Unit 6 ( CONSTRUCTION OF THE FLEXIBLE PAVEMENT )

Highway Engineering Engineering

CONSTRUCTION OF THE

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.


CONSTRUCTION OF THE

C3010 / UNIT 6

INPUT CONSTRUCTION OF THE FLEXIBLE PAVEMENT

6.0 6.0

INTR INTROD ODUC UCTI TION ON

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.

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.


CONSTRUCTION OF THE

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

FUNCTI FUNCTIONS ONS OF FLEXIBL FLEXIBLE E PAVEME PAVEMENT NT 6.2.1 6.2.1 SUB-GR SUB-GRADE ADE 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


CONSTRUCTION OF THE

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. Plat Plate e bear bearin ing g test test 3. Triax Triaxial ial com compre press ssion ion test 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


CONSTRUCTION OF THE

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. 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.


CONSTRUCTION OF THE

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 pavement roads given below.

Construction Depth

6.2

Write down the short notes about the functions functions of each layer of the flexible pavement. SURFACE_________________________________________ __________________________________________________ __________________________________________________ __________________________________________________ __________________________________________________

ROAD BASE_______________________________________ __________________________________________________ __________________________________________________ __________________________________________________ __________________________________________________


CONSTRUCTION OF THE

C3010 / UNIT 6

SUB BASE_________________________________________ __________________________________________________ __________________________________________________ __________________________________________________ __________________________________________________

SUB GRADE_______________________________________ __________________________________________________ __________________________________________________ __________________________________________________ __________________________________________________

6.3

What are the differences differences between base course and wearing wearing course in the surface layer?

SURFACE LAYER

Base Course ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________

Wearing Course ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________


CONSTRUCTION OF THE

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 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.


CONSTRUCTION OF THE

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 Engineering 6.3

CONSTRUCTION OF THE

C3010 / UNIT 6

FLEXIBL FLEXIBLE E PAVEME PAVEMENT NT CONSTR CONSTRUCT UCTION ION PROCES PROCESS S

6.3.1 PREPARATION PREPARATION SUB-GRADE 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 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 CONSTRUCTIO CONSTRUCTION N AND COMPACT COMPACTING ING THE SUB-BASE 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.


CONSTRUCTION OF THE

C3010 / UNIT 6

6.3.3 CONSTRUCTIO CONSTRUCTION N OF OF ROAD 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 CONSTRUCTIO CONSTRUCTION N OF OF ROAD ROAD SURFAC SURFACE E

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.


CONSTRUCTION OF THE

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

HOPPER

LEVELLING WIRE

ELEVATION

CONVERYER HOPPER CONVERYER

P U T A N D F IT

PLAN

Figure 6.2 : Construct Bitumen Highway Machine

P A V E M E N T

B IT U M E N


CONSTRUCTION OF THE

C3010 / UNIT 6

ACTIVITY 6

“WANT TO IMPROVE YOUR UNDERSTANDING? TRY THESE ACTIVITIES AND GOOD LUCK!!!”

6.4

6.5

Complete Complete the chart chart by filling filling in the missing missing stages. stages.

1.________________ _________________ _________________ _________________

2. Constructing and compacting the sub base

4.________________ _________________ _________________ _________________

3.________________ _________________ _________________ _________________

Describ Describe e brief briefly ly the constr constructi uction on of road surface. surface. •

•

•

•

•

_______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________ _______________________________________


CONSTRUCTION OF THE

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.


CONSTRUCTION OF THE

C3010 / UNIT 6

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

2. The road road surface surface is constru constructed cted with with bitumen bitumen material. material. Describe Describe the road road surface construction include the compaction work. 3. State the functions of wearing course are as follows:


CONSTRUCTION OF THE

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.

1. C.B.R test


CONSTRUCTION OF THE

C3010 / UNIT 6

2. Plat Plate e bear bearin ing g test test 3. Triax Triaxial ial com compre press ssion ion test 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. 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


CONSTRUCTION OF THE

C3010 / UNIT 6

force from the surface. The wearing course is the top most layers in a pavement. The functions of this layer are as follows: •


•


•


water. •



2.

The The roa road d sur surfa face ce is cons constr truc ucte ted d wit with h bit bitum umen en mate materi rial als, s, such 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.


CONSTRUCTION OF THE

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 The wea weari ring ng cour course se is the the top top most most laye layers rs in a pav pavem emen ent. t. The The functions of this layer are as follows: •


•


•


water. •



Unit 6 ( CONSTRUCTION OF THE FLEXIBLE PAVEMENT )

Recommend Documents