Compressible Material

[L775]

We have an existing post-tensioned concrete deck that we are building on top of it a 5-foot-deep swimming pool with 12" thick slab. We are proposing a 2" or 3" GAP between the bottom of the 12" slab of the swimming pool and the top of the existing concrete deck. As usual we are taking all precautions to protect the existing deck by post shoring is before casting the swimming pool on top.
At the same time we need to eliminate the possibility of load transfer between the new construction and the existing one thru the GAP once concrete is cured and the new deck is put to service.
(In case you are wondering, all the loads are transferred directly to the existing columns spaced at 30 feet o.c. both ways.)
Question: what is the best material to use in the GAP that will effectively eliminate any load transfer to the existing slab?

1. In my opinion, using Styrofoam on such a large area will definitely transfer almost the entire new superimposed load.
2. I think that sheets of premolded joint filler will work better than Styrofoam as a compressible material.

thanks for your comments.

 

[JStephen]

They make void forms for purposes similar to this (pier-supported slab over clay, for example). Would that work?

 

[L775]

I am not sure what you mean by "void forms". how does that work?

 

[JStephen]

Try

http://www.surevoid.com.

I've not used these personally. But the idea is that they support a concrete slab while it is poured, but lose enough strength that expanding clay won't pick up the slab later.