Crocodile cracking: definition, and causes of crocodile cracking
Crocodile cracking is a type of crack that occurs on the surface of an asphalt paved road as a result of repetitive distress or flexing under stress. This type of cracking resembles the skin of a crocodile or alligator. As a result, it’s also interchangeably referred to as alligator cracking. There are different levels of severity depending on the extent of damage. The simplest or earliest stage of the cracking are longitudinal cracks which may or may not interconnected resembling a hairline fracture. The next stage is more severe where the surface cracks into a network of pieces which are interconnected known as spalling of the surface. This stage can be defined as an intermediate stage of severity. The final and more advanced stage resembles the skin and texture of a crocodile which means more pronounced cracks which are chunks of asphalt which can lead to hazards. By this stage, the fixing of the cracks at a surface level is often not possible and demands road closure to avoid accidents. Crocodile cracking is often localised and if the subgrade is severely impacted may have repetitive regions of breakdown. Crocodile cracking is a type of fatigue cracking that refers to a general type of cracking which is caused by iterative traffic loads, over a period of time. Repetitive surface stress on the asphalt pavement in sections where the tensile strain and stress are high under vehicular loads leads to deformation. This repetitive flexion or bend leads to interconnected cracks, which spread and propogate further at right angles as more time passes. There are three contributory factors that lead to crocodile cracking: namely freeze-thaw cycles, water intrusion into the subgrade, or lastly, subgrade compromise due to water softening from leakage leading to deformation. Crocodille cracking can also be bifurcated based on whether it’s under the path of a wheel, or wheel path, or non-wheeled path. If cracks appear along a wheel path, along the length of the road, or pavement, it’s largely attributed to fatigue under loads. However, if it’s not under a wheel path, yet parallel to the centre of the pavement, we can assume these type of cracks are due to the subgrade being impacted by moisture content, leading to cracks in the surface. These point more to the quality of the construction than surface level cracks caused by pressure.
Common instances of crocodile cracking:
There are some asphalt roads that are more prone to crocodile cracking than others. Typically, higher than planned vehicular load leads to asphalt pavement cracking. Therefore, airports, haul roads, industrial areas, residential roads with water logging, and busy intersections are often more likely to develop this distress. Cylical exposure to loads leads to formation of these cracks, or holes. While one can resurface these pavements, often this is a temporary solution as the cracks just propogate to a new layer, leading to a phenomenon called “reflective cracking”. In essence, an asphalt overlay on top of a cracked paved road is a temporary solution if there are more fundamental problems. Asphalt degradation can be attributed to one of three causes: environmental causes, repetitive stress of traffic, or inferior construction quality.
How to avoid crocodile cracking?
By providing tensile reinforcement within the pavement structure, geogrids distribute the tensile stresses induced by traffic loads evenly. This redistribution of stresses prevent the formation of localized areas of high strain, known as stress concentrations or “peaks,” at the bottom of the asphalt layer. Geogrids reduce the development of peaks in strain at the bottom of the asphalt layer in a paved road. These peaks in strain, if left uncontrolled, can lead to premature pavement failure and reduce the service life of a road expanse. Geogrid acts as a reinforcement layer that interlocks with the surrounding soil and asphalt layers.