I got a good deal on some Gates concrete wall forming equipment that had been repossessed by a bank. This is the same stuff the contractors used to pour the walls of our house. I am going to use it to pour an extension on our house so the kids can have their own rooms, after that? The possibilities are endless. I can't wait to get started.
One of my conclusions was if you can pour it thick, then pour the cheap stuff like it's going out of style. 12 inches is so thick and heavy that primary and secondary reinforcement should be used. Just let the concrete company know you are making foot thick slabs and they should be able to set you up with a mix that is extra resistant to cure cracking.
In our current house the exterior walls are 12" and the interior walls are 8", I don't remember what strength I ordered. The walls have a 18" x18" rebar pattern, I think the roof was a 12" x12" rebar pattern plus wire.
If you want to double the compressive strength leave it wet for up to a year. If you dont have a year even if only a few weeks could result up to 25% stronger.