Download 6.1 structure of flexible pavement

Highway Engineering
CONSTRUCTION OF THE
FLEXIBLE PAVEMENT
C3010 / UNIT 6
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.
Highway Engineering
CONSTRUCTION OF THE
FLEXIBLE PAVEMENT
C3010 / UNIT 6
INPUT
CONSTRUCTION OF THE FLEXIBLE
PAVEMENT
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 subgrade. 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.
Highway Engineering
CONSTRUCTION OF THE
FLEXIBLE PAVEMENT
C3010 / UNIT 6
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.
Surface layer
Road Base
Construction
Depth
Sub-base
Sub-grade is the natural
soil beneath road
figure 6.1
construction
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 subbase, 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
Highway Engineering
CONSTRUCTION OF THE
FLEXIBLE PAVEMENT
C3010 / UNIT 6
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 subgrade. 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
Highway Engineering
CONSTRUCTION OF THE
FLEXIBLE PAVEMENT
C3010 / UNIT 6
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.
Highway Engineering
CONSTRUCTION OF THE
FLEXIBLE PAVEMENT
C3010 / UNIT 6
ACTIVITY 6A
“WANT TO IMPROVE YOUR UNDERSTANDING? TRY THESE
ACTIVITIES AND GOOD LUCK!!!”
6.1
Label the layers of the flexible pavement roads given below.
Construction
Depth
6.2
Write down the short notes about the functions of each layer
of the flexible pavement.
SURFACE_________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
ROAD BASE_______________________________________
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
Highway Engineering
CONSTRUCTION OF THE
FLEXIBLE PAVEMENT
C3010 / UNIT 6
SUB BASE_________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
SUB GRADE_______________________________________
__________________________________________________
__________________________________________________
__________________________________________________
__________________________________________________
6.3
What are the differences between base course and wearing
course in the surface layer?
SURFACE
LAYER
Base Course
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
Wearing Course
___________________
___________________
___________________
___________________
___________________
___________________
___________________
___________________
Highway Engineering
CONSTRUCTION OF THE
FLEXIBLE PAVEMENT
C3010 / UNIT 6
FEEDBACK ON
ACTIVITY 6A
Let’s Check The Answer!
6.1
Surface
Road Base
Construction
Depth
Sub Base
Sub-grade
6.2
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 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.
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.
Highway Engineering
CONSTRUCTION OF THE
FLEXIBLE PAVEMENT
6.3
C3010 / UNIT 6
SURFACE
LAYER
Base Course
It is the second layer
before wearing course.
Its function is to
spreads the force from
the surface to the road
base.
Wearing Course
It provides smooth and
dense riding surface. As
a top course, it receives
the traffic forces
directly.
Highway Engineering
6.3
CONSTRUCTION OF THE
FLEXIBLE PAVEMENT
C3010 / UNIT 6
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.
Highway Engineering
CONSTRUCTION OF THE
FLEXIBLE PAVEMENT
C3010 / UNIT 6
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.
Highway Engineering
CONSTRUCTION OF THE
FLEXIBLE PAVEMENT
C3010 / UNIT 6
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 PAVEMENT
HOPPE
R
ELEVATION
CONVERYER
PLAN
Figure 6.2 : Construct Bitumen Highway
Machine
BITUMEN
PAVEMENT
HOPPER
PUT AND FIT
CONVERYER
LEVELLING
WIRE
Highway Engineering
CONSTRUCTION OF THE
FLEXIBLE PAVEMENT
C3010 / UNIT 6
ACTIVITY 6
“WANT TO IMPROVE YOUR UNDERSTANDING? TRY THESE
ACTIVITIES AND GOOD LUCK!!!”
6.4
6.5
Complete the chart by filling in the missing stages.
1.________________
_________________
_________________
_________________
2. Constructing and
compacting the sub
base
4.________________
_________________
_________________
_________________
__
3.________________
_________________
_________________
_________________
__
Describe briefly the construction of road surface.





_______________________________________
_______________________________________
_______________________________________
_______________________________________
_______________________________________
_______________________________________
_______________________________________
_______________________________________
_______________________________________
_______________________________________
Highway Engineering
CONSTRUCTION OF THE
FLEXIBLE PAVEMENT
C3010 / UNIT 6
FEEDBACK ON
ACTIVITY 6
Let’s Check The Answer!
6.4
1. Preparing the subgrade layer.
2. Constructing and
compacting the sub
base.
4. Constructing the
road surface.
3. Constructing the
road base.
6.5





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.
Highway Engineering
CONSTRUCTION OF THE
FLEXIBLE PAVEMENT
C3010 / UNIT 6
Question
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:
Highway Engineering
CONSTRUCTION OF THE
FLEXIBLE PAVEMENT
C3010 / UNIT 6
Answer
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 subbase, 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.
Highway Engineering
CONSTRUCTION OF THE
FLEXIBLE PAVEMENT
C3010 / UNIT 6
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 subgrade. 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.
Highway Engineering
CONSTRUCTION OF THE
FLEXIBLE PAVEMENT
C3010 / UNIT 6
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:

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.
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.
Highway Engineering
CONSTRUCTION OF THE
FLEXIBLE PAVEMENT
C3010 / UNIT 6
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:

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.