Comparision Between Rigid and Flexible Pavement

Topics: Flexural strength, Crack, Crack cocaine Pages: 33 (7522 words) Published: May 21, 2011
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Md. Tahmidul Islam Farabi
06 02 03 031
4th Year 2nd Semester
Department of Civil Engineering
Ahsanullah University of Science & Technology


The road pavement is the actual surface on which the vehicles will travel. It's purpose is two fold, to provide friction for the vehicles and to transfer normal stresses to the underlying soils. Typically, pavements are built for three main purposes:

1. Load support: Pavement material is generally stiffer than the material upon which it is placed, thus it assists the in situ material in resisting loads without excessive deformation or cracking. 2. Smoothness: Pavement material can be placed and maintained much smoother than in situ material.  This helps improve ride comfort and reduce vehicle operating costs. 3. Drainage: Pavement material and geometric design can effect quick and efficient drainage thus eliminating moisture problems such as mud and ponding (puddles). Types of pavements

1. Flexible pavement
2. Rigid pavement
The pavements can be classified based on the structural performance into two, flexible pavements and rigid pavements. In flexible pavements, wheel loads are transferred by grain-to-grain contact of the aggregate through the granular structure. The flexible pavement, having less flexural strength, acts like a flexible sheet (e.g. bituminous road). On the contrary, in rigid pavements, wheel loads are transferred to sub-grade soil by flexural strength of the pavement and the pavement acts like a rigid plate (e.g. cement concrete roads). In addition to these, composite pavements are also available. A thin layer of flexible pavement over rigid pavement is an ideal pavement with most desirable characteristics. However, such pavements are rarely used in new construction because of high cost and complex analysis required.

Flexible pavement
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 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 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...
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