3.1 IDENTIFICATION OF DEFECTS:

Ø Fatigue cracking (Alligator cracking):

Fatigue cracking is commonly called alligator cracking. This is a series of interconnected
cracks creating small, irregular shaped pieces of pavement. It is caused by failure of the
surface layer or base due to repeated traffic loading (fatigue). Eventually the cracks lead to
disintegration of the surface, as shown in Figure. The final result is potholes. Alligator cracking
is usually associated with base or drainage problems. Small areas may be fixed with a patch or
area repair. Larger areas require reclamation or reconstruction. Drainage must be carefully
examined in all cases.

Longitudinal cracking:

Longitudinal cracks are long cracks that run parallel to the center line of the roadway.
These may be caused by frost heaving or joint failures or they may be load induced.
Understanding the cause is critical to selecting the proper repair. Multiple parallel cracks may
eventually form from the initial crack. This phenomenon, known as deterioration, is usually a
sign that crack repairs are not the proper solution

Transverse cracking :

Transverse cracks form at approximately right angles to the centerline of the roadway.
They are regularly spaced and have some of the same causes as longitudinal cracks. Transverse
cracks will initially be widely spaced (over 20 feet apart). They usually begin as hairline or very
narrow cracks and widen with age. If not properly sealed and maintained, secondary or
multiple cracks develop, parallel to the initial crack. The reasons for transverse cracking, and
the repairs, are similar to those for longitudinal cracking. In addition, thermal issues can lead
to low-temperature cracking if the asphalt cement is too hard. Figure shows a low-severity
transverse crack.

Block cracking:

Block cracking is an interconnected series of cracks that divides the pavement into
irregular pieces. This is sometimes the result of transverse and longitudinal cracks intersecting.
They can also be due to lack of compaction during construction. Low severity block cracking
may be repaired by a thin wearing course. As the cracking gets more severe, overlays and
recycling may be needed. If base problems are found, reclamation or reconstruction may be
needed. Figure shows medium to high severity block cracking.

Slippage cracking:

Slippage cracks are half-moon shaped cracks with both ends pointed towards the
oncoming vehicles. They are created by the horizontal forces from traffic. They are usually a
result of poor bonding between the asphalt surface layer and the layer below .The lack of a
tack coat is a prime factor in many cases. Repair requires removal of the slipped area and
repaving. Be sure to use a tack coat in the new pavement.

Reflective cracking:

Reflective cracking occurs when a pavement is overlaid with hot mix asphalt concrete
and cracks reflect up through the new surface. It is called reflective cracking because it reflects
the crack pattern of the pavement structure below. As expected from the name, reflective
cracks are actually covered over cracks reappearing in the surface. They can be repaired in
similar techniques to the other cracking noted above. Before placing any overlays or wearing
courses, cracks should be properly repaired.

Edge cracking:

Edge cracks typically start as crescent shapes at the edge of the pavement. They will
expand from the edge until they begin to resemble alligator cracking. This type of cracking
results from lack of support of the shoulder due to weak material or excess moisture. They
may occur in a curbed section when subsurface water causes a weakness in the pavement. At
low severity the cracks may be filled. As the severity increases, patches and replacement of
distressed areas may be needed. In all cases, excess moisture should be eliminated, and the
shoulders rebuilt with good materials. Figure shows high severity edge cracking.