Crocodile cracking

Crocodile cracking, also called alligator cracking and perhaps misleadingly fatigue cracking, is a common type of distress in the wearing course road surface. The following is more closely related to fatigue cracking which is characterized by interconnecting or interlaced cracking in the seal layer resembling the hide of a crocodile. Cell sizes can vary in size up to 11.80 inches (300 mm) across, but are typically less than 5.90 inches (150 mm) across. Fatigue cracking is generally a loading failure, but numerous factors can contribute to it. It is often a sign of sub-base failure, poor drainage, or repeated over-loadings. It is important to prevent fatigue cracking, and repair as soon as possible, as advanced cases can be very costly to repair and can lead to formation of potholes or premature pavement failure. Crocodile cracking, also called alligator cracking and perhaps misleadingly fatigue cracking, is a common type of distress in the wearing course road surface. The following is more closely related to fatigue cracking which is characterized by interconnecting or interlaced cracking in the seal layer resembling the hide of a crocodile. Cell sizes can vary in size up to 11.80 inches (300 mm) across, but are typically less than 5.90 inches (150 mm) across. Fatigue cracking is generally a loading failure, but numerous factors can contribute to it. It is often a sign of sub-base failure, poor drainage, or repeated over-loadings. It is important to prevent fatigue cracking, and repair as soon as possible, as advanced cases can be very costly to repair and can lead to formation of potholes or premature pavement failure. It is usually studied under the transportation section of civil engineering. Fatigue cracking is a sealed pavement distress most often instigated by failure of the surface due to traffic loading. However, fatigue cracking can be greatly influenced by environmental and other effects while traffic loading remains the direct cause. Frequently, overloading happens because the base or subbase inadequately support the surface layer and subsequently cannot handle loads that it would normally endure. There are many ways that the subbase or base can be weakened. Poor drainage in the road bed is a frequent cause of this degradation of the base or subgrade. A heavy spring thaw, similarly to poor drainage, can weaken the base course, leading to fatigue cracking. Stripping or raveling is another possible cause of fatigue cracking. Stripping occurs when poor adhesion between asphalt and aggregate allows the aggregate at the surface to dislodge. If left uncorrected, this reduces the thickness of the pavement, reducing the affected portion's ability to carry its designed loading. This can cause fatigue cracking to develop rapidly, as overloading will happen with loads of less magnitude or frequency. Edge cracking is the formation of crescent-shaped cracks near the edge of a road. It is caused by lack of support of the road edge, sometimes due to poorly drained or weak shoulders. If left untreated, additional cracks will form until it resembles fatigue cracking. Like wheel-path fatigue cracking, poor drainage is a main cause of edge cracking, as it weakens the base, which hastens the deterioration of the pavement. Water ponding (a buildup of water which can also be called puddling) happens more frequently near the edge than in the center of the road path, as roads are usually sloped to prevent in-lane ponding. This leads to excess moisture in the shoulders and subbase at the road edge. Edge cracking differs from fatigue cracking in that the cracks form from the top down, where fatigue cracks usually start at the bottom and propagate to the surface. Fatigue cracking manifests itself initially as longitudinal cracking (cracks along the direction of the flow of traffic) in the top layer of the seal. These cracks are initially thin and sparsely distributed. If further deterioration is allowed, these longitudinal cracks are connected by transverse cracks to form sharp sided, prismatic pieces. This interlaced cracking pattern resembles the scales on the back of a crocodile or alligator, hence the nickname, crocodile cracking. More severe cases involve pumping of fines, spalling, and loose pieces of pavement. The most severe cases of fatigue cracking often occur with other pavement distresses, but are exemplified by: potholes, large cracks(3/8' or larger), and severely spalled edges. There are many different ways to measure fatigue cracking, but in general a pavement distress manual or index will be used. For example, the Pavement Condition Index is widely used to quantify the overall level of distress and condition of a section of road. Measurement of fatigue cracking specifically (and pavement distress in general) is necessary to determine the overall condition of a road, and for determination of a time-line for rehabilitation and/or repair. There are many other rating systems, and many rating systems currently in use are based on the AASHO Road Test.