Carriageway
A carriageway consists of a
width of road on which a vehicle is not restricted by any physical barriers or
separation to move laterally. A carriageway generally consists of a number of
traffic lanes together with any associated shoulder, but may be a sole lane in
width.
Pavement
Pavement is the actual
travel surface especially made durable and serviceable to withstand the traffic
load commuting upon it. Pavement grants friction for the vehicles thus
providing comfort to the driver and transfers the traffic load from the upper
surface to the natural soil. In earlier times before the vehicular traffic
became most regular, cobblestone paths were much familiar for animal carts and
on foot traffic load.
pavement |
Pavements are primarily to
be used by vehicles and pedestrians. Storm water drainage and environmental
conditions are a major concern in the designing of a pavement. The first of the
constructed roads date back to 4000 BC and consisted of stone paved streets or
timber roads. The roads of the earlier times depended solely on stone, gravel
and sand for construction and water was used as a binding agent to level and
give a finished look to the surface. All hard road pavements usually fall into
two broad categories namely
Flexible Pavement
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
underground 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). 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 die to traffic
loads, therefore inferior material with lower cast can be used in the lower
layers.
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 subgrade 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.
Comparison of Rigid and flexible pavement
Flexible pavement
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Rigid pavements
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Deformation in the sub grade is transferred to upper layers
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Deformation in the sub grade is transferred to subsequence
Layers
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Have low flexural strength
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Have high flexural Strength
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Load transferred to gain to gain contract
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No such phenomenon of grain to grain load transferred
exist
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Have low completion test but high repairing cost
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Have low repairing cost but high completion cost
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Damaged by oil and chemicals
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No damage by oil or Greece
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Sesign Based on load distribution factor
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Design based on Flexural strength or slab action
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