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[[1]]Alligator Cracking Picture ask Joe how to format

Crocodile Cracking, also called alligator cracking, is a common type of distress in asphalt pavement. It is characterized by interconnecting or interlaced cracking in the asphalt layer resembling the hide of a crocodile. Cell sizes can vary in size up to 300mm across, but are typically less than 150mm across. It is often a sign of sub-base failure, poor drainage, or repeated over-loadings.

Moderate to severe crocodile cracking.

Development

Crocodile Cracking manifests itself initially as longitudinal cracking(cracks along the direction of the flow of traffic) in the top layer of the hot mix asphalt. These cracks are initially thin and sparsely distributed. If further deterioration is allowed, these longitudinal cracks are connected by latitudinal cracks to form sharp sided, prismatic pieces. This interlaced cracking pattern is the origin of the name "Crocodile Cracking". More severe cases involve pumping of fines, spalling, and loose pieces of pavement. The most severe cases of crocodile cracking often occur with other pavement distresses, but are exemplified by: potholes, large cracks(3/8" or larger), and severely spalled edges.

Another form of crocodile cracking is edge cracking, which is simply crocodile cracking located near the edge(within 1-2 feet)of the asphalt pavement. The failure begins at the edge of the pavement, and continues towards the center as condition worsens. Further Deterioration proceeds in much the same manner as with in-lane crocodile cracking.

Causes

Crocodile Cracking is an asphalt pavement distress most often instigated by failure of the surface due to traffic loading. Frequently, the base or subgrade inadequately support the surface layer, and subsequently it can't handle loads that it could normally endure. Poor drainage in the road bed is a frequent cause of this degradation of the base or subgrade.

Edge cracking is caused in much the same way as in-lane crocodile cracking, but has some causes that are more prevalent. Water ponding(build up of water)is a main cause of edge cracking, as it weakens the base which hastens the deterioration of the pavement.

Repair/Prevention

Preventing crocodile cracking can be as simple as preventing the common causes. For example, reducing overloading on an asphalt pavement or alleviating water ponding and poor drainage can prevent crocodile cracking in many cases. However, often the specific cause is fairly difficult to determine, and prevention becomes difficult correspondingly.

When repairing pavement affected by crocodile cracking, the main cause of the distress should be determined. Any investigation should involve digging a pit or coring the pavement to determine the pavement's structural makeup as well as determining whether or not subsurface moisture is a contributing factor. Fatigue crack repair generally falls into one of two categories:

When the crocodile pattern becomes visible, and the repair by crack sealing is generally ineffective.

   * Small, localized fatigue cracking indicative of a loss of subgrade support.  Remove the cracked pavement area then dig out and replace the area of poor subgrade and improve the drainage of that area if necessary.  Patch over the repaired subgrade.
   * Large fatigue cracked areas indicative of general structural failure.  Place an HMA overlay over the entire pavement surface.  This overlay must be strong enough structurally to carry the anticipated loading because the underlying fatigue cracked pavement most likely contributes little or no strength (Roberts et. al., 1996).