Two mixers on the road in front of your house
If your pour needs more than one load, you are likely to see the second truck sitting at the road while the first one discharges. That is not a scheduling mistake, it is the plan. Ready mix is ordered in 10 cubic yard loads, and anything past that comes out of more than one truck. The loads get staged so the next one is arriving while the current one is emptying.
What you will almost never see on a house-sized job is two chutes running into the same forms at the same moment. There is rarely room, and there is rarely a reason. A crew can only place, screed and finish so fast, so the real constraint on a pour is the crew at the forms, not the number of trucks parked outside.
The gap between loads is the thing that matters
The reason loads get staged tightly is a cold joint. Concrete that has already begun to stiffen does not knit properly to concrete placed against it later. The seam reads as a line across the finished surface and it is a weak plane through the slab, which is the opposite of what a monolithic pour is for.
So the second truck is scheduled to arrive before the first one is done, not phoned for once it runs dry. If a load does run late, the crew has choices and none of them are free. Keep working the edge of the placed concrete so it stays live. Stop at a planned joint line instead of a random one. In a bad case, cut the pour short and come back for the rest, which nobody wants.
Through the pump, the hopper is where the trucks take turns
When the concrete goes through our line pump, the trucks feed a hopper rather than the forms. One truck backs to the hopper and discharges into it, the pump keeps pushing concrete down the line at whatever rate the finishers can take, and when that truck is empty the next backs into the same spot. At the placement end, nothing stops.
That is one of the quieter advantages of pumping a multi-load job. The hopper holds a buffer, so the changeover at the truck end does not have to be instant to keep the far end moving. The operator watches the hopper level and eases the pump speed to stretch what is in it if the next truck is still a few minutes out.
When two trucks really do discharge at once
It does happen, mostly on large open flatwork where there is room for two trucks to set up at opposite ends of a slab and enough people on site to place and finish both streams. That is a commercial situation more than a residential one, and it takes two placement crews rather than one crew running back and forth between them.
On a driveway, a patio or a garage slab it is almost never the right call. Two trucks discharging into forms that one crew is finishing just puts concrete in the forms faster than anybody can work it, and then you are chasing a slab that set ahead of you. Nothing about that produces a better finish.
How many trucks your job actually takes
Work the volume first. Length times width times thickness, all in feet, divided by 27, then add 10 percent for waste. Most residential driveways, patios and garage slabs land inside a single 10 cubic yard load, which means one truck and no staging conversation at all. Foundations and bigger flatwork are where the second and third loads come in.
A job that lands just over a load boundary orders the next full load, and our page on by the yard versus by the job walks through what that does to the numbers. For planning your pour day, the only thing you really need to know is whether you are a one truck job or not. We will tell you that when we come out and measure.