6.1 Types of Pavement

  

The highway structure, which is constructed with combination of natural as well as artificial materials and have a sufficient strength to take and transfer the traffic load from surface to under laying strata is called pavement.

An ideal road pavement shall have following requirements

• Sufficient thickness to distribute the wheel load stresses to a safe value on the sub-grade soil.
• Structurally strong to withstand all types of stresses imposed on it.
• Adequate coefficient of friction to prevent skidding of vehicles.
• Smooth surface to provide comfort to road users even at high speed.
• Produce less noise from moving vehicles.
• Dust proof surface so that traffic safety is not impaired by reducing visibility.
• Long design life with low maintenance cost.

Types of pavement

Flexible pavement: Flexible pavement can be defined as the one consisting of a mixture of asphaltic or bituminous material and aggregates placed on a bed of compacted granular material of appropriate quality in layers over the sub-grade. Water bound macadam roads and stabilized soil roads with or without asphaltic toppings are examples of flexible pavements. There can be grading in the quality of materials used, the materials with high degree of strength is used at or near the surface. Thus the strength of sub-grade primarily influences the thickness of the flexible pavement.

Advantage

• The construction of flexible pavement is ease and fast.
• These are economical road pavement.
• Maintenance of flexible pavement is easy.
• There is less possibility of formation of ice glaze.

Disadvantage

• The duration of flexible pavement is short.
• The maintenance cost of flexible pavement is relatively high.
• Easy to damage.
• The edge of flexible pavement if weak so higher chances of erosion.

Rigid pavement: A rigid pavement is constructed from cement concrete or reinforced concrete slabs. Grouted concrete roads are in the category of semi-rigid pavements. The design of rigid pavement is based on providing a structural cement concrete slab of sufficient strength to resists the loads from traffic. The rigid pavement has rigidity and high modulus of elasticity to distribute the load over a relatively wide area of soil. In the design of a rigid pavement, the flexural strength of concrete is the major factor and not the strength of sub-grade.

Advantage

• Rigid pavement has higher life span.
• These require less maintenance cost.
• Can be constructed in poor soil areas.
• These pavements have higher load carrying capacity.

Disadvantage

• Rigid pavement has higher initial cost.
• So many joints are required on pavement.
• These pavements have rough riding quality.
• The maintenance cost is relatively high.

Difference between Flexible Pavements and Rigid Pavements

S.N	Flexible pavement	Rigid pavement
1	It consists of a series of layers with the highest quality materials at or near the surface of pavement.	It consists of one layer Portland cement concrete slab or relatively high flexural strength.
2	It reflects the deformations of sub-grade and subsequent layers on the surface.	It is able to bridge over localized failures and area of inadequate support.
3	Its stability depends upon the aggregate interlock, particle friction and cohesion.	Its structural strength is provided by the pavement slab itself by its beam action.
4	Pavement design is greatly influenced by the sub-grade strength.	Flexural strength of concrete is a major factor for design.
5	It functions by a way of load distribution through the component layers	It distributes load over a wide area of sub-grade because of its rigidity and high modulus of elasticity.
6	Temperature variations due to change in atmospheric conditions do not produce stresses in flexible pavements.	Temperature changes induce heavy stresses in rigid pavements.
7	Flexible pavements have self healing properties due to heavier wheel loads are recoverable due to some extent.	Any excessive deformations occurring due to heavier wheel loads are not recoverable, i.e. settlements are permanent.