Reading the surface
Why does the edge of my driveway crumble?
Driveway edges crumble because there is nothing beside them holding the asphalt up, so anything that drives onto the edge breaks a piece off.
The numbers
- An edge is unsupported on one side by design. It is the weakest part of any drive.
- Wheels dropping off the edge do most of the damage.
- Water runs to the edges, so the base there is the wettest base on the drive.
- Soil or sod built up level with the edge protects it. A drop of several inches invites the failure.
Why an edge is different from the middle
In the middle of a drive, asphalt under a wheel is held up on all sides by the asphalt around it and the compacted stone under it. At the edge, half of that support is missing. A wheel that runs onto the last few inches is bending a piece that has nothing to lean on, and eventually it snaps off.
The pieces that break away take the edge back another inch, so the next wheel does it again a little further in.
The water half of it
The drive sheds water to the sides, so the ground at the edges stays wettest. In northwestern Wisconsin that ground freezes and heaves in winter, which lifts and cracks the edge from underneath, and the spring thaw leaves it soft when it takes the most traffic.
A downspout discharging next to the drive puts that whole cycle into one spot, which is why one section of an otherwise sound edge is often the worst of it.
What holds an edge together
Ground built up level with the asphalt. If there is a drop from the drive to the dirt, the edge is a cantilever waiting for a tire. Filling that with soil and letting grass root into it gives the edge something to bear on and keeps water moving away instead of straight down the side.
Where the edge has already gone, the broken material gets cut back to sound asphalt and new material goes in against a clean vertical face. A wedge of asphalt smeared onto a broken edge has nothing to bond to.