Causes of AC Distress
The following table summarizes the types of distresses that may be identified during a PCI survey of asphalt pavements, as well as brief descriptions and probable causes of each distress type.
| Distress Type | Distress Description | Probable Cause of Distress |
|---|---|---|
| Alligator Cracking | A series of interconnected or parallel cracks, frequently in a wheel path. | Fatigue failure of the asphalt concrete surface under repeated traffic loading. |
| Bleeding | A film of bituminous material on the pavement surface. | Excessive amounts of asphalt cement or tars in the mix and/or low air void content. |
| Block Cracking | Extensive interconnected cracks intersecting at approximately right angles, at a 1- to 10-ft spacing. | (1) Shrinkage of the asphalt concrete and daily temperature cycling (it is not load associated), or (2) a progression of longitudinal and transverse cracking. |
| Corrugation | A series of closely spaced ridges and valleys at regular intervals perpendicular to the traffic direction. | Traffic action combined with an unstable pavement layer. |
| Depression | A localized area at a lower elevation than the surrounding pavement. | Settlement of the foundation soil, or can be “built up” during construction. |
| Jet-Blast Erosion | Darkened and carbonized areas of pavement. | Bituminous binder has been burned or carbonized. |
| Joint Reflection Cracking | Cracks caused by underlying movement at PCC joints. | Movement of the concrete slab beneath the asphalt surface because of thermal and moisture changes. |
| Longitudinal and Transverse (L&T) Cracking | Any cracking on the pavement surface that does not fall into any other category. | (1) poorly constructed paving lane joint, (2) shrinkage of the AC surface due to low temperatures or hardening of the asphalt, or (3) reflective cracks caused by cracks in an underlying concrete slab. |
| Oil Spillage | Localized softening of the pavement surface. | Spilling of oil, fuel, or other solvents. |
| Patching | Removal and replacement of material for a repair or a utility cut. | A patch is often used to repair pavement distresses, or repair the pavement after a utility cut has been made. |
| Polished Aggregate | Extensive area of smoothed or polished aggregate. | Repeated traffic applications. |
| Raveling | Loss of coarse aggregate particles from the surface; also used to record scaling of slurry seals. | Asphalt binder may have hardened significantly, leading to loss of adhesion to coarse aggregate. |
| Rutting | A surface depression caused by load; typically occurs in a wheel path. | Usually caused by consolidation or lateral movement of the materials due to traffic loads. |
| Shoving | Swelling and cracking of AC pavement adjacent to PCC pavement. | Where PCC pavements adjoin flexible pavements, PCC “growth” may shove the AC pavement. |
| Slippage Cracking | Pattern of crescent or half-moon shaped cracks, frequently where traffic turns or brakes. | Low strength surface mix or poor bond between the surface and next layer of pavement structure. |
| Swelling | A localized area of pavement higher than the surrounding pavement; not due to shoving. | Usually caused by frost action or by swelling soil. |
| Weathering | Loss of fine aggregate particles and asphalt binder. | Asphalt binder may have hardened significantly. |