Repairing Asphalt with Concrete: Why It Fails and What to Do Instead

No, you should not repair asphalt with concrete, and you should not patch concrete with asphalt. The two materials flex, expand and bond differently, so the edge of the patch opens up, lets water in and breaks down. Repair asphalt with hot-mix asphalt and concrete with a concrete repair material. The exception is a planned concrete pad, designed with proper joints, set inside an asphalt lot.

Can you repair asphalt with concrete? The short answer

Not as a patch. A hole in asphalt should be filled with asphalt, and a hole in concrete should be filled with a material made for concrete. The table shows the right and wrong fix for the common cases on a commercial lot.

The last row is the one place where concrete belongs in an asphalt lot. It is a design change with its own details, not a patch, and it is covered below.

Why a concrete patch in asphalt fails

Asphalt is a flexible pavement. It bends a little under load and passes that load into the stone base beneath it. Concrete is rigid. It carries load as a slab and moves in a different way when the temperature changes. Put one inside the other and the seam between them has to take the difference every day.

Three things go wrong at that seam.

• No bond. Asphalt binder and cement paste do not stick to each other. The patch sits in the hole like a plug, held only by friction.
• Movement. In an Ontario winter the pavement shrinks, freezes and heaves. The asphalt and the concrete respond differently, so the seam opens.
• Water. Water enters the seam, reaches the base and freezes. That is the same freeze-thaw cycle that turns cracks into potholes, and it now works along the whole edge of the patch.

The patch edge also gets caught by plows. A concrete plug that stands a little proud of the asphalt is hit by the blade, and one that sits low collects water. Concrete also needs time to cure before it can take traffic, while hot-mix can be opened once it has cooled. The lot ends up blocked off for longer to make a repair that does not last.

Why an asphalt patch on concrete fails

The reverse fails too. Asphalt does not bond to a clean concrete surface, and a thin asphalt layer feathered out at the edges will ravel and be scraped away by plows. Cold patch pushed into a concrete spall sits in a hole with no way to lock in, so it loosens and is carried away on tires.

Concrete also keeps moving. Its joints and cracks open and close, and an asphalt layer over them cracks above each joint. That is why resurfacing a concrete lot with asphalt is a design decision with its own limits, not a patch. If the slab is rocking or settling, fix the cause first.

The right repair for a pothole or failed patch in asphalt

The lasting method is a cut-and-patch with hot-mix asphalt, or an infrared repair that blends the patch into the surrounding pavement. Cold patch is a temporary fix. In order:

1. Find the cause. A pothole that keeps coming back usually points to ponding, a blocked inlet or a soft base.
2. Mark and cut. Saw-cut a square or rectangle outside the damage, so the edges are straight and vertical.
3. Remove failed material. Dig down to firm base. Repair or replace any wet or soft base.
4. Tack the edges. A thin tack coat helps the new asphalt bond to the old.
5. Place and compact. Lay hot-mix in layers and compact each one, finishing flush with the surface.
6. Seal the joint. Many contractors seal the perimeter of the patch with hot-pour sealant to keep water out.

In Ontario, hot-mix is generally not available through the coldest months, so a winter patch is a stopgap. Plan a permanent fix in spring. For the methods in more detail, see the asphalt patching methods guide and the pothole repair guide.

Narrow cracks are a different job. A Canadian national guide to crack treatment says cracks wider than about 20 mm are really elongated potholes that suit patching or rehabilitation, and crack sealing is for active cracks up to that width, the ones that open and close with the seasons.

The right repair for concrete, and what about crack filler?

A concrete spall or pothole is repaired with concrete repair material, not asphalt. A good job has these features:

• Saw-cut, vertical edges. Feathered edges break away.
• Removal of weak concrete back to sound material.
• A clean surface, prepared as the product instructions say, including any bonding agent.
• A repair material rated for exterior freeze-thaw and de-icing salt exposure.
• Joints kept open through the patch, then sealed.
• Proper curing before traffic.

A rocking or settled panel is a base problem. Patching the surface will not fix it, and replacing the panel usually will. Concrete slab repair is its own trade. The commercial concrete repair guide covers the common concrete defects.

Can you use asphalt crack filler on concrete?

Not the cold-pour kind sold for asphalt cracks. Concrete joints and cracks move, and they need a sealant that is made for that movement and for bonding to concrete. Some hot-applied sealants are specified for both asphalt and concrete pavements, so the product data sheet decides. Check that the product lists concrete before it goes into a concrete joint.

When a concrete pad inside an asphalt lot is the right design

Some spots wear asphalt out. Dumpster pads take the point load of a container and a truck, plus spills. Loading aprons and truck turning areas see slow, heavy, twisting wheels. Drive-through lanes get stopping loads and drips of fuel and oil. Petroleum products soften asphalt, and heat and standing loads make it rut. Many commercial sites use concrete in these spots and asphalt in the parking field, a pattern covered in the concrete vs asphalt parking guide.

A pad is designed, not poured as a patch. It has a prepared base, a thickness and joint layout chosen for the loads, and a detailed edge where it meets the asphalt. For heavy trucks, have a qualified designer specify it. At the edge, the asphalt is saw-cut straight, the base is compacted, the asphalt is set flush so plows do not catch, and the joint is sealed with a flexible sealant that suits both surfaces. The asphalt around the pad also has to be repaired or paved to match, so the plan should cover both.

Questions to ask when a contractor proposes a mixed-material fix

If a proposal mixes asphalt and concrete in one patch, ask these questions, and ask for the answers in writing.

• What caused the failure, and does the fix deal with it?
• What material goes in the hole, and why that one?
• Will the edges be saw-cut, and how deep will the patch go?
• What happens at the seam, and how will it be sealed?
• How long before traffic is allowed, and which stalls are closed?
• If concrete is used, is it a designed pad, and who designed it?

A contractor who cannot answer is guessing. D&D Commercial Services does pothole and patch repair and crack sealing as part of parking lot maintenance, with a free written estimate that lists the scope, materials and timing. A spring walk-through after snow season is the easiest time to catch plow damage, heaved curbs and sunken catch basins before they become bigger repairs.

Asphalt and concrete repair questions property managers ask

Can you repair potholes with concrete?

Not in asphalt. Concrete does not bond to asphalt, moves differently with temperature and leaves a seam that lets water in. Repair asphalt potholes with a cut-and-patch in hot-mix asphalt. Use concrete only where a designed concrete pad replaces a failed area under heavy loads, with proper joints.

How do you repair a pothole in concrete?

Saw-cut square edges, remove weak concrete back to sound material, clean the surface, then place a concrete repair material rated for exterior freeze-thaw and salt. Keep joints open through the patch and cure it before traffic. Rocking or settled slabs need the base fixed, usually by replacing the panel.

Can you use asphalt crack filler on concrete?

Not the cold-pour filler made for asphalt cracks. Concrete joints and cracks move and need a sealant made for concrete. Some hot-applied sealants are specified for both surfaces, so read the product data sheet and confirm that concrete is listed before the sealant goes into a joint.

Can you put asphalt over concrete?

It is done, but it is a resurfacing decision, not a patch. Joints and cracks in the concrete tend to show through the asphalt. Rocking or settling slabs must be fixed first. Ask a contractor how the joints will be treated and what the plan is for the edges.

Devon Moore, Operations Lead Founder & Operations Lead — D&D Commercial Services

Devon Moore is the founder and Operations Lead at D&D Commercial Services, delivering professional commercial property maintenance across Waterloo Region.