unit 6 ( construction of the flexible pavement )

CONSTRUCTION OF THE FLEXIBLE PAVEMENT

Highway Engineering C3010 / UNIT 6

CONSTRUCTION OF THE FLEXIBLE

PAVEMENT

OBJECTIVES

General Objective

To understand general items of flexible pavement constructions.

Specific Objectives

At the end of the unit you should be able to:-

identify the structural element of flexible pavement.

describe the functions of each layer in flexible pavement.

explain the process of constructing the flexible pavement.

UNIT 6UNIT 6



6.0 INTRODUCTION

The pavement is the hardest layer of the road structure. It does not

include the side walk of the road. Its location is on the ground formation on sub-

grade. It is away of traffic. The nature of the soil is usually not strong enough to

stand the weight of the heavy vehicles and does not have a balanced surface.

That is why the pavement layer should be constructed on original ground surface

so that the force can be divided equally. This is to ensure that road user will have

a save and comfortable journey. There are two types of pavement, namely

Flexible Pavement and Rigid Pavement.

6.1 STRUCTURE OF FLEXIBLE PAVEMENT

Flexible pavement is any kind of pavement that is not constructed using

concrete. In Malaysia the pavement is commonly, constructed by using flexible

pavement. Pavements with very low flexural strength and are flexible in their

structural behaviour when under a load are called flexible pavements. The layers

of this type of pavement reflect the deformation of the lower layers that are

beneath the top surface. Thus, if the lower layer is deformed, the surface of the

pavement will also be deformed.

INPUT




The structure of the road mainly consists of the following layers.

i. Sub-grade soil or simply sub-grade.

ii. Sub-base.

iii. Road Base.

iv. Surface layer.

figure 6.1

6.2 FUNCTIONS OF FLEXIBLE PAVEMENT

6.2.1 SUB-GRADE

Sub-grade is a layer of natural soil or filled soil, ready to receive the

pavement material over it. Traffic load moving on the surface of the road is

ultimately transferred to the sub-grade through intermediate layer of sub-

base, base and surface layer. For the success full construction of the

road, it is necessary that the soil sub-grade should never be over

stressed. Stress intensity on the sub-grade should not be of the magnitude

that may cause excessive deformation in the sub-grade. It is this reason

that the strength properties of the soil sub-grade should be evaluated. The

pavement design assumes sub-grade strength as the basis for designing

the pavement. If strength properties of the sub-grade are inferior to the

Construction Depth

Surface layer

Road Base

Sub-base

Sub-grade is the natural soil beneath road

construction

Figure 6.1



expected ones, it is given suitable treatment to impart improvement in its

performance.

There are a number of tests which can be used to measure

strength properties of the soil sub-grade. All these tests are empirical and

are useful in their correlation in the design. Following are some of the

standard tests, used to evaluate the strength properties of the soil.

1. C.B.R test

2. Plate bearing test

3. Triaxial compression test

6.2.2 SUB-BASE

Sub-base is one course that is constructed with quality materials.

This is the lowest layer of pavement that is constructed onto the sub-

grade. The functions of sub-grade:

Support the road base and spreads the force to the sub-grade.

Prepares the drainage using rough materials.

Prepares a cover at any layer that is constructed.

Bears the pressure from heavy vehicles so the sub-grade will not

crack.

Prevent the sub-grade from traffic flow.

6.2.3 BASE

Base or road base is the main course to absorb force from surface

directly and spread the force to the thickest layer. This layer is normally

made from broken stones which may be bounded or unbounded. It is used

to help spread traffic load on large area of sub-grade so that the stress

intensity remains within the capabilities of the sub-grade. Thus undue



deformation caused by the consolidation of the sub-grade is prevented.

This layer is evaluated by plate bearing test or stabilometer test.

6.2.4 SURFACE

The surface is the top layer in a pavement. The pavement is

divided into two layers that is Base course and wearing course on the top.

a. Base Course

In resurfacing, this layer is usually known as a binder course. It is

the second layer before the wearing course. The function is to

spread the force from the surface.

b. Wearing Course

The wearing course is the top most layers in a pavement. The

functions of this layer are as follows:

Provides smooth and dense ridding surface.

Takes up wear and tear due to traffic.

Provides water tight surface against filtration of surface water.

Provides hard surface which can withstand the pressure exerted

by tyres of vehicles.



“WANT TO IMPROVE YOUR UNDERSTANDING? TRY THESE

ACTIVITIES AND GOOD LUCK!!!”

6.1 Label the layers of the flexible pavement roads given below.

6.2 Write down the short notes about the functions of each layer

of the flexible pavement.

ACTIVITY 6A

Construction Depth

SURFACE_________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

ROAD BASE_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________



6.3 What are the differences between base course and wearing

course in the surface layer?

SUB GRADE_______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

SUB BASE_________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

SURFACELAYER

Base Course________________________________________________________________________________________________________________________________________________________

Wearing Course________________________________________________________________________________________________________________________________________________________



Let’s Check The Answer!

6.1

6.2

FEEDBACK ON ACTIVITY 6A

Surface

Road Base

Sub Base

Sub-grade

Construction Depth

SURFACE is the top layer of the road pavement. It provides a smooth and dense surface. It provides water tight surfaces against filtration of surface water.

ROAD BASE is the main course of the road pavement. It absorbs force from surface directly and spreads the force to the sub base.

SUB GRADE is a layer of natural soil. It is ready to receive all the forces from the surface to the sub base. This is the important part of the road structure.

SUB BASE is one course that is constructed to prepare the drainage from rough materials, and it absorbs forces from road base directly and spreads the forces to the sub grade.



6.3 SURFACELAYER

Base CourseIt is the second layer

before wearing course. Its function is to

spreads the force from the surface to the road

base.

Wearing CourseIt provides smooth and

dense riding surface. As a top course, it receives

the traffic forces directly.



6.3 FLEXIBLE PAVEMENT CONSTRUCTION PROCESS

6.3.1 PREPARATION SUB-GRADE LAYER

Prepare the sub-grade layer, it is done after placing the drainage

system, piping and electric cable. The sub-grade surface will be

compacted levelled and be cut to make camber as in plan. If the material

of the soil did not have a good quality, it will be changed with suitable

material.

Base formation covers with 50-75mm sand layer or quarry dust and

will be compacted with 8-10 tone compactors. This job must be done to

prevent the clay from absorbing into the stone layer of sub-base and

reduce the shear strength of the pavement.

6.3.2 CONSTRUCTION AND COMPACTING THE SUB-BASE

After the sub-base has been prepared with list materials, it will be

placed and constructed into two layers if the thickness is more then

150mm. Every layer will be compacted according to the plan. Sub-base

layer must be compacted carefully with compactor machine. Compactors

with rubber roller can compact 120mm layer in 12 times. Compacting

should start from the side of the road hen slowly towards the middle of the

road in horizontal way. In super-elevated bends compaction machine will

start at the lowest part and slowly towards the higher level. The finished

part not be more than 20mm from the plan.



6.3.3 CONSTRUCTION OF ROAD BASE

Before road base is constructed, sub-grade surface and sub-base

must be formed perfectly and compacted enough. The lowest layer and

sub-base must be prepared at least distance of 200m from the base

construction.

The road base in Malaysia is commonly constructed with a material

known as crusher run. This material is place and compacted to on the

surface of the road. The road base must be constructed in two layers of

same thickness. Each layer should not exceed 150mm.

6.3.4 CONSTRUCTION OF ROAD SURFACE

The road surface is constructed with bitumen materials, such as

concrete asphalt, macadam bitumen and so on. The constructed should

be free from dust and waterproof. To construct the surface layer, the base

course must be prepared first. Prime coat is poured onto the road base

surface to be a binder between the road bases and the base course. To

pour the prime coat, the temperature must be according to the

specifications stipulated.

Base course is built on one layer only with a pavers’ machine. After

this layer is constructed, it is placed before it is compacted. The surface is

checked and corrected if there are any differences.



The compacting must be done immediately. It should be compacted

from the side towards the middle of the road. It there is a super elevated

bend, then it should be compacted from lower part to higher part. The type

of compactors must be according to the specifications.

Finally wearing course is prepared. Like always, base course

should be cleaned before tack coat is poured. The compacting job is done

the same way as the base course.

BITUMEN HAD BEEN PAVEMENTHOPPE

LEVELLING WIRE

CONVERYER

CONVERYER

HOPPER

PU

T A

ND

FIT

BIT

UM

EN

P

AV

EM

EN

T

PLAN

ELEVATION

Figure 6.2 : Construct Bitumen Highway Machine



“WANT TO IMPROVE YOUR UNDERSTANDING? TRY THESE

ACTIVITIES AND GOOD LUCK!!!”

6.4 Complete the chart by filling in the missing stages.

6.5 Describe briefly the construction of road surface.

ACTIVITY 6

1.___________________________________________________________________

4.___________________________________________________________________

3.___________________________________________________________________

2. Constructing and compacting the sub base

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________



Let’s Check The Answer!

6.4

6.5

FEEDBACK ON ACTIVITY 6

1. Preparing the sub- grade layer.

4. Constructing the road surface.

3. Constructing the road base.

2. Constructing and compacting the sub base.

Road surface is constructed with bitumen materials such as concrete asphalt and bitumen.

The base course must be prepared first. Prime coat is poured onto the road base

surface to be a binder between the layers. The base course is built on one layer only

using the pavers’ machine. It is compacted and checked for any problems

that may occur after the process.



1. Describe briefly the functions of flexible pavement by each layer.

2. The road surface is constructed with bitumen material. Describe the road

surface construction include the compaction work.

3. State the functions of wearing course are as follows:

Question



1.

SUB-GRADE

Sub-grade is a layer of natural soil or filled soil, ready to receive the

pavement material over it. Traffic load moving on the surface of the road is

ultimately transferred to the sub-grade through intermediate layer of sub-

base, base and surface layer. For the success full construction of the

road, it is necessary that the soil sub-grade should never be over

stressed. Stress intensity on the sub-grade should not be of the magnitude

that may cause excessive deformation in the sub-grade. It is this reason

that the strength properties of the soil sub-grade should be evaluated. The

pavement design assumes sub-grade strength as the basis for designing

the pavement. If strength properties of the sub-grade are inferior to the

expected ones, it is given suitable treatment to impart improvement in its

performance.

There are a number of tests which can be used to measure

strength properties of the soil sub-grade. All these tests are empirical and

are useful in their correlation in the design. Following are some of the

standard tests, used to evaluate the strength properties of the soil.

Answer



1. C.B.R test

2. Plate bearing test

3. Triaxial compression test

SUB-BASE

Sub-base is one course that is constructed with quality materials.

This is the lowest layer of pavement that is constructed onto the sub-

grade. The functions of sub-grade:

Support the road base and spreads the force to the sub-grade.

Prepares the drainage using rough materials.

Prepares a cover at any layer that is constructed.

Bears the pressure from heavy vehicles so the sub-grade will not

crack.

Prevent the sub-grade from traffic flow.

BASE

Base or road base is the main course to absorb force from surface

directly and spread the force to the thickest layer. This layer is normally

made from broken stones which may be bounded or unbounded. It is used

to help spread traffic load on large area of sub-grade so that the stress

intensity remains within the capabilities of the sub-grade. Thus undue

deformation caused by the consolidation of the sub-grade is prevented.

This layer is evaluated by plate bearing test or stabilometer test.

SURFACE

The surface is the top layer in a pavement. The pavement is

divided into two layers that is Base course and wearing course on the top.



In resurfacing, this layer is usually known as a binder course. It is

the second layer before the wearing course. The function is to spread the

force from the surface. The wearing course is the top most layers in a

pavement. The functions of this layer are as follows:






2. The road surface is constructed with bitumen materials, such as

concrete asphalt, macadam bitumen and so on. The constructed

should be free from dust and waterproof. To construct the surface

layer, the base course must be prepared first. Prime coat is poured

onto the road base surface to be a binder between the road bases

and the base course. To pour the prime coat, the temperature must

be according to the specifications stipulated.

Base course is built on one layer only with a pavers’ machine. After

this layer is constructed, it is placed before it is compacted. The

surface is checked and corrected if there are any differences.

The compacting must be done immediately. It should be compacted

from the side towards the middle of the road. It there is a super

elevated bend, then it should be compacted from lower part to

higher part. The type of compactors must be according to the

specifications.



Finally wearing course is prepared. Like always, base course

should be cleaned before tack coat is poured. The compacting job

is done the same way as the base course.

3. The wearing course is the top most layers in a pavement. The

functions of this layer are as follows:






unit 6 ( construction of the flexible pavement )

Documents