What Choke Stone Does on an Open-Graded Asphalt Base

Open-graded stone has large voids. A thin layer of finer choke stone locks the surface so hot mix does not slump into the holes and so the paver has a tight grade. Too much choke can hold water. It does not replace the thickness of the open stone below.

Open free asphalt tonnage calculator →

The holes are the reason it exists

Open-graded stone is mostly large pieces with big spaces between them. Those spaces drain, and they also swallow smaller material. If hot mix is placed straight on that open face, mix can slump into the holes, the grade can punch down under the screed, and the mat thickness you calculated at 145 pounds per cubic foot is no longer the thickness you get. A thin layer of finer choke stone is placed to lock that surface. It gives the paver a tight grade to ride and keeps the hot mix up on top of the rock. The choke is a surface lock, not a second driveway. Call it by its job when you read a quote so a line for choke is not mistaken for the structural thickness of the open stone.

Too much of a good lock holds water

A thin choke fills the voids at the top and stops. A thick blanket of fine stone can plug the drainage that the open grade was built to provide, and water then sits in the layer you meant to keep open. That is why more choke is not a safer order. It can also rut under the paver if it is deep and loose, which puts waves in the asphalt. The open stone below still has to be the thickness the section calls for. Choke does not substitute for that thickness. If someone shortens the open rock and thickens the choke to make the same total inches, the base is a different product. Ask how thick the open layer is, and ask for the choke as a thin lock on top of it.

How it shows up in the tons

Order the open stone from its own area and finished thickness, using about 1.4 tons per cubic yard only as a planning default, and let the quarry ticket be the real weight. The choke, if it is truly thin, is a much smaller tonnage than the open layer, but it is still stone you buy by weight. Do not fold a vague choke allowance into the asphalt tons. Hot mix stays on the plant ticket at the compacted thickness you place after the grade is tight. If the surface is still open when the trucks arrive, the mix yield will look heavy because material is disappearing into voids, and the coverage formula will seem wrong. Fix the choke and the grade first. Then compare asphalt tickets with the measured mat, not with a base that was still full of holes.

A practical sequence

Recognize choke as a thin finer layer on top of open-graded stone.
Use it to lock the surface so hot mix does not fall into the voids.
Keep the choke thin so it does not plug the drainage of the open stone.
Do not count choke thickness as a replacement for the open stone below it.

The mistake to skip

Paving hot mix directly on open stone and then blaming the tonnage formula for the lost depth.

Questions people ask

What problem is choke stone solving?

Open-graded rock has large voids. A thin finer layer locks the top so asphalt does not slump into those holes and so the paver has a tight grade. It is a surface treatment of the base, not the structural thickness. Too thick a choke layer can hold water that the open stone was meant to drain.

Can I skip the open stone if I place more choke?

No. Choke does not stand in for the thickness of the open-graded layer under it. Shortening the open stone and thickening the fines changes the base. Ask for both layers by name, and weigh the main stone with the quarry ticket as the real weight.

As an Amazon Associate, AsphaltTons.com earns from qualifying purchases. Product links below are sponsored.