Pavement Structure.pdf

7/27/2019 Pavement Structure.pdf

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Pavement Structure

Cross section of Typical Rural Road


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Cross section of Typical Pavement Structure

Definition of a Pavement

Pavement refers to the hard paved part of the road that

carries the vehicular traffic.

Though in some British literature the term means only

footpath, pavement is also known as carriageway or crust.

A highway pavement is a structure consisting of superimposed

layers of selected and processed materials which supports

applied traffic loads and distributes that load to the soil.

The pavement is a special type of structure where its major

part is kept below the surface but the top portion is exposed to

traffic and different environmental effects.

There are two basic functions of a pavement i) to support

the applied traffic load and ii) to enable the vehicles to move

over the surface smoothly and safely


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Pavement design is concerned with developing the most

economical combination of pavement layers that will

ensure that stress and strains transmitted from top layers

do not exceed supportive capacity of each layer. The

effects of the major parameters that are to be considered

in pavement design are soil strength, traffic, sub-surface as

well as outside environment, and materials.

Types of Pavements

Primarily there are two types of pavementsA flexible pavement is a pavement structure that maintains

intimate contact with the sub-grade. The structural

mechanics of flexible pavement is such that the pressure is

transmitted to the sub-grade through the lateral distribution

of the applied load depending upon depth. The aggregate

interlock, particle friction and cohesion distribute the load

and contribute to the stability to the pavement structure. A

classical flexible pavement has a number of unbound and / or

bituminous bound granular layers that are topped by a

bitumen bound surface layer. Internationally now-a-days

flexible pavement refers to any pavement other than cement

concrete one. Water bound macadam road, bituminous

roads are examples of flexible pavements.


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Comparison of Flexible and Rigid Pavement

Characteristics Rigid Pavement Flexible Pavement

Design Life 30-40 years 10-20 years

Capital cost High Low [cost for High qualitybituminous road is not muchhigher than RP

Maintenance Cost Low High

Basic Design method Mechanistic Empirical

Stage Construction Not possible Possible

Construction period Required 28 days beforeopening to traffic

May be opened after rolling

Material Main item cement isindigenous

Bitumen is imported, othermaterials are locally available

Surface type Smooth, non skidding,

discomfort at joints

Susceptible to quick

deteriorationWater penetration Impervious except joints Not fully impervious

Visibility Cause glare Glare effect less

Utility maintenanceand repair

To be provided afterwell planning

Well planning is not essential

Properties of Good Pavement

A good pavement structure should have the following

properties:

Adequate Stability: - Stability of a pavement means the ability

to resist the lateral deformation.

Adequate Durability: - Durability is the ability to retain stability

for long time in varying traffic and environmental conditions.

Adequate Load Distribution Ability: - This is the load carrying

mechanism of each layer of the pavement to distribute the

load to the lower layer.

Adequate Strength of the Soil: - The soil over which the

pavement to be built should have adequate strength to carry

the load that comes from the main pavement structure.


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Good Pavement Surface: - the good surface should have

the following properties:

a) Smooth,

b) Skid resistant,

c) Easy drainage of rain water,

d) Good visibility and resistant to glare and light reflection,

e) low noise,

f) Protection to the underlying layers of the pavement from

abrasion, impact and disturbing forces of traffic andenvironmental effect.

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