1. Flexible pavement
2. Rigid pavement

Flexible pavement:

Rigid pavement:

Flexible pavement: Definition

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: Definition

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

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
   
   

   Flexible Pavements

   Rigid Pavements

   Deformation in the sub grade is transferred to the upper layers Design is based on load distributing characteristics of the component layers Have low flexural strength Load is transferred by grain to grain contact Have low completion cost but repairing cost is high Have low life span (High Maintenance Cost) Surfacing cannot be laid directly on the sub grade but a sub base is needed No thermal stresses are induced as the pavement have the ability to contract and expand freely Thats why expansion joints are not needed Strength of the road is highly 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 the upper layers. Damaged by Oils and Certain Chemicals

   Deformation in the subgrade is not transferred to subsequent layers Design is based on flexural strength or slab action Have high flexural strength No such phenomenon of grain to grain load transfer exists Have low repairing cost but completion cost is high Life span is more as compare to flexible (Low Maintenance Cost) 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 Thats 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 No Damage by Oils and Greases