What is a pot hole or alligator cracking and what causes it?

Pot Hole

A pothole (sometimes called kettle and known in parts of the Western United States as a chuckhole) is a type of disruption in the surface of a parking lot where a portion of the asphalt material has broken away, leaving a hole. Most potholes are formed due to fatigue of the pavement surface. As fatigue cracks develop they typically interlock in a pattern known as "alligator cracking". The chunks of pavement between fatigue cracks are worked loose and may eventually be picked out of the surface by continued wheel loads, thus forming a pothole. The formation of potholes is exacerbated by cold temperatures, as water expands when it freezes and puts more stress on cracked pavement. Once a pothole forms, it grows through continued removal of broken chunks of pavement. If a pothole fills with water the growth may be accelerated, as the water 'washes away' loose particles of road surface as vehicles pass. In temperate climates, potholes tend to form most often during spring months when the subgrade is weak due to high moisture content. However, potholes are a frequent occurrence anywhere in the world, including in the tropics (Costa-Rica).

Potholes can grow to feet in width, though they usually only become a few inches deep, at most. If they become large enough, damage to tires and vehicle suspensions can occur.

The Birth of a Pothole (Step 1)	The Birth of a Pothole (Step 2)
1. Potholes begin after snow or rain seeps into the soil below the road surface.	2. The moisture freezes when temperatures drop, causing the ground to expand and push the pavement up.

The Birth of a Pothole (Step 3)	The Birth of a Pothole (Step 4)
3. As the temperatures rise, the ground returns to normal level but the pavement often remains raised. This creates a gap between the pavement and the ground below it.	4. When vehicles drive over this cavity, the pavement surface cracks and falls into the hollow space leading to the birth of another pothole.

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Alligator Cracking Of The Pavement

• Alligator Cracking – is a series of interconnection cracks caused by fatigue failure of asphalt concrete surface under repeated traffic loading.
• Cracking begins at the bottom on the asphalt surface (base) where tensile stress and strain are highest under a wheel load. The cracks propagate to the surface initially as a series of parallel longitudinal cracks.
• After repeated traffic loading, the cracks connect, forming many-sided, sharp-angled pieces that develop a pattern resembling chicken wire or the skin of an alligator. The pieces are less than 2 ft. (.6m) on the longest side.
• Alligator cracking occurs only in areas subjected to repeated traffic loading, such as wheel paths.
• Alligator cracking is considered a major structural distress and is often accompanied by rutting.
• This type of distress often will have two or three levels of severity often within one distressed area. If these portions can be easily distinguished from each other, they should be measured and recorded separately.

Low Severity Alligator

Low: Fine, longitudinal hairline cracks running parallel to each other with one or only a few interconnecting cracks. The cracks are not spalled.

This crack is in a wheel path and is oriented in the direction of travel.

Medium Severity Alligator

Medium: Further development of light alligator cracking into a pattern or network of cracks that may be lightly spalled.

High Severity Alligator

High: Network or pattern cracking has progressed so that the pieces are well defined and spalled at the edges. Some pieces may rock under traffic. Potholes of all sizes are recorded as high severity alligator cracking.



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Asphalt Repair Procedure

The asphalt is marked into rectangles.

The asphalt is saw-cut and removed down to the sub-base. Upon excavation, the sub-base is evaluated for any areas of compromise which may need to be replenished.

Depending on your project specifications and the depth of the patch, we may install a 2” lift of binder. A tack coat is then applied to help the two asphalt surfaces bond properly.

Hot mix asphalt is purchased from the local hot mix plant.

Hot mix asphalt is then graded and luted in place for compaction.

Hot mix asphalt in place for compaction.

The asphalt is then compacted with a 1 – 3 ton vibratory roller.

The edges of the patch are then hot sealed to prevent any further water infiltration.