply because if moisture gets trapped between the concrete then it will expand when it freezes and crack the top layer.