Question

I need information regarding fatigue cracking and block cracking in flexible pavements, information should include but not limited to ; causes, severity levels,measurement methods, maintenance procedures and preventive measures.

please write 3 or more references.

Thank you!

Answer 1

Several different types of cracks can develop in asphalt pavements. The repair depends on the type of crack. Some cracks are load-related and some are attributable to temperature or environment.

Fatigue Cracking.
Fatigue cracking is sometimes called alligator cracking due to the interconnected cracks which resemble an alligator�s skin. Fatigue cracking is caused by load-related deterioration resulting from a weakened base course or subgrade, too little pavement thickness, overloading, or a combination of these factors.

Block Cracking.
Block cracking is a series of large (typically one foot or more), rectangular cracks on an asphalt pavement�s surface. This type of cracking typically covers large areas and may occur in areas where there is no traffic. Block cracking is typically caused by shrinkage of the asphalt pavement due to temperature cycles.

The severity of cracks is categorised as low, moderate and high. Cracking is checked regularly by survey which can be manual or mechanical. Some strecthes are generally surveyed as it is not feasibile to survey enite pavemet length. Pavement evaluation is done by following methods:

1. Surface condition

2. Serviceability

3. Structural Capacity

4. Surface friction

In order to prevent some of the potential hazards associated with pavemen~
cracking, the following proposals are offered:
1. That adequate thickness of surfacings, bases, and subbases be
used so as to support the traffic loads for the life of the pavement desired.
2. That potential vertical rise is kept as low as possible, perhaps
below half-inch, and this may mean moisture control of clay subgrade prior
and subsequent to subgrade rolling operations. This will probably involve
ponding areas where layers are capable of producing considerable amounts
of volume change and covering subgrade with a suitable layer capable of
retarding evaporation.
3. That swell-shrink conditions of clay subgrades are controlled by
the use of shoulders consisting of granular and/or stabilized soils that are
wide enough to control moisture fluctuations.
4. That the soil binder portion of flexible base materials to be used
in frost susceptible areas of Texas should not contain more than 25 percent
minus 0.005 mm. material.
5. That when feasible all base and pavement layers should be con-
constructed out of materials whose ratio of compressive to tensile strength
varies from a minimum of 11 for 1500 psi. compressive strength material
to a minimum of 22 for 40 psi. material.
6. That highway research sections, especially in cuts, involving
marls, jointed clays, etc. which have high swell potential be treated with
several cycles of lime injection prior to paving. If the fairly large differential
movements due to volume change of soils are anticipated, especially such as

at grade points, fence lines, old road crossings, etc., it is recommended
that serious consideration be given to use of the Oklahoma Deep Mixing
process of lime treatment of subgrades.

Craking in flexible pavements can be repaired to some extent by removing some of the materials form the side of the cracked area, restructuring the pavement there with the original materials, and coating with the surface layer.