Thanks to this thread I was able to make a very solid base for my safe on top of my post-tensioned slab. I scored the existing slab using the OP's method, created a form that perfectly fit the upper edge of the existing slab line, cut and tied rebar to the rebar spacers, painted on the concrete adhesive and poured the high-strength concrete all in about a day and a half. The hardest part was loading the 12 bags of concrete into the truck at Lowes!
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