civil engineering laboratory testing equipment
Asphalt Stripping
Description
The loss of bond between aggregates and asphalt binder that typically begins at the bottom of the HMA layer and progresses upward. When stripping begins at the surface and progresses downward it is usually called raveling.
Although the displacement of asphalt on the aggregate particle surface by water (stripping) is a complex phenomena and is not yet fully understood, mineralogy and chemical composition of the aggregate have been established as important contributing factors (Roberts et al., 1996[1]). In general, some aggregates have an affinity for water over asphalt (hydrophilic). These aggregates tend to be acidic and suffer from stripping after exposure to water. On the other hand, some aggregates have an affinity for asphalt over water (hydrophobic). These aggregates tend to be basic and do not suffer from stripping problems. Additionally, an aggregate’s surface charge when in contact with water will affect its adhesion to asphalt cement and its susceptibility to moisture damage. In sum, aggregate surface chemistry seems to be an important factor in stripping. However, specific cause-effect relationships are still being established.
Problem
Decreased structural support, rutting, shoving/corrugations, raveling, or cracking (fatigue and longitudinal)
Possible Causes
Bottom-up stripping is very difficult to recognize because it manifests itself on the pavement surface as other forms of distress including rutting, shoving/corrugations, raveling, or cracking. Typically, a core must be taken to positively identify stripping as a pavement distress.
- Poor aggregate surface chemistry
- Water in the HMA causing moisture damage
- Overlays over an existing open-graded surface course. Based on experience, these overlays will tend to strip.
Repair
A stripped pavement should be investigated to determine the root cause of failure (i.e., how did the moisture get in?). Generally, the stripped pavement needs to be removed and replaced after correction of any subsurface drainage issues.