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Civil Engineering Highway Engineering Types of Pavements - Flexible vs Rigid Pavement

 

Pavements - Types of Pavements

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Definition:

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.

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

    1. Flexible Pavement
    2. Rigid Pavement

Download Flexible Pavement Design Manual

Flexible pavement: Definition

Are those pavements which reflect the deformation of subgrade 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.

aThe 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.

aFlexible 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.

aAs 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.

aTo 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: Definition

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.

aThe rigid pavements are made of cement concrete either plan, reinforced or prestressed concrete.

aCritical condition of stress in the rigid pavement is the maximum flexural stress occurring in the slab due to wheel load and the temperature changes.

aRigid pavement is designed and analyzed by using the elastic theory.

 

Advantages of Rigid Pavement

  1. Rigid lasts much, much longer i.e 30+ years compared to 5-10 years of flexible pavements.

  2. In the long run it is about half the cost to install and maintain. But the initial costs are somewhat high.

  3. Rigid pavement has the ability to bridge small imperfections in the subgrade.

  4. Less Maintenance cost and Continuous Traffic and Flow.

  5. High efficiency in terms of functionality

Comparison of Flexible and Rigid Pavement

Flexible Pavements
Rigid Pavements
  1. Deformation in the sub grade is transferred to the upper layers

  2. Design is based on load distributing characteristics of the component layers

  3. Have low flexural strength

  4. Load is transferred by grain to grain contact

  5. Have low completion cost but repairing cost is high

  6. Have low life span (High Maintenance Cost)

  7. Surfacing cannot be laid directly on the sub grade but a sub base is needed

  8. No thermal stresses are induced as the pavement have the ability to contract and expand freely

  9. Thats why expansion joints are not needed

  10. Strength of the road is highly dependent on the strength of the sub grade

  11. Rolling of the surfacing is needed

  12. Road can be used for traffic within 24 hours

  13. Force of friction is less Deformation in the sub grade is not transferred to the upper layers.

  14. Damaged by Oils and Certain Chemicals
  1. Deformation in the subgrade is not transferred to subsequent layers

  2. Design is based on flexural strength or slab action

  3. Have high flexural strength

  4. No such phenomenon of grain to grain load transfer exists

  5. Have low repairing cost but completion cost is high

  6. Life span is more as compare to flexible (Low Maintenance Cost)

  7. Surfacing can be directly laid on the sub grade

  8. Thermal stresses are more vulnerable to be induced as the ability to contract and expand is very less in concrete

  9. Thats why expansion joints are needed

  10. Strength of the road is less dependent on the strength of the sub grade

  11. Rolling of the surfacing in not needed

  12. Road cannot be used until 14 days of curing

  13. Force of friction is high

  14. No Damage by Oils and Greases
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