Historically, pavements have been divided into two broad categories, rigid and flexible. These classical definitions, in some cases, are an over-simplification. However, the terms rigid and flexible provide a good description of how the pavements react to loads and the environment.
The flexible pavement is an asphalt pavement. It generally consists of a relatively thin wearing surface of asphalt built over a base course and subbase course. Base and subbase courses are usually gravel or stone. These layers rest upon a compacted subgrade (compacted soil). In contrast, rigid pavementsare made up of portland cement concrete and may or may not have a base course between the pavement and subgrade.
The essential difference between the two types of pavements, flexible and rigid, is the manner in which they distribute the load over the subgrade. Rigid pavement, because of concrete’s rigidity and stiffness, tends to distribute the load over a relatively wide area of subgrade. The concrete slab itself supplies a major portion of a rigid pavement’s structural capacity. Flexible pavement, inherently built with weaker and less stiff material, does not spread loads as well as concrete. Therefore flexible pavements usually require more layers and greater thickness for optimally transmitting load to the subgrade.
The major factor considered in the design of rigid pavements is the structural strength of the concrete. For this reason, minor variations in subgrade strength have little influence upon the structural capacity of the pavement. The major factor considered in the design of flexible pavements is the combined strength of the layers.
One further practical distinction between concrete pavement and asphalt pavement is that concrete pavement provides opportunities to reinforce, texture, color and otherwise enhance a pavement, that is not possible with asphalt. These opportunities allow concrete to be made exceedingly strong, long lasting, safe, quiet, and architecturally beautiful. Concrete pavements on average outlast asphalt pavements by 10-15 years before needing rehabilitation.
Comparison of Flexible and Rigid Pavement
- Deformation in the sub grade is transferred to the upper layers (Flexible) & Deformation in the subgrade is not transferred to subsequent layers (Rigid)
- Design is based on load distributing characteristics of the component layers (Flexible) & Design is based on flexural strength or slab action (Rigid)
- Have low flexural strength (Flexible) & Have high flexural strength (Rigid)
- Load is transferred by grain to grain contact (Flexible) & No such phenomenon of grain to grain load transfer exists (Rigid)
- Have low completion cost but repairing cost is high (Flexible) & Have low repairing cost but completion cost is high (Rigid)
- Have low life span (Flexible) & Life span is more as compare to flexible (Rigid)
- Surfacing cannot be laid directly on the sub grade but a sub base is needed (Flexible) & Surfacing can be directly laid on the sub grade (Rigid)
- No thermal stresses are induced as the pavement have the ability to contract and expand freely (Flexible) & Thermal stresses are more vulnerable to be induced as the ability to contract andexpand is very less in concrete (Rigid)
- Thats why expansion joints are not needed (Flexible) & Thats why expansion joints are needed (Rigid)
- Strength of the road is highly dependent on the strength of the sub grade (Flexible) & Strength of the road is less dependent on the strength of the sub grade (Rigid)
- Rolling of the surfacing is needed (Flexible) & Rolling of the surfacing in not needed (Rigid)
- Road can be used for traffic within 24 hours (Flexible) & Road cannot be used until 14 days of curing (Rigid)
- Force of friction is less Deformation in the sub grade is not transferred to the upper layers. (Flexible) & Force of friction is high (Rigid)
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