Description Problem Possible Causes Description: Problem Possible Causes

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4.4.2 AlligatorFatigue Cracking:

Low severity Medium severity High severity Figure 4.3 Severity levels of Alligator cracking

a. Description:

Alligator fatigue cracking is a series of interconnecting cracks caused by fatigue failure of the asphalt concrete surface under repeated traffic loading. Cracking begins at the bottom of the asphalt surface or stabilized 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 crocodile, see Figure 4.3. Alligator cracking is considered a major structural distress.

b. Problem

Indicator of structural failure, cracks allow moisture infiltration, roughness, may further deteriorate to a pothole.

c. Possible Causes

1- Repeated traffic loading. 2- Poor materials used in pavement. 3- Insufficient thickness of the pavement. 4- Poor drainage. 78

d. Options for Repair Cures

Treatment based on the severity and intensity of cracks starting using overlays, surface patching or re-construction.

4.4.3 Block cracking

Low severity Medium severity High severity Figure 4.4 Severity levels of Block cracking

a. Description

Blocks are interconnected cracks that divide the pavement up into rectangular pieces. Blocks range in size from approximately 0.1m 2 1 ft 2 to 9m 2 100 ft 2 .larger blocks are generally classified as longitudinal and transverse cracking. Block cracking normally occurs over a large portion of pavement area but sometimes will occur only in non-traffic areas see Figure 4.4.

b. Problem

Allows moisture infiltration, roughness.

c. Possible Causes

Typically caused by an inability of asphalt binder to expand and contract with temperature cycles because of: - Asphalt binder aging - Poor choice of asphalt binder in the mix design. 79

d. Options for Repair Cures: