Weathering

As pavement ages and hardens, the asphalt binder and fine aggregate may begin to wear away. This process is called weathering. As weathering progresses, coarse aggregate becomes exposed, dislodged, and missing; a distress called raveling. This usually results in a pavement surface with an increasing FOD potential. Weathering is only identified as a distress when observed on the surface of dense mix AC pavements.

Severity	Distress Example	Description
Low		Low-severity weathering is recorded when the surface begins to show signs of aging which may be accelerated by climatic conditions. Loss in the fine aggregate matrix is noticeable and may be accompanied by fading of the asphalt color. Edges of the coarse aggregates are beginning to be exposed less than 0.05 in (1 mm). Pavement may be as new as 6 months old.
Medium		Medium-severity weathering is recorded when the loss of the fine aggregate matrix is noticeable and the edges of the coarse aggregate have been exposed up to 1/4 of the longest side. As implied by low-severity, the coarse aggregate is exposed greater than 0.05 in (1 mm), but less than 1/4 of their width as determined by their longest side.
High		High-severity weathering is recorded when the edges of the coarse aggregate have been exposed greater than 1/4 of their width (of the longest side). This considerable loss of the fine aggregate matrix can lead to FOD potential and loss of coarse aggregate; a distress identified as raveling.