Asphalt Pavement Defects

Surface Distortions

• 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

• 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

• 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

Patch

• 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

Pavement Cracking

Alligator Cracking

• 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

• 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/Transverse Cracking

• 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

• 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

Pavement Deformation

Rutting

• 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

• 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

• 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

• 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

Pavement Surface Defects

Bleeding

• 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