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. 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.
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