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I'm concerned about the way my raised concrete patio is being constructed and thought I'd do a sanity check here. 14x16 raised screened in porch. Footers, concrete block and brick foundation with the concrete patio floor to be poured on top of the concrete block. The foundation sits about 30" above the top of the footers. The contractor filled the cavity with loose dirt from the footer excavation then topped with 3" of gravel. How concerned should I be that no compaction was done? They haven't poured the floor yet but does the fact that it sits on top of the concrete block lessen the need to have a compacted fill as the floor when cured, would be suspended when settling of fill occurs.

  • Does the concrete slab that is about 30” above the surrounding grade rest on top of the foundation on all 4 sides? – Lee Sam Jul 1 at 1:39
  • no, 3 sides. the 4th side is rebar terminated into the brick foundation. – emanon Jul 3 at 0:39
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The fill is not intended to support the new concrete slab indefinitely. It’s merely fill for the initial concrete pour. The fill will settle overtime, regardless of how well it’s compacted.

Therefore, the slab becomes a “structural slab” and the reinforcing steel MUST be placed exactly correct, or it will fail. That is to say, it won’t just crack, but it will crack so severely it will fail.

We all know the reinforcing needs to be on the tension side (bottom) of the slab, but the slab could have “reverse bending” at the edges and the rebar will need to be on the top of the slab. (Occasionally the slab will be designed with the rebar in the center, in order to eliminate the need to transfer the rebar to the opposite side .)

How thick is the slab and how much rebar is called for in each direction?

  • Slab is 4"-6" think sitting on block on 3 sides and rebar terminated into brick foundation on the 4th side (side without block support is 14'). rebar is @ 2' oc both directions. – emanon Jul 3 at 0:41
  • I would be very concerned unless the sub soil was compacted. 3” of rock is fine for soil that has been scraped of topsoil then a layer of rock added ok that woyluld be fine but dirt fill on top of rock without compaction is a failure waiting to happen. – Ed Beal Aug 30 at 2:37

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