I have an above-ground doughboy pool that was installed in the ground. Doughboy recommends backfilling around the pool with slurry. Would a polyurethane foam (the type used to fill voids under concrete) also be a suitable back fill material? Slurry is heavy and can push the walls in when being poured, even with the water in the pool up to the brim. The foam would be lightweight, and easy to cut away if needed in the future for any wall repairs. It is also waterproof.
Any thoughts?
You need to be more clear about "Slurry"
Controlled Low Strength Material (CLSM) aka Flowable Fill is cement, water, and admixtures. It is indeed heavier than an equal amount of water, and lateral pressures should be considered while placing.
Lightweight Cellular Concrete (LCC) aka Lightweight Flowable Fill, is cement, water, and a foaming agent. It is light enough that lateral pressures can, for most applications, be ignored.
Expansive foam, as you suggest, also exerts lateral pressures (that is why it can lift concrete structures, and bow window and door frames.
Also, not all foams are waterproof. High Density Closed Cell foams are. Most others are water resistant. Open cell foams are like a sponge. They will get soaked and hold water against your pool.
Water resistant is not water proof. Cement board is water resistant - you can throw it in a lake and a year later drag it out and it will still be good. However it is not water proof. If you were to build a box out of cement board and fill it with water, it will eventually weep through.
