Causes of Asphalt Pavement Failure

Insufficient asphalt binder, insufficient compaction, and segregation can cause surface distortions
Oxidation of asphalt binder and abrasive action of tires can also contribute to surface distortions
Severity levels of surface distortions:
- Low: Loss of fine aggregate matrix, fading of asphalt color, and exposure of coarse aggregate edges
- Medium: Edges of coarse aggregate exposed up to ¼ layer width
- High: Edges of coarse aggregate exposed more than ¼ layer width

Raveling is the dislodging of coarse aggregate
Causes of raveling:
- Insufficient asphalt binder
- Insufficient compaction
- Segregation
- Moisture or stripping of asphalt binder film from aggregate
- Oxidation of asphalt binder
- Abrasive action of tires
Severity levels of raveling:
- Medium: Considerable loss of coarse aggregate
- High: Surface is very rough and pitted
Raveling is measured in square meters of surface area

Pothole is a small, usually less than 750 mm in diameter, bowl-shaped depression in the pavement surface
Causes of pothole formation:
- Failure of the base or subgrade
- Poor drainage
- Structurally deficient pavement structure
- Inadequate pavement thickness
- No enough residual asphalt binder
Severity levels of pothole:
- Not specified
Pothole is measured in square meters of surface area

A patch is an area of pavement that has been replaced with new material to repair the existing pavement
A patch is considered a defect no matter how well it is performing
Severity levels of patch:
- Low: Patch is in good condition and satisfactory
Patch measurement:
- Not specified

Alligator or fatigue cracking is a series of interconnecting cracks caused by fatigue failure of the asphalt concrete surface under repeated traffic loading
Causes of alligator cracking:
- Inadequate base or subgrade support
- Lack of drainage
- Insufficient structural strength
- Overloading of the pavement
Severity levels of alligator cracking:
- Low: Longitudinal parallel hairline and non-spalled cracks with no or only a few interconnecting cracks
- Medium: Connected light alligator cracks, which form a network of cracks that may be lightly spalled
- High: Progressed cracks, while the pieces are well-defined and spalled at the edges
Alligator cracking is measured in square meters of surface area

Block cracking is a type of cracking that divides the pavement into rectangular pieces
Causes of block cracking:
- Shrinkage of the asphalt concrete or bases underneath and daily temperature cycling
- Non-load associated
- Insufficient compaction during construction
- Oxidation and hardening
Severity levels of block cracking:
- Low: < 6 mm and non-filled – filled cracks
- Medium: 6-12 mm and moderately spalled – filled cracks surrounded by light cracks
- High: Severely spalled cracks - > 12 mm and non-filled
Block cracking is measured in square meters of surface area

Longitudinal cracks are parallel to the pavement’s centerline or laydown direction, while transverse cracks are perpendicular
Causes of longitudinal/transverse cracking:
- Load-induced longitudinal cracks occur in the wheel path and eventually become alligator cracks
- Inadequate bonding of the sections during construction
- Segregation of asphalt mixture
- Joint in the underlying layer and construction joint
Severity levels of longitudinal/transverse cracking:
- Low: Non-filled crack width is less than 10 mm, or filled crack of any width
- Medium: Width of 10-75 mm and Non-filled; or, filled crack of any width surrounded by light random cracking
- High: Non-filled crack width greater than 75 mm, or cracks surrounded by severely cracked
Longitudinal/transverse cracking is measured in linear meters of crack

Slippage cracking is characterized by crescent or half-moon shaped cracks, usually transverse to the direction of travel
Causes of slippage cracking:
- Braking or turning wheels
- Poor bond between the surface and the next layer of the pavement structure
- Inadequate surface thickness
- High stresses due to braking and acceleration
Severity levels of slippage cracking:
- Low: Crack width < 10 mm
- Medium: Crack width (10 – 40) mm; or, the surrounding area is moderately spalled
- High: Crack width > 40 mm, the area around the crack is broken into easily removed pieces
Slippage cracking is measured in square meters of surface area

Rutting is a surface depression in the wheel paths accompanied by pavement uplift along the sides
Causes of rutting:
- Consolidation or lateral movement of the materials under traffic loading
- Poor compaction, high moisture content, or lack of lateral resistant
- Low design air voids, excessive asphalt binder, excessive sand or mineral filler, rounded aggregate particles, and low voids filled in mineral aggregate
- Insufficient structural strength in the pavement
Severity levels of rutting:
- Low: Rut depth is 6 to 13 mm
- Medium: Rut depth is 13 to 25 mm
- High: Rut depth is larger than 25 mm
Rutting is measured in square meters of surface area

Corrugation is a series of closely spaced ridges and valleys (ripples) occurring at a 3 m regular intervals
Causes of corrugation:
- Traffic action combined with an unstable pavement
- Too soft asphalt, high sand content, and an excessive presence of smooth and rounded aggregate in the mix
Severity levels of corrugation:
- Low: Low severity ride quality
- Medium: Medium severity ride quality
- High: High severity ride quality
Corrugation is measured in square meters of surface area

Shoving is a permanent, longitudinal displacement of a localized area of the pavement surface
Causes of shoving:
- Traffic pushes against the pavement
- The braking action of trucks
- The low stability asphalt mixture due to low air void content, excessive asphalt binder content, excessive sand, round aggregates
Severity levels of shoving:
- Low: Low severity ride quality
- Medium: Medium severity ride quality
- High: High severity ride quality
Shoving is measured in square meters of surface area

Depression is a localized pavement surface area with elevations slightly lower than those of the surrounding pavement
Causes of depression:
- Settlement of trenches
- Consolidation in the poorly compacted subgrade
- Change of moisture in the subgrade
Severity levels of depression:
- Low: Depth is 13 to 25 mm
- Medium: Depth is 25 to 50 mm
- High: Depth is larger than 50 mm
Depression is measured in square meters of surface area

Bleeding is a film of bituminous material on the pavement surface that creates a shiny, glasslike, reflecting, and sticky surface
Causes of bleeding:
- Excessive amounts of asphaltic cement or low air void content
- Moisture damage
Severity levels of bleeding:
- Low: Very slight degree - noticeable only during a few days of the year - Asphalt does not stick
- Medium: Asphalt sticks to shoes and vehicles during only a few weeks of the year
- High: Asphalt sticks to shoes and vehicles during at least several weeks of the year
Bleeding is measured in square meters of surface area