Asphalt paving can develop cracks for a myriad of reasons. Knowing when to repair and when to replace depends on the type of crack and its cause.
1. Alligator Cracks
These cracks form a scale-like pattern on the surface of the asphalt, similar to the skin on an alligator. The cracks form due to load fatigue from supporting too much weight. A weak paving base or an overly thin asphalt layer are the most common causes of poor support and alligator cracking, but even overly heavy traffic compared to what the paved area was designed for can lead to the problem. Temporary repairs with crack filler are possible, but reconstruction of the damaged area is best.
2. Block Cracks
Block cracking earns its name from the way several cracks meet to form a square in the paving. Typically, this type of cracking forms as a series of interlocking cracks that form multiple squares. The cracks form in response to expansion and contraction due to temperature changes, usually when the wrong binder for the local climate was used in the asphalt mix. The damaged area should be removed and replaced with new asphalt using the proper binders.
3. Longitudinal Cracks
These cracks affect roads and driveways. The cracks form along the direction that travel occurs on the paving. Temperature fluctuations or a poorly placed expansion joint is the usual culprit. If the asphalt and base materials are in good condition, then the cracks are often repairable without replacement. Small cracks require a simple asphalt filler, while larger cracks may first be stuffed with a foam expansion joint before the asphalt filler is installed.
4. Edge Cracks
Edge cracks are caused when the edge of the base material doesn't extend out far enough to properly support the edge of the asphalt. Prevention is better than repair. These cracks can sometimes be avoided by putting concrete skirting and curbs around the perimeter of the paving. Bad drainage along the edge can also cause edge cracking. In severe cases, the base and asphalt edge may need to be rebuilt to fix the problem.
5. Upheaval Cracks
An upheaval crack is when the paving on one side of the crack sits higher than on the other side. It's usually caused by frost heave, but sometimes tree roots or other causes of soil movement lead to an upheaval crack. Installing a sufficiently deep and stabilized base is the best prevention. A repair usually means rebuilding the paving from the base up.
Contact an asphalt paving contractor for more information.