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5. FLEXIBLE PAVEMENT
Flexible pavements are those pavements which reflect
the deformation of sub grade and the subsequent layers
to the surface.
Flexible, usually asphalt, is laid with no reinforcement or
with a specialized fabric reinforcement that permits limited
flow or repositioning of the roadbed under ground
changes.
The design of flexible pavement is based on load
distributing characteristic of the component layers.
The black top pavement including water & gravel bound
macadam fall in this category.
Flexible pavement on the whole has low or negligible
flexible strength flexible in their structural action).
6. The flexible pavement layers transmit the vertical or
compressive stresses to the lower layers by grain transfer
through contact points of granular structure.
The vertical compressive stress is maximum on the
pavement surface directly under the wheel load and is equal
to contact pressure under the wheels.
Due to the ability to distribute the stress to large area in the
shape of truncated cone the stresses get decreased in the
lower layer.
As such the flexible pavement may be constructed in a
number of layers and the top layer has to be strongest as the
highest compressive stresses.
To be sustained by this layer, in addition to wear and tear, the
lower layer have to take up only lesser magnitude of stress
as there is no direct wearing action due to traffic loads.
Therefore, inferior material with lower cast can be used in
the lower layers
7.
8. RIGID PAVEMENT
The rigid characteristic of the pavement are associated
with rigidity or flexural strength or slab action so the load is
distributed over a wide area of sub grade soil.
Rigid pavement is laid in slabs with steel reinforcement.
The rigid pavements are made of cement concrete either
plan, reinforced or pre stressed concrete.
Critical condition of stress in the rigid pavement is the
maximum flexural stress occurring in the slab due to wheel
load and the temperature changes.
Rigid pavement is designed and analyzed by using the
elastic theory.
9.
10. ADVANTAGES OF RIGID PAVEMENT
Rigid lasts much, much longer i.e 30+ years compared
to 5-10 years of flexible pavements.
In the long run it is about half the cost to install and
maintain. But the initial costs are somewhat high.
Rigid pavement has the ability to bridge small
imperfections in the sub grade.
Less Maintenance cost and Continuous Traffic and Flow.
High efficiency in terms of functionality
11. COMPARISON OF FLEXIBLE AND RIGID PAVEMENTS
Deformation in the sub grade is transferred to
the upper layers
Design is based on load distributing
characteristics of the component layers
low flexural strength , completion cost and
life span
Load is transferred by grain to grain contact
repairing cost is high
Surfacing cannot be laid directly on the sub
grade but a sub base is needed
No thermal stresses are induced in the
pavement.
Thats why expansion joints are not needed
Strength dependent on the strength of the
sub grade
Rolling of the surfacing is needed
Road can be used for traffic within 24 hours
Force of friction is less
Deformation in the sub grade is not
transferred to subsequent layers
Design is based on flexural strength or
slab action
Have high flexural strength and Life
span
No such phenomenon of grain to grain
load transfer exists
Have low repairing cost but completion
cost is high
Surfacing can be directly laid on the sub
grade
Thermal stresses are more vulnerable to
be induced as the ability to contract and
expand is very less in concrete
That's why expansion joints are needed
Strength of the road is less dependent
on the strength of the sub grade
Rolling of the surfacing in not needed
Road cannot be used until 14 days of
curing
Force of friction is high
Flexible Rigid