transportation

1. AFTAB JAMIL 2012-BT-CIVIL-18
IMTIAZ KHAN 2012-BT-CIVIL-04
MALIK AMJAD 2012-BT-CIVIL-32

2. Alligator cracking is characterized as a series of interconnected cracks
creating small, irregular shaped pieces of pavement. The sizes of these
irregular shaped pieces vary, from less than 12-inches to 24-inches. The
cracking pattern is similar to the pattern found on alligator skin, and
therefore the source of its name.

3.  Relative movement of pavement layer material
 Repeated application of heavy wheel loads
 Swelling or shrinkage of subgrade or other layers due to moisture
variation
 Increase in loading (e.g., more or heavier loads than anticipated in design)
 Inadequate structural design
 Poor construction (e.g., inadequate compaction)

4. Low Severity Cracking
Medium Severity Cracking
High Severity Cracking

5. An area of cracks with no or very few interconnecting cracks and the cracks
are not spalled. Cracks are <= 0.25 in (6mm) in mean width. Cracks in the
pattern are no further apart than 1 foot (0.328 m). May be sealed cracks
with sealant in good condition and a crack width that cannot be determined.

6. An area of interconnected cracks that form a complete pattern. Cracks may
be slightly spalled. Cracks are >0.25 in. (6 mm) and <= 0.75 in. (19 mm) or
any crack with a mean width <= 19 mm and adjacent low severity cracking.
Cracks in the pattern are no further apart than 6 in. (150 mm).

7. An area of interconnected cracks forming a complete pattern. Cracks are
moderately or severely spalled. Cracks are >0.75 in (19mm) or any crack
with a mean width <= 0.75 in (19mm) and adjacent medium to high severity
random cracking.

18. A fatigue cracked pavement should be investigated to determine the root
cause of failure. Any investigation should involve digging a pit or coring the
pavement to determine the pavement’s structural makeup as well as
determining whether or not subsurface moisture is a contributing factor.
Once the characteristic alligator pattern is apparent, repair by crack sealing
is generally ineffective

19. 1. Small, localized fatigue cracking indicative of a loss of subgrade support.
2. Large fatigue cracked areas indicative of general structural failure.

20. Small, localized fatigue cracking indicative of a loss of subgrade support.
Remove the cracked pavement area then dig out and replace the area of
poor subgrade and improve the drainage of that area if necessary. Patch over
the repaired subgrade.

21. Large fatigue cracked areas indicative of general structural failure.
Place an HMA overlay over the entire pavement surface. This overlay must be
strong enough structurally to carry the anticipated loading because the underlying
fatigue cracked pavement most likely contributes little or no strength