I'd like to erect a small shop about 20x30. This might be a timber framed structure. I have a backhoe to dig for footings and foundation. My question is about the concrete. I have an access problem for big trucks, so I'll have to mix the concrete myself. Is it reasonable to think that I can mix and pour from a 3pt mixer and end up with it done right?
No.
Concrete is going to be drying on you faster then you can mix it and spread it out.
As for how did they do it before concrete trucs were available, in allot of cases, they didn't. Look at allot of old buildings and you will see pier and beam foundations and/or wood floors. In a few examples where it was done, you'll see that it took allot of manpower to accomplish it. Multiple mixers and people hauling it back and forth.
In theory, with enough people, mixers and wheelbarrows, it could be done. It would have to be planned out, laid out and organized. That alone requires experience in order to have enough material on hand and that it's spread out before it hardens.
United Rentals has one yard buggies that you rent and pull behind your vehicle. They have gas motors that keep the mud mixed and allow you to tilt it to dump it when you back up to the pour site. One yard doesn't go very far, and you have a pretty big pad to pour.
Depending on your location, you might need to dig down pretty deep for you footings.
You could pour just the footings and then fill the pad in smaller squares to get a concrete floor. This makes getting it flat easier, but it requires allot of planning and engineering to make sure it stays flat and level. Things like freezing, moisture and soil types will dictate on what you use under the concrete for a base and how thick it needs to be.
Or you could build a pole buildings and leave the floor dirt, or add gravel at a later date.
It's real easy to get in over your head with concrete. It might look simple, but it's a skill that takes practice to be able to do well. It's backbreaking work that will wear you out long before you are done working it, and it's unforgiving. Make a mistake, and you have to live with it forever.
Good luck,
Eddie