Basic Knowledge about Road Pavement you must know: Rigid and Flexible Pavement - engineeringnepal.com.np - Engineering Nepal, The complete engineering website.

Basic Knowledge about Road Pavement you must know: Rigid and Flexible Pavement


Road pavement:

Rigid ad Flexible Pavement

Road pavement is a specified space required for the movement of traffic, vehicle below or above the ground level.

In other word a stable layer constructed over the natural soil can be defined as road pavement.

The main function of road pavement is to support and transfer the wheel road of vehicle                  over a wide area on the under laying soil sub-grade.

         A pavement consists of one or more layer normally sub-grade, sub base, base, wearing course.

Ø  The top most layer is wearing or surfacing course, the purpose of which is to provided smooth, abrasion resisting surface water infiltration & strong layer.

Ø  Base course is the layer of graded material located below the wearing course to transfer the stress to sub-grade through pavement sub base.
Ø  The agg/ gravel located between pavement sub-grade and base course to provided additional support for distributing the stress is called sub base.
Ø  Sub-grade is an integral part of road pavement as it provided the support to the pavement from beneath.

Type of road pavement

Based on structural behavior, the road pavement are generally classified into two types.

a)      Flexible pavement:



The pavement which have negligible flexural strength in their structural action under the load are known as flexible pavement. The flexible pavement, layer transmits the vertical compressive stress to the lower layer by grain to grain transfer through the point of contract. The vertical compressive stress is maximum on the pavement surface directly under the wheel road and successively decrease to lower layer. Their to bottom layer also decrease corresponding to resulting stress to minimize the cost of road. Its example are local soil made road, general, WBM or bituminous road.

b)      Rigid pavement:

The pavement which have worthly flexural strength are known as rigid pavement. The rigid pavement are made of plan reinforcement or pre-stressed. Rigid pavement consists of cement concrete slab, below which a granular sub base or base course over sub-grade soil, the plan cement concrete are excepted to take up to kg/cm2 flexural stress.

c)      Semi rigid pavement:


Semi rigid the pavement which have flexural strength in between rigid and flexible pavement are known as semirigid pavement. It is made of lean cement concrete, soil cement, pozzolanic concrete.
Difference between rigid & flexible pavement:
Rigid pavement
Flexible pavement




1
Initial cost is more
1
Initial cost is less




2
Maintenance cost is less
2
Maintenance cost is more




3
The life of well designed
3
The life of well designed

pavement is about 40 years

pavement is about 20 years.
4
It is done at a time
4
It can be done in a stage



construction.
5
Less Gloaring effects.
5
More Gloaring effects.




6
Better for night visibility
6
Less better for night visibility

consideration.

consideration then compair to



rigid pavement.
7
Pavement surface is good.
7
Pavement surface is worse.




8
Design of the pavement is
8
Design of the pavement is done

done with high accuracy.

with less accuracy.

Function of pavement layers:

1)      Subgrade is layer of natural:

Soil of field soil prepared to received the pavement material over it. It acts as a foundation for the pavement layers.
Ø  It should provide support to all the load imposed on pavement.

Ø  Subgrade soil should not collect water and should have good drainage.
Ø  Should be compacted permanently.

Ø  Should be course grained soil.

2)      Function of sub base course:


Ø  Improve bearing capacity of subgrade.

Ø  Helps base and surface course to distribute load.
Ø  Minimize the damage course by superimposed load on subgrde.

Ø  Facilities drainage of free water accumulated below pavement.
Ø  Check capillary rise of sub-soil water.

Ø  Support sub-base broken stones.

3)      Function of base course:


Ø  Generally broken brick, broken stone, stabilized soil are used in this layer.
Ø  Acts as a structural portion of pavement to distribute load imposed on pavement.

Ø  Pavement instrusion of fine grained road material into the pavement if load directly over the subgrade.

4)      Function of surface course:

Ø  Performs a structural portion of pavement.

Ø  Resist abrasion.
Ø  Reduce penetration of surface water into pavement.

Ø  Provide skid resistance.
Ø  Provide smooth and comfort riding surface.


Materials of pavement layers:

1.      Sub-grade soil (Natural soil)
2.      Natural stone aggregate.

3.      Broken stone aggregate. (water bond macadam type)
4.      Bituminous material
5.      Water

6.      Stone dust (stabilized soil base course)
7.      Kerosene

8.      Portable cement.

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