I currently live in an townhouse. Unfortunately, this subdivision was built on swamp land. The homes seem to be okay but several of the concrete porches are sinking and pulling away from their homes. Luckily, this is not the case with my home. The homeowners association is requiring a neighbor to replace the porch and is now requiring the owner to use the HOA’s contractor and charging my neighbor $5,000. The block that is to be replaced is 77″ long x 62″ wide x 17″ tall. By my calculations, this pad could weigh upwards of 3.5 tons (please correct me if I’m wrong here). My neighbor’s pad was replaced about a decade ago and I’m concerned that replacing the pad with an identical one will just result in the pad sinking and pulling away once again. I thought that there was a process the uses large Styrofoam blocks and then places a shell or façade of concrete on the block. I was also thinking that we could use concrete with small Styrofoam balls inside to reduce the weight. Has anyone heard about either of these processes and are there any other solutions to this problem? I am attaching a picture of my unaffected patio to this message. I will try to send some photos of my neighbor’s porch
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You can absolutely use rigid insulation within a concrete pour to eliminate the amount of concrete needed. I've seen it done often in commercial construction where the insulation helps thermally too.
In your case it will eliminate some concrete but it may not prevent the slab from moving. That is likely due to frost heave or settling substrate.