The progressive disintegration of an HMA layer from the surface downward as a result of the dislodgement of aggregate particles.
- Loss of bond between aggregate particles and the asphalt binder as a result of:
- A dust coating on the aggregate particles that forces the asphalt binder to bond with the dust rather than the aggregate
- Aggregate Segregation. If fine particles are missing from the aggregate matrix, then the asphalt binder is only able to bind the remaining coarse particles at their relatively few contact points.
- Inadequate compaction during construction. High density is required to develop sufficient cohesion within the HMA. The third figure above shows a road suffering from raveling due to inadequate compaction caused by cold weather paving.
- Mechanical dislodging by certain types of traffic (studded tires, snowplow blades or tracked vehicles). The first and fourth figures above show raveling most likely caused by snow plows.
A raveled pavement should be investigated to determine the root cause of failure. Repair strategies generally fall into one of two categories:
- Small, localized areas of raveling. Remove the raveled pavement and patch.
- Large raveled areas indicative of general HMA failure. Remove the damaged pavement and overlay.