What goes on the order before a truck ever loads
A ready mix order is more than volume. The plant needs to know the strength the job requires, whether the load will face freeze-thaw and needs to be air-entrained, and how the concrete is going to be placed. A load headed for a chute and open forms is proportioned differently than one headed through a line pump, because it has to travel through hose without separating or packing. Fiber and any admixtures, including anything that changes set time, belong on that same order.
None of that gets sorted out at the site. It gets settled on the phone with the plant, before the truck is loaded, so the mix that shows up is already built for the job it is going into.
How it arrives, and what happens once it does
Ready mix comes by the truckload, and a standard load runs 10 cubic yards. A job that needs more than one load has trucks staged and spaced so the crew is never standing around waiting, and so concrete already placed is not sitting exposed to sun or wind longer than it should while the next truck is on its way.
Once it is on site, the mix does not get adjusted with a garden hose to make it easier to place. If a load looks stiffer than expected, that is a call back to the plant, not a decision made at the tailgate.
Ready mix versus mixing on the job
Small patch work sometimes gets mixed by hand from bagged material, but anything of real size, a driveway, a patio, a foundation, gets ordered as ready mix. The reason is consistency. Every batch coming out of a plant is built to the same design, so the strength and the mix do not drift from wheelbarrow to wheelbarrow the way a hand-mixed batch can.
Whose job the mix is once it is on our schedule
When we form, pour and finish a job ourselves, the ready mix order is on us. We spec it, we call it in, and if a load shows up wrong we are the ones on the phone with the plant sorting it out, not you. When we are only subbing the pumping for another contractor, the mix stays theirs to order, and what we bring is a straight read on whether that mix and yardage will run clean through our line before pour day.