Tag Archives: what is pavement

Road Pavement Layers – Components and Functions

Road pavement structure: Road is the most important structure that decides the economic growth of a country. The road structure is to be constructed based on the traffic requirements, climatic conditions of the area, terrain, etc. The road structure has to withstand abrasion loads and climatic and terrain conditions without failure. This article is about the components of a flexible pavement structure.

  1. Road pavement structure
    1. Road pavement – Subgrade
      1. Function of subgrade
    2. Sub base course
      1. Functions of subbase coarse
    3. Base course
      1. The function of base course
    4. Surface course or wearing course
      1. Function of Surface or Wearing Course

Road pavement structure

The road pavement structure layers are as follows.

  • Subgrade or road bed
  • Sub base course
  • Base Course
  • Surface coarse or wearing course

Also read: Components of Road pavement structure – Parts of a road and functions

Also read: 4 Types of Pavement |Flexible and Rigid Pavement Full Details

Also Watch : The flexible pavement vs Rigid Pavement Youtube video

Road pavement – Subgrade

The subgrade is the compacted natural soil below the pavement layers and it is the finished or compacted surface on which the pavement rests. They are also known as the formation and serve as the foundation of pavement layers.
Depending on the nature of the terrain the sub-grade can be an embankment or a cutting or it will be in line with the natural ground level. The load-bearing strength of the sub-grade structure is determined by the California bearing ratio test (CBR).
The material used for subgrade shall be locally available, strong, and cheap.


Function of subgrade

Serves as the foundation and acts as a uniform support to pavements.

Sub grades bear the  entire load of the payments along with the service load of traffic.

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Sub base course

The sub-base course comes between the base coarse and sub-grade. The material used for this layer shall satisfy the specifications in terms of gradation, strength, and plastic characteristics.
This layer is necessary if the sub grade is of poor quality. In that case, an additional layer of burnt clinkers, gravel, slag, etc is provided to strengthen the sub grade.

Functions of subbase coarse

  • The sub-base layer enhances the bearing capacity of the subgrade and improves the load distribution capacity of the base course and wearing course.
  • The sub-base course prevents the entry of finely graded sub-grade soil to the base course layer.
  • They prevent the capillary rise of water and enable free drainage of water entering the pavement. The sub-base material must be free draining for this application with suitable systems must be included in the pavement design for collecting and removing any accumulated water from the sub-base.
  • This layer provides insulation to sub-grades against frost
  • The sub-base course is used for raising the heights of pavements to be in line with the natural water table.
  • The Sub-base course provides a perfect hard stratum for remaining construction activities.

Base course

The base course is a layer or layers of specified or select material of designed thickness placed on a subbase or subgrade (if a subbase is not used) to provide a uniform and stable support for binder and surface courses.
The base course is the most important layer of a road structure which transfers the stresses developed due to traffic impacts through the wearing course. The base course layer provides the required foundation stiffness and structural strength.
Good quality crushed aggregates in line with technical specifications have to be used. If the crushed aggregate does no meet the required criteria it can be stabilised with Portland cement, lime, or asphalt. In the case of high-quality pavements, the crushed aggregates are treated with asphalt or Portland cement.


The function of base course

  • To act as the foundation of the road pavement and to transfer the traffic load safely to the sub-base and subgrade.
  • To withstand high shearing stresses due to the impact of traffic.
  • To prevent the undesirable entry of subgrade soil in the pavement when the base course is constructed directly over the subgrade.

Surface course or wearing course

The surface course is multiple layers of pavement structure where the top layer is directly exposed to traffic. The surface course is also called the wearing course. For flexible pavements, the bituminous surface is the wearing course whereas in rigid pavement the concrete surface act as the base course cum wearing course. The wearing course reduces the percolation of water and provides an anti-skid and abrasion-resistant riding surface.


Function of Surface or Wearing Course

The Function of surface or wearing course are as follows:

  • To provide a smooth and uniform rigid surface.
  • To resist the abrasive forces of traffic.
  • To prevent dust nuisance.
  • To act as a structural part of the pavement.

4 Types of Pavement |Flexible and Rigid Pavement Full Details

Types of pavement are mainly four. I will show you each of them in detail with the advantages and disadvantages.

Before we begin, let’s look into what a pavement is.

What is pavement?

The pavement is a hard surface that’s built with concrete or asphalt, like a road or a driveway.

Based on the structural behavior, road pavements are classified as

  • Flexible pavement
  • Rigid pavement
  • Semi-rigid pavements
  • Interlocking cement concrete block pavement (ICBP)

Without any due, let’s jump onto the first type of pavement.

Flexible pavement

Figure shows one type of road pavement
One type of road pavement

Flexible pavement is the pavement which possess negligible flexural strength. And,

  • The flexible pavement layer may reflect the non recoverable as well as recoverable deformations of the lower layer including sub grade on the upper layers and also to the pavement surface.
  • The vertical compressive stress is maximum on the pavement surface directly under the wheel load and is equal to the contact pressure under the wheel
  • The lower layers of pavement has to take up only lesser magnitudes of stresses and there is no direct wearing action due to traffic loads and weathering action due to environmental factors. Therefore inferior materials with lower cost can be used in the lower layers.
  • In flexible pavement layers, top layer has to be the strongest as the highest compressive stresses are to be sustained by this layer, in addition to the wear and tear due to the moving traffic and varying factors due to weather.

Also read: Electronic Toll Collection-4 subsystems of ETC Full details

Next, let’s peep into advantages and disadvantages of flexible pavements.

Advantages of flexible pavement

figure shows road pavement
Road pavement
  • Initial cost can be reduced by constructing thin bituminous surface layer
  • Standard design load in terms of CSA (Cumulative Standard Axles)
  • Functional deterioration
  • Strengthening by overlay
  • High salvage value
  • Can be open to traffic after 24 hours

Disadvantages of flexible pavements

  • Deterioration under stagnant water
  • Periodic maintenance
  • Patching of pot holes is expensive
  • Thickness is very high
  • Night visibility is very low

That’s it about flexible pavement. Let’s move onto the next type of pavement.

Also read: Classification of roads- 5 types of roads full details

Rigid pavement

Rigid pavements are those which possess noteworthy flexural strength of flexural strength or flexural rigidity.

See more details below.

  • Rigid pavements are generally made of Portland cement concrete hence known as ‘cc pavement’
  • Construction of rigid pavement using high quality plane cement concrete known as ‘pavement quality concrete (PQC)
  • The CC pavement made of PQC are generally expected to sustain up to 45kg/cm2 of flexural stresses
  • In rigid pavements, the stresses are not transferred from grain to grain to the lower layers as in the case of flexible pavement layers.
  • Slab action is capable of  transmitting the wheel load cases through a much wide area below pavement slab

Having the details in back pack, ready to know the advantages and disadvantages of rigid pavements?

Advantages of rigid pavement

  • No deterioration under stagnant water
  • Thickness is less
  • Service life 30 years
  • Life cycle cost is very less
  • Night visibility is high

Disadvantages of rigid pavement

  • Axle load study is required
  • Design should be for 30 years
  • Possible to restore the pavements under crack
  • Surface may become smooth or slippery
  • Long period of 28 days is required to open traffic

Let’s conclude the section with a comparison.

Comparison between flexible and rigid pavements

Flexible pavementRigid pavement
Bitumen is mostly used for construction Otherwise called concrete pavements
Bitumen becomes soft due to low temperature and bleeds leading to failure of pavementHave longer life and is practically maintenance- free
When water enters the pavement during raining, resulting in potholes Can withstand extreme weather conditions
Due to low temperature in winter season, bitumen becomes brittle leading to cracking of pavementInitial cost higher comparatively, but economical in long term
Comparison between flexible and rigid pavements

Now, you know about flexible and rigid pavement. Time to meet some not-so-famous type of pavement.

Also read: Gauges in railway- All Details About Broad, Metre and Narrow Gauges

Semi rigid/ composite pavements

Semi-rigid pavements are an intermediate state between the Flexible and the Rigid pavement. The flexural strength of the pavement is less than a concrete slab. Nevertheless, it finds support by the lateral distribution of loads through the pavement depth as in flexible pavement.

When the intermediate class of semi-rigid materials like soil cement, lean cement concrete are used in the sub-base or base course of layers of pavements, they are called semi-rigid pavement.

Pavement consisting of both flexible pavement layers and one or more semi rigid pavement layers are called composite pavements.

The last member is ICBP or Interlocking concrete block pavement.

Interlocking Concrete Block Pavement (ICBP)

interlocking concrete block pavement
Interlocking Concrete Block Pavement (ICBP)

Interlocking Concrete Block Pavement (ICBP) has been extensively used in a number of countries for quite sometime as a specialized problem-solving technique for providing pavement in areas where conventional types of construction are less durable due to many operational and environmental constraints

That was the trip through the types of pavement. Have any doubts regarding this? Just drop it in comments.

See you there. Happy learning!