I have a circular fire pit that I am removing and I need to replace with patio pavers and a concrete base. Looking for guidance on pouring the concrete base given that it is in the middle of the existing patio. Do I need expansion joint between this circular addition and do I need to tie it into the existing concrete base? Any special concrete mix since it is surrounded by existing concrete. Fire pit is 4 foot diameter and the hole is roughly 3 feet in diameter.