Types Of Pavements | Flexible vs. Rigid

Pavements form the basic supporting structure in highway transportation. Basically, all hard surfaced pavement types can be categorized into two groups, flexible and rigid.The manner in which the loads are distributed to the subgrade makes the difference between flexible and rigid pavements. Details of these two are presented below:

1. FLEXIBLE PAVEMENTS

Flexible pavements are those which are surfaced with bituminous (or asphalt) materials and they will transmit wheel load stresses to the lower layers by grain-to-grain transfer through the points of contact in the granular structure.  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. A typical cross section of the flexible pavement is shown below.

2. RIGID PAVEMENTS

Rigid pavements are generally used in constructing airports and major highways, such as those in the interstate highway system. In addition, they commonly serve as heavy-duty industrial floor slabs, port and harbor yard pavements, and heavy-vehicle park or terminal pavements. Like flexible pavements, rigid highway pavements are designed as all-weather, long-lasting structures to serve modern day high-speed traffic. Offering high quality riding surfaces for safe vehicular travel, they function as structural layers to distribute vehicular wheel loads in such a manner that the induced stresses transmitted to the subgrade soil are of acceptable magnitudes.
Compared to flexible pavement, rigid pavements are placed either directly on the prepared sub-grade or on a single layer of granular or stabilized material. Since there is only one layer of material between the concrete and the sub-grade, this layer can be called as base or sub-base course.

Comparison of Flexible and Rigid Pavement

 

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
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.
Deformation in the sub grade 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
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


 

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