Then what's the point of an expansion joint. Decks are meant to move freely from the coping. If you have expansive soil the deck will move up when the soil expands and pop your coping off the pool. Have your builder set the coping on some concrete.that way you can have a expansion joint that works.

In regards to Pools94 comment, the builder should pour a small concrete ledge below the coping at least 6" - 8" deep and then to the copings edge.
A band of rebar (tied to pools rebar) should also be considered as it will strengthen this ledge.
Install the coping and then set up and pour the deck to this point, thus the expansion joint will then work properly.
I have had to do this on many jobs even when the coping is 12" deep . . . on account of the gunite beam not being true to form. Saves cracking deck / coping problems later.
Depending on your contract and material choices you may end up paying for this added work but it is well worth it.