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I agree with funfer, any residential slab with any mesh should be fine. The big difference between a two post and four post relative to loading is 4 post is all compressive strenght and zero tension. With a two post there are bending moments on the base plate which result in tension. Concrete in tension is not a desirable trait, it is best when compressed that is why bridge supports have an bow so that they are always being compressed. Once again amount of load has to be considered, alot of nothing is nothing and that is what is found with these lifts for our cars.
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