You cross your car park the morning after a night of rain and notice a thin dark line in the asphalt. From a distance, it looks like a surface mark. Up close, you can see it’s a crack.
Asphalt cracks when the movement or strain placed on it exceeds its ability to flex. Whether that happens depends on all sorts of factors, most notably traffic, temperature, water, ageing and movement below the surface.
So, what now? The earlier you can identify the cause, the better your chance of containing the problem. Here at Midlands Road Surfacing, we support businesses and councils across the Midlands with reliable asphalt repair services. On this page, we’ve put together the basics of what you need to know about preventing and repairing cracks in asphalt surfaces.
What does the crack pattern tell you?
Don’t just reach for a filler. The pattern of the cracks can tell you a lot about what’s going on.
For example:
- A long crack along a construction joint may show that the joint hasn’t bonded or compacted properly, or that it has opened over time.
- A crack running across the road may form as the asphalt expands and contracts with changes in temperature.
- A crack in an older layer may travel upwards through the newer asphalt. Contractors call this reflective cracking.
- Cracking near an edge without a kerb often means vehicles have overrun it or the material below no longer supports it.
- Cracks around gullies, inspection covers and utility trenches can indicate settlement or poor compaction around the reinstated area.
- Crescent-shaped cracks near entrances, junctions or turning areas may mean the upper asphalt layer has slipped over the layer beneath it. Contractors call this slippage cracking. The reason is usually poor bonding between the layers.
- If cracks join into small, irregular shapes within the wheel paths, known as crocodile cracking, repeated wheel loads have fatigued the pavement. The asphalt may be too thin for the traffic, the supporting layers may have weakened or both.
- Larger cracks dividing the surface into roughly rectangular sections are known as block cracking. Unlike crocodile cracking, they usually result from age-related hardening and temperature movement rather than traffic loads alone.
Of course, the pattern doesn’t provide a complete diagnosis. It does, however, give your surfacing contractor a good indication of where to start investigating.
How does water make cracking worse?
Water often isn’t the original cause of a crack. Traffic loads, temperature changes, ageing or movement beneath the asphalt may create the first break. However, water can contribute to cracking if poor drainage saturates and weakens the pavement’s supporting layers.
Once a crack, open joint or damaged edge gives water a route through the surface, the deterioration can accelerate.
This being England, there isn’t much you can do about the rain. You can, however, control where the water goes. Blocked gullies, poor falls and sunken wheel tracks allow it to collect on the surface. If it then enters the pavement, it may soften moisture-sensitive ground, reduce the stiffness of the unbound foundation or help displace fine material.
The asphalt loses support and flexes further under traffic.
The resulting movement widens the crack.
The resulting wider crack lets in more water.
And so the cycle continues.
Winter adds freeze-thaw action into the mix. Water inside cracks and gaps freezes, expands and widens the defect. It then thaws, allowing even more water to enter before passing tyres break away the weakened edges. Over repeated cycles, a narrow crack can lead to loose material and, eventually, a pothole.
How does traffic affect asphalt cracking?
Each passing vehicle bends (flexes) an asphalt surface by a small amount. It’s designed to accommodate this movement, but thousands of repeated loading cycles gradually fatigue the material. Eventually, the resulting strain can cause cracks to form.
The rate of damage certainly depends on the number of vehicles, but there’s more to it than that. Heavier axle weights and a weaker sub-base beneath the asphalt will mean defects appear sooner. A surface designed for cars may cope for years, then start failing when your site receives more HGVs, buses, plant or refuse vehicles than its original specification allowed. A pavement designed and built for those loads should cope with them without premature cracking.
The most likely places you’ll see fatigue cracks developing are in wheel paths, entrances, loading areas and turning points. These areas receive the most concentrated traffic and the greatest forces from braking, acceleration and sharp turns.
Cracking caused by continued movement or loss of support will usually spread unless you address the cause. As a vehicle moves over the crack, the surface flexes even more. This accelerates fatigue and allows the crack to spread even further.
Will asphalt always crack eventually?
Exposure to air and weather also hardens the bitumen binder, so older asphalt loses some flexibility. You can’t stop this ageing process altogether, but planned maintenance and suitable surface treatments can slow the deterioration. You can often see this kind of natural ageing through small block-shaped cracks across a surface rather than one isolated failure below.
Poor construction will also lead to cracks forming quicker. An unsuitable specification, a weak or thin sub-base, inadequate compaction, cold joints and unsupported edges all create weak points.
Laying new asphalt over untreated cracks can also allow the existing cracks to reflect through the new layer because the underlying cause hasn’t been addressed.
How can you prevent asphalt cracking?
You can’t keep asphalt crack-free forever, but you can delay cracking by designing the whole surface for its location and use.
Before laying starts, work with a trusted local surfacing contractor like MR Surfacing to assess the ground, drainage and expected traffic. Specify the materials and layer thickness for the heaviest regular vehicles, not just the average use. A stable, compacted sub-base spreads those loads. Correct falls and clear drainage routes carry water away, while edge restraints support the perimeter.
Crews must also place and compact the asphalt at the right temperature to form tight joints and bond each layer.
Once the surface is in use, inspect your asphalt after wet or cold weather, when cracks and standing water are easier to spot. Keep gullies and channels clear, remove soil and vegetation from the edges and stop vehicles overrunning unsupported margins.
What should you do when a crack appears?
If the damage creates a safety risk or is worsening under traffic, restrict access until a contractor can assess it. Serious damage on a road may require formal traffic management or a temporary closure.
The right repair depends on how far the damage has travelled. If you catch a narrow, isolated crack while the surrounding asphalt remains stable, you may only need to clean and seal it. However, if the crack has formed because the ground has settled, the visible line is only the surface symptom. Your contractor may need to cut out the failed material, repair the support below and compact a new asphalt patch into place.
Once cracks spread across wheel paths or form a crocodile pattern, filling each line won’t restore the surface’s strength. Before resurfacing, your contractor should repair unstable areas and treat any existing cracks. Planing and resurfacing may be enough if the damage remains within the upper layer. Road planing removes the failed asphalt so the crew can lay a new surface course while retaining the stable construction below, avoiding full-depth reconstruction. If the base or sub-base has also failed, it must be excavated and rebuilt before the surface is replaced.
If you’re unsure what the cracks in your asphalt mean, MR Surfacing can inspect your road, car park, driveway, yard or access route and recommend crack treatment, patching, drainage work, planing, resurfacing or reconstruction. Speak with our team today.