Alligator Cracking (fatigue cracking)
"Alligator cracks are interconnected cracks forming a series of small blocks resembling an alligator's skin.
Alligator cracking is caused by excessive deflection of the pavement surface. This can be caused by the subgrade or granular base course weakened by moisture; insufficient pavement thickness; an asphalt surface too thin; or overloading of the pavement. The affected areas are generally not large but often will cover entire sections of pavement. When this happens, it probably is due to repeated heavy loads that exceed the load carrying capacity of the pavement. If the asphalt is thin, alligator cracking can quickly progress into potholing.
A full-strength patch is the best repair. If the distress level is very light, temporary maintenance such as a slurry seal or other surface treatment or skin patching can help extend the time before a permanent repair is needed. Crack sealing is not the most cost effective way to repair alligator cracking."
depressions a.k.a. 'bird baths'
"Depressions are low areas of limited size that may be accompanied by cracking. These 'bird baths' collect water and are not only a source of pavement deterioration but are a hazard to motorists. These depressions can be noticed in dry weather where the pavement is stained.
Depressions may be caused by traffic overloading, or by consolidation, settlement or failure of the lower pavement layers.
Minor settlements and depressions can be repaired by surface treatments or micro-surfacing. Larger areas are repaired by a skin patch or full depth patching."
Block cracking (Shrinkage cracking)
"Block cracks are interconnected cracks forming a series of large blocks, 1-3 meters (3 to 10 feet) across, usually with sharp corners or angles.
Often it is difficult to determine whether block cracks are caused by volume change in the asphalt mix or in the base or subgrade. Frequently, they are caused by volume change of fine aggregate asphalt mixes that have a high content of low penetration asphalt and adsorptive aggregates. Lack of traffic hastens shrinkage cracking in these pavements. Another cause is the daily temperature cycles and the hardened (aged) asphalt. Block cracking is not load related.
Generally, block cracks are too numerous to economically seal with a crack sealant. Typically a surface seal can be applied. Fill large cracks with asphalt emulsion slurry followed by a surface treatment or a slurry seal. An overlay may also be required."
oil & Gasoline Spills
Oil, gasoline and transmission fluid spills soften the asphalt leading to its deterioration. Once the asphalt has deteriorated, moisture intrusion into the base layers is possible which can lead to alligator cracking and potentially potholes.
A full-depth patch is recommended to repair areas showing signs of deterioration due to engine fluid spills.
reflective cracking
"These are cracks in asphalt overlays that reflect the crack pattern, in the pavement structure underneath. The pattern may be longitudinal, transverse, diagonal, or block. They occur most frequently in asphalt overlays on pcc and on cement or pozzolanic-treated bases. They may also occur in asphalt overlays on asphalt pavements where cracks in the old pavement have not been properly repaired.
Reflective cracks are caused by vertical or horizontal movements in the pavement beneath the overlay, induced by expansion and contraction with temperature or moisture changes. They can also be caused by traffic or earth movements or by a loss of moisture in subgrades with high clay contents.
Seal or repair cracks based upon size and severity."
slippage cracks
"These are crescent shaped cracks resulting from horizontal forces induced by traffic. The ends of the curved crack point in the direction of the thrust of wheels on the pavement surface. This does not mean they invariably point in the direction of traffic flow. If brakes are applied on a vehicle going downhill the thrust of the wheels is reversed due to braking action. Slippage occurring in this circumstance will result in cracks pointing uphill.
Slippage cracks result from the lack of bond between the surface layer and the course beneath. The lack of bond may be due to dust, oil, rubber, dirt, water or other non-adhesive material between the two courses. Usually, such a lack of bond exists when no tack coat has been used or when no prime coat was used with a thin asphalt lift placed on the aggregate base. Slippage cracks may result from mixtures having a high sand content, as well as due to improper compaction.
Remove the affected asphalt layer and replace with a surface patch."
