TM 5-623
since faulting is incorporated into the severity level
(4) Shoving.
definitions of cracks. Crack definitions are also used in
(5) Swells.
defining corner breaks and divided slabs.
b. To determine the effects these distresses have
(2) Joint seal damage is not counted on a
slabby-slab basis. Instead, a severity level is assigned
on ride quality, the inspector should use the following
based on the overall condition of the joint seal in the
severity-level definitions of ride quality:
(1) L (low). Vehicle vibrations (e.g., from
area.
(3) Cracks in reinforced concrete slabs that
corrugation) are noticeable, but no reduction in speed is
are less than Y inch wide are counted as shrinkage
necessary for comfort or safety, and/or individual bumps
cracks.
Shrinkage cracks should not be used to
or settlements cause the vehicle to bounce slightly, but
determine if the slab is broken into four or more pieces.
create little discomfort.
(4) If the original distress of a patch is more
(2) M (medium).
Vehicle vibrations are
severe than the patch, the original distress is the distress
significant and some reduction in speed is necessary for
type recorded.
safety and comfort, and/or individual bumps or
(5) Low-severity scaling (i.e., crazing) should
settlements cause the vehicle to bounce significantly,
only be counted if there is evidence that future scaling is
creating some discomfort.
likely to occur.
(3) H (high).
Vehicle vibrations are so
c. The above is not intended to be a complete list.
excessive that speed must be reduced considerably for
To properly measure each distress type, the inspector
safety and comfort, and/or individual bumps or
must be familiar with its individual criteria.
settlements cause the vehicle to bounce excessively,
d. The severity level of blow-up and railroad
creating substantial discomfort, and/or a safety hazard,
distress in jointed concrete pavements is rated according
and/or high potential vehicle damage.
to the distress effect in ride quality (para B-4).
c. Ride quality is determined by riding in a
standard-size automobile over the pavement section at
B-4. Ride quality
the posted speed limit. Pavement sections near stop
a. Ride quality must be evaluated in order to
signs should be rated at the normal deceleration speed
used when approaching the sign.
establish a severity level for the following distress types:
(1) Bumps.
(2) Corrugation.
(3) Railroad crossings.
ALPHABETICAL LISTING OF DISTRESS TYPES-ASPHALT-SURFACED PAVEMENT
Name of Distress:
Alligator Cracking.
Description:
Alligator or 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 tensil 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 feet
on the longest side.
Alligator cracking occurs only in areas subjected to repeated traffic loading, such as wheel
paths. Therefore, it would not occur over an entire area unless the entire area were
subjected to traffic loading. (Pattern-type cracking which occurs over an entire area
that is not subjected to loading is called block cracking, which is not a load
associated distress.)
Alligator cracking is considered a major structural distress and is usually accompanied by
rutting.
Severity Levels:
L-Fine, longitudinal hairline cracks running parallel to each other with none or only a few
interconnecting cracks. The cracks are not spalled * (figs B-1 and B-2).
*Crack spalling is a breakdown of the material along the sides of the crack.
B-2
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