Types of Road Pavement

Difference Between Flexible and Rigid Pavement:

Flexible pavements can be defined as one consisting of a mixture of asphaltic or bituminous materials and aggregate placed on a bed of compacted granular material of appropriate quality in layers over the subgrade.

Rigid pavements are constructed from cement concrete or reinforced concrete slabs. Grouted concrete roads are the types of semi-rigid pavements.

Difference Between Flexible and Rigid Pavement

The following is difference between rigid and flexible pavement,

Flexible Pavement Rigid Pavement
1. Inflexible pavement deformation in the sub
the grade is transferred to the upper layers
1. In Rigid pavement deformation in the
the subgrade is not transferred to
2. Design is based on load distributing
characteristics of the component layers
2. Design is based on flexural strength or
slab action
3. Flexible pavement has a low flexural strength3. Rigid pavement has a high flexural strength
4. Inflexible pavement, the load is transferred
by grain to grain contact
4. In Rigid pavement, no such phenomenon of
grain to grain load transfer exists
5. Flexible pavement have low completion
cost but repairing cost is high
5. Rigid pavement have low repairing
cost but completion cost is high
6. Flexible pavement have a low life span6. Rigid pavement life span is more as
compared to flexible
7. Inflexible pavement surfacing cannot
be laid directly on the subgrade but a sub
base is needed
7. In Rigid pavement, the surfacing can be
directly laid on the subgrade
8. In Flexible pavement, no thermal stresses
are induced as the pavement can contract
and expand freely
8. In Rigid pavement thermal stresses
are more vulnerable to be induced
as the ability to contract and expand
is very less in concrete
9. That’s why expansion joints are not
needed in Flexible pavement
9. That’s why expansion joints are
needed in Rigid pavement
10. In Flexible pavement strength of the
the road is highly dependent on the strength
of the subgrade
10. In Rigid pavement strength of the road
is less dependent on the strength of
the subgrade
11. Rolling of the surfacing is needed in
Flexible pavement
11. Rolling of the surfacing is not needed
in Rigid pavement
12. The road can be used for traffic
within 24 hours in flexible pavement
12. The road cannot be used until 14 days
of curing in rigid pavement
13. In flexible pavement Force of friction
is less Deformation in the subgrade is not
transferred to the upper layers.
13. In Rigid pavement Force of friction is high

Road Pavement

A highway pavement is a structure consisting of superimposed layers of processed materials above the natural soil sub-grade, whose primary function is to transmit the applied vehicle loads to the sub-grade. There two main types of road pavement used namely Rigid and Flexible Pavement.

The structure of pavement should be potentially strong to provide a good surface of acceptable riding quality, adequate skid resistance, favorable light-reflecting characteristics, and low noise pollution.

The main purpose is to confirm that the transmitted stresses due to the thrust load of wheels are sufficiently reduced so that they will not exceed the bearing capacity of the sub-grade.

There are two types of road pavements are generally recognized as serving this purpose, namely flexible pavements, and rigid pavements. Unsuitable design of pavements may lead to the early failure of pavements affecting the riding quality.

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Types of Road Pavements

There are mainly two categories in which road pavements are classified:

  1. Flexible Pavements
  2. Rigid Pavements

1. Flexible Pavements

Flexible pavements can be defined as one consisting of a mixture of asphaltic or bituminous materials and aggregate placed on a bed of compacted granular material of appropriate quality in layers over the subgrade.

Water-bound macadam (WBM) roads and stabilized soil roads with or without bituminous toppings are examples of flexible or bituminous pavements. It is one of the most used types of road pavement.

The design of flexible pavements is based on the principle that for a load of any magnitude, the intensity of a load diminishes as the load is transmitted downwards from the surface by virtue of laying over an increasingly larger area, by carrying it deep enough into the ground through the layers of granular materials.

Flexible Pavement
Flexible Pavement

The wheel load acting on the pavement will be disturbed to a wider area and the stress decreases with the depth. By taking advantage of this stress distribution characteristic in bituminous pavements, pavements normally have many layers.

Flexible pavement layers reflect the deformation of the lower onto the surface layer. The lower layers will have undergone a lesser magnitude of stress and low-quality material can be used. Flexible pavements are constructed using bituminous materials.

The following types of construction have been used in flexible pavements:

A) Conventional Layered Flexible Pavements

Conventional flexible pavements are uniformly placed layered systems with magnificent quality materials that are placed among the high wherever stresses are high and quality low-priced materials are placed in lower layers.

B) Full-depth Asphalt Pavements

Fill-depth asphalt pavements are constructed by placing bituminous layers directly on the soil subgrade. This is preferable when there is high traffic and local materials are not available in the nearby market.

C) Contained Rock Asphalt Mat

Contained rock asphalt mats are created by installing dense/open-ranked combination layers in between 2 asphalt layers.

Changed dense ranked asphalt concrete overlays on top of the sub-grade can significantly cut back the vertical compressive strain in soil sub-grade and cover from surface water.

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2. Rigid Pavements

Rigid pavement is constructed from cement concrete or reinforced concrete slabs. Grouted concrete roads are the types of semi-rigid pavement.

The design of rigid pavements is based on providing a structural cement concrete slab of sufficient strength to resists the loads from traffic.

The rigid pavements have rigidity and high modulus of elasticity to distribute the load over a relatively wide area of soil. It is the most durable types of road pavement.

Rigid Pavement
Rigid Pavement

Minor variations in subgrade strength have little influence on the structural capacity of rigid pavements in the design of rigid pavement, the flexural strength of concrete is the important factor but not considered as the strength of subgrade.

Due to this property of pavement, when the subgrade deflects beneath the rigid pavement, the concrete slab is able to bridge over the localized failures and areas of inadequate support from the subgrade because of slab action.

Rigid types of road pavement are made by Portland cement concrete and will be analyzed by plate theory than layer theory. Bending of the block due to wheel load and temperature variation and ensuring tensile and flexural stress.

The following are types or classifications of rigid pavements:

A) Jointed Plain Concrete Pavements

Jointed plain concrete pavements are constructed with closely spaced contraction joints. Dowel bars and aggregate interlocks are generally used for load transfer across joints. They normally have a joint spacing of 8 to 15m.

B) Jointed Reinforced Concrete Pavements

Jointed Plain Concrete Pavements
Jointed Reinforced Concrete Pavements

Although reinforcements do not improve the structural capacity significantly, they can highly increase the joint spacing to 10 to 30m. Dowel bars are required for load transfer. Reinforcements help to keep the slab together even after cracks appear on the surface of the concrete.

C) Continuous Reinforced Concrete Pavements:

Continuous Reinforced Concrete Pavements
Continuous Reinforced Concrete Pavement

In continuous reinforced concrete types of road pavements, there is complete elimination of joints of reinforcement.

D) Pre-stressed Concrete Pavements

Pre-stressed concrete types of road pavement are designed and produced to be pre-stressed to bear tensile forces caused by external loads by various live objects such as vehicles on the roads or aircraft in the airports.

As compared to asphalt pavements, pre-stressed concrete pavements are more resistant to airplane’s or vehicle’s wheel thrust and also it cause less wear and tear to themselves. This type of road pavement is also useful to minimize maintenance costs.

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