A car and a heavy truck are not the same question
New concrete does not switch on at some fixed hour and become ready for anything with wheels. It gains strength on a curve, fast at first and then slower, and different loads need different points on that curve. A sedan or a pickup sitting on a residential driveway is a light, evenly spread load, and the slab is usually ready for that around the one week mark.
A dump truck, a delivery truck, a loaded trailer, or a piece of equipment on tracks or tires is a different animal. The load is heavier, it often sits on a smaller footprint, and it may sit and idle in one spot instead of rolling straight across. That combination asks more of concrete that has not finished curing, which is why the honest number for heavy loads is closer to full strength, around 28 days out, not the one week figure that covers a car.
The slab you got may already be built for this
If you tell us up front that a dumpster, a camper, delivery trucks, or equipment will be crossing a pad or a driveway on a regular basis, that changes what we build, not just what we tell you to wait for. A slab poured thicker and reinforced for that load can be ready for it sooner than a standard residential thickness would be, because it was designed to carry more from the start.
That is a decision made before the pour, not after. If your slab is already down and nobody discussed a heavy load ahead of time, treat it as a standard residential pour and give it the longer wait. Call and describe what is going to cross it, and we will tell you plainly whether the timeline changes for your specific slab.
What the extra weeks of curing actually buy
Concrete does not dry out the way a puddle does. It cures, a chemical reaction between cement and water that keeps adding strength for weeks after the surface looks finished and dry. Most of that strength is in place by 28 days, which is where the psi-rating you hear quoted actually applies. A slab tested at three days or seven days is nowhere near that number yet, even though it already looks and feels solid underfoot.
That is the gap a heavy truck exposes that a car does not. A car's weight is well inside what a young slab can already carry. A loaded truck or a piece of equipment is testing the slab closer to its limit, and the margin you have at day seven is a lot thinner than the margin you have at day 28.
The edges take the worst of it
Whatever the calendar says, the outside edges of a slab are its thinnest and least supported part, and that is where a heavy tire does the most damage. Keep truck and trailer tires away from the perimeter and toward the middle of the slab, and ease onto concrete in a straight line rather than turning the wheel while the vehicle is standing still. A tire that pivots in one spot scuffs and can chip a slab that a straight roll-on would not touch at all.
If a job needs equipment or trucks crossing a slab we just poured, ask us for guidance specific to that pour rather than going by a general rule. Mix, thickness, and the weather it went down in all shift where the real safe date lands.