Strength is settled at the plant, before the machine is anywhere near it
What a slab ends up at is decided by the mix design: how much water is in there against how much cement, what the aggregate is, how much air is entrained, and what the plant batched against the strength you ordered. All of that happens in a drum well before it reaches your site. Nothing downstream of it adds strength, and only a short list of things take any away.
The water to cement ratio is the heart of it. More water in the same amount of cement means a weaker paste holding everything else together, every time, with no way to make it up later. That is why the number on the ticket is the number that matters and why the ticket is worth reading before the load goes anywhere.
Exterior work here is normally ordered at 4,000 PSI with air entrainment in it, because Virginia freeze-thaw is what the slab has to live through. Entrained air is not strength in the way people normally mean the word. Those tiny bubbles are somewhere for trapped water to expand into on the nights it freezes, from November on, instead of that expansion working against the underside of the surface until it lets go.
The trip through the hose, which is the part people are actually asking about
A trailer line pump swaps gravity out for pressure. The mixer empties into a hopper on the back of the trailer, a piston shoves that material into 2.5 inch or 3 inch hose, and it makes the rest of the trip as one moving column sliding on a film of mortar against the hose wall. Cement, stone and water are exactly what they were when the drum left the plant. Travel does not rewrite a mix design.
One thing in there is genuinely sensitive to pressure, and that is the entrained air. Air belongs to the fresh concrete rather than to the finished slab, which is one more reason the plant hears the word pump before it batches anything. Told in advance, they design for the trip. Not told, nobody ever ran the numbers on it, and that is the gap worth closing.
So the honest version is not that hose is harmless magic. It is that a pumped load is a load somebody designed for pumping, and the design is where all of this actually gets handled.
Where strength really goes missing on a job site
Water added at the truck to loosen a stiff load is the big one, and it is the same theft whether the concrete was headed into hose, a barrow or straight down a chute. It buys workability with strength you already paid for, it never comes back, and it does not surface for years. When it does, it shows as a slab that dusts under a broom or scales off across a handful of winters.
A pour that drags on is the other one. Concrete laid in one continuous pass meets material that is still soft enough to join with it, and the slab comes up as a single piece the way it was drawn. Stretch the same pour over a long afternoon and one end is going off while the other end is still empty, and where those two ages meet you get a cold joint sitting in the middle of a slab that was never meant to have one. That is not something a trowel can take back out. A pump works against that problem rather than toward it, since the operator is matching his stream to whatever pace the crew can screed at.
Then there is the curing, which is where more residential slabs are weakened than anywhere in the placing. Concrete gains strength by staying wet long enough to keep hydrating, not by drying out. What happens in the days after the finishers pack up has its own guide on this site and it is worth the read whether your pour came off a chute or out of a hose.
What a pumped pour looks like when it goes right
Steady. That is the whole description, and it is meant to be unremarkable. Trucks come in on a spacing that keeps the line moving, the hose hand lays concrete where the finishers call for it, and the crew screeds and floats behind them at a pace nobody is fighting. Any finisher will tell you a continuous pour comes to a better surface than a stop and start one.
Done like that, a pumped slab is as strong as the mix it came out of, chute or no chute, because it is the same concrete either way. All the machine did was carry it the last hundred feet, and it carried it fast enough that nobody on site ever stood there wondering whether to loosen a load up.