I was removing old thinset and self-leveling cement in an area in preparation to tile it when the 6" chisel and demo hammer I was using sunk in to a specific spot. I found that this specific spot had been filled with debris and had about 1" of cement poured on top of it. Quite obviously, this wasn't sufficient, and the end result was a series of cracks in this area and a hollow sound here. I removed the debris and was left with about a 2' by 3' hole. It's obvious that someone made a (bad) patch here in the past. There was even a discarded bandaid wrapper and fibers from orange shag carpeting in the hole.
There's no plumbing that I can find below and the plastic 6mil vapor barrier is in good condition with a few minor tears that could be repaired with tuck tape. There are two roots running below; they are rotting and probably belong to something long dead. There is a crack running from the door to the right of the picture to the hole. I plan to repair this crack at the same time by broadening and deepening the crack slightly and using a cement patching compound.
What product should I use to fill the larger hole? Plain ol' Quickrete, or some other form of cement? Aggregate or not? Any specific PSI ratings I should look for, or other prep work that I should do besides washing the areas that I hope the new concrete will bond to and making sure that there's enough clearance under the wire for the cement to engage it?