Notched Wedge Joint: Better Longitudinal Joints in Asphalt

A notched wedge joint is a way to build the seam between two paving lanes so it compacts properly. Instead of leaving a vertical, unsupported edge on the first lane, the paver forms a short vertical notch at the top and a long, gentle taper below it. The second lane is then placed over the taper and rolled against a supported surface. The result is a joint with better density and less early cracking.

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Why longitudinal joints fail

The edge of a freshly placed lane has nothing holding it in when the roller passes, so it slumps outward and stays low in density. When the next lane is placed against it, the cold, open edge does not bond or compact well. Water gets in, the joint ravels and opens up, and the road develops a long crack down the centerline. See construction joint between paving passes for the basic joint types.

How a notched wedge is built

A wedge-forming device on the screed shapes the edge of the first lane: a short vertical step of roughly 1/2 inch at the top, then a taper of about 1 to 12 down to the existing surface.
A small roller or a weighted wheel attached to the paver compacts the tapered wedge.
Before the second lane, the taper is cleaned and tack coated; see tack coat.
The second lane is placed so its mat overlaps the wedge, and rollers compact it with the taper providing support underneath.

Example geometry (made-up numbers)

On a 2-inch lift with a 1/2-inch notch, the remaining 1.5 inches taper at 1 to 12 over about 18 inches. The adjacent lane then has 18 inches of overlap that is compacted against a sloped, supported face, rather than against a raw vertical edge.

Benefits

Higher joint density. Studies including NCAT work have reported better, more uniform joint density compared with butt joints.
Safer for traffic. A tapered edge is much less dangerous than a 2-inch vertical drop when one lane is open to traffic overnight.
Better bond. More contact area and tack on the sloped face.

Limits

Lifts thinner than about 1.5 inches leave too little material to form a useful wedge.
Coarse, large-stone mixes can tear when shaped into a thin taper.
The wedge must be kept clean; dirt or debris on the taper ruins the bond.

Alternatives

Echelon paving places both lanes hot, side by side, avoiding a cold joint altogether.
Joint heaters and joint adhesives treat a cold edge before the next lane.
Cutting back the low-density edge with a cutting wheel before placing the next lane.

Whatever the method, check joint density with cores or a nuclear density test, and roll while the mix is above the right compaction temperature. For tonnage on your project, use the asphalt tonnage calculator.

Questions people ask

What is a notched wedge joint?

A longitudinal joint where the first lane's edge is paved as a vertical notch at the top followed by a gentle taper, so the second lane overlaps and is compacted against a sloped face instead of an unsupported edge.

What taper is used on a notched wedge?

A slope of about 1 to 12 is common, with a vertical step of roughly 1/2 inch at the top, though agency specs vary.

What lift thickness is needed for a notched wedge joint?

It works best on lifts of about 1.5 inches or more. Very thin lifts do not leave enough material to form the taper.

Does the notched wedge joint improve density?

Field studies, including work by NCAT, have generally found higher and more consistent joint density compared with a conventional butt joint.

Can traffic drive on a notched wedge?

Yes, which is one of its advantages. The gentle slope is far less hazardous than a vertical drop-off when traffic runs next to an unfinished lane.

How is the wedge compacted?

Usually with a small roller or a weighted wheel attached to the paver, then the adjoining lane is tacked and placed over it.

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