Types
Of Flexible & Rigid Pavement
Failures
Failure In Rigid Pavements
A Rigid Pavement
failure is observed by the development of structural cracks of break resulting
in progressive subsidence of some portions
of pavements. Moderate irregularities in the supporting layers beneath
the cement concrete pavements are sustained due to inherent
bending strength of these pavements. Rigid pavements therefore are capable of
withstanding slight variations in the underlying support and they bridge the
localized gaps moderately. It is the combination of many factors that induce
the failure conditions in the rigid pavements.
SCALING OF CEMENT CONCRETE
Scaling of rigid pavement simply means, peeling off or
flaking off of the top layer or skin of the concrete surface. This may be due
to the following reasons
- Improper
mix design
- Excessive
vibration during compaction of concrete
- Laitance
of concrete
- Performing
finishing operation while bleed water is on surface
SHRINKAGE CRACKS
Formation of hairline shallow cracks on concrete slab is
the indication of shrinkage cracks.
Shrinkage cracks develop on concrete surface during the
setting & curing operation. These cracks may form in longitudinal as well
as in transverse direction.
JOINT SPALLING
Joint spalling is the breakdown of the slab near edge of
the joint. Normally it occurs within 0.5 m of the joints. The common reasons
for this defect are
- Faulty
alignment of in-compressible material below concrete slab
- Insufficient
strength of concrete slab near joints
- Freeze-thaw
cycle
- Excessive
stress at joint due to wheel load
WARPING CRACKS
In hot weather, concrete slab tends to expand. Therefore,
the joints should be so designed to accommodate this expansion. When joints are
not designed properly, it prevents expansion of concrete slab and therefore
results in development of excessive stress. This stress cause formation of
warping cracks of the concrete slab near the joint edge.
This type of crack can be prevented by providing proper
reinforcement at the longitudinal and transverse joints. Hinge joints are
generally used to relieve the stress due to warping.
PUMPING
When material present below the road slab ejects out
through the joints or cracks, it is called pumping. When soil slurry comes out
it is called mud pumping.
The common reasons for this defect are
- Infiltration
of water through the joints, cracks or edge of the pavement forms soil
slurry. Movement of heavy vehicles on pavement forces this soil slurry to
come out causing mud pumping.
- When
there is void space between slab and the underlying base of sub-grade
layer
- Poor
joint sealer allowing infiltration of water
- Repeated
wheel loading causing erosion of underlying material
Failure In Flexible Pavements
A Flexible Pavement failure is defined by formation of
pot holes, ruts, cracks, localized depressions and settlements. The localized
depression normally is followed with heaving in the vicinity. The sequence
develops a wavy pavement surface. The failure of any one or more components of
the pavement surface or longitudinal ruts and shoving. Pavement unevenness may
itself be considered, as a failure, when it is excessive.
Ruts
The longitudinal depressions or cuts in flexible pavement
is known as ruts. These are usually formed ion earth or W.B.M roads of one lane
width due to repetitive traffic wheel loads on the same location, particularly
under wheeled traffic.
Pot Holes
The isolated depressions, more or less circular in shape
formed in flexible pavements are called pot holes or patches. These are usually
formed in all types of flexible pavements due to disintegration of road metal
or lack of binding surface course with the underlying base.
Frost Heaving
A localized heaving up of pavement portion is known as
frost heaving.
The water which may find access to pavement structure freezes
in cold climates. The expansion accompanying this frost action causes upheaval
which in turn may crack the pavement surface.
Shear Failure Cracking
The formation of a fracture or cracking due to upheaval
of pavement portion followed by a depression called shear failure cracking.
This type of failure occurs due to localized weakness in the pavement.
Longitudinal Cracking
The formation of cracks in the longitudinal direction of
a road pavement is called longitudinal cracking.
This failure is caused due to frost action, different
volume changes in sub-grade, settlement of filling material or due to sliding of
side slopes.
Map Cracking
The development of irregular cracks, usually formed on
bituminous surfacing is called map cracking.
This type of flexible road failure is due to excessive
wear of the road surface or due to localized weakness in the underlying base
course.
