(2) Surface deformation :


Pavement deformation is the result of weakness in one or more layers of the pavement
that has experienced movement after construction. The deformation may be accompanied by
cracking. Surface distortions can be a traffic hazard. The basic types of surface deformation
are:




1. Rutting


2. Corrugations


3. Shoving


4. Depressions


5. Swell




Ø Rutting




Rutting is the displacement of pavement material that creates channels in the wheel
path. Very severe rutting will actually hold water in the rut. Rutting is usually a failure in one or
more layers in the pavement. The width of the rut is a sign of which layer has failed. A very
narrow rut is usually a surface failure, while a wide one is indicative of a sub grade failure.
Inadequate compaction can lead to rutting. Figure shows an example of rutting due to sub
grade Failure. Minor surface rutting can be filled with micro paving or paver-placed surface
treatments. Deeper ruts may be shimmed with a truing and leveling course, with an overlay
placed over the shim. If the surface asphalt is unstable, recycling of the surface may be the
best option. If the problem is in the sub grade layer, reclamation or reconstruction may be
needed.




Ø Corrugation




Corrugation is referred to as wash boarding because the pavement surface has
become distorted like a washboard. The instability of the asphalt concrete surface course may
be caused by too much asphalt cement, too much fine aggregate, or rounded or smooth
textured course aggregate. Corrugations usually occur at places where vehicles accelerate or
decelerate. Minor corrugations can be repaired with an overlay or surface milling. Severe
corrugations require a deeper milling before resurfacing.



 Shoving

Shoving is also a form of plastic movement in the asphalt concrete surface layer that
creates a localized bulging of the pavement. Locations and causes of shoving are similar to
those for corrugations. Figure shows an example of shoving. Repair minor shoving by removing
and replacing. For large areas, milling the surface may be required, followed by an overlay.

Ø Depressions

Depressions  are  small,  localized  bowl-shaped  areas  that  may  include  cracking.
Depressions  cause  roughness,  are  a  hazard  to  motorists,  and  allow  water  to  collect.
Depressions are typically caused by localized consolidation or movement of the supporting
layers beneath the surface course due to instability. Repair by excavating and rebuilding the
localized depressions. Reconstruction is required for extensive depressions
Ø Swell
A swell is a localized upward bulge on the pavement surface. Swells are caused by an
expansion of the supporting layers beneath the surface course or the sub grade. The
expansion is typically caused by frost heaving or by moisture. Sub grades with highly plastic
clays can swell in a manner similar to frost heaves (but usually in warmer months). Repair
swells by excavating the inferior sub grade material and rebuilding the removed area.
Reconstruction may be required for extensive swelling.

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