Asphalt Shoving: Causes and Repair

Shoving is when the asphalt surface gets pushed sideways or forward into a ripple, wave, or bulge. On a driveway, you typically see it where cars stop, start, or turn: at the bottom of a slope, at the street entrance, or right up against a garage slab or curb. The underlying reason is usually that the asphalt layer is not stable enough, or not stuck firmly to what's beneath it, to resist the horizontal push of braking and turning tires. Small areas are repaired by cutting out and patching. Large areas need the affected layer removed and repaved.

Fixing ruts in asphalt → Driveway soft spots →

What Shoving Looks Like

• A raised ridge or bulge running across the direction of travel
• Ripples that look like a rug pushed across a floor
• A hump next to a hard edge such as a garage slab, sidewalk, or drain
• Crescent-shaped cracks near the bulge in some cases, when the top layer slides over the one below

The Washington Asphalt Pavement Association describes shoving as an abrupt wave across the surface, usually where the asphalt butts up against something rigid, such as a concrete slab. Corrugation, a closely related problem, is a series of ripples (sometimes called washboarding) that WAPA says usually forms where traffic starts and stops.

How It Differs From Other Bumps

• Tree roots produce a ridge near a tree, usually with cracks radiating from it.
• Frost heave comes and goes with the seasons.
• Rutting is a groove in the wheel path, not a bulge.
• Blisters are round domes that appear on hot days.

Shoving is directional. The bulge sits on the side toward which the tires push.

Raised blisters and bubbles have different causes; see what causes asphalt to bubble.

Asphalt Shoving Causes

An Unstable Mix

The Asphalt Paving Handbook, published by the Airport Asphalt Pavement Technology Program, traces both shoving and rutting mainly to a mix that isn't stable. Things that make a mix unstable include:

• Too much binder or moisture in the mix, according to the handbook
• A poorly balanced aggregate blend, such as what the handbook calls a hump in the fine aggregate grading curve, which leaves the mix acting more like putty than a stone framework
• Rounded, smooth aggregate that doesn't interlock, which Pavement Interactive lists among the causes of tender, unstable mixes
• Thick lifts of sand mix placed very hot. The handbook warns that both problems are especially common when a sand mix is laid thicker than 1½ inches at temperatures above 280°F

Poor Bond Between Layers

When an overlay or top layer isn't well bonded to the one below, it can slide. That can come from skipping the tack coat, applying it unevenly, or paving over a dirty or dusty surface. Pavement Interactive lists both too little and too much tack coat among the causes of a poor bond.

Weak or Wet Base

A soft or saturated base lets the whole structure flex and move. The asphalt can shove even if the mix itself is fine. If there's also sponginess, the soft spots guide shows how to check.

Construction Problems

Rollers stopping or reversing abruptly on a hot, tender mat can push a ridge into it during paving. Traffic that's allowed on too soon, especially in hot weather, can do the same.

Where Loads Concentrate

Even decent asphalt can shove under repeated heavy braking or turning: delivery trucks, trailers, or a heavy vehicle that always turns at the same spot. Hot weather makes it worse, since asphalt softens as it warms.

Shoving right at the garage slab or street edge often goes hand in hand with a failing apron, covered in asphalt apron repair.

Repair Options

Small, Stable Ridge

If the bulge is small and the surrounding pavement is sound, a contractor may grind or mill off the high spot so the surface is smooth again. This works only if the asphalt has stopped moving.

Localized Shoving

The usual fix starts with cutting clean edges around the shoved section, taking out the displaced material, and checking what lies below. If the base is soft or wet, it gets dug out and replaced with compacted crushed stone. The hole is then filled with hot mix, compacted in lifts, and edge-sealed. For a closer look at that method, see cut-and-fill hot patching, which walks through it.

Widespread Shoving

When shoving covers a large area, the unstable layer usually needs to be milled off and repaved, or the whole driveway replaced. Overlaying without removing the unstable layer tends to let the problem come back.

Estimating Material

For a repair patch, figure the area and the compacted depth. Enter them in the tons calculator; it assumes hot mix at about 145 pounds per cubic foot once compacted. Plant-price hot mix generally falls between roughly $90 and $130 a ton, trucking not included, but ask local suppliers for current figures.

Preventing Shoving

• A properly designed mix with angular stone
• A clean, tacked surface before any overlay
• A well-drained, compacted base
• Keeping heavy vehicles off fresh asphalt in the heat
• Avoiding sharp turns and hard braking in the same spot on warm days
• Concrete in high-stress areas, such as a delivery turnaround, if trucks are frequent

Bottom Line on Asphalt Shoving

The main asphalt shoving causes are an unstable mix, a poor bond between layers, and a weak or wet base, made worse by braking, turning, and heat. Small, stable ridges can be ground smooth. Active shoving needs to be cut out and repaired down to sound material, or repaved over larger areas.