Raveling

Description

The progressive disintegration of an HMA layer from the surface downward as a result of the dislodgement of aggregate particles.

Figure 1: Raveling due to low density.

Figure 2: Raveling from snowplow operations.

Figure 3: Raveling caused by segregation.

Loose debris on the pavement, roughness, water collecting in the raveled locations resulting in vehicle hydroplaning, loss of skid resistance

Several including:

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.