I've read through this entire thread and no one has mentioned that the math on the amount of concrete for a 40' x 48' pad 4" thick is a little short at 21-yards. My calculations come to 23.7 and I would order 26-yards if I was doing the project. I have poured a lot of concrete in the 10-12-yard range always with the same 2 guys helping that also know what they are doing. I am no novice, but seriously doubt I would even begin to pour that much concrete at once myself. Dumping out 25 yards is one thing. Getting it flat, level, and ultra smooth is another. Doing in stages could be an option, but anything over 10-12 ft wide is impossible to strike off with a 2x6. You need a professional that mainly does large slabs for a living. You might think it's a lot of money to pay now, but when you have to jackhammer it all out and start over later you'll wish you had it a pro do it. There are places to save money and places to spend money. This is a spend the money place.
Tom
