In a bituminous pavement, alligator cracking is mainly due to

Explanation:

Alligator Cracking (Fatigue Cracking):

• Alligator cracking, also called fatigue cracking, appears as interconnected cracks resembling the scales of an alligator.

• It is one of the most common and severe distresses in flexible (bituminous) pavements.

• The primary cause is fatigue failure of the pavement structure, especially the bituminous layers, due to repeated traffic loads over time.

• Cracks usually initiate at the bottom of the asphalt layer and propagate upward when the tensile strain exceeds the material's fatigue limit.

• It generally occurs in areas of high wheel load repetition, like wheel paths.

 Additional Information

• An excess amount of bitumen in the mix leads to bleeding, where bitumen comes to the surface, making it shiny and slippery.

• It can also result in rutting due to low stiffness and deformation under wheel loads, especially in hot climates.

• However, excessive bitumen does not cause the material to crack, and is unrelated to the fatigue-based cracking mechanism of alligator patterns.

• The sub-base layer distributes loads to the subgrade and adds structural strength to the pavement system.

• If the sub-base is too thin or weak, it can lead to differential settlement, increased deflection, and loss of support for the upper layers.

• This can accelerate fatigue failure, but the root mechanism for alligator cracking remains repeated stress application, not just sub-base deficiency.

• The wearing course is the top layer of the flexible pavement that provides smooth riding quality and skid resistance.

• If it is too thin or poorly constructed, surface defects like raveling, potholes, or bleeding may occur.

• While it may expose the underlying layers to moisture and oxidation over time, it does not directly cause fatigue cracking, which starts due to tensile stress in lower asphalt layers.