evaluation of flexible and rigid pavements …
TRANSCRIPT
EVALUATION OF FLEXIBLE AND RIGID PAVEMENTS
CONSTRUCTION IN BANGLADESH
BY
MOHAMMAD ARIFUZZAMAN BHUYAN
DDEEPPAARRTTMMEENNTT OOFF CCIIVVIILL EENNGGIINNEEEERRIINNGG
BBAANNGGLLAADDEESSHH UUNNIIVVEERRSSIITTYY OOFF EENNGGIINNEEEERRIINNGG && TTEECCHHNNOOLLOOGGYY
DDHHAAKKAA,, BBAANNGGLLAADDEESSHH
OCTOBER 2009
EVALUATION OF FLEXIBLE AND RIGID PAVEMENTS CONSTRUCTION IN
BANGLADESH
BY
MOHAMMAD ARIFUZZAMAN BHUYAN
A project submitted to the Department of Civil Engineering, Bangladesh University of
Engineering and Technology, Dhaka, in partial fulfilment of the requirements
For the degree of
Master of Engineering in Civil Engineering (Transportation)
DDEEPPAARRTTMMEENNTT OOFF CCIIVVIILL EENNGGIINNEEEERRIINNGG
BBAANNGGLLAADDEESSHH UUNNIIVVEERRSSIITTYY OOFF EENNGGIINNEEEERRIINNGG && TTEECCHHNNOOLLOOGGYY
DDHHAAKKAA,, BBAANNGGLLAADDEESSHH
OCTOBER 2009
The project titled “EVALUATION OF FLEXIBLE AND RIGID PAVEMENTS
CONSTRUCTION IN BANGLADESH”, Submitted by ‘MOHAMMAD
ARIFUZZAMAN BHUYAN, Roll No. 040404433F, Session: April 2004’ has been
accepted as satisfactory in partial fulfilment of requirement of the requirement for the
degree of Master of Engineering in Civil Engineering (Transportation) on 27th
October,
2009.
BOARD OF EXAMINERS
________________________________________
DR MD. SHAMSUL HOQUE Professor Chairman
Department of Civil Engineering (Supervisor)
BUET, Dhaka.
________________________________________
DR. ALAMGIR MOJIBUL HOQUE Professor Member Department of Civil Engineering
BUET, Dhaka.
________________________________________
DR. TANWEER HASAN Professor Member Department of Civil Engineering
BUET, Dhaka.
ACKNOWLEDGEMENT
First, all praise to almighty Allah Who has given the capabilities to perform this research work. The author is greatly indebted to Dr. Md. Shamsul Hoque, Professor, Department of Civil Engineering, BUET and my supervisor for his all assistance, proper advice, affectionate guidance and above all continuous encouragement at every step of this research work. It would have been impossible to carryout this study without his dynamic direction under a number of constraints. The author is also thankful to Dr. Alamgir Mojibul Hoque and Dr. Tanweer Hasan, Professors, Department of Civil Engineering, BUET for their valuable advices to complete this work. Special thanks are expressed to Mr. Sukur Ali, attendance of BUET Transportation Laboratory for his hard assistance in the field and laboratory experiments without the help of whom this research work cannot be completed. Special gratitude is also expressed for all concerned officers and staffs of different organizations (LGED, RHD and DCC) for their assistance in questionnaire survey. Also, the sincere support and help of the contractors and labors during field experiment and data collection can never be ignored. Last and important is the unlimited inspiration and support by my family members at different stages of this research.
DECLARATION
I hereby declare that the research work presented in this project has been performed by me and any part of it has not been submitted elsewhere for any other purposes except for publication.
October, 2009 MOHAMMAD ARIFUZZAMAN BHUYAN
ABSTRACT
The aim of this study was to find the pavement type which would be more cost effective and would give good serviceability in the long run in the context of Bangladesh. In this regard field investigations were carried out to identify the problems associated with the various stages of quality control in the construction of pavements. Samples were collected from two construction sites for both field and laboratory experiments. The performance evaluation of few completed flexible road construction projects was made. In order to assess the level of understanding regarding the proper way of constructing flexible pavement, all together 12 Engineers from different Government Organizations as well as from the Contractor’s side were interviewed. In addition to that 15 field staffs particularly from the Contractor’s side were also interviewed. Unit costs of flexible and rigid pavements were estimated by determining life cycle cost (LCC) of a few completed projects. Finally, a comprehensive comparative analysis between flexible and rigid pavements was made from the viewpoint of locally available binding material, amount of aggregates and type of equipment requirements, construction and maintenance cost, quality control issues and above all performance under submerged condition. From the field and laboratory investigations it was found that due to improper way of heating and mixing bitumen, its properties change significantly particularly with the manual method of construction. Aggregate gradation is hardly maintained in the preparation of pavement mixtures and thereby lower Marshall stability and flow values along with higher void contents are obtained in the laboratory investigation. Also temperature measurements in the field at different stages of construction process show that bitumen quality is deteriorated significantly at the time of heating and mixing with aggregates. Overall, it is observed that in every stage of pavement resurfacing works there is a serious lack of quality control particularly in maintaining appropriate temperature of aggregates and bitumen as well as of placing and compaction of mixture. In reality, serious ignorance exists both with the field engineers and contractors related to pavement construction works. They have little ideas about the compliance of maintaining specific temperature at a particular step of pavement construction works. Field observation revealed that where both flexible and rigid pavements are built side by side by different organizations, the performance of rigid pavements is relatively better. Rigid pavement as constructed by LGED in Sunamganj district has found to be performing well under daily tidal submergence cyclic loading pattern. It was observed that for per km construction of a standard 2-lane width road, material requirement is almost 50% higher in case of flexible pavement as compared to the rigid pavement. From the unit rate analysis of binders, it was found that over a period of four years (2004-2008) the cost of bitumen has increased by two and half times as compared to the cost of cement, which has increased by nearly one and half times during the same period of time. It was found that in 2004 the unit cost of flexible paving mix was lower than that of the cost of cement concrete paving mix and after that its price has been increasing very rapidly and has crossed the price of concrete pavement by 2006. Now, the unit cost of bituminous pavement is more than one and half times as compared to the unit cost of concrete mix.
From the evaluation of different completed projects it was revealed that though overloading and drainage are the main causes of premature pavement failure in Bangladesh, manifestation of lack of poor quality of work, use of excessive binder, bonding problem between new and old layers are also found to be contributory factors for premature failure of flexible pavement. From the questionnaire survey it was observed that the persons concerned with the construction of flexible pavements, both the client and contractor’s side, have poor understanding on the proper way of doing the construction of flexible pavement job. As such, there is a need for pavement construction method which is simple and requires no heating requirement, compaction work and above all not so sensitive to the quality control, which essentially suggests that rigid pavement construction would be the appropriate method of road construction for the local conditions. In the end recommended areas of applying rigid pavement instead of flexible pavement are also presented.
vii
TABLE OF CONTENTS
Title
Declaration iii
Page
Acknowledgement iv
Abstract v
Contents vii
List of Tables xiii
List of Figures xv
List of Photographs xvi
CHAPTER 1: INTRODUCTION 1
1.1 Introduction 1
1.2 Motivation of the Research 2
1.3 Objectives of the Research 3
1.4 Scope of the Thesis 4
1.5 Organization of Thesis 4
CHAPTER 2: LITERATURE REVIEW 5
2.1 Introduction 5
2.2 Comparison of Rigid Pavement and Flexible Pavement 6
2.2.1 Flexible Pavement 6
2.2.2 Rigid Pavement 7
2.3 History of Concrete Pavements in different Countries of the World 15
2.4 History of Pavements in Bangladesh 18
2.5 Road Construction in Bangladesh- Current Condition 19
2.6 Availability of Bitumen for Road Construction in Bangladesh 20
2.7 Materials for Rigid Pavement Construction in Bangladesh 21
2.8 Effects of Flexible Pavement Construction in Bangladesh 22
2.9 Overview 25
viii
CHAPTER 3: METHODOLOGY 26
3.1 Introduction 26
3.2 Outlines of the Research Methodology 26
3.3 Methods of Data Collection 27
3.3.1 Data collection from field for laboratory experiment 27
3.3.2 Data collection for case study and economic analysis 28
3.3.3 Data collection for Questionnaire Survey 28
3.3.4 Data Collection for Comparative Analysis for Flexible &
Rigid Pavements 29
3.4 Evaluation Techniques 29
3.4.1 Laboratory Experiments 29
3.4.2 Case Study and Economic Analysis 30
3.4.3 Questionnaire Survey 30
3.6 Overview 30
CHAPTER 4 COMPARATIVE ANALYSIS OF FLEXIBLE AND
RIGID PAVEMENTS 31
4.1 Introduction 31
4.2 Factors of Comparison 31
4.2.1 Equipment Requirement 31
4.2.2 Material Requirements (per unit volume) 32
4.2.3 Availability of Binding Materials 33
4.3 Methods of Pavement Construction 34
4.3.1 Flexible Pavement 35
4.3.1.1 Preparation of the Mixture 35
4.3.1.2 Temperature and Mixing Time 36
4.3.1.3 Transportation of Mixture 37
4.3.1.4 Preparation of Base 37
4.3.1.5 Placing Mixture 37
4.3.1.6 Compaction of the Mixture 39
4.3.2 Rigid Pavement 40
ix
4.3.2.1 Placing of Forms 40
4.3.1.2 Installation of the Joints 41
4.3.1.3 Mixing of Concrete 42
4.3.1.4 Concrete Temperature 42
4.3.1.5 Compaction of Concrete 43
4.3.1.6 Roughening Concrete before Depositing Fresh Concrete 43
4.3.1.7 Protection and Curing of Concrete 43
4.3.1.8 Quality Control 44
4.4 Development of Pavement Structures 44
4.4.1 Design Precision 44
4.4.2 Subsurface Layer System 44
4.4.3 Stage Construction 45
4.5 Maintenance Works 45
4.6 Pavement Distresses due to Local Weather Conditions 47
4.6.1 Submergence Problems 47
4.12.1
4.6.2 Flushing due to hot Climatic Condition 52
4.7 Safety Aspects of Pavement 54
4.7.1 Skid Resistance and Surface Texture 54
4.7.2 Riding Quality 55
4.7.3 Visibility and Reflectivity 55
4.8 Fuel Savings for Heavy Vehicles 58
4.9 Utility Location 58
4.10 Environmental Considerations 59
4.11 Life Cycle Costs 59
4.11.1 Unit Cost of Flexible Pavement 59
4.11.2 Unit Cost of Rigid Pavement 61
4.12 Case studies 62
Case Study-1: Cost Estimation for Debogram-Progoti
4.12.2
Sharani Link Road Project 63
Case Study-2: Cost Estimation for Dhaka-Sylhet
Highway Project
4.14 Differentiation between Flexible and Rigid Pavements 73
66
4.13 Economic Analysis 71
4.13.1 Price Escalation of Binders and Mixes 71
x
4.15 Plausible Causes of Premature Failure of Pavement 78
4.16 Overview 79
CHAPTER 5 FIELD INVESTIGATION ON THE CONSTRUCTION
OF FLEXIBLE PAVEMENT 82
5.1 Introduction 82
5.2 Method of Assessment 83
5.3 Field Data Collection 83
5.3.1 Site Selection 84
5.3.2 Equipment 84
5.3.3 Field Study 85
5.3.3.1 Preparing Marshal Specimens in the field 85
5.3.3.2 Collection of Ingredients 86
5.3.3.3 Collection of Hot Paving Mixture 86
5.3.3.4 Measurement of Temperature at Different 87
5.3.3.5 Stages of Constructions 87
5.3.4 Laboratory Testing 88
5.3.4.1 Bitumen Extraction Test 89
5.3.4.2 Test on Extracted Aggregates and Bitumen 91
5.3.4.3 Marshall Test 93
5.4 Analysis of Test Results 95
5.4.1 Asphalt Content 96
5.4.2 Moisture Content 97
5.4.3 Properties of Bitumen 100
5.4.3 Gradation of Aggregates 102
5.4.4 Strength Properties of Mixes 103
5.4.5 Temperature Measurement at Different Stages of Construction 103
5.5 Field Observations on the Completed Roadway Projects 104
5.5.1 Project: Nalka-Hatikamrul-Bonpara Road 104
5.5.2 Project: Dhaka Bypass Road 105
5.5.3 Other Roadway Projects with Premature Failure 107
5.5.3.1 Dhaka-Chittagong Highway 108
5.5.3.2 Dhaka-Tangail Road 112
xi
5.5.3.3 Sylhet-Sunamgaj Road 113
5.5.3.4 Jamuan Bridge Access Road 114
5.5.3.4 Approach Road of 1st
6.2.1 Findings from Comparative Analysis 138
China-Bangladesh Friendship Bridge 115
5.6 Observations on the Adhesion Problems of Flexible Pavement 116
5.7 Non-uniform Density of Asphalt Concrete 119
5.7.1 Due to Aggregate and Temperature Segregations 120
5.7.2 Due to Mix Spreading Problem 121
5.8 Assessment based on the Questionnaire Survey 124
5.8.1 Introduction 125
5.8.2 Assessment on the Level of Understanding of the Engineers 126
5.8.3 Rigid Pavement Roads Constructed by DCC, LGED and RHD 127
5.8.3.1 Rigid Pavements Constructed by DCC 129
5.8.3.2 Rigid Pavements Constructed by LGED 130
5.8.3.3 Rigid Pavements Constructed by RHD 132
5.8.3.4 Rigid Pavement Constructed by Private Initiatives 133
5.9 Overview 134
CHAPTER 6 CONCLUSIONS AND RECOMMENDATIONS 137
6.1 Introduction 137
6.2 Summery of the Findings 138
6.2.1.1 Requirement of Equipment and Materials 139
6.2.1.2 Availability of Binding Materials 139
6.2.1.3 Methods of Pavement Construction 140
6.2.1.4 Distresses due to Submergence and Hot Climatic Condition 140
6.2.1.5 Safety Aspects of Pavements 141
6.2.1.6 Life Cycle Cost 141
6.2.2 Findings from Field Investigations 142
6.2.2.1 Qualitative Observations 143
6.2.2.2 Quantitative Observations 145
xii
6.2.3 Findings from Questionnaire Survey 146
6.2.4 Findings on Rigid Pavement Roads Constructed by DCC, LGED, RHD 149
6.2.4.1 Rigid Pavements Constructed by DCC 149
6.2.4.2 Rigid Pavements Constructed by LGED 149
6.2.4.3 Rigid Pavements Constructed by RHD 149
6.2.4.4 Rigid Pavement Constructed by Private Initiatives 149
6.2.5 Price Escalation of Binders and Mixes 150
6.3 Recommendations 151
6.4 Limitations of the Study 153
REFERENCE 154
APPENDIX-A 157
APPENDIX-B 158
APPENDIX-C1 161
APPENDIX- C2 162
xiii
LIST OF TABLES Table no & tilte
Table 2.3: Roads under LGED/City Corporation/Pourashava 19
Page Table 2.1: Concrete pavements in Florida 16
Table 2.2: Road network under Roads & Highways Department 19
Table 2.4: Cement production in Bangladesh 21
Table 2.5: Budget Allocation for Road Construction
and Maintenance by RHD 23
Table 4.1: Relative thickness of both type of pavement 33
Table 4.2: Cost comparison of bitumen and cement 34
Table 4.3: Maintenance cost of flexible and rigid pavement 47
Table 4.4: Other Costs Involved with the Maintenance of Flexible Pavements 47
Table 4.5: Per km Cost of Standard 2-lane Road for 10 years Design Period 61
Table 4.6: Per km Cost of Standard 2-lane Road for 10 years Design Period 62
Table 4.7: Calculation for flexible pavement construction for case study-1 64
Table 4.8: Unit Cost of Flexible Pavement for 30 yrs
Design Period (Case Study-1) 64
Table 4.9: Total Cost of Rigid Pavement for 10 years
Design Period (Case Study-1) 65
Table 4.10: Unit Cost of Rigid Pavement for 30 years
Design Period (Case Study-1) 65
Table 4.11: Unit Cost of Flexible Pavement for 10 yrs
Design Period (Case Study-2) 67 Table 4.12: Unit Cost of Flexible Pavement for 30 yrs
Design Period (Case Study-2) 67 Table 4.13: Unit Cost of Rigid Pavement for 10 years
Design Period (Case Study-2) 68
Table 4.14: Unit Cost of Rigid Pavement for 30 years
Design Period (Case Study-2) 68
xiv
Table 4.15: Unit Cost (in Tk.) of Bitumen, Cement, Flexible and
Rigid Pavements 71
Table 5.1: Properties of Virgin and Extracted Bitumen for Site – 1 96
Table 5.2: Properties of Virgin and Extracted Bitumen for Site – 2 97
Table 5.3: Aggregate Gradation of Site-1 98
Table 5.4: Aggregate Gradation of Site- 2 99
Table 5.6 (a): Marshall Test Results of Specimens Collected
from Site-1 (Khilgaon site) 100
Table 5.6 (b): Marshall Test Results of Specimens Collected
from Site-2 (Shahbagh site) 101
Table 5.7: Measured Temperatures at Different Stages
of Construction for Site-1 and 2 102
Table 5.8: Road Cutting Demurrage Fees 129
xv
LIST OF FIGURES
Figure no & title
Page
Figure 2.1 : Distribution of Load and Deflection of Pavements 8
Figure 2.2 : Load Distribution in Pavements 9
Figure 2.3 : Distribution of Pressure under Single-wheel Load
for Flexible Pavements 10
Figure 4.1 : Pavement Deflection Results in Tensile and Compressive
Stresses in Pavement Structure 29
Figure 4.2 : Pavement under submerged condition 50
Figure 4.3 : Sequence of pavement failure under submerged condition 50
Figure 4.4 : Sequence of pavement failure under submerged condition 55
Figure 4.5 : Stopping Sight Distances (SSD) w.r.t. Pavement Surface Types 56
Figure 4.6 : Change of Surface Friction with Pavement Age 57
Figure 4.7 : Light reflection from asphalt and concrete pavement surface 58
Figure 4.8 : Case 1 - More street poles needed for asphalt pavement 58
Figure 4.9 : Case 2 - Higher watt bulbs needed for asphalt pavement 59
Figure 4.10 (a) : Layers of flexible pavement 64
Figure 4.10 (b) : Layers of rigid pavement 66
Figure 4.11 (a) : Case 1-Layer thickness of flexible pavement 68
Figure 4.11 (b) : Case 1-Layer thickness of rigid pavement 70
Figure 4.12(a) : Case 2-Layer thickness of flexible pavement 72
Figure 4.12(b) : Case 2-Layer thickness of rigid pavement 72
Figure 4.13: Price Escalation of Bitumen and Cement 73
Figure 4.14: Price Escalation of Bituminous and Cement Concrete Mixes 73
Figure 5.1 : Aggregates Gradation Charts for Site 1 & 2 with Specified Envelope 99
Figure 5.2 : Aggregate Segregation in a Stockpile 119
Figure 5.3 : Temperature Differentials 120
xvi
xvi
LIST OF PHOTOGRAPHS
Photograph no & title Page Photo 2.1 : Flexible pavement 7
Photo 2.2 : Rigid pavement 7
Photo 2.3 : Concrete road in German Autobhan 15
Photo 2.4 : Concrete highway in Florida 16
Photo 2.5 : Concrete road in Mumbai-Pune express way and Delhi-Mathura road 17
Photo 2.6: Concrete roads in European countries 18
Photo 2.7: Pollution problem caused by on-site open method
of heating the ingredients 24
Photo 4.1: Bituminous Paving Operation by using Paver 39
Photo 4.2: Tandem and Pneumatic Rollers in Compaction of
Hot Mix Asphaltic Pavement 40
Photo 4.3: Wooden Formworks for Concrete Pavement 41
Photo 4.4: Plying of Heavy Vehicles under Submerged Condition 51
Photo 4.5: Suction Force created by Heavy Current of Flowing Flood Water 51
Photo 4.6 : Pavement Deterioration after Rainy Season 52
Photo 4.7: Distresses of Pavement Surface due to Hot Climatic Condition 54
Photo 5.1: Preparation of Marshall Specimen at Site-1 85
Photo 5.2: Preparation of Marshall Specimen at Site-2 85
Photo 5.3: Collection of Aggregates 86
Photo 5.4: Collection of Bitumen 86
Photo 5.5: Collection of Paving Mixes 86
Photo 5.6: Temperature Measurement of Aggregates just before
Mixing Operation 87
Photo 5.7: Temperature Measurement of Bitumen just before
Mixing Operation 87
Photo 5.8: Measurement of Mixture Temperature at the time of Mixing 87
Photo 5.9: Temperature Measurement of Paving Mixture just
xvii
before Compaction 87
Photo 5.10: Bitumen Extraction Test 88
Photo 5.11: Test of Aggregate Gradation 89
Photo 5.12: Penetration Test 89
Photo 5.13: Marshall Test on Specimens Collected from Field 90
Photo 5.14: Different manual methods of road construction in Bangladesh 96
Photo 5.15: Flood-proof concrete road built to provide sustained pavement 129
1
CHAPTER 1
INTRODUCTION
1.1 Introduction
Pavements in a country have been rightly compared to the arteries of a human being and
their importance in the economic uplift of a country can never be ignored. A good
network of road and an effective system of transport are therefore, essential for economic
prosperity and industrial development. Bangladesh is a developing country; its
infrastructure facilities in the transportation sector are not so good to treat it as a better
communication system. But the need for good roads and highways are increasing day by
day and for enhancing the economic development of this country there is no alternative to
give communication sector priority. The present trend of road construction in Bangladesh
is almost 95% bituminous pavement [RRD, 2006]. This is due to the fact that the
concerned organizations are constructing flexible pavement without taking any attempt of
pavement selection process and making any comparative analysis. But considering safety,
economy (in the long run), serviceability and comfort, concrete or rigid pavement
construction can be a reasonable option now a day. While construction of rigid pavement
gaining popularity around the world in consideration of better performance as well as
environmental reasons it would be worth exploring to the prospect of using rigid
pavement in road construction of Bangladesh particularly in consideration of better
performance under submerged conditions, requirement of lesser amount of aggregates,
locally available large quantity of cement as well as recent price escalation of petrol in the
international market.
If new roads are built with cement concrete and if blacktopped roads needing
strengthening are over-laid with cement concrete, the future requirement of bitumen for
these roads can be avoided.
2
1.2 Motivation of the Research
In Bangladesh, rigid pavement is not normally used in roads, because
engineers think that this type of construction involves high initial cost without any
comparative economic analysis. Road planners and designers in Bangladesh have
misconception about the use/implementation of rigid pavements and also misconception
about the constructional method and its associated costs.
Though, one of the main drawbacks of rigid pavement is high initial cost of construction,
but in consideration of several functional and operational advantages and above all from
the viewpoint of life cycle cost, the cement concrete roads are becoming popular around
the world [World Highways, 2004]. Advent of modern techniques in the production of
durable concrete, price escalation of petrol and above all participation of private sector in
road infrastructure development made the selection of concrete pavement in many high
standard road projects particularly built under BOT concept [World Highways, 2004 &
Internet Documents, 2006]. Literature obtained from the Internet reveals that the
advantage of long life is widely favorable to private sector projects where the lease period
is up to 30 years, since a careful investor would expect that his project should last for the
full period of franchise without the need for major repairs, overhauls or rehabilitation. A
bituminous pavement, however carefully constructed, requires significant periodic
renewals when the pavement deteriorates functionally and structurally, and this can
happen once in every 7 years on an average as found in actual care [World Highways,
2004, & Internet Documents, 2007]. Now-a-days reduction of maintenance works
particularly on busy roads is one the main concerns of traffic management measures.
In Bangladesh, due to poor quality of construction coupled as well as due to heavy
rainfall and submerged condition, flexible pavement deteriorates prematurely and thereby
requires maintenance work more frequently. In consequence government has to spend a
lot of money every year for maintenance work of pavement all over the country. As such
there is a need for undertaking a comparative study between flexible and rigid pavements
and field investigation for indentifying the problems associated with the construction of
flexible pavement – with a view to find out the appropriate type of pavement for the local
weather and traffic conditions.
3
1.3 Objectives of the Research
The main objectives of this study deal with the importance of using cement concrete
pavement in roadway construction of Bangladesh. Also it attempts to focus on
comparative analysis between flexible and rigid (concrete) pavements considering mainly
cost, material availability, pavement performance under climatic and submerged
condition and long time serviceability. The specific objectives of the proposed project
are:
- To review the present pavement selection and construction practices followed by
RHD, LGED and DCC.
- To examine the weaknesses associated with the construction and quality control of
flexible pavement.
- To explore the performance of flexible pavement in particular relation to submerged
conditions.
- To understand the difficulties presently associated with the construction of flexible
pavement.
- To compare unit cost of flexible and rigid pavement in consideration of life cycle cost
(LCC).
- To explore the possibility of using rigid pavement from the view point of locally
available binding material, amount of aggregates and type of equipment requirements,
construction and maintenance cost, quality control issues and above all performance
under submerged condition.
It is expected that the findings of the research would help in better way of understanding
the problems associated with the construction of flexible pavement. Besides, it is also
expected that the research findings would help to explore the potential of rigid pavement
and thereby would encourage the use of locally available cement in place of imported
bitumen in pavement construction in Bangladesh.
4
1.4 Scope of the Research
In this research work, efforts are made to explore identifying the problems associated
with the construction of flexible pavement and the potentiality of using rigid pavement in
the context of Bangladesh.
1.5 Organization of the Research
In this study the research work carried out is divided into different topics and presented in
six chapters, they are as follows.
A brief introduction of statement of the problem is presented in the first chapter with
special emphasis on the objectives of the proposed study.
Chapter 2 of this thesis covers a review of comparative figure of flexible and rigid. It
includes a detail description of these two types of pavement regarding design concepts,
construction, maintenance and rehabilitation procedures, economic analysis,
serviceability etc.
Chapter 3 describes the methodology and investigation techniques employed in this
research to fulfill the objectives set out in Chapter 1 and also describes the short
description of the field and laboratory tests.
Chapter 4 illustrates the comparative analysis of both flexible and rigid pavements on
especial emphasis of life cycle cost, procurement of material, quality control of
construction and economic analysis for 30 years design life.
Chapter 5 describes the field and laboratory investigations. This Chapter contains the
detail description of test spot selection, performing various experiments at the spots,
various tests in the BUET laboratory etc. This chapter also enumerates the analysis of test
results on the field and lab prepared samples. It also includes the finding on evaluation of
test results and compared them with the standard values.
The conclusions of the whole study and some recommendations for future research are
presented in Chapter 6.
Appendixes are attached at the end of this report, which contains all raw data, graphs and
various reports used in this research.
5
CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
Concrete pavements, often called rigid pavements, are made up of Portland Cement
Concrete (PCC) and may or may not have a base course between the pavement and sub
grade. The concrete pavement, because of its rigidity and high modulus of elasticity,
tends to distribute the applied load over a relatively wide area of soil; thus, the slab itself
supplies the major portion of the structural capacity. This is in contrast to the flexible
pavement, wherein building up relatively thick layers of sub base, base, and wearing
course brings the strength of the pavement. Concrete pavement has several distinct
advantages over bituminous pavement. Few of them are – it has more useful life, low cost
of maintenance, provide good visibility for night driving, it requires lesser amount of
aggregates and no flame thereby more environmental friendly, can be constructed under
unfavorable soil condition, practically unaffected by weather and temperature etc. Most
importantly for flooding potential areas it offers better performance than that of flexible
pavement.
One of the main drawbacks of rigid pavement is high initial cost of constructions. But in
consideration of several functional and operational advantages and above all from the
viewpoint of life cycle cost, the cement concrete roads are becoming popular around the
world. Advent of modern techniques in the production of durable concrete, price
escalation of petrol and above all participation of private sector in road infrastructure
development made the selection of concrete pavement in many high standard road
projects particularly built under BOT concept. Literature obtained from the Internet
[Thomas, 1999] reveals that the advantage of long life is widely favorable to private
sector projects where the lease period is up to 30 years, since a careful investor would
expect that his project should last for the full period of franchise without the need for
major repairs, overhauls or rehabilitation. A bituminous pavement, however carefully
6
constructed, requires significant periodic renewals when the pavement deteriorates
functionally and structurally, and this can happen once in every 7 years on an average as
found in actual care [David at el., 2000
2.2 Comparison of Rigid Pavement and Flexible Pavement
]. Now-a-days reduction of maintenance works
particularly on busy roads is one the main concerns of traffic management measures.
Traffic loads on highways and local roads are increasing day by day. Automobile, bus,
truck and traffic are growing every year and the loads are getting heavier. Today’s
highways often handle two or three times the traffic they were designed to carry. Heavier
loads, increased traffic and higher speeds are creating greater demands on present
overcrowded transportation network. Concrete pavement is only paving solution able to
carry the load. Adequately designed and well-constructed cement concrete pavement
provides a service life of 40 to 50 years [Barry, 2006]. It is often said that the life of a
cement concrete slab is limitless and can be prolonged to almost any desired period. This
is achieved by careful design, construction under strictly controlled condition, careful
monitoring of the performance, providing adequate maintenance whenever required.
However, several distinct points differ concrete pavement form flexible pavement. The
wide acceptability of cement concrete as a road pavement material is mainly due to
certain principal advantages it scores over bituminous material. A set of comparisons of
two types of pavements from different point of view is described in this chapter.
Highways are hard surfaced structures/pavements that allow vehicles on pneumatic tire
and other vehicles with different tires to move from one place to another. All hard
surfaced pavement types can be categorized into two groups: flexible and rigid.
2.2.1 Flexible Pavement
Flexible pavements are those, which are surfaced with bituminous (or asphalt) materials.
These can be either in the form of pavement surface treatments or, HMA surface courses
as depicted in photograph 2.1. These types of pavements are called "flexible" since the
total pavement structure "bends" or "deflects" due to traffic loads. A flexible pavement
structure is generally composed of several layers of materials, which can accommodate
7
this "flexing". A flexible pavement is a structure that maintains intimate contact with and
distributes loads to the sub grade (Photograph 2.1) and depends on aggregate interlock,
particle friction, and cohesion for stability.
Photograph 2.1: Flexible Pavements
2.2.2 Rigid Pavement
Rigid pavements are composed of a PCC (Portland Cement Concrete) surface course.
Such pavements are substantially "stiffer" than flexible pavements due to the high
modulus of elasticity of the PCC material. Further, these pavements can have reinforcing
steel as illustrated in photograph 2.2, which is generally used to reduce or eliminate
joints. A rigid pavement is a rigid structure that distributes the wheel loads over a wider
area to the sub grade and depends on concrete slab strength for stability.
Photograph 2.2: Rigid Pavements
8
Structural and functional differences of these two types of pavements are described
below.
(a) Layer system: The flexible pavement is an asphalt pavement. It generally consists of
a relatively thin wearing surface of asphalt built over a base course and sub base course.
Base and sub base courses are usually gravel or stone. These layers rest upon a compacted
sub grade (compacted soil). In contrast, rigid pavements are made up of Portland cement
concrete and may or may not have a base course between the pavement and sub grade.
Figure 2.1 represents the layered structure and cross sections of two types of pavements.
Layer Deflections and Cross sections of Pavements
Figure 2.1: Distribution of Load and Deflection of Pavements
9
The essential difference between the two types of pavements (from figure 2.2 and 2.3),
flexible and rigid, is the manner in which they distribute the load over the sub grade.
Rigid pavement having high modulus of elasticity of materials (because of concrete's
rigidity and stiffness) tends to distribute the load over a relatively wide area of sub grade.
The concrete slab itself supplies a major portion of a rigid pavement's structural capacity.
So no surface deformation occurs when wheel load passes over it.
Flexible pavement having relatively less modulus of elasticity of materials (inherently
built with weaker and less stiff material) does not spread loads as well as concrete and
deflects when wheel load passes over it. Therefore flexible pavements usually require
more layers and greater thickness for optimally transmitting load to the sub grade.
Figure 2.2: Load Distribution in Pavements
10
Figure 2.3: Distribution of Pressure under Single-wheel Load for Flexible
Pavements
(b) Design Precision and Criteria:
A cement concrete pavement is amenable to a much more precise structural analysis than
flexible pavement. The fact is that the flexural strength of concrete, which is used as the
main basis for design, is well understood. The most common design method for rigid
pavement is Portland Cement Association method (PCA, 1984). AASHTO design method
considers the following factors:
1. Effective modulus of sub grade reaction
2. Concrete elastic modulus
3. Concrete modulus of rupture
4. Load-transfer coefficient
5. Drainage coefficient
6. Reliability and standard deviation
7. Traffic load applications
8. Serviceability loss
According to the PCA (Portland Cement Association) Method the criteria are:
1. Fatigue
2. Erosion
11
Flexible pavement design methods are mainly empirical. Latest research in understanding
the performance of bituminous materials has furthered the knowledge on their behavior.
Computer aided analysis of layered system is making the flexible pavement design more
exact than previous. The most common design methods for flexible pavement design are:
1. The Asphalt Institute method:
2. AASHTO flexible pavement design method:
According to the AASHTO design method a structural number is determined based on the
following:
1. Traffic
2. Reliability
3. Sub grade soil property
4. Environmental effects
5. Loss of serviceability
(c) Design Life & maintenance Period:
One of the most well known advantages of concrete is its superior durability and longer
structural life. A 1998 life cycle cost report by ERES Consultants Inc. indicates that the
expected life of an asphalt road is 17 years compared to 34 years for concrete. The report
also indicates that asphalt highways require maintenance activities every three to five
years and major rehabilitation becomes more and more frequent after the initial 17th year
overlay. Maintenance cost is large sealing cracks; potholes, resurfacing and resealing are
done frequently. Major maintenance / rehabilitation required after few years of service.
Traffic adversely affected due maintenance creating extra difficulties in urban areas.
Audit of maintenance is difficult and gives opportunity for misuse of public funds.
Maintenance budget is relatively smaller. Requires less maintenance cost. Use of CRCP
reduces number of joints and hence their maintenance.
Concrete on the other hand, requires its first minor maintenance after 12 years and
retexturing of the concrete surface at year 18, allowing roadway users to get to their
destination with fewer delays.
12
(d) Initial Cost Analysis:
The initial cost of making of a rigid pavement is high compared to flexible pavement.
Therefore, for low budget road construction flexible pavement is preferable.
(e) Life Cycle Cost Analysis (LCCA):
When LCCA is used, concrete pavement is often cost-effective than asphalt pavement of
equivalent design for high truck traffic highways. Because flexible pavement needs more
frequent maintenance work than rigid pavement and its design life is also smaller.
(f) Mode of failure:
The mode of failure flexible pavement is by fatigue and Rutting; on the other hand it for
rigid pavement is Cracking (due to temperature), fatigue and joint failure due to improper
construction or inadequate reinforcement or aggregate interlock. High temperature,
submergence effect severely damage flexible pavement for the countries like Bangladesh.
Rigid pavement does not experience such kind of failure.
(g) Stage construction:
Due to extreme scarcity of resources in the country, road construction is generally done
adopting a policy of stage construction, especially for low volume roads. Stage
construction is possible for flexible pavements. A new flexible road, for example is
constructed with barest minimum specification, as traffic grows, additional layers can be
added on with respect to traffic growth. Cement concrete slabs do not fit into such scheme
of stage construction.
(h) Surface characteristics:
A good cement concrete surface is smooth and free from rutting, potholes and
corrugations. A well-constructed cement concrete pavement can have permanent non-skid
surface. But if the design is faulty, the surface may become very smooth in course of
time. If it does, it will be costly to restore the non-skid characteristics. A bituminous
13
surface can also be designed to have a good skid-resistant surface. If it fattens up, a rough
seal coat with a brushing of coarse aggregates can easily restore the lost property.
(i) Concrete Pavement provides fuel savings for heavy vehicles:
Heavy vehicles cause greater deflection on flexible pavements than on rigid pavements.
This increased deflection of the pavement absorbs part of the vehicle energy that would
otherwise be available to propel the vehicle, thus, the hypothesis can be made that more
energy and therefore more fuel, is required to drive on flexible pavements. Concrete’s
rigid design reduces road deflection and corresponding fuel consumption.
A study for the Federal Highway Administration (FHWA, 2007) to update the difference
in fuel consumption performance of heavy vehicles operating on concrete and asphalt
pavements shows that the savings in fuel consumption for heavy vehicles traveling on
concrete versus asphalt pavements was up to 20%.
(j) Penetration of water:
A cement concrete slab is practically impervious, except at joints. If joints are sealed and
well maintained, water will not penetrate and soften the sub grade. A bituminous surface
is not impervious. Water can find its way into the lower layers through cracks and pores.
Such water can impair the stability of the pavement.
(k) Utility location:
For concrete pavement it is difficult to rip open the slab and restore it to the original
condition if any changes in the utility lines are to be made. For this purpose, gaps are left
in the pavement. In flexible pavement random cut in pavement structure is possible. So
for an unplanned and densely populated city flexible pavement is preferable because
utility cutting is a very common feature in these road areas.
(l) Traffic dislocation:
A cement concrete pavement requires 28 days before it can be thrown open to traffic. On
the other hand a bituminous surface can be thrown to open to traffic shortly after it is
14
rolled. So, from construction point of view concrete pavements cause longer dislocation
of traffic than flexible pavements. But maintenance work needed for flexible pavement is
very frequent than rigid pavement, which causes small dislocation or disturbance of
traffic very frequently over the lifetime of flexible pavement.
(m) Pavement Recycling:
All pavements eventually have to be rehabilitated. In case of concrete pavement
recycling, the recycled material is used as granular fill, base course for new pavement, or
as aggregate to strengthen new concrete pavement. Asphalt pavement can be recycled as
"Reclaimed Asphalt Pavement" (RAP). RAP is essentially old pavement that is reclaimed
for use. In its most common form, it is collected in loose granular form as a byproduct of
pavement rehabilitation or reconstruction. RAP can be used in a variety of ways such as:
• As an addition to regular HMA
• As an aggregate in cold-mix asphalt
• As a granular base course when pulverized
• As a fill or embankment material
(n) Environmental Consideration:
During construction of a flexible pavement where bituminous layers are to be provided,
the process of heating of bitumen and aggregates and mixing them together in hot-mix
plants can prove to be much more hazardous to the environment than cement concrete
construction where no heating of any material is involved. Use of bitumen cutbacks can
also prove to be environmentally hazardous due to evaporation of volatile constituents
into the atmosphere. Concrete pavement is longer lasting and therefore environment
friendly in a sense that
• They don’t need to be rehabbed or reconstructed as often.
• This means fewer raw materials are used both in the short term and over the life of
the pavement.
• This also means fewer pollutants are going into our water, air, and soil.
• It also results in less energy being used in construction. i.e. less motor fuels and
oils are needed for heavy construction equipment.
15
• Longer lasting concrete helps reduce traffic congestion because there are simply
fewer construction work zones slowing traffic flow.
Besides, there are many other advantages of concrete pavement over flexible pavement.
Cement concrete pavement requires significantly less construction time; less number of
heavy equipment consumes less fuel and lubricant and is environmentally safe. Also
flexible asphalt pavement requires more aggregate materials than concrete pavement.
Cement concrete pavement enhances protection of ecology and conservation. Concrete
pavement provides better visibility, skid resistance, higher abrasion, and enhances cross
drainage over pavement, better road environment and surface condition etc. Cement
concrete pavement significantly improves the safety performance of road pavements and
reduces road accidents risks.
2.3 History of Concrete Pavements in different Countries of the World
Based on systematic evaluation of the possible alternatives and advantages and
disadvantages of the various pavement types, concrete pavements have been used
extensively for several years in many countries for main roads and expressways.
Germany:
The most illustrious pioneering example of is the German Autobahn System as illustrated
in photograph 2.3, which comprised a
total length of around 2100 km., by
1945 [Hyde F., 1996]. Out of this
length, 90 per cent was constructed
using concrete, convinced of the
superiority of this specification; the
Federal Republic of Germany
continued to use concrete for its
expressways in the post-war period.
Heavy military equipment like tanks and trucks moved over the German Autobahns
during the Second World War, carrying weights and traffic intensities vastly in excess of
those for which they were designed; even then they did not disintegrate.
Photo 2.3: Concrete road in German Autobhan
16
United States of America:
In the USA over 50% of the Interstate Highway System (about 350000 km) has been
constructed in concrete or mixture of asphalt and concrete [Rosenberg, 1998]. Table 2.1
shows some of Concrete pavements in Florida’s highway and their present status and
photograph 2.4 shows concrete highway presently used in Florida.
Table 2.1: Concrete pavements in Florida, USA [FCPA, 2008]
Sl No Road Name Originally Built Status
01 I-95 Miami 1963 First rehab in 1984, second rehab
in 1999
02 I-4 Polk Country 40 years ago No rehabilitation required till date
03 SR 98 Lakeland 60 years ago First rehabilitation in 1999
04 US 17 Deland 60 years ago Minimal maintenance till to date
05 SR 228 65 years ago No rehabilitation to date
Photograph 2.4: Concrete Highway in Florida
17
Middle East Countries:
Significant stretches of the Trans-European Motorway running form the Baltic to
Southern Turkey have been built as concrete roads. In Jordan, a recently completed
prestigious project opted for concrete [TEM, 2005].
India:
In India cement concrete roads were built in 1920s and 1930s. For example, the city roads
of Hyderabad were built in 1928 as cement concrete roads, the Marine drive in Bombay
was built in 1939 and cement concrete road in Chandni Chowk in Delhi was built in
1936. Many stretches of main highways were also constructed in cement concrete.
Though these roads were constructed in thin slabs (around 100 mm thickness), they
successfully withstood the severe loads of war traffic and of later years. Many roads
survived for 40-50 years, despite the heavy punishment they received that had never
anticipated by the designers. India constructed its last major cement roads in the 1960s
(Agra-Mathura road) but abandoned the cement concrete option thereafter. After a lapse
of nearly 25 years, a 100 km long stretch of cement concrete road is now being built
between Delhi and Mathura [ASCE, 2007] as illustrated in photograph 2.5. Some of the
city streets of Bombay are also being repaved with cement concrete at present. Mumbai-
Pune-6 lane 94 km expressway constructed with cement concrete pavement opened in
2000 is considered the best road in India [Nashikkar at el, 2000]. In India cement concrete
pavement is under construction in new 2-lane out of 4-lane Highway of Prime Minister’s
Development project- Golden Quadrilateral. In India, the Asian Development Bank
preferred the concrete pavement option for the new carriageway of the four-laning project
between Delhi and Mathura [Business line, 2000]. This project is now in use for last 05
years.
Photograph 2.5 : Concrete Roads in India
Mumbai-pune Expressway Delhi-Mathura Road
18
European Countries:
In the 1950s and 60s notably Austria, Belgium, France, Netherlands, and Switzerland
made considerable use of concrete for their most heavily trafficked roads. among these,
some remarkable road sections are illustrated in photograph 2.6. Others countries such as
Great Britain and Spain have since followed this example [FHWA, 2007].
Photograph 2.6: Concrete Roads in European Countries
Other Countries:
In Thailand, Malaysia and Hong Kong, cement concrete pavements are in use now [Parry,
1985]. These worldwide success stories amply demonstrate that compared to bituminous
pavements concrete pavements are better for expressways and super national highways.
2.4 History of Pavement in Bangladesh
The rigid pavement in Bangladesh was constructed during World War 2 and in early
fifties with thickness between 5 to 6 inches (125mm to 150mm); when the volume of
traffic was either negligible or very small [Parry, 1985]. The concrete pavement
construction was done without following any standard design procedures, modern
construction technique and quality control. All these concrete roads served 40 to 50 years,
and were damaged partially which could be maintained or re-strengthen by placing a
layer of overlay surfacing. In many sections, the conditions of rigid pavements was quite
fair and could be made further useable for another say 10 years by placing a layer of
asphalt or cement concrete overlay [Parry, 1985]. In developed countries, pavement
design engineers and consultants never recommend to remove fully such partially
damaged concrete pavement and to construct a new flexible asphalt pavement replacing
the partially damaged concrete pavement. Structurally, such old concrete pavement is a
Concrete Road in Belgium after 55 yrs Concrete road in Netherlands
19
good foundation for surface course – both international and local pavement engineers
working in Bangladesh do not realize this.
During the late sixties and seventies, the price of cement spiraled upwards as well as there
was a severe paucity of cement in the country, since cement was an imported material at
that period (there was only one cement factory which could not even meet the demand of
the building construction). Whilst, the national economic development policy, particularly
after independence of Bangladesh in 1971, greatly emphasized on providing paved road
connectivity to all Zilla and Upazilla towns and develop paved road network for
improving land transport system in the country. During this period, bitumen was
comparatively cheaper. So the obvious choice was to prefer the asphalt pavement to cater
for rapid road network construction policy. Thus since the seventies, cement concrete
pavement has become a forgotten type of pavement in Bangladesh.
2.5 Road construction in Bangladesh- current practice
The road networks in Bangladesh are classified into several categories such as:
National highways, Regional highways, Zilla roads, Rural roads and Urban (Municipal)
roads.
Roads under different organizations are illustrated in Table 2.3 and 2.4.
Table 2.2: Road Network under Roads & Highways Department (RHD)
Year (till 30
June)
National
Highway (km)
Regional
Highway (km)
Feeder road A
/Zilla road (km)
Total (km)
2005 3,570 4,323 13,678 21,571
Source:
Table 2.3: Roads under LGED/City Corporation/Pourashava
Annual report of RHD, 2005
Road Type Pucca (km) Kuccha (km)
Zilla parishad+Feeder Road B 7,121 15,659
Pourashava/City Corporation 9,820 3,528
Thana Parishad 2,428 42,730
Union Parishad - 10,6660
Source: Annual report of LGED, 2006
20
All most all the paved roads are made of flexible pavements. There are a small amount of
rigid pavement roads constructed by Dhaka City Corporation (DCC) and Local
Government Engineering Department (LGED). Altogether the Dhaka City Corporation
has constructed about 285 km concrete road where as Local Government Engineering
Department has constructed nearly 2% concrete road of about 40,000 km rural road
network [LGED, 2006].
The current practice for pavement design and construction in Bangladesh is “Flexible
Pavement” without any engineering and economic considerations. The materials for such
types of pavement are mainly of two types: (a) aggregates (brick or stone chips, sand) and
(b) bitumen. The aggregates are collected locally but key element bitumen is mainly an
imported material. Only EBL (Eastern Refinery Limited) of Bangladesh imports bitumen
from different countries by expending lot of foreign currency every year.
2.6 Availability of Bitumen for Road Construction in Bangladesh
Bitumen is many a foreign material. Every year the Government of Bangladesh has to
spend a lot of foreign money to procure bitumen by Refinery Limited (ERL), which is the
only importing company of bitumen in Bangladesh. With every new kilometer of road
built, as a flexible pavement is nothing but burdening the economy to find bitumen every
year for its maintenances, resurfacing and rehabilitation. Another factor is that Bitumen is
derived from petroleum crude, whose supply is shrinking gradually. Thus considering
long-term availability, bitumen is likely to become scarcer and scarcer as the decades roll
on.
According to the information of Bangladesh Petroleum Corporation (BPC), the annual
consumption in Bangladesh is one lakh MT for road construction by DCC, LGED, and
RHD. The main supplier of this bitumen is Eastern Refinery Limited (ERL) whose own
production capacity is 70,000 MT per year. Remaining huge quantity of bitumen is
imported from abroad by ERL and different non-government organizations at the cost of
lot of hard foreign currencies. But quality of such kind of bitumen is lower compared to
the ERL that may hamper the quality of bituminous road construction seriously. So,
demand of ERL produced bitumen is high. When bitumen production of ERL is often
temporarily stopped due to lack of drum sheet or other technical problem, road
21
construction works are badly hampered and bitumen import is greatly enhanced in
contrast to the normal situation. A newspaper report stating the above statement is
presented in the appendix A.
2.7 Materials for Rigid Pavement Construction
The chief constituent material for construction of rigid/concrete pavement is cement.
There is huge scope of implementing rigid pavement construction practice in our country.
Because, at present a huge quantity of cement is produced locally. Bangladesh has
reached in cement production in such a state that it can export huge amount of cement
every year after meeting its local demand. Bangladeshi cement has a wide market in
northeast Indian state since 2004. Holcim, Lafarge Surma cement plant etc. are
worldwide known cement factories established in Bangladesh and working with full
capacity to meet the local demand as well as for export. The availability of cement is
now assured, since the country has 60 cement factories with sufficient production
capacity. A recent statistics of cement production in our country is given in the following
Table 2.4.
Table 2.4: Cement production in Bangladesh
Sl.
No.
Description of the item Amount*
1 Total no. of cement factories 60 nos.
2 Annual production of cement 30 million tons
3 Annual consumption of cement locally 7 million tons
4 Surplus cement for export 23 million tons
Source: Weekly “HOLIDAY-Business & Finance” on 31st August 2007
So locally produced cement would be available in abundant quantities in future to meet
the requirement of road construction.
Also it is often said that the cost of concrete pavement construction is extremely high.
According to ACI 330R-01, simple maintenance costs of other pavement systems
(asphalt, gravel, and paver) made over 20 year span often equal or exceed the initial
construction costs. Concrete pavements on the other hand, require little upkeep over their
20-year design life- keeping maintenance costs to a minimum. ACI 330R-01 also explains
22
that there are many things that can be done to keep the cost of concrete pavements under
control. Each of these tips can also improve the life, appearance and durability of the
concrete pavement.
• Do not stabilize the sub base
• Use integral curb
• Specify 4,000 psi concrete
• Do not use reinforcement
• Do not seal joints.
So it is high time to construct cement concrete pavement for roads in Bangladesh.
2.8 Effects of Flexible Pavement Construction in Bangladesh
As already stated that to go for flexible pavement construction by road planners and
designers of Bangladesh now a day is unscientific and misconception. Recurring
maintenance and submergence of roads become most unfavorable issues now a day. Also
some other aspects indicate that concrete pavement may get preference over flexible
pavement. In the following articles, problems of using flexible pavement in Bangladesh
are discussed based on some statistics.
a) Maintenance Cost of Pavements in Bangladesh – recent scenario:
Bangladesh Government is playing principal role in road infrastructure development till
now. Every year a substantial amount of money has been spending for developing an
appropriate road in countrywide and associated maintenance cost for the built roads. This
continues on creating pressure on government fund. To meet up the demand and to
maintain the quality of road network, recently Government is trying to attract the foreign
fund for development and maintenance of road network in Bangladesh. Every year, a lot
of government fund is utilizing for the maintenance of roads in Bangladesh, which are
mainly flexible pavement in nature. The execution of maintenance works should include
an expanded periodic that on the national and regional highway network, about 700 km of
thin overlay or other bitumen surface treatment should be undertaken each year [IDC,
23
1999]. The following table shows the budget allocation for both development and
maintenance of road by RHD for the fiscal years from 1994-95 to 2005-06.
Table 2.5: Budget Allocation for Road Construction and Maintenance by RHD
Source: Annual Report of RHD, 2006
From the above table, an important point that must be given attention that during the last
10 years, every year the Government had to spend on an average 15% of the total
allocated budget for the maintenance of roads and highways.
b) Effect of Submergence:
The pavements of Bangladesh are greatly suffered from submergence due to flood, heavy
rainfall, water logging due to inadequate drainage etc. A common enemy of the
bituminous pavement is the effect of water. Access of water into the pavement layers or
the sub grade is one of the normal causes of pavement failure. This situation is
particularly serious in areas of heavy rainfall; water logged locations, flood prone zones
and areas with poor surface drainage. This is why bituminous surfaces are very often
damaged after the monsoons; which is very common in Bangladesh. Almost every year
Financial year
Budget allocation (in crore Tk.) Expense (in crore Tk.) % of Yearly expenses
in road maintenance
Development Sector
Maintenance Sector (Gov.
fund) Total
Development Sector
Maintenance Sector (Gov.
fund) Total
1994-1995 1290.89 226.99 1517.88 1243.87 226.45 1470.32 14.92%
1995-1996 877.46 227.00 1104.46 788.56 225.57 1014.13 20.42%
1996-1997 1022.70 212.00 1234.70 1015.90 211.38 1227.28 17.12%
1997-1998 1087.05 248.00 1335.05 1061.00 246.06 1307.06 18.43%
1998-1999 1525.56 270.00 1795.56 1453.51 269.99 1723.50 15.04%
1999-2000 1719.87 281.00 2000.87 1790.97 281.00 2071.97 14.04%
2000-2001 2519.33 312.00 2831.33 2133.71 311.97 2445.68 11.02%
2001-2002 2282.84 331.00 2613.84 2014.24 330.99 2345.68 12.66%
2002-2003 2369.95 375.00 2744.95 2137.27 374.97 2512.24 13.66%
2003-2004 2487.68 576.60 3064.28 2197.60 574.60 2772.19 18.75%
2004-2005 2361.31 866.86 3228.17 2206.00 866.86 3072.86 26.85%
2005-2006 2319.79 901.50 3221.29 944.64 420.91 1365.55 13.07%
24
the roads are submerged by floodwater or continuous rainfall that severely damages the
flexible pavement.
c) Pollution Problem:
The present road maintenance practice in Bangladesh is a serious threat to the
environment. Road side heating of bitumen /aggregate or mixture of both openly in public
places produces black smoke that continues to mix with the environment and spoils
natural condition of the air. It causes pollution and serious health hazards (photo 2.7).
Photograph 2.7: Pollution problem caused by on-site open method of heating the
ingredients
25
2.8 Overview
The preceding articles present a brief but reasonably comprehensive view of bituminous
pavement construction. It has intended to present problems of using flexible (bituminous)
pavement in our country considering initial and yearly maintenance cost and high foreign
currency involvement in procuring bitumen. As such, it is believed to provide a viable
alternative to adopt rigid pavement construction considering it’s zero maintenance cost
and availability of cement in Bangladesh. To cope with this, past experience of rigid
pavement construction in our country and present trend of adopting rigid pavement
construction can be taken into consideration.
26
CHAPTER 3
METHODOLOGY
3.1 Introduction
The aim of this paper is to choose the pavement type which would be more cost effective
and give good serviceability in the long run in the context of Bangladesh. In this regard
extensive literature review needs to be carried out to acquire knowledge about past and
present trend of pavement system in the world as well as in Bangladesh. Besides field
investigations are to be carried out to identify the problems associated with various stages
of quality control maintained in the construction of flexible pavement. Comparative
analysis about various factors in flexible and rigid pavements is also to be carried out
carefully. To progress the research work in an efficient and appropriate way the choice
and selection of suitable methodologies are of prime requirement. This chapter outlines
the overall design of the study and research methodologies that would be followed to
achieve the objectives set out in the Chapter 1.
3.2 Outline of the Research Methodology
In order to carry out a comprehensive study in line with the objectives set out in the
preceding article, the following methodology is proposed:
• Problem associated with the construction of flexible pavement would be examined by
undertaking field investigation on the construction as well as quality control (QC)
practices followed by the Contractors. In this regard, for laboratory investigation
Marshall Samples would be made at the construction site using the mix prepared by
the Contractors and construction material viz. aggregates and bitumen would also be
collected for further parametric studies. Close scrutiny on quality control would be
made by observing and taking relevant data during materials heating, mixing, mix
transportation to the construction site, laying, compaction operations etc. Observation
would be made both on manual and mechanized method of constructions.
27
• Information regarding the use of rigid pavement in national highways will be traced
back.
• Detail information about the rigid pavement works so far undertaken by RHD, LGED
and DCC will be collected from the concerned Authorities.
• In order to know the present pavement selection and construction practices followed
by RHD, LGED and DCC in particular what are the underlying reasons behind not
selecting rigid pavement in road construction, a questionnaire survey will be carried
out among the Engineers of these organizations.
• Information will also be objectively gathered regarding
o Total annual consumption of bitumen in pavement construction & maintenance
works and amount of foreign currency is being spend
o Performance and durability of flexible pavement particularly under submerged
condition, its maintenance frequency and cost involvement.
• Unit cost of flexible and rigid pavements will be estimated by undertaking several
case studies of completed projects and getting relevant information from home and
abroad in particular consideration of life cycle cost (LCC).
• A comprehensive comparative study between flexible and rigid pavements would be
carried out from the viewpoint of locally available binding material, amount of
aggregates and type of equipment requirements, construction and maintenance cost,
quality control issues and above all performance under submerged condition etc.
3.3 Methods of Data Collection
3.3.1 Data Collection from Field for Laboratory Experiment
In order to judge the quality control that is maintained in the construction works of
flexible pavement; in this research work field investigations and experiments are
performed at two different ongoing construction sites. One site is selected where flexible
construction is going on by following the manual method of construction and other spot is
where paving work is going on by using plant mix and paver. For experimental purposes
specimens will be prepared on the spots by using mixes and ingredients are collected for
further investigation in the laboratory. In order to see the level of deviation from the
standard method, at every step of construction temperature is measured by using a special
thermometer. Moreover, each step of the construction method is observed critically and
documented by taking necessary Photographs.
28
3.3.2 Data Collection for Case Study and Economic Analysis
In order to compare the initial and life cycle cost of both flexible and rigid pavements,
case studies are made on the following road sections.
(a) Debogram-Progoti Sharani Link Road Project
(b) Dhaka-Sylhet Highway Restrengthening Project
The Dhaka-Sylhet highway-restrengthening project has already completed by RHD and
the Debogram-Progoti Sharani road project was initially designed by RHD and
subsequently modified by the Consultant of Bangladesh University of Engineering &
Technology (BUET). For the purposes of comparative and economic analysis relevant
design data are collected from the concerned organizations.
To determine the suitable option for pavement type in context of Bangladesh, a
comparative economic evaluation or analysis is required between flexible and rigid
pavement. In this research comparison is performed based on price escalation of the chief
constituent materials of two types of pavements i.e. bitumen and cement for couple of
consecutive years and also unit cost of bituminous and concrete pavement.. For this
analysis, the cost of cement and bitumen as well as unit cost of flexible and rigid
pavement of various years is taken from PWD rates of schedule.
3.3.3 Data Collection for Questionnaire Survey
In order to see the level of understanding regarding the construction of flexible pavement
as well as to know the present practice of selecting pavement type and other related issues
a questionnaire survey will be conducted among the concerned engineers of several
government organizations related to road design, construction, and maintenance activities.
These are:
o LGED (Local Government Engineering Department)
o RHD (Roads & Highways Department)
o DCC (Dhaka City Corporation)
29
The questionnaire survey is also conducted among the field staffs and concerned
engineers from Contractor side.
3.3.4 Data Collection for Comparative Analysis for Flexible & Rigid Pavements
For comparative analysis of flexible and rigid pavement following factors are considered:
(a) Procurement of materials
(b) Material requirement
(c) Equipment required
(d) Initial & life cycle cost
(e) Effect of environment, i.e. specially tropical climate & submersible condition
Relevant data is collected from the Eastern Refinery and from the BCA (Bangladesh
Cement Association). To evaluate the initial and life cycle cost of both types of
pavements, data is collected from RHD design manuals and form PWD rate of Schedule.
3.4 Evaluation Techniques
3.4.1 Laboratory Experiment
A number of tests are performed at different locations where flexible pavement
construction is going on and samples are collected for different tests in the laboratory.
The main purpose of these tests is to evaluate the quality control that is maintained in
field. The numbers of tests that are performed in laboratory are listed below:
(a) Gradation of aggregates
(b) Properties of aggregates and bitumen
(c) Marshall tests on both field prepared sample and laboratory prepared sample
(d) Temperature check at different stages of flexible pavement construction
Evaluation is made by comparing the test results of lab specimens prepared by using the
ingredients collected from construction sites with that were prepared on the spot using the
field mixes.
3.4.2 Case Studies and Economic Analysis
30
In case study, a same road section that is constructed as a flexible pavement will be
analyzed as a rigid pavement to compare the cost involvement of both type of pavements
for 30 years design period. The test sections that are selected already mentioned in the
previous article. The following factors are mainly considered in the cost analysis of
selected pavement sections:
(a) Initial construction cost
(b) Pavement routine and periodic maintenance cost
(c) Renewal of pavement
The cost analysis of the two case studies will be based on PWD rates of schedule,
technical report of FINNROAD LIMITED (an international consulting agency of road
construction) and RHD design manual.
In economic analysis using price escalation method, unit costs of bitumen, cement,
bituminous mixes and concrete mixes would be determined and price escalations of these
materials/mixes would be compared over the span of four-year periods
3.4.3 Questionnaire Survey:
The various findings of questionnaire survey conducted on different organizations,
engineers and other stuffs will be summarized. Based on this survey, reasonable
explanations will be given to identify the problems associated with the construction of
bituminous pavement and reasons of not going to the options of rigid/concrete pavement
construction.
3.5 Overview
In order to achieve the objectives set out in Chapter 1, the research methodology is
selected. At first, the research areas are selected and thereafter methods of data collection
and evaluation techniques are described. To conduct a meaningful research, questionnaire
surveys have been designed. The evaluation techniques on which outcome of the research
work will depend are illustrated. In short, the overall ins and out of this research is
expressed in this chapter.
31
CHAPTER 4
COMPARATIVE ANALYSIS OF FLEXIBLE AND RIGID PAVEMENTS
4.1 Introduction
The present trend of road construction in Bangladesh is almost 95% bituminous pavement
construction [RRD, 2006]. Without taking any attempt of pavement selection process and
making any comparative analysis concerned organizations are constructing flexible
pavement. But considering safety, economy (in the long run), serviceability and comfort,
concrete or rigid pavement construction can be a reasonable option now a day. The main
objectives of this study deal with exploring the possibility of using cement concrete
pavements in the road construction of Bangladesh. Also it attempts to focus on relative
advantages of flexible pavement particularly in the context of Bangladesh.
4.2 Factors of Comparison
There are many factors to look at the differentiation between flexible and rigid
pavements. But with respect to the circumstances of Bangladesh, a few important factors
like equipment requirement, material requirement, quality control in pavement
construction, maintenance cost, life cycle cost, effect of submergence and climatic
condition etc. are addressed with great emphasis. The factors are described in the
following articles.
4.2.1 Equipment Requirement
A fleet of heavy equipment including costly asphalt batching plants, pavers and rollers
required for construction of flexible pavement. Comparatively lesser number of costly
heavy equipment is required for the construction of concrete pavement. As such, initial
investment cost for heavy equipment is relatively less in the case of construction of
concrete pavement. For concrete pavement, the usage time of machineries and equipment
32
are almost round the year, whereas, the idle hours of machineries and equipment for the
construction of asphalt pavement are exorbitantly high due to weather conditions.
4.2.2 Material Requirements
Considering the scarcity of construction materials in Bangladesh, the amount of materials
required for road construction should be an important factor for the selection of pavement
type. In this article, requirement of materials for the construction of per km (standard 2-
lane width) flexible and rigid pavements are determined. For the two types of pavement
typical thicknesses, for a heavily trafficked highway (assumed as over 10,000 AADT) on
a good subgrade for 30 years design period and according to Road Note-29 are given in
the following Table 4.1. In the case of flexible type pavement, overlay is considered to be
required at every 10 years of its service life i.e. after 11th and 21st
Cement Concrete Pavement
(30 years)
year of its construction.
Table 4.1: Relative Thicknesses of Rigid and Flexible Pavements
Flexible Pavement
(10 years)
Flexible Pavement
(30 years)
Cement concrete
slab
300 mm Bituminous
wearing course
50 mm Bituminous
wearing course
50 mm
Lean cement
concrete base
150 mm Bituminous
binder course
100 mm Bituminous
binder course
100 mm
Total 450 mm Aggregate base
course
300 mm Aggregate base
course
300 mm
Sub-base 200 mm Sub-base 200 mm
Total 650 mm Overlay at 11th 100 mm yr.
Overlay at 21st 100 mm yr.
Total 850 mm
From the above Table 4.1, it is clear that material requirements for the construction of per
km pavement made of flexible pavement are almost 50% higher than rigid pavement for
30 years design period. Even if design period is considered to be 10 years i.e. flexible
pavement without overlay, it is found that rigid pavement requires 30% less materials
than the flexible pavement.
33
As the soil condition deteriorates, the thickness of the flexible pavement increases
considerably. For a very poor soil, the thickness may even be about 1000 mm the
thickness of the cement concrete pavement is on the other hand is marginally affected by
soil conditions. Flexible pavements unlike rigid ones also need road materials for regular
maintenance. Thus when considering the overall life cycle, flexible pavement are
wasteful of natural resources. It is definitely suggests that the cement concrete pavement
conserves road construction materials significantly, which is very important for the road
construction in Bangladesh where there is a dearth of construction materials and their
available is also limited to only few remote border areas of the country.
4.2.3 Availability of Binding Materials
Now-a-days cement is locally produced in Bangladesh. The availability of cement is now
assured since the country has 60 cement factories with producing annual capacity of 30
million tones against annual consumption of about 7 million tonnes [BCMA, 2007]. So
locally produced cement would be available in abundant quantities in future to meet the
requirements of the road construction.
On the other hand, bitumen is mostly an imported material and for road construction
every year government of Bangladesh has to spend a lot of foreign currency for procuring
bitumen from abroad. Besides bitumen is one of the derivatives of crude petroleum,
whose supply worldwide is gradually shrinking and price is going high. Thus considering
the long-term availability of bitumen is likely to become scarcer and scarcer as the
decades roll on. Moreover, it is also learnt from the questionnaire survey that in
Bangladesh often the construction of flexible pavement disrupts due to short supply of
bitumen and thereby delay the project completion time and also increase the cost of
construction. Another factor to be reckoned is that with every new kilometer of road built
as a flexible pavement, it burdens the economy to find bitumen for its yearly
maintenance, resurfacing and rehabilitation. If new roads are built with cement concrete
and if existing black topped roads needing strengthening are overlaid with cement
concrete, the future requirement of bitumen for these roads can be avoided.
A comparative cost figure of bitumen and cement is presented in the following Table 4.2.
34
Table 4.2 : Cost Comparison of Cement and Bitumen for Road Construction
Bitumen Cement
Bitumen + Aggregate + Filler Cement + Aggregate + Water + Admixture (may
or may not)
Cost per tonne of bitumen is taka
30,000.00/=
Cost per tonne of cement is about taka 6,500.00/=
Only Eastern Refinery can import
bitumen from abroad
About 60 companies can produce cement
Yearly consumption of bitumen is
3,000 tonnes which is 100%
imported. This amount is paid in
foreign currency
Yearly consumption of cement is 7,000,000
tonnes for various constructional works while
production capacity is 30,000,000 tonnes per year
Yearly expenses for bitumen
procurement is 30,000*3,000/= =
9,00,00,000/= taka which is paid in
foreign currency.
If rigid pavement construction practice is started
in Bangladesh, consumption of cement can be met
up locally and material requirement will also be
less as compared to flexible construction. So, huge
amount of foreign currency will be saved.
Source: Pamphlet published by Eastern Refinery and Bangladesh Cement Manufacturers
Association (BCMA), 2007.
4.3 Methods of Pavement Construction
In this section, the construction process of flexible and rigid pavements are described
elaborately with a particular emphasis given to find out the stages where quality control
are needed both for flexible and rigid pavements. The specific procedures described here
are primarily intended to be applicable to the construction of wearing surfaces, although
the same procedures are also generally applicable to the construction of base and leveling
courses. It is expected that this comparative analysis on the quality control requirements
of pavement constructions would lead to find out the method, which would be more
appropriate for Bangladesh.
35
a. Preparation of the mixture
4.3.1 Flexible Pavement
The fundamental steps in the construction of a high-type hot-mix bituminous pavement
are listed as follows:
b. Preparation of base and leveling courses
c. Transportation and placing of the surface course mixture
d. Joint construction
e. Compaction and final finishing
Each step of construction must be performed following the specified guidelines and
methods prescribed by the organizations like the Asphalt Institute (AI), ASTM and
AASHTO.
4.3.1.1 Preparation of the Mixture
To ensure the desired quality and production of uniform hot paving mixture there is a
need for very close control over quality of ingredients, proper gradation of aggregates,
heating aggregates & binder and proportioning of ingredients. The general precautions
that are involved in preparation of aggregate-bitumen mixture are :
The hot-mix flexible pavement mix design is very sensitive to the quality of aggregate, its
gradation, binder grade and their proportioning. The design job mix formula has to meet
the stringent mix design criteria with respect to stability, flow, % air voids, % voids in
mineral aggregate (VMA), % voids filled with asphalt (VFA). It appears that the mix
design of flexible pavement needs to meet not only the strength criteria but also the
consistency and most importantly the voids requirements. As such, mix design meeting
all the requirements is a very difficult and intricate job.
In the field, as sources of aggregate often changes during the progress of construction
work, it is a daunting task to maintain the specified aggregate gradation unless proper
monitoring is maintained both from the client and contractor sides. Moreover, according
to load bearing mechanism of flexible pavement - the traffic load is carried by aggregate
intergranular friction, therefore aggregates with high angularity and low flakiness and
36
elongation index are required to ensure good interlocking as well as to prevent in-service
fracturing of aggregates. In addition to that since the presence of dust in the aggregates is
harmful for proper bonding between binder and aggregates in a way helpful for stripping
(separation of binder from aggregates) problem, aggregates have to be dust free or need to
be cleaned before mixing to ensure durability of pavement. In the field, this is another big
quality control challenge particularly with the manual method of construction. The
selection of an appropriate grade of binder and ensuring its use throughout the
construction are also a sensitive issue.
From the above discussion it is clearly appeared that the selection of proper ingredients
and their proportioning are very vital to ensure the quality of flexible pavement.
4.3.1.2 Temperature and Mixing Time
The aggregates and bituminous material are handled separately prior to their combination
in the mixing unit. The bituminous material is uniformly heated to a specified temperature
in a tank or “kettle” whereas the aggregates are heated and dried in the drier. The
temperature of asphalt is carefully controlled in order to prevent overheating or “burning”
of the material with consequent destruction of certain desirable qualities. As such it
should not be heated without stirring and for long duration and most importantly it should
not be heated beyond the specified limit. The temperature of the bitumen prior to its
mixing with the aggregates should be between 107°C to 163°C. The temperature –
viscosity relationship of asphalt should be used to arrive at a proper mixing temperature.
In order of produce a uniform and homogeneous mix, aggregates are also needed to be
thoroughly heated and dried at the same temperature. Based on the asphalt viscosity, it is
recommended that mixture should be prepared between 121°C and 135°C. To ensure
consistent and proper mixture, the mixing time should be held to a minimum. In general,
total time in the mixing operation should be in the range of 55 to 70 sec.
From the above recommended method of heating the binder, aggregates and preparing
mix, it is clear that the quality of flexible pavement is very sensitive to the its heating
process. In order to maintain the recommended stringent guidelines in heating binder,
aggregates and preparing mix, there is a need for continuous recording of asphalt and
aggregate temperatures and most importantly use of batch plant is of utmost important,
37
which are very difficult to ensure in majority of pavement construction works in
Bangladesh.
4.3.1.3 Transportation of Mixture
In order to protect the mix from the weather and
resulting heat loss in the mixture during hauling, the
mixture needs to be transported to the job site by
using truck covered with a canvas as shown in the
adjacent picture. The vehicles that are used also
required having tight and smooth metal beds that have
previously been cleaned of all foreign materials and
treated with a light coat of limewater or soap solution to prevent adherence of the
mixture.
4.3.1.4 Preparation of Base
Before placing the hot mix asphalt on new or existing bases requires thorough sweeping
and cleaning to remove loose dirt and other foreign materials. Often, particularly in the
surface maintenance works, the existing surface requires corrective measures in the form
of patchwork or placing leveling course to rectify the irregularities or defects in the
existing surface. Then a tack coat needs to be applied on the cleaned and dried surface at
the specified rate with a pressure distributor to provide adhesion or bond between the
existing surface and the new bituminous wearing surface.
It is clearly evident that proper sweeping and cleaning of the old surface and application
of tack coat are absolutely essential to promote perfect bond between old and new layers.
In this regards, any negligence may led to early wear out of the new layer particularly
where maintenance work involves application of thin wearing course. Corrective and
remedial treatments of old surface defects are also very sensitive to prevent reflection
problems.
4.3.1.5 Placing Mixture
Placement of the bituminous concrete mixture is permitted only when the base is dry and
under favorable weather condition. The lay down temperature of the mixture depends on
38
site-specific situation. The minimum temperature of the surface of the base for mixture
placement varies with the mixture temperature measured just prior to dumping in the
spreader and the lift thickness. The values range from 2°C to 49°C depending on these
variables. The steps of spreading and finishing of mixture should be accomplished by the
use of mechanical spreading and finishing machines like pavers to maintain the desirable
properties of the mixtures and most importantly to lay mixture with uniform lift thickness
which is the precursor of getting even and smooth finished surface. The paver-based
operation is depicted in the following Photograph 4.1.
In placing mixture in the job site, special attention must be given so that after finishing
operation the laid mixture of entire surface have nearly equal temperature and warm
enough for effective compaction. Moreover, special attention must also be given to the
construction of joints between old and new surface or between successive days’ work.
From the above discussion it appears that paver based mixture laying system is essential
for obtaining pavement with uniform thickness as well as for ensuring smooth riding
quality. It is to be noted here that smooth profile at the road surface could bring benefits
including reduced local ponding, reduced noise, reduced dynamic loading and pavement
deformation, improved fuel savings and reduced use of materials.
Photo 4.1: Bituminous Paving Operation by using Paver
39
4.3.1.6 Compaction of the Mixture
When the spreading and finishing operations have been completed and while the mixture
is still hot, rolling is begun accordingly. Compaction should be finished as early as
possible such that asphalt mix is above the minimum temperature (85˚C) at which
densification can be achieved. In order to ensure better compaction of the mixture, the
rolling operation should be planned and executed properly. In general rolling should
begin at the edges and gradually progressing toward the center. Total rolling operation
should be divided into initial or breakdown rolling, intermediate rolling and finishing
rolling. The breakdown and intermediate phases provide needed density and the final
rolling gives the required smoothness. In the total compaction process different types of
rollers viz. three wheel or tandem rollers and pneumatic rollers are required. Use of
tandem and pneumatic rollers in compaction of a hot mix asphaltic pavement is illustrated
in Photograph 4.2.
Moreover, the density of the compacted mixture is needed to be determined by using
nuclear density gauge or cutting core samples from the completed mat.
Photo 4.2 Tandem and Pneumatic Rollers in Compaction of Hot Mix Asphaltic Pavement
It is therefore evident that for proper compaction of the mixture, the minimum
temperature requirement has to be maintained as well as standard rolling operation using
different types of rollers has to be followed. Besides, density measurement test is
necessary to ensure quality control of the compaction works.
40
4.3.2 Rigid Pavement
As compared to flexible pavement, construction steps of concrete pavement are quite
simple. The following are the sequences for the construction of a rigid pavement:
a. Placing of forms
b. Installation of the joints
c. Batching of aggregates and cement
d. Mixing and placing concrete
e. Finishing concrete
f. Curing
Each step of construction must be performed following the specified guidelines and
methods prescribed by the organization like the American Concrete Institute (ACI) and
ASTM.
4.3.2.1 Placing of Forms
Unless slip form paver is
used, the construction of
concrete pavement needs
wooden or steel forms. The
formworks are placed on
the prepared subgrade or
sub base course as shown in
the Photograph 4.3.
Formwork joints shall be
perfectly close and tight to
prevent the escape of liquid
from the concrete.
Photo 4.3: Wooden Formworks for Concrete Pavement
41
4.3.2.2 Installation of the Joints
The installation of various types of joints that may be used in a concrete pavement is a
very important step in the construction process. Function wise there are three types of
joints that are as follows:
Contraction Joints
are used to prevent irregular shrinkage cracks
are used to make sure that cracking will occur at a predetermined desired locations
are used to relieve tensile stress resulting from contraction and warping of the
concrete
constructed by cutting a groove at the pavement surface; groove may be formed
by sawing or by placing a metal strip
dowel bars are used to transfer load across the joints
to permit freedom of movement dowel should be lubricated plain bars
Expansion joints
are used to permit thermal expansion of slab and to prevent blowup at the slab
edges
are used to relieve compressive stress resulting from expansion of the concrete
constructed with a clean break throughout the depth of the slab
usually joint opening of 19mm (3/4") to 25mm (1") is used
dowel bars are used to transfer load across the joints
to permit freedom of movement, dowel bars must be smooth and lubricated on at
least one side
an expansion cap must also be provided to allow space for dowel bar to move
during the expansion process
filler (cork/plastic/rubber) and sealant materials are needed to concealed the joints
to reduce infiltration of water or pumping effect and to reduce clogging of joint
with hard material or chance of blowup problem
expansion joints are susceptible to pumping action
periodic maintenance is required
42
Construction joints
are used at the transition from old to new construction, such as at the end of a
day's pour or at longitudinal joints
instead of dowel bars, usually key form is used to act as load transferring device
and
deformed or hooked tie bars are used to hold/anchored two adjacent segments
firmly to prevent movement
It appears that joints are the most delicate element in the construction of concrete
pavement. Fabrication and placement of the load transferring device i.e. dowel bar
assembly require special attention. For proper functioning of the pavement these joints
need to be constructed as well as maintained properly throughout the service life.
4.3.2.3 Mixing of Concrete
Usually all ingredients of the concrete including the water are batched and mixed at a
central location. The fresh concrete is then transported to the paving site in transit mixers
or in trucks. The aggregates should be clean free from foreign materials like chert, lignite,
mica, vegetable matters and other deleterious substances. In order to find out the mix
proportions and thereby to produce concrete mix with specified strength, trial mixes shall
be performed in the laboratory. To produce a dense impermeable durable concrete, the
water-cement ratio shall be kept as low as possible but without sacrificing the
workability. In this regards if needed admixture can be used to achieve desired
workability or to make self-compacting concrete mixture with low water-cement ratio. It
is found that if the design concrete strength is less than 21 MPa (3,000 psi), the quality
control is not so sensitive to the aggregate types and gradation [Barry P. H., 2006].
Moreover, using low cost mixture machine can easily produce 3,000 psi concrete.
4.3.2.4 Concrete Temperature
Concrete construction in hot weather without appropriate measures impairs the properties
of fresh as well as hardened concrete. A higher temperature of fresh concrete results in
more rapid hydration and leads, therefore, to accelerated setting and a lower strength of
hardened concrete. The concrete temperature should be kept as low as practical to
43
improve placement and structural qualities. The temperature of fresh concrete at the time
of placement shall be in the range of 16 to 32°C (60 to 90°F).
As the ambient temperature during both the winter and summer periods in Bangladesh is
within this specified limit, it is not such a big challenge to maintain in the field. During
extreme summer time when temperature goes well above the maximum specified limit,
using cool/ice water can easily carry out the construction work.
4.3.2.5 Compaction of Concrete
The maximum time elapsed between mixing and placing shall not be more than 45
minutes. The vibrator must be used for compacting concrete. Over vibration causing
segregation and laitance shall be avoided.
4.3.2.6 Roughening Concrete before Depositing Fresh Concrete
In order to provide surface skid resistance, the fresh concrete surfaces shall be thoroughly
roughened with a stiff bristle or wire brush, pick or other cutting tool so that no smooth
skin of concrete is left, but without disturbing the coarse aggregate.
4.3.2.7 Protection and Curing of Concrete
The concrete work shall be protected from the possibility of damage. When the placing of
concrete in any section of the work has been completed, the exposed surfaces thereof
shall be covered with two layers of damp hessian, which must be kept damp for 24 hrs.
After 24 hours, all pavement concrete shall be subjected to block ponding for curing. The
whole of that section of the work, including the formwork, shall also be protected from
direct sunlight, so that both the evaporation of water from the concrete and the
temperature changes of the surfaces of the concrete are kept to a minimum. These
coverings and protection shall remain in place for at least a further 7 days for plain
concrete or 14 days for reinforced concrete. In concrete pavement construction works
curing is very important to control initial shrinkage cracks and thereby to ensure durable
concrete.
44
4.3.2.8 Quality Control
In order to check the strength of the hardened concrete, Schmidt hammer test or test on
cored cylinder samples shall be carried out.
4.4 Development of Pavement Structures
4.4.1 Design Precision
The major factor considered in the design of rigid pavements is the structural strength of
the concrete. For this reason, minor variations in subgrade strength have little influence
upon the structural capacity of the pavement. The major factor considered in the design of
flexible pavements is the combined strength of the layers.
Moreover, due to analytical in nature the structural design of cement concrete pavement is
much more precise than the flexible pavement. The rigid pavement design methods are
based on the well-established elastic theory and are less sensitive to soil as well as less
susceptible to weather conditions. In contrast the design methods of multi layered flexible
pavement are mainly semi-empirical in nature and these are meant for the local conditions
where the observations were made in developing the design method. These design
methods of flexible pavement are directly related to the soil behavior and most
importantly to the weather conditions of the country of origin. As such, in order to
produce better precision in pavement design, before using these methods to other local
conditions there is a need for rigorous time dependent calibration process considering the
local prevailing road-traffic, soil properties as well as climatic conditions which often not
properly done.
4.4.2 Subsurface Layer System
Flexible pavements require more layers than that of rigid pavements and naturally for the
new construction, performance of flexible pavement structure largely depends on the
quality of sub-surface layer construction particularly in maintaining proper gradation of
aggregates, lift thickness, optimum moisture content and most importantly on proper and
uniform compaction of the layer. Moreover, uniform support condition is one of the main
45
prerequisites for ensuring even surface of the flexible pavement. As flexible pavement
allows differential settlement, if sub-surface layers are not compacted properly and
uniformly, the weaknesses of these layers reflect with time and most importantly it is
become very difficult to repair any weakness that exists with the underlying layers. In
addition, as differential settlement increases the amplitude of impact loading it further
increases differential settlement recursively and thereby gradually riding quality of
pavement surface reduces drastically. As such, for obtaining better and sound roadway
structure, the same level of monitoring is needed for the construction of all the subsurface
layers including the wearing course. Since, post quality control checking of the
subsurface layers is not easy to perform with the multilayered flexible pavement structure
there is an ample opportunity for the contractor to compromise with the specified
specifications unless the sincere and honest field engineers supervise it which is very
scarce in Bangladesh.
4.4.3 Stage Construction
Due to extreme scarcity of resources in the country, road construction is generally done
adapting a policy of stage construction, especially for low volume roads. Stage
construction is possible for flexible pavements. A new flexible road, for example is
constructed with the minimum specification, as traffic grows, additional layers can be
added on with respect to traffic growth. Cement concrete slabs do not fit into such scheme
of stage construction though CC block based road could be an alternatively.
4.5 Maintenance Works
Maintenance of any type of pavement can be divided into two parts i.e. routine and
periodic. Routine maintenance is performed every year and periodic maintenance is
required after certain years. Deterioration such as rutting, raveling, deformation and loss
of strength of binder etc. are very common in bituminous surface; which do not happen in
case of cement concrete pavements. As a result, maintenance operations such as patch
repairs, resealing, crack filling, frequent resurfacing and strengthening, pothole repairs
which are needed on a bituminous surface, are absent in the case of cement concrete
roads. The only maintenance required is at the joints, where oxidized joint fillers and
sealants have to be periodically replaced by new materials. But the scale of this operation
46
is very small as compared to the routine and periodic maintenance operations needed for
bituminous road. Maintenance operations and works on bituminous roads often disrupt
traffic flow and cause congestion & diversion related problems for the road users as well
as adversely affects the road environment. On the contrary, traffic dislocations and
inconveniences to road users are minimal for maintenance of concrete pavement. The
FINNROAD Limited has estimated maintenance costs of both types of roads (flexible and
concrete) for 30 years design period [FINNROAD, 2008] based on the information
collected from different road infrastructure development organizations of Bangladesh.
Estimated maintenance costs are presented in the Table 4.3.
Table 4.3: Maintenance Costs of Flexible and Rigid Pavements
Source: Finnroad Limited, 2008
Based on different road works undertaken by RHD, the Finnroad Consultants also
estimated tangible and intangible costs associated with the maintenance of flexible
pavements.
Table 4.4: Other Costs Involved with the Maintenance of Flexible Pavements
Source: Finnroad Limited, 2008
Pavement type Maintenance works Maintenance cost
Flexible pavement Routine maintenance 0.5 lacs every year
Periodic maintenance Cost for 10 cm asphalt overlay after every 10 yrs
Rigid pavement Routine maintenance 0.5 lacs every year
Periodic maintenance No cost required
Sl.
No.
Item of Cost Amount
1. Resealing/ Overlay / Resurfacing (at every 11th Tk8000/m³ year)
2. Engineering Overhead 10% of overlay/resealing etc.
3. Miscellaneous 5% of overlay/resealing etc.
4. Economic loss for traffic delay & road user
discomfort
2% of overlay/resealing etc.
47
4.6 Pavement Distresses due to Local Weather Conditions
Most of roads and highways in Bangladesh are flexible construction. For situational
circumstances, these flexible pavements suffer from several distresses beyond the
constructional fault. The situational circumstances are mainly due to weathering factors
like heavy rainfall and resulting flooding & submergence and hot summer temperature.
Both submergence and hot weather coupled with overloading conditions cause premature
failure of pavement in the form of reveling, potholes, bleeding/flushing, loss of skid
resistance etc. As a result, every year a large amount of money need to spend by different
organizations for the maintenance purposes. In this Article distresses of flexible pavement
that are caused by the submergence and hot weather conditions are explained with special
focus on susceptibility of flexible pavement with the local weather condition as compared
to the rigid pavement.
4.6.1 Submergence Problems
Bangladesh is a riverine country and situated in a flood prone region in the sub
continental. During the rainy season and subsequent occurrence of flood, often a
substantial part of the total land area of Bangladesh goes under water and in consequence
a large amount of road networks become submerged for a considerable period of time.
Due to this submergence condition, flexible pavements suffer a serious type of distress
called raveling where the aggregate and binder become separated due to stripping effect
and in the absence of proper bonding loss of aggregates start. Eventually, potholes with
different sizes and depths developed on the pavement surface and riding quality or its
present serviceability index deteriorated severely and road become unworthy for riding.
In urban areas, due to the lack of sewerage facilities as well as maintenance problems,
roads suffer submergence condition immediately after moderate to heavy rainfall. When
rain or floodwater washes away, bituminous pavement seriously deteriorates. In the rural
or sub-urban areas, roads mainly suffer from seasonal floods. Flood water flashes over the
national or regional highway. At this moment, when truck, bus or such type of heavy
vehicles run over the pavement, cracks are developed due to tension force at the upper
surface of the pavement layer particularly near the tire contact areas and water enters into
the pavement layer through these cracks or void spaces. As vehicle moves forward, tire
48
creates compression on the same surface that was under tension few moments ago. At that
time the water that entered into the surface developed pore pressure and come out
forcefully to release the pressure. This ejection of water breaks the bond between
aggregates and help stripping of binder from the aggregates. With the movement of
vehicles, this process of successive tension (ingress of water) and compression (ejection
or digress of water) on the wearing surface causes serious distress in the form of raveling
and premature failure of the pavement. The mechanics of pavement raveling process
under submerged condition can be seen from the following Figures 4.1 to 4.4.
Figure 4.1:
Figure 4.2:
49
Besides, uplift and suction forces induced by the buoyancy effect of water submergence,
action of running flood water, traction force caused by moving wheel and suction caused
by tread-less smooth tire (which acts as a smooth sponge sandal) etc. accelerate the
process of losing aggregates from the upper layer of pavement and helps in the creation of
Figure 4.4:
Figure 4.3:
Figure 4.4:
50
potholes. In the absence of appropriate traffic control and enforcement measures, plying
of heavily loaded vehicles during the submergence condition also act as a catalyst in the
development of premature pavement distresses. In consequence, each year after rainy
season flexible pavement based roads and highways of Bangladesh needs recurrent
rehabilitation work and thereby besides immense suffering to the motorists it increase the
life cycle cost of flexible pavements. A few snap shots are presented below to depict the
problems associated with the pavement submergence.
Photo 4.4: Plying of Heavy Vehicles under Submerged Condition
Photo 4.5: Suction Force created by Heavy Current of Flowing Flood Water
51
Photo 4.6 : Pavement Deterioration after Rainy Season
During submerged condition due to unavailability of alternative road, in most of the cases
the management of traffic movements becomes virtually impossible. As such, if
pavement remains under submerged condition for couple of days and movements of
overloaded vehicles are allowed to ply without any restriction, then even newly
constructed well designed pavement is bound to fail. Moreover, if water enters the
various layers of the pavement, it adversely affects the performance of the pavement
layers. If the water reaches the subgrade, it can soften the subgrade and reduce its load
bearing capacity as supporting base. Access of water into the pavement layers or the
subgrade is one of the normal causes of pavement failure. The situation is particularly
serious in areas of heavy rainfall; water logged locations, flood-prone zones and areas
with poor surface drainage. This is why bituminous surfaces are very often damaged after
the monsoons; which is very common in Bangladesh. Cement concrete is particularly
impervious to water and does not allow water to reach the subgrade provided joints are
well maintained. As a result, cement concrete pavements perform better under adverse
conditions caused by water and poor drainage.
52
A cement concrete slab is practically impervious, except at joints. If joints are sealed and
well maintained, water will not penetrate and soften the subgrade. A bituminous surface
is not impervious; water can find its way into the lower layers through cracks and pores.
Such water can impair the stability of the pavement as well as embankment structure.
It has long been recognized that presence of water in the pavement section often results in
premature failure of the pavement. Separation and removal of asphalt binder from
aggregate surface due primarily to the action of moisture and/or moisture vapors is
generally termed "stripping". In the identification of the cause of stripping practitioners
have, historically, tended to focus their attention on the sensitivity of the aggregate and
asphalt system in the presence of moisture. This type of stripping can be classified as a
physical-chemical incompatibility of the asphalt-aggregate system.
The pavement gets saturated due to available free water within the pavement structure.
Under saturated conditions all asphalt mixes may fail as a consequence of cyclic
hydraulic stress, which physically scours the asphalt binder from the aggregate. This
stripping may be classified as a mechanical failure of the asphalt pavement system.
If a pavement base becomes saturated, pore water pressure due to traffic loading can
negate the load spreading support function of the aggregate base course. Consequently,
the traffic load will be applied to the subgrade over a small area. The localized loading
may exceed the bearing capacity of the subgrade, causing progressive failure of the
pavement. Pore pressures can also result in significant scouring and jetting pressures.
Water jetting from cracks or joints can transport base and subgrade materials to the road
surface, creating a void under the pavement and eventual pavement failure.
It is therefore evident that climate with high rainfall and recurrent flood demands high
performance pavement system particularly which is not susceptible to water.
4.6.2
Flushing due to hot Climatic Condition
Bangladesh is situated in a tropical region; where in a typical mid day ambient
temperature of bituminous black top surface often rises above 42oC [Chowdhury, A.S.
2001]. This high summer temperature along with the presence of overloaded vehicles in
53
the traffic stream causes a severe type of distress called flushing. Flushing (or bleeding) is
indicated by an excess of bituminous
material on the pavement surface, which presents a
shiny, glass-like reflective surface that may become sticky in hot temperatures. As
bleeding in the form of excessive asphalt cover up the surface aggregates it reduces skid
resistance and at extreme case it often causes instability to moving vehicles due to sticky
surface and thereby makes roadway operation hazardous for the motorists. The pavement
with skid-resistance less surface becomes more slippery and dangerous particularly
during rainy days. Moreover, another common drawback of the bitumen surfaces is their
inherent property of becoming soft under high temperatures. Due to poor creep behavior
of bituminous binder, the soft surface course loses its stability and is easily rutted and
deformed particularly by the stopped or parked vehicles. In contrast cement concrete is
not so susceptible to the temperature and can withstand high temperatures without any
softening. This property is likely to be of great value in tropical countries like
Bangladesh. The following photographs show the slippery surface and wheel paths on the
soft flexible pavements that are caused by binder’s bleeding problem.
Photo 4.7: Distresses of Pavement Surface due to Hot Climatic Condition
54
4.7 Safety Aspects of Pavement
4.7.1 Skid Resistance and Surface Texture
The concrete pavements provide more friction for skid resistance than asphalt pavements
not only just after construction, but also over their entire life. The surface of concrete
pavement provides better road conditions, rough texture, better visibility, better skid
resistance and more prominent road markings, resulting in enhanced road safety, better
driving conditions and thereby reduces the risks of road accidents. Whereas, in the case of
asphalt surfaced pavements, these advantages are required to be made with special
treatment to pavement. From the following Figures it can be seen that due to better skid
resistance with concrete pavement, it significantly reduces the minimum stopping sight
distance (SSD) even at wet condition, which is very sensitive for safe stopping maneuver
particularly at surprised situation. It can also be seen from the second Figure 4.6 that the
surface friction of rigid pavement last longer as compare to the flexible pavement.
Moreover, as concrete pavement is naturally brighter and more reflective than asphalt
pavement, it provide better visual queue for nighttime driving particularly during dark
Figure 4.5: Stopping Sight Distances (SSD) w.r.t. Pavement Surface Types
55
night with heavy down pore when marking in rural road goes under thick lamination of
water and thereby enhance road safety significantly.
In addition, drainage channels in the texture can lead water away, thus avoiding formation
of a film between the tire and the road surface, thereby preventing hydroplaning.
4.7.2 Riding Quality
Because cement concrete does not suffer consolidation under traffic, unlike bituminous
surfaces, which are prone, to do so, cement concrete pavements are practically free from
rutting and deformations in profile. Consequently, a very good riding quality is provided
throughout the pavement life. Bituminous road start losing its riding quality the moment it
is subjected to traffic. Rough undulated roads cause loss of speed and high wear and tear
of vehicles, besides increased fuel consumption. Thus it can be claimed that the road
users’ costs on a cement concrete road are like to be much lower than on a bituminous
road. Obviously, good riding surfaces are pre-requisite for good road environment leading
to safer roads. Consequently, cement concrete pavements enhance road safety by
reducing accident risks.
Figure 4.6: Change of Surface Friction with Pavement Age
56
4.7.3 Visibility and Reflectivity
Cement concrete has a light-colored surface. Hence its-reflectivity characteristics are very
good compared to dark and normal black surfaces of bituminous pavements. Because of
this high diffusing power, a cement concrete surface requires less illumination level to
obtain a desired lumination for guiding and management purposes than that of bituminous
surfaces. Thus, providing lower lighting levels for cement concrete surfaces can save
lighting energy. Also road marking paints lasts longer in case of concrete pavements.
Additionally, because of better visibility, cement concrete surfaces are safer for night
driving. Accordingly, cement concrete roads have a distinct advantage of providing safer
roads.
Concrete is naturally brighter and more reflective than asphalt. This requires less energy
to illuminate comparable areas, which is good for the environment. The following Figure
4.7 is presented to demonstrate the fact.
Figure 4.7: Light reflection from asphalt and concrete pavement surface
To overcome the lack of light reflectance, an asphalt pavement requires either:
(1) More street lights per mile than a concrete pavement, or
(2) Higher watt light bulbs at the same light pole spacing as a used on a concrete
pavement.
These issues can be seen from the following Figures 4.8 and 4.9.
57
4.8 Fuel Savings for Heavy Vehicles
Heavy vehicles cause greater deflection on flexible pavements than on rigid pavements.
This increased deflection of the pavement absorbs part of the vehicle energy that would
otherwise be available to propel the vehicle, thus, the hypothesis can be made that more
energy and therefore more fuel, is required to drive on flexible pavements. Concrete’s
rigid design reduces road deflection and corresponding fuel consumption. A study [World
Highways, 2000 & 2002] for the Federal Highway Administration (FHWA) to update the
difference in fuel consumption performance of heavy vehicles operating on concrete and
asphalt pavements shows that the savings in fuel consumption for heavy vehicles
traveling on concrete versus asphalt pavements was up to 20%. A similar study carried
out recently in India has revealed that even an under-designed cement concrete pavement
gives a fuel saving up to 9% [World Highways, 2004].
4.9 Utility Location
For concrete pavement it is difficult to rip open the slab and restore it to the original
condition if any changes in the utility lines are to be made. For this purpose, expensive
conduit systems are needed to be laid in the pavement beforehand. In flexible pavement
random cut in pavement structure is possible. In this consideration, for an unplanned and
densely populated city, the flexible pavement is preferable because utility cutting is a very
common feature in these areas.
Figure 4.8: Case 1 - More street poles
needed for asphalt pavement
Figure 4.9: Case 2 - Higher watt bulbs
needed for asphalt pavement
58
4.10 Environmental Considerations
During construction of a flexible pavement where bituminous layers are to be provided,
the process of heating of bitumen and aggregates and mixing them together in hot-mix
plants can prove to be much more hazardous to the environment than cement concrete
construction where no heating of any material is involved. Use of bitumen cutbacks can
also prove to be environmentally hazardous due to evaporation of volatile constituents
into the atmosphere. Concrete pavement is longer lasting and therefore environment
friendly in a sense that:
• They don’t need to be rehabbed or reconstructed as often.
• This means fewer raw materials are used both in the short term and over the life of
the pavement.
• This also means fewer pollutants are going into water, air, and soil.
• It also results in less energy used in construction i.e. less motor fuels and oils are
needed for heavy construction equipment.
4.11 Life Cycle Costs
Life Cycle Cost Analysis (LCCA) is a method which allows owners, agencies, engineers,
or any competent person to evaluate different alternatives of infrastructure projects. This
analysis method is based on the estimated or calculated costs of each alternative over its
design life. In applying this concept to pavements, the designer should consider initial
(first) costs, maintenance costs, rehabilitation costs, user costs, and reconstruction costs.
The designer must also make sure that the different pavement alternatives are designed
for the same amount of traffic. LCCA is defined in the Transportation Equity Act for the
21st Century (TEA-21) as "a process for evaluating the total economic worth of a usable
project segment by analyzing initial costs and discounted future costs, such as
maintenance, user costs, reconstruction, rehabilitation, restoring, and resurfacing costs,
over the life of the project segment" [FHWA Report, 2007]. TEA-21 focuses on the
engineering (project) costs and does not directly identify the social costs - air quality,
accidents and noise - which form the external costs of infrastructure construction and
management. Life cycle cost of pavement can be broadly divided into following parts:
initial/investment cost and routine/periodic maintenance cost.
59
At present prices of cement and bitumen, cement concrete roads compared favorably with
flexible pavements even in the initial cost itself. The comparison becomes favorable to
cement concrete roads in regions where stone aggregates are costly; this has been the
worldwide experience. It is more relevant in Bangladesh context where granular
aggregates are scarce and available only in the northern border districts. And, because of
the fact that flexible pavement needs more frequent maintenance work than rigid
pavement and its design life is also smaller, when the cost of annual maintenance is
added, the whole-life-cycle cost of cement concrete roads is confirmedly much lower than
flexible pavements of equivalent loading and design lifetime.
In order to verify this observation, a case study is undertaken and presented in the
following section. Before going to determine the life cycle cost it is necessary to calculate
the per km cost for standard roads of both type of pavements for same soil and traffic
conditions. In this life cycle cost calculation, traffic volume of 10,000 AADT on a typical
2-lane road with 3% CBR and design life of 30-year period is considered. The costs of the
unit area of rigid and flexible pavements (excluding the land acquisition and embankment
costs) are calculated and presented below:
4.11.1 Unit Cost of Flexible Pavement
According to the Road Note-29, for a heavily trafficked highway taking over 10,000
AADT on a good soil subgrade (CBR 3%) condition, the various layer thickness of 2-lane
flexible pavement for 10 years design period are:
Bituminous wearing course = 50 mm
Bituminous binding course = 100 mm
Aggregate base course = 300 mm
Aggregate sub-base = 200 mm
Total = 650 mm
60
Figure 10(a): Layers of flexible pavement
Taking the unit rates from the PWD rate of schedule (2006), the analysis of per km cost
of 2-lane pavement for 10 years design life is given in the following Table 4.5.
Table 4.5: Per km Cost of Standard 2-lane Road for 10 years Design Period
Item Thickness
(m)
Length
(m)
Width
(m)
Quantity
(m³)
Unit Rate*
(Tk.)
Amount
(lacs)
Sub-base,
20 cm thick 0.20 1,000 7.3 1,460 M³ 2,111 30.82
Base course, 30
cm thick
(Brick aggregate)
0.30 1,000 7.3 2,190 M³ 2,500 54.75
Asphalt concrete,
15 cm thick 0.15 1,000 7.3 1,095 M³ 13,100 143.45
* Values are taken from PWD rate of Schedule, 2008 Total = 229.02
Therefore, cost per km of standard 2-lane width for 10 years = Tk. 229.02 lacs
Now, considering 50 cm overlay in the 11th year,
Cost per km for 20 years = Cost for 10 years + Cost for 50 mm overlay
= Tk. (229.02 + (0.05*1,000*7.3*8,000)/1,00,000)
= Tk. (229.02 + 29.2) lacs
= Tk. 258.22 lacs
150 mm
300 mm
200 mm
61
Considering another 50 mm thick overlay in the 21st
4.11.2 Unit Cost of Rigid Pavement (without dowel bar)
year,
Cost per km for 30 years = Cost for 20 years + Cost for 50 mm overlay
= Tk. (258.22 + (0.05*1,000*7.3*8000)/1,00,000)
= Tk. (258.22 + 29.2) lacs
= Tk. 287.42 lacs
According to Road Note-29, for a heavily trafficked highway taking over 10,000 AADT
on a good soil sub grade (CBR 3%) condition, the various layer thickness of 2-lane rigid
pavement for 30 years design period are:
Pavement concrete (with panel size: 6m x 3.65m) = 300 mm
Sub-base = 150 mm
Total = 450 mm
Figure 10(b): Layers of rigid pavement Taking the unit rates from PWD rate schedule, per km cost of 2-lane pavement for 30 years design life is given in the following Table. Table 4.6: Per km Cost of Standard 2-lane Road for 10 years Design Period
Item Thickness
(m)
Length
(m) Width
(m)
Quantit
y
(m³)
Unit
Rate
*
(Tk.)
Amount
(Lacs)
Sub base, 15cm thick 0.15 1000 7.3 1,095 M³ 2111 23.12
Pavement concrete,
30 cm thick 0.30 1000 7.3 2,190 M³ 6687 146.45
*Values are taken from PWD rate of Schedule, 2006 Total = 169.57
300 mm
150 mm
62
According to Rode Note-29, the minimum weight of reinforcement for concrete slab is
required to be 5.5 kg/m2
4.12 Case Studies
. Considering unit cost of rebar is Tk.64/=; the cost for
reinforcement appeared to be = 1000*7.3*5.5*64 = 25.70 lacs.
As no overlay would be required for the cement concrete pavement for 30 years design
life, hence the cost per km of rigid pavement of standard 2-lane width for 30 years =
(169.57 + 25.70) = 195.27 lacs.
From the above calculation, it can be concluded that for 30 years design period of per km
standard 2-lane pavement, life cycle cost of concrete pavement is almost 32% lower than
the flexible pavement. It is to be noted that in the comparison purposes here only the
construction and maintenance costs are considered. If the cost of traffic delay associated
with the poor riding quality as well as traffic disruption and diversion during overlay
works of the flexible pavement were considered, the rigid pavement would have more
economical and favorable.
In order to examine the cost effectiveness of flexible and rigid pavements, an attempt is
made in this section to determine the life cycle costs for two road projects. The cost
analysis of these two road sections for both flexible and rigid construction is made
considering 30 years design life, unit costs and maintenance costs as presented in the
previous articles. The road sections selected for the case studies are:
(a) Debogram – Progoti Sharani Link Road Project
(b) Dhaka – Sylhet Highway Project
The Debogram-Progoti Sharani Link Road or Prubachal access road is a proposed project
that is being constructed by RAJUK as a flexible pavement and the Dhaka-Sylhet
highway has already been constructed as a flexible pavement. In this cost comparison
analysis, both road sections are analyzed as flexible pavement and then again as rigid
pavement with the same data (soil condition, traffic etc.). It is to be noted that the costs of
land acquisition and embankment are excluded from the cost comparison exercise.
63
4.12.1 Case Study-1 : Cost Estimation for Debogram-Progoti Sharani Link Road
The design of this 13 km road segment was initially made by RHD and afterward it was
checked by BUET. This analysis part will follow the procedure as followed by BUET.
The data for this road section are given below:
Given Data:
Functional Classification = National Highway
Road length = 13 km
Lane width = 3.65 m
Road Type = Divided 4-lane
Estimated Traffic = 15.86*106 ESAL (for 10 years design life)
= 110.0*106
Pavement layer
ESAL (for 30 years design life)
Calculated pavement layer thicknesses (along with the corresponding CBR
values) are shown graphically in figure
CBR Thickness (mm)
Bituminous carpeting - 150
Aggregate Base, Type 1 • 80% 225
Sub-base • 25% 300
Sub-grade • 8% 400
Figure 11(a): Case 1-Layer thickness of flexible pavement
Cost of Flexible Pavement for 30 years Design Period
150 mm
225 mm
300 mm
400 mm
64
The total cost of flexible pavement for 4-lane 14.6 m width and 13 km length is
determined by using Road note-29 and initially considering 10 years design life and based
on the PWD rate of Schedule are given in the following Table 4.7.
Table 4.7 : Total Cost of Flexible Pavement for 10 yrs Design Period (Case Study-1)
Pavement Layer Unit Quantity Rate *
(Tk.)
Amount
(in million Tk.)
Sub-grade (400 mm) cu.m 75,920 550 41.76
Sub-base (300 mm) cu.m 56,940 2111 123.20
Aggregate base type-I (225 mm) cu.m 42,705 2,500 106.76
Bituminous carpeting (150 mm) cu.m 28,470 13,100 372.96
*Values taken from PWD Rate of Schedule, 2006 Total = 641.68 Therefore, per km cost of pavement (in million Tk) = 641.68/13 = 49.36
Now, the unit cost of this pavement (per km) considering 30 years design period is
calculated, based on the above unit cost for 10 years design period and considering the
routine & periodical maintenance costs that would be required as per Article 4.5. The
calculated cost is presented in the following Table 4.8.
Table 4.8: Unit Cost of Flexible Pavement for 30 yrs Design Period (Case Study-1)
Sl.
No. Item of cost
Amount (in
million taka)
1. Investment cost for 10 years Design period 49.36
2. Routine maintenance cost @ Tk. 0.5 lac per year * 1.50
3. After 10 yrs. resealing / overlay cost @ Tk. 8000 per m3 11.60 **
4. After 20 yrs. resealing / overlay cost @ Tk. 8000 per m3 11.60 **
5. Engineering overhead cost, 10% of overlay/ resealing etc. ** 2.50
6. Miscellaneous costs, 5% of overlay / resealing etc. ** 1.20
7. Economic loss for traffic delay & road user discomfort, 2% of
overlay/resealing etc. ** 0.25
*From Table 4.3 & ** From Table .4.4 Total = 78.01
65
Cost of Rigid Pavement for 30 years Design Period
For the purposes of comparative analysis, the unit cost of the Purbachal Satellite town
access road is also calculated considering rigid pavement and initially for 10 years design
life and based on the PWD rate of Schedule is presented as follows. The thicknesses of
pavement layer system are determined based on Road Note 29.
Calculated pavement layer thickness (along with the corresponding CBR values) are
shown graphically in figure
Pavement layer CBR Thickness (mm)
Pavement concrete - 300
Sub-base • 25% 80
Sub-grade • 8% 300
Figure 11(b):Case 1- Layer thickness of rigid pavement
Table 4.9: Total Cost of Rigid Pavement for 10 years Design Period (Case Study-1)
Item Unit Quantity
(m³)
Rate*
(Tk.)
Amount
(million Tk.)
Sub grade (300 mm); CBR>=8% cu.m 56,940 550 31.32
Sub-base (80 mm thick) [According to
Road Note-29, TRRL, UK] cu.m 15,184 2111 32.05
Pavement Concrete (300 mm thick) cu.m 56,940 6687 380.76
*Values taken from PWD Rate of Schedule, 2008 Total = 444.13
Therefore, per km cost of plain rigid pavement (in million Tk.) = 444.13/13 = 34.16
300 mm
80 mm
300 mm
66
As per Road note-29, the minimum reinforcement requirement is 5.55 kg/m2
Sl No.
. Cost of per
kg steel is 64/- (PWD Rate of schedule, 2008).
Therefore, per km cost of reinforcement = 5.55*1000*14.6*64/=
= 5.20 million Tk.
Per km cost of reinforcement rigid pavement = (34.16+5.20) = 39.36 million Tk.
Now, per km cost of this pavement section for 30 years design period considering routine
and periodical maintenance cost is calculated in the following Table. As there is no
periodic maintenance requirement in case of concrete pavement, only routine
maintenance cost is included here.
Table 4.10: Unit Cost of Rigid Pavement for 30 years Design Period (Case Study-1)
Item of cost Amount (in million taka)
1. Investment cost for 10 years design period 39.36
2. Routine maintenance cost @ 0.5 lac per year 1.50
Total Cost = 40.86
Therefore, it appears that the per km cost of standard 4-lane width reinforced concrete
pavement for 30 years design period is Tk. 40.86 million which is found to be 48% lower
than that of the cost of flexible pavement (Tk. 78.01 million) for Debogram-Progoti
Sharani Link Road project.
4.12.2 Case Study-2: Cost Estimation for Dhaka-Sylhet Highway Project
The Roughton International Ltd. (U.K.) has designed the Dhaka-Sylhet Highway project
as flexible pavement. For cost comparative analysis, the thickness of rigid pavement is
determined on the basis of Road Note-29, TRRL, UK that was used in the design of
flexible pavement of the highway project. The same traffic data is used for the
comparative study. The sub-grade design CBR has been taken from the study of the same
project. This analysis part will follow the procedure as followed by Roughton
International Ltd. The data for this road section are given below:
67
Given data:
Functional Classification = National Highway
Highway Type = 2-lane Single Carriageway
Lane Width = 3.65 m
Traffic = Cumulative ESAL for 30 years= 113*10
Pavement layer
6
Designed pavement layer thicknesses (along with the corresponding CBR values)
are shown in figure:
CBR Thickness (mm)
Asphalt concrete (Base and wearing course) - 150
Aggregate Base, Type 1 • 80% 240
Sub-base • 30% 400
Sub-grade • 3% 300
Figure 12(a): Case 2- Layer thickness of flexible pavement
Cost of Flexible Pavement for 30 years Design Period
The per km unit cost of flexible pavement of this 2-lane width national highway
considering 10 years of design life is given in the following Table 4.11.
150 mm
240 mm
400 mm
300 mm
68
Table 4.11: Unit Cost of Flexible Pavement for 10 yrs Design Period (Case Study-2)
Pavement Layer Unit Quantity Rate*
(Tk.)
Amount
(in million Tk)
Sub-grade (300 mm) cu.m 2,190 550.00 1.20
Sub-base (400 mm) cu.m 2,920 2,111.00 6.16
Aggregate base type-I (240 mm) cu.m 1,752 2,500.00 4.38
Bituminous carpeting (150 mm) cu.m 1,095 13,100.00 14.34
*Values taken from PWD Rate of Schedule, 2008 Total Cost = 26.08
Now, the unit cost of this pavement (per km) considering 30 years design period is
calculated, based on the above unit cost for 10 years design period and considering the
routine & periodical maintenance costs that would be required as per Article 4.5. The
calculated cost is presented in the following Table 4.12.
Table 4.12: Unit Cost of Flexible Pavement for 30 yrs Design Period (Case Study-2)
Sl.
No. Item of cost
Amount (in
million taka)
1. Investment cost for 10 years Design period 26.08
2. Routine maintenance cost @ Tk. 0.5 lac per year * 1.50
3. After 10 yrs. resealing / overlay cost @ Tk. 8000 per m3 5.80 **
4. After 20 yrs. resealing / overlay cost @ Tk. 8000 per m3 5.80 **
5. Engineering overhead cost, 10% of overlay/ resealing etc. ** 1.16
6. Miscellaneous costs, 5% of overlay / resealing etc. ** 1.20
7. Economic loss for traffic delay & road user discomfort, 2% of
overlay/resealing etc. ** 0.25
*From Table 4.3 & ** From Table .4.4 Total Cost = 41.79
Cost of Rigid Pavement for 30 years Design Period
The unit cost of the Dhaka-Sylhet Highway is also calculated considering rigid pavement
and initially for 10 years design life and based on the PWD rate of Schedule is presented
as follows. The thicknesses of pavement layer system are determined based on Road Note
29.
69
Designed pavement layer thick nesses (along with the corresponding CBR values) are
shown in figure:
Pavement layer CBR Thickness (mm)
Pavement concrete - 300
Sub-base • 30% 150
Sub-grade • 3% 300
Figure 12 (b): Case 2- Layer thickness of rigid pavement
Table 4.13: Unit Cost of Rigid Pavement for 10 years Design Period (Case Study-2)
Item Unit Quantity
(m³)
Rate *
(Tk.)
Amount
(in million Tk.)
Sub grade (300 mm);
CBR>=3% cu.m 2,190 550.00 1.20
Sub-base (150 mm thick);
CBR>=30%
[According to Road Note-29]
cu.m 1,095 2111.00 2.31
Pavement Concrete (300 mm thick) cu.m 2,190 6687.00 14.64
*Values taken from PWD Rate of Schedule, 2008 Total Cost = 18.15
Per km cost of pavement is 18.15 million Tk. From Road Note-29, the minimum
reinforcement requirement for the given traffic load is 5.55 kg/m2.
300 mm
150 mm
300 mm
70
Per km cost of reinforcement = 5.55*1000*7.3*64 = 2.60 million Tk.
Per km cost of reinforced pavement = (18.15+2.60) = 20.75 million Tk.
Now, per km cost of this pavement section for 30 years design period considering routine
and periodical maintenance cost is calculated in the following Table. As there is no
periodic maintenance requirement in case of concrete pavement, only routine
maintenance cost is included here.
Table 4.14: Unit Cost of Rigid Pavement for 30 years Design Period (Case Study-2)
Sl
No. Item of cost Amount (in million taka)
1. Investment cost for 10 years design period 20.75
2. Routine maintenance cost @ 0.5 lac per year 1.50
Total Cost = 22.25
Therefore, the cost per km for concrete pavement of standard 2-lane width for 30 years
design period is found to be 22.25 million Tk, which is 47% lower than that of the unit
cost of flexible pavement for Dhaka-Sylhet Highway project.
4.13 Economic Analysis
In order to make a true cost comparison between flexible and rigid pavements, in this
section an economic analysis is made by using price escalation of two types pavements’
costs i.e. change of unit costs of bituminous and rigid pavements and materials-bitumen
and cement for couple of consecutive years.
4.13.1 Price Escalation of Binders and Mixes
In order to see the price escalation of bitumen and cement as well as bituminous and
concrete pavements, unit costs of these items were collected from the PWD rate of
Schedule for the years 2004, 2006 and 2008. The unit costs and price escalations of
binder and mixes over the span of four-year periods are presented in the Table 4.15 and
graphically shown in the Figures 4.13 and 4.14.
71
Table 4.15 Unit Cost (in Tk.) of Bitumen, Cement, Flexible and Rigid Pavements
Source : PWD Rate of Schedule
Figure 4.13: Price Escalation of Bitumen and Cement
Year Bitumen (Ton)
% Increase
Cement (Ton)
% Increase
Flexible Pavt. (cu.m)
% Increase
Rigid Pavt.(1:2:4)
(cu.m) %
Increase
2004 16,000 - 5,000 - 4,567 - 5,212 - 2006 28,000 43 6,500 23 5,876 22 5,500 5 2008 40,000 30 7,200 10 8,637 32 5,620 2
72
Figure 4.14: Price Escalation of Bituminous and Cement Concrete Mixes
From the Table 4.15 it can be seen that over a period of four years the unit cost of
bitumen has increased by two and half times as compared to the unit cost of cement,
which has increased by nearly one and, half times during the same period of time. From
the Figure 4.13 it is clearly evident that the rate of change of bitumen price is very high as
compared to the cement. Inferring the present trend it can be reasonably conclude that in
the coming year this asphaltic binder would be more expansive and scares commodity.
Most importantly close observation of the Figure 4.14 it was found that in 2004 the unit
cost of flexible paving mix was lower than that of the cost of cement concrete paving mix
and after that its price is increasing very rapidly and crossed the price of concrete
pavement by 2006. Now, the unit cost of bituminous pavement is more than one and half
times as compared to the unit cost of concrete mix. Though in the PWD rate of Schedule
2008, the unit cost of bituminous premix for wearing course is shown as Tk. 8637/= per
cu.m, but in reality currently the cost is more than that of the Schedule rate.
Review of Bill of Quality of the 4-laning Dhaka-Chittagong highway, which has recently
been tendered, shows that the estimated unit cost of bituminous concrete is Tk. 12,436/=.
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This essentially suggests that with time the cost of flexible pavement is increasing at
unusually very high rate as compared to the concrete pavement.
4.15 Differentiation between Flexible and Rigid Pavements
Besides above mentioned characterization of the flexible and rigid pavements, here both
the pavement systems are further differentiate from the various point of view and are
summarized as follows:
Flexible Pavements Rigid Pavements
Courses
Multilayered system consisting of
1. Surface Course
2. Base course
3. Sub base (optional)
4. Sub grade (existing soil)
Single Layered system consisting of
1. Surface course
2. Base course (optional)
3. Subgrade (existing soil)
Load Distribution
1. In comparison with rigid pavements the
load is distributed over a smaller area.
2. Each layer receives the loads from the
above layer, spreads them out, then
passes on these loads to the next layer
below.
3. The load distribution is wedge shaped.
1. Due to the relative rigidity, the pavement
structure distributes loads over a wide area
with only one, or at most two structural
layers.
Structural Capacity
74
1. Load is carried by aggregate
intergranular friction
2. The structure begins with a coarse
aggregate skeleton that supports the
load through stone-on-stone contact.
1. Load is carried by slab action
Aggregate Type
1. Aggregates with high angularity are
required to ensure good interlocking
1. Rounded aggregates may be used as they
only fill the voids
Thickness of Layers
The combined thickness of the sub base, base,
surface course must be great enough to reduce
the stress occurring in the subgrade to values
that do not exceed the bearing capacity of the
subgrade or cause excessive displacement of
the soil layer.
If the bearing capacity is exceeded then either
the number of layers is increased or the
thickness of each of the layers is increased.
The thickness of the slab must be sufficient to
withstand:
1. The wheel loads and
2. The effects due to impact, fatigue and
erosion.
Stress and deformations
1. Permanent deformation under wheel
paths
2. Compressive and tensile stress occur
3. Transient deflection takes place
1. No surface deformation
2. Tensile stress underneath slab
3. No transient deflection
Design Criteria
75
According to the AASHTO design method a
structural number is determined based on the
following :
1. traffic
2. reliability
3. subgrade soil property
4. environmental effects
5. loss of serviceability
AASHTO design method considers the following
factors :
1. effective modulus of subgrade reaction
2. concrete elastic modulus
3. concrete modulus of rupture
4. load-transfer coefficient
5. drainage coefficient
6. reliability and standard deviation
7. traffic load applications
8. serviceability loss
Preparation of subgrade soil
The surface course, base and sub base all lie
directly on the subgrade and any irregularities
will be reflected in the surface. Thus the
subgrade must be adequately compacted for
flexible pavements.
Rigid pavements possess a degree of beam
strength that allows them to span over minor
irregularities in the subgrade.
The subgrade must be stabilized but minor
irregularities may be overlooked.
Modulus of elasticity
The modulus of elasticity of materials is less
and therefore the pavement structure deflects
as wheel load passes over it.
Modulus of elasticity is high
Joints
No special joints are required The most common types of pavement joints are :
1. Contraction,
2. Expansion,
3. Construction.
Load transfer across transverse joints/cracks is
generally accomplished using one of three basic
methods: aggregate interlock, dowel bars, and
reinforcing steel.
Mode of failure
1. Failure is by fatigue 1. Cracking (due to temperature)
76
2. Rutting
3. Shear
2. Fatigue
3. Joint failure due improper construction or
inadequate reinforcement or aggregate
interlock
Maintenance
1. Maintenance cost is large
2. Sealing cracks, potholes, resurfacing
and resealing are done frequently.
3. Major maintenance / rehabilitation
required after few years of service
4. Traffic adversely affected due to
maintenance creating extra difficulties
in urban areas
5. Audit of maintenance is difficult and
gives opportunity for misuse of public
funds
1. Maintenance budget is relatively smaller
2. Requires less maintenance
3. Use of CRCP reduces number of joints and
hence their maintenance
Cost
1. Initial cost is low
2. Maintenance cost is quite high
1. Initial cost is relatively high
2. Maintenance cost is lower
3. Life cycle cost is low
Advantage
1. Initial cost very low
2. Stage construction possible (no
investment in advance of demand)
3. Skid resistant property can be restored
easily by rough seal coat and brushing of
aggregates
4. Does not glare under sunlight
5. Cutting can easily place utility lines and
digging and surface can be easily
repaired.
6. No reinforcement is required
1. Lifecycle cost is relatively lower
2. Surface is smooth, free from rutting,
potholes and corrugations
3. Permanent non-skid surface
4. Requires less street lighting
5. Concrete slab is practically impervious
except at joints
6. Uniform support condition is not a
prerequisite
7. Can deal with very heavy traffic
8. Require little maintenance
77
9. Provide pleasing appearance
10. They perform quite satisfactory even when
constructed on poor sub-grade
11. Less susceptible to weather - specially at
submerged condition
12. Heating of aggregates and cement is not
required
Disadvantage
1. Construction method is very strict and
quality control must be very high
2. Maintenance cost is high
3. Lifecycle cost is high thereby
uneconomic.
4. Bituminous surface is not impervious
5. Requires more street lighting
6. Process of heating bituminous materials
and aggregate are more hazardous to
the environment.
7. Susceptible to weather - bleeding at
high temperature, cracking at low
temperature and stripping under
submerged condition
8. Short life span
9. Required uniform support
10. Reflect the deformation of lower layers
11. Performance is very sensitive to surface
as well as sub-surface drainage
condition
12. Produce high ambient temperature in
built up area
1. Very difficult to restore skid resistance
2. Stage construction is not possible
3. Digging is not difficult to locate and repair
utility lines.
4. Ducts have to be provided beneath concrete
slab to place utilities. Usually top portion
of storm sewers are used and sufficient
manholes have to be provided to allow
access for repair and new connections.
5. May cause glaring under bright sunlight
6. Reinforcement is required to reduce
number of joints
7. Produce high noise due to wear and tear of
vehicles
78
4.16 Plausible Causes of Premature Failure of Pavement
(a) Adopting unscientific method of road construction:
Poor compaction and quality control in the construction of subgrade and sub-
surface layers
Carpeting is constructing without proper
Correction of underlying weakness (which reflects later on)
Cleaning and drying of existing road surface (resulting weak bond between
old and new layers)
Application of tack coat (causes no effective bonding between layers)
Improper/uncontrolled heating of pavement materials
Overheating/long time heating of bitumen reduces the binding property of
binder. Moreover, in mixing burning volatile substance of binder further
reduces binding quality of bitumen (resulting weak bonding between
aggregate and binder and accelerates binder aging/hardening)
Inconsistent heating of aggregate and binder (resulting non-uniform mix of
aggregates and binder)
Manual method of laying and spreading of paving mixes causes
Maximum loss of heat before starting compaction (resulting poor compaction)
Aggregate and temperature segregations (resulting non-uniform density of
pavement)
Uneven surface
(b) Poor drainage condition and lack of controlling traffic movements during
submerged conditions:
Poor, inadequate and ill maintained drainage facilities
Local ponding caused by inconsistent road surface level
Movements of heavy/overloaded vehicles while pavement in submerged condition
(c) Plying of heavily overloaded traffic during summer period
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4.17 Overview
In this chapter a comprehensive comparative analysis of flexible and rigid pavements is
made considering mainly material & equipment requirements, availability of binder
material, pavement design, method of construction, maintenance, pavement performance
under hot climate and submerged conditions, life cycle cost, long time serviceability,
safety aspects of pavement etc. with particular emphasis given in the context of
Bangladesh. Moreover, in this comparative analysis the possibility of using rigid concrete
pavement was explored in the roadway construction of Bangladesh.
From the comparative analysis it was found that flexible pavement requires significantly
more construction time, more number of heavy equipment, consumes more fuel and
lubricant. Also flexible pavement requires one third more aggregate materials than that of
the concrete pavement with the same design parameters. In contrast, the cement concrete
pavement enhances protection of ecology and conserves nature.
It was also observed that in the case of flexible pavement construction the key ingredient
bitumen is an imported material for which government is spending a lot of foreign
currency every year. In contrast cement, the binding material of rigid pavement
construction is abundantly produced in Bangladesh and it is now a home grown product.
Analyzing the complete method of construction it was observed that the construction of
heat based flexible pavement involves a series of operations, which need very careful
planning and coordination so that the construction proceeds with a minimum loss of time.
Each of the separate steps must be done carefully and preciously so that the completed
pavement meets the stringent standard specifications.
In consideration of the fact that preparation of flexible mixture requires proper heating of
ingredients and most importantly binder’s properties are very sensitive to improper way
of heating, virtually without plant facility it is not possible to prepare paving mix
properly. Moreover, the construction of flexible pavements is sensitive to the quality
control to ensure proper qualities, central mixing plants for the preparation of bituminous
paving mixture are used in the developed countries, which may be of continuous or batch
type. Due to lack of this equipment, conventional practices of heating and drying of
aggregates and mixing of aggregates and bitumen in open places are very common in
80
Bangladesh. As such, the proper way of constructing flexible pavement would not be
possible for local narrow roads or for small amount of works particularly where batch
plant cannot be justified. Even if plant mix is available, without the availability of mixture
transporting truck, paver and a set of rollers it would not be possible to ensure properly
compacted pavement. Unlike flexible pavement cement concrete pavement does not
require heating the ingredients, involvement of roller to compact mix and most
importantly does not involve so many stages for quality control.
Comparative analysis revealed that one of the common causes of flexible pavement
failure in Bangladesh is due to weather conditions mainly hot climatic condition and
excessive moisture coupled with poor drainage condition and most importantly
unrestricted movements of over loaded vehicles during the periods when the pavement
goes under submerge condition. In contrast simultaneous effects of high temperature and
rainfall/flood do not deteriorate the cement concrete pavement much.
It is found that as concrete pavement provides better visibility, skid resistance, enhances
cross drainage over pavement, better road environment and surface condition etc. it
significantly improves the roadway safety and thereby reduces road accidents risks. Due
to its better light reflectance, it has the potential to improve road safety at night time,
particularly for the roads and highways in rural/open areas with no proper road marking
and street light which is very common in Bangladesh.
From the comparative analysis, regarding the life cycle cost of pavements it was found
that though the initial cost of concrete pavement is slightly higher than the flexible
pavement, but with longer design period the cost of concrete pavement becomes cheaper.
The overall maintenance cost for cement concrete pavements is also small as compared to
flexible pavements. In consideration of these, it is high time to construct cement concrete
pavement for major roads and highway of Bangladesh.
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CHAPTER 5
FIELD INVESTIGATION ON THE CONSTRUCTION OF
FLEXIBLE PAVEMENT
5.1 Introduction
In the true sense, the procedures of flexible pavement construction are very elaborate and
sensitive. Quality control is badly needed at every stage of construction of this type of
pavement. The main purpose of the quality control (QC) in road construction is to ensure
that all materials are selected, mixed and compacted are in conformity with the specified
requirements and are in line with the construction guidelines set out in the standard
manuals. As such, none but qualified; sincere and honest field staffs as well as contractors
are required to construct long lasting flexible pavements.
From the literature review it is understood that the construction of flexible pavements
requires strict procedure in heating binder and aggregates at appropriate temperatures and
mixing, laying, compacting operations are also need to be performed at specified
temperatures. In general there is a notion in Bangladesh that the Contractors are hardly
follow these stringent construction requirements and thereby flexible pavements do not
last up to the period that it should have been. Although, now-a-days modern mixing plant
and paver based mix laying equipment are available in Bangladesh, even then proper
specifications, guidelines and quality control in construction works are hardy ensured. In
order to assess the level of slackness in the construction of flexible pavements, field
investigations were undertaken in the form of critically observing the construction
procedures and measuring associated deviations from the specified standards, comparing
strength parameters between samples prepared in the field using job mix and samples
prepared in the laboratory with the materials collected from the construction sites.
82
Moreover, in order to assess the level of understanding regarding the standard method of
flexible pavement construction a questionnaire survey and personal interview are
undertaken among the concerned engineers. Present status of rigid pavement construction
by different governmental organizations is also assessed by interview survey as well as by
field observation. The performance evaluation of few completed flexible road
construction projects is made and problem associates with the construction of flexible
pavement were also highlighted. This chapter presented the results of these field
investigations.
5.2 Method of Assessment
The contractors and persons related to the construction works shall be responsible for the
quality control of the work during the entire construction period particularly for a large
project. For this purpose, there shall be a site laboratory to carry out all the tests necessary
under the supervision of engineer and consultant. But these arrangements are not
generally seen in the construction sites. Also during the execution of pavement works, it
is essential that material qualities and completed works should be properly controlled by
careful and diligent inspections with tests and measurement performed whenever
required. But unfortunately this is often avoided in bituminous pavement construction
works. In this section emphasis has been given on some items of field construction such
as aggregate-bitumen properties before and after execution of works, comparison of
Marshall design criteria of field specimen with the standard specimen prepared in the
laboratory, temperatures measured at different stages of construction and comparing with
the standard specified values etc. by field and laboratory experiments undertaken for two
construction sites. Here it will also be tried to identify to what extent the quality of works
are sacrificed during the construction of bituminous pavement jobs.
5.3 Field Data Collection
In order to carryout field investigations regarding various aspects of flexible pavement
construction, data was collected in the form of critical observation of construction
practice, paving mix ingredients and specimens are also collected from two construction
sites of Dhaka city.
83
5.3.1 Site Selection
In order to observe whether proper method is followed in the construction of flexible
pavement, data is collected from two resurfacing construction sites in Dhaka city. These
two construction works were undertaking by Dhaka City Corporation (DCC) engaging
local contractors. These two road sections had different geometric features and traffic
loading patterns.
Description of the Selected Sites
Site-1: It is a lightly traveled local road segment situated in Khilgaon area near Khilgaon
flyover. Actually it is a link road between two main roads. As such, there was no
disruption of vehicular movements during the time of construction. The
construction work was mainly of resurfacing the deteriorated pavement and was
implemented by using on-site prepared paving mix and laying it manually.
Relevant data were collected in day time.
Site-2: A road section situated in Shahbagh near PG hospital which is mainly used by
medium to heavy traffic. This is a very busy arterial road of Dhaka City. Hence,
resurfacing maintenance work was not possible during day time due to vehicular
movements. At this site, construction work was done at night time and thereby
experimental data had to collect at late night. The construction work was also
mainly of resurfacing the deteriorated pavement and was implemented by using
plant mix and paver.
5.3.2 Equipment
In order to prepare the Marshall specimens at the study sites, the following equipments
were used. A digital camera was also taken to document every step of the construction
method that was followed in the field.
List of equipments:
(a) 4 no. molds, 2 no. base plates and 1 no. collar
(b) 2 no. knives, 1 no. kunni and 1 no. tang
(c) 4 no. bowls and 1 no. balance
(d) 1 no. hammer (for preparation of Marshall specimen)
84
5.3.3 Field Study
After getting necessary permission from the City Corporation and considering the time of
construction works, the field visit to the Site-1 was made on 20th April 2007 in the early
morning and to the Site-2 was made on 16th May 2007 at midnight. The field visits to the
sites were made along with the laboratory technicians, helpers as well as with the
necessary equipments.
(a) Preparing Marshal Specimens in the field
After reaching the sites, hot mix paving mixtures were collected from the job site for
preparing Marshall specimens. In order to ensure that the specimens are compacted at
the mix laying temperature, the paving mixes of necessary amount was collected from
tray (in case of Site-1) and paver (in case of Site-2) just before its laying. Three
numbers of Marshall specimens were prepared for each job site on the spot using
necessary equipment. The following photographs were taken to show the preparation
of Marshall samples at the spot.
Photo 5.2: Preparation of Marshall
Specimen at Site-2
Photo 5.1: Preparation of Marshall Specimen at Site-1
85
(b) Collection of Ingredients
In order to prepare Marshall specimens in the laboratory, for Site-1 mix ingredients
viz. coarse and fine aggregates were collected from the site stacks and for Site-2 from
the plant mix yard and unheated semisolid raw bitumen was collected from the intact
drums. The collection of mix ingredients is shown in the following photographs.
(c) Collection of Hot Paving Mixture
Hot bituminous paving mixtures were
also collected from the both
construction sites for determining
bitumen content in the mixture as well
as for determining gradation of
aggregates. The mixtures were also used
to observe the effect of improper way of
heating the binder material.
(d) Measurement of Temperature at
different Stages of Constructions
One of the main objectives of the study
was to assess the level of quality control that are practiced in the construction of
flexible pavements. In view of this, the whole construction process was observed
Photo 5.5: Collection of Paving Mixes
Photo 5.3: Collection of Aggregates Photo 5.4: Collection of Bitumen
86
critically and most importantly the temperature measurements were taken at every
step i.e. from heating ingredients up to compacting asphalt mixes. The measurements
of temperature at various stages of construction are demonstrated by the following
photographs.
Photo 5.6: Temperature Measurement of Aggregates just before Mixing Operation
Photo 5.7: Temperature Measurement of Bitumen just before Mixing Operation
Photo 5.8: Measurement of Mixture Temperature at the time of Mixing
Photo 5.9: Temperature Measurement of Paving Mixture just before Compaction
87
5.3.4 Laboratory Testing
Samples collected from field such as aggregates, bitumen, loose paving mixtures,
Marshall specimens (those are prepared in the field) etc. were brought to the BUET
laboratory and subsequently the following tests were performed.
(a) Bitumen Extraction Test
In the laboratory, bitumen was extracted from the paving mixtures that were
collected from the field by using tri-chloroethylene. Later on, different tests were
conducted on the extracted aggregates and bitumen to study on their physical
properties. The process of bitumen extraction is shown in the following
photograph.
Photo 5.10: Bitumen Extraction Test
88
(b) Test on Extracted Aggregates and Bitumen
Sieve analysis and gradation
tests were conducted on the
aggregates; those were
obtained from the bitumen
extraction test, to compare
the observed gradation with
that of standard gradation
specified by AASHTO. The
gradation test setup is shown
in the adjacent photograph.
Bitumen was collected both
from drum (original
bitumen) and paving
mixture (extracted bitumen).
With the original and
extracted bitumen, different
tests are performed in the laboratory such as specific gravity, loss on heating,
penetration test, softening point
test, ductility test, flash & fire
point test, solubility test etc.
The aim of these tests was to
find out the properties of
original bitumen and then to
compare these properties with
the properties of extracted
bitumen from paving mixtures
that were used in the field
construction.
Photo 5.12: Penetration Test
Photo 5.11: Test of Aggregate Gradation
89
(c) Marshall Tests
Marshall test was performed to compare the stability and flow values between
Marshal specimens that were prepared on the spots by using the field mix and
Marshall specimens prepared in the laboratory using the same ingredients and mix
proportions. In the absence of any specification in the preparation of paving mixes
for both construction sites, mix proportions were set by knowing the ingredient
proportions in mixes collected from the field. The Marshall test setup is shown in
the following Photograph.
Besides laboratory investigation, the method of construction followed by the field crew
was also observed critically to find out the deviations from the standard method. During
this study work, other than these two sites, observations on the construction of flexible
pavement were also made on a few other projects that were being implemented in and
around Dhaka city. It is to be mentioned here that in order to get the durable pavement,
stringent specifications needed to be followed particularly in case of the construction of
Photo 5.13: Marshall Test on Specimens Collected from Field
90
flexible pavement. The important observations that were documented during the field
investigation are listed below:
• Long duration heating of bitumen without any stirring action; it was observed that
the bitumen was heated in the same drum till the construction work has
completed; ideally bitumen should not be heated continuously for more than one
and half hours
• Burning of bitumen during mixing
• Though cleaning of aggregates in a way dust free aggregates are a prerequisite to
reduce stripping potential of the paving mix, it was observed that before use the
aggregates were not cleaned up though there were lots of mud and dust
particularly with the coarse aggregates
• Aggregates contained moisture
• To maintain mix proportion, no weighing device or volume measuring unit was
found
• Aggregates and asphalt were poured in the tray by using head basket and
container
• No use of thermometer and timer to control temperature and time of mixing
• In case of plant mix, the mixture was transported to the construction site without
any protection against heat loss; moreover often it was observed that tip truck was
waiting too long before mix was poured into the paver
• Tack coat was sprayed long before paving mix is laid
• Tack coat was sprayed on old surface without proper cleaning of the surface
• Distresses in the form of potholes, undulation, alligator cracks etc. that were
present on the existing pavement were not repaired properly before placing the
new surface course
• Mix spreaded by using rack shows successive ridges & valleys and uneven spread
of mixture
• Long waiting before start of the compaction work; even at one site (Kafrul, Dhaka
Cantonment) the compaction started after 5 hr. of laying the paving mix
The following snapshots are presented to demonstrate the method of flexible pavement
works that is generally practiced in the field:
91
92
93
94
From the above observations of the method of construction, it can be reasonably
concluded that quality control is hardly followed either in heating & mixing of
ingredients, transporting, laying and compacting paving mix, particularly in the case of
manual method of construction. Most importantly, due to total ignorance regarding
heating of the binder, in the manual method of construction the properties of bitumen
changed significantly. Due to long overheating without stirring and burning during
mixing, in the end instead of binder the bitumen become merely a black substance which
seriously lacks softening and binding properties due to excessive age hardening. As such,
the present practice of flexible pavement construction particularly the manual method was
found to be totally an unscientific method of construction.
5.4 Analysis of Test Results
In the previous articles, site descriptions, sample collections and relevant laboratory tests
are described. The test results are discussed in the following sections.
5.4.1 Asphalt Content
With the bituminous paving mixture collected from the field, extraction test of bitumen
from the aggregates was carried out with the help of tri-chloroethylene and measurement
of the percentage of bitumen in the paving mixture was made in the laboratory. It is to be
mentioned here that from each site paving mix sample was collected from three separate
batches. From the calculations it was found that the range of bitumen content for Site-1
and Site-2 were 5.1 – 5.6% and 5.4 – 5.5% respectively, which implies that variation of
bitumen content is relatively higher for Site-1 than that of Site-2. This may be due to the
fact that at Site-1 paving mix was prepared in the field manually without much control on
adding exact amount of ingredients in the mix where as at Site-2, mix was prepare by
using batch plant built-in facility.
It is to be worth mentioning here that the average bitumen content obtained from the
extraction tests were used in preparing Marshall specimens in the laboratory.
95
5.4.2 Moisture Content
The coarse and fine aggregates that were collected from Site-1 were tested in the
laboratory for the determination of moisture content. It was obtained based on measuring
initial weight of the aggregates collected from fields and comparing it with the oven dried
weight. From the calculation it was found that the coarse and fine aggregates contained
0.7% and 4% moisture content respectively.
5.4.3 Properties of Bitumen
Raw bitumen was collected from both the study sites and tested in the laboratory to find
out the properties of virgin bitumen. Later on the paving mixtures from both the spots
were also collected and bitumen was separated from aggregates in the laboratory for
testing the properties of bitumen that was used in the pavement resurfacing works. The
properties of raw or virgin bitumen and extracted bitumen are presented in Table 5.1 and
5.2.
Table 5.1: Properties of Virgin and Extracted Bitumen for Site - 1
Properties Test Method Virgin
Bitumen
Extracted
Bitumen Comments
Specific Gravity AASHTO T228-93/
ASTM D 70-76 1.0168 1.048
Value increased
significantly
Loss on Heating
(%)
AASHTO T51-93/
ASTM D113-79 0.02% 0.07% --
Penetration
(1/10th mm, 250
AASHTO T49-93 /
ASTM D5-86 C 91 77
Value decreased
significantly
Softening Point
(0
AASHTO T47-8/
ASTM D6-80 C) 55 48
Value decreased
significantly
Ductility (cm) AASHTO T53-92/
ASTM D36-89 100+ 95
Value decreased
significantly
Flash & Fire
Point (0ASTM D 92/ T-48
C) 250 & 280 285 & 330
Both values increased
significantly
Solubility (% of
insoluble) AASHTO T-44 0.20% 0.212% ---
96
From the above Table 5.1 it can be seen that in general all the properties describing the
quality of binder have deteriorated significantly with the extracted bitumen. For instance,
penetration and ductility values which indicate consistency of the binder shown that these
two properties of extracted bitumen have decreased significantly, from 91 to 77 and from
100+ to 95 respectively, as compared to that of virgin bitumen. These changes essentially
suggest that the consistency of the binder has decreased due to improper way of heating
the bitumen in the field. Besides, close observation of the Table 5.1 shows that Sp. Gr. as
well as Flash & Fire points of extracted bitumen have increased significantly, which
implies that the density of bitumen has increased due to the excessive loss of volatile
substances. Obtaining decreased softening value (480C) for extracted bitumen as
compared to that of original bitumen (550
Properties
C) also suggests that binder’s susceptible to
temperature in a way its softness has deteriorated may be due to long time heating as well
as overheating of the bitumen without any stirring and most importantly burning volatile
compound of binder during the mix preparation operation. In summary, it can be
concluded that due to uncontrolled method of heating as well as burning of bitumen
during mixing operation in the tray have caused age hardening of the binder.
Table 5.2: Properties of Virgin and Extracted Bitumen for Site - 2
Test Method Virgin
Bitumen
Extracted
Bitumen Comments
Specific Gravity AASHTO T228-93/
ASTM D 70-76 1.0165 1.035 Value increased
Loss on Heating
(%)
AASHTO T51-93/
ASTM D113-79 0.022% 0.02%
Penetration (1/10th
mm, 250
AASHTO T49-93 /
ASTM D5-86 C 89 83 Value decreased
Softening Pt
(0
AASHTO T47-8/
ASTM D6-80 C) 54 51
Ductility (cm) AASHTO T53-92/
ASTM D36-89 100+ 98 Value decreased
Flash & Fire Pt, 0 ASTM D 92/ T-48 C 250 & 280 265 & 300 Both values increased
Solubility (% of
insoluble) AASHTO T-44 0.20% 0.22%
97
It appears from the Table 2 that bitumen properties of Site-2 where plant mix is used also
have changed as compared to the virgin material. Test results for both Sp. Gr. and Flash
& Fire point show that values for extracted bitumen have increased though not as such as
that of Site-1. Similarly, Penetration and Ductility values have decreased for extracted
bitumen. These experimental results revealed that for Site-2 even if paving mix is
produced by using batch plant, the properties of binder material have changed though not
so significantly as compared to the amount of changes occurred for Site-1. This definitely
suggests that manual method of pavement construction causes more age hardening of
binder than that of machine made paving mix.
5.4.3 Gradation of Aggregates
Pavement mixture collected from the field was separated into bitumen and aggregate and
determination of percentage of bitumen and gradation of aggregate was done in the
laboratory. In the absence of specified aggregate gradation for the construction works, the
results of the gradation of aggregates found in the laboratory are compared with the
AASHTO standard gradation specified for wearing course. The results of the gradation of
combined aggregates found in the laboratory are compared with the AASHTO standard
designation for the Study Sites 1 and 2 are tabulated below. The corresponding aggregate
gradation charts along with the specified gradation envelope are graphically depicted in
Figure 1.
Table 5.3: Aggregate Gradation of Site-1
Sieve Size Wt. of material retained
(gms)
Percentage of material
retained
Standard range
(% by weight)
Comment
1/2• 5.68 1 0-6
3/8• 57.64 6 9-40 Not in specified range
No. 4 578.87 61 9-45 Not in specified range
No.10 198.95 21 8-27 ---
No.40 73.23 8 6-22 ---
No.80 8.44 1 8-27 Not in specified range
No.200 14.91 2 5-17 Not in specified range
Total 946 100 ---
98
Table 5.4: Aggregate Gradation of Site-2
Sieve Size Wt. of material
retained
(gms)
Percentage
of material
retained
Standard range
(% by weight)
Comment
1/2• 149.68 16 0-6 Not in specified range
3/8• 57.72 6 9-40 Not in specified range
No. 4 107.17 11 9-45 ---
No.10 63.17 8 8-27 ---
No.40 266.12 27 6-22 Not in specified range
No.80 175.66 19 8-27 ---
No.200 113.37 13 5-17 ---
Total 944 100 ---
Figure 5.1: Aggregates Gradation Charts for Site 1 & 2 with Specified Envelope
It is found from the Tables 1 & 2 and Figure 1 that the aggregate gradations, which were
used in the resurfacing works, did not comply with the standard range specified by the
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AASHTO. For the Site-1, aggregate gradation is found to be deficient at 4 sieves and for
the Site-2 gradation of aggregates went beyond the specified limit at three occasions.
Moreover, from the gradation results it is found that both the field gradations that were
used in the preparation of paving mixtures were gap-graded instead of well-graded.
Which implies that at both the Sites no quality control was followed in achieving a good
graded mixture, that has the potential to produce durable surface course with minimum
porosity or voids.
5.4.4 Strength Properties of Mixes
Three Marshall test specimens were prepared in the field using paving mix collected from
both the study sites and experiments were made in the laboratory for determining the
Marshal stability and flow value and also to measure bulk volume, specific gravity, and
unit weight etc. Again, aggregates and bitumen were collected separately from the field to
prepare Marshall specimen in the laboratory with the same aggregates and bitumen
content that were used in the construction Site 1 and 2. For each study site, three Marshall
specimens were prepared in the laboratory following the standard method and same
experiments as stated above were carried out in the laboratory. Data sheets for Marshall
Stability and flow value were prepared for these purposes are tabulated in the Appendix
C1 & C2 and results for both sites are shown in Table 5.5 and 5.6.
Table 5.5: Marshall Test Results of Specimens Collected from Site-1
Marshall method
mix criteria
Design Criteria
for Light Traffic
Marshall values for
Specimens Prepared
in the Laboratory
Marshall values for
Specimens Prepared
in the Field Min Max
No of blows 35 35 35
Stability, N 750 - 2077 1526
Flow, 0.25 mm 8 18 15.9 6.5
Percent air voids (%) 3 5 8.63 10.0
% Voids in mineral
aggregate (VMA) 14.2 - 11.5 10.6%
Percent voids filled
with asphalt (VFA) 70 80 44.73 35.0
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From the Marshall test results presented in Table 5.5 it is found that though the stability
values for both the field and laboratory specimens satisfied with the design criteria but in
all other respects i.e. flow, % air void, % voids in VMA and % VFA have failed to meet
the limiting values. Obtaining lower flow value 6.5 for the field specimens as compared
to the flow value for laboratory specimens 15.9 indicates excessive age hardening of the
bitumen in the field. It is to be noted here that at the Site-1, paving mixture was prepared
at road side manually. Higher percent air voids for both the laboratory (8.63%) and field
specimens (10%) as compared to the design criteria (3-5%) essentially imply poor
grading of aggregates. Non-compliance of VMA and VFA results also indicates weakness
in aggregate gradations. Getting relatively higher % air voids (10%) with the field
specimen as compared to the laboratory specimen (8.63) might be due to low compaction
temperature of the mix.
Table 5.6: Marshall Test Results of Specimens Collected from Site-2
Marshall method
mix criteria
Design Criteria
for Heavy Traffic
Marshall values for
Specimens Prepared
in the Laboratory
Marshall values for
Specimens Prepared
in the Field Min Max
Compaction, no of
blows each end of
specimen
75 75 75
Stability, N 1800 - 2205 1869
Flow, 0.25 mm 8 14 13.2 12.8
Percent air voids
(%) 3 5 8.8 8.6
% voids in mineral
aggregate (VMA) 14.2 - 12.6 13.0%
Percent voids filled
with asphalt (VFA) 65 75 54.73 37.0
Marshall results for the Site-2, where plant mix was used in the construction, show that
both stability and flow values for field as well as laboratory specimens satisfied the
Marshall design criteria. Though, like the Site-1, % air voids, %VMA and %VFA did not
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fulfill the design criteria for both the specimens, which also indicates that the problems
lies with the aggregate gradation.
Comparing the results shown in Table 5.5 and 5.6 it can be concluded that besides age
hardening of bitumen associated with the manual method of construction, mainly poor
aggregate gradations, that were used both in manual and plant mix method of
constructions, and resulted non standard mixes.
5.4.5 Temperature Measurement at Different Stages of Construction
The standard requirements of temperature at different stages of construction are presented
in the literature review chapter. In order to verify the field temperatures with the standard
requirements, measurements were taken at different stages of construction at Site-1 and
Site-2 for aggregates, bitumen and for paving mixture by a special thermometer and the
results are given in the Table 5.7 along with the Standard temperatures as specified by the
AASHTO.
Table 5.7: Measured Temperatures at Different Stages of Construction for Site-1 and 2
Sl.
No. Stage of Construction
Standard
values as per
AASHTO
Temperature
(Site-1)
Manual Mix
Temperature
(Site-2)
Plant Mix
01 Dry aggregates (Stone chips)
before mixing with bitumen 163°C 72°C -
02 Heated Bitumen in the drum 163°C > 300°C -
03 Bitumen temperature at the
time of making mixture 135-163°C 199°C -
04 Paving mixture temperature 139-163°C 123°C 121°C
05 Laying temperature of Paving
mixture over pavement 120-150°C 98°C 94°C
06 Compaction of the mixer 100-120°C 50°C 75°C
It is to be noted here that for the Site-2 as the paving mix was prepared by using batch
plant it was not possible to measure the temperatures of dry aggregates as well as
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bitumen. Due to the same reason, the mixing temperature was also could not be measured
for Site-2 though it was learnt from the batch plant operator that the AASHTO specified
temperatures for different stages of mixing process was set initially and maintained
throughout the mix production operation. It was also gathered that after installation of the
batch plant in 2004, no calibration of the machine has been performed.
The Table 5.7 shows that at Site-1, temperature of the aggregates was found to be much
lower (72°C) than that of the temperature specified (163°C) by AASHTO. This may be
due to the fact that unlike bitumen, which was found to be heated continuously in the
drum for a long time, aggregates were heated in the tray batch by batch and not for long
time. It is to be recalled here that from the moisture content test it was observed that both
coarse and fine aggregates contained moisture which implies that there was a need for
drying the aggregates for a long period to make them completely dried and raise the
temperature up to the specified limit. In the field, as no arrangement was made by the
Contractor to check the temperature of the aggregates, it has resulted much lower
temperature of the aggregates.
On the other hand, from the Table 5.7 it appears that in every observation the temperature
of the bitumen in the drum was found to be more than 300°C, which was not suppose to
be more than 163°C. In the field, it was observed that the bitumen was heated
continuously without any stirring action. According to AASHTO, the binder should not
be heated beyond 163°C and should be heated gently with continuous stirring action to
avoid any chance of local overheating of the binder. Moreover, the bitumen should not be
heated for more than 1½ hr.
The temperature of bitumen before pouring into the tray was found to be 199°C which
was much lower than the temperature (300°C) of the bitumen observed in the drum, this
is due to the fact that the bitumen was transferred from the drum to the mixing tray by
using a container which was often found to be kept aside for a long time before pouring it
in the mixing tray.
The significant difference in temperatures between aggregates and bitumen is not good at
all for obtaining homogeneous bituminous mixes. For uniform mixing, it is utmost
important that both ingredients must be heated at the same temperature. Otherwise, if
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aggregates are hotter than bitumen, during mixing operation instead of coating the
aggregates the bitumen will drops downward and will accumulate at the bottom of the
mixture tray vis-à-vis if aggregates are cooler than the bitumen, during mix when bitumen
will come in contact with relatively cooler surface of the aggregates it will be stuck on the
surface and will results non-uniform coating.
From the Table 5.7, it can be seen that for both the Sites paving mixing, laying and
compaction temperatures are much lower than the standard value specified by AASHTO,
which essentially suggests that resulting pavement would not be a good and durable one.
5.6 Field Observations on the Completed Roadway Projects
In this section observations on the performance of a few completed flexible road
construction projects are made based on the investigations conducted by BUET as well as
news report published in the daily news paper.
5.6.1 Project : Nalka-Hatikamrul-Bonpara Road
From the investigation study conducted by a Team of Consultant, Department of Civil
Engineering, BUET, it is found that serious distresses in pavement have occurred at some
portion of the Nalka-Hatikamrul-Bonpara Road within one and half years of its
construction [BUET, 2005]. At present the road is virtually become unusable and
hazardous for the road users. It is not only causing immense suffering to the road users
but also incurring huge economic losses in the form of increased travel time, high
depreciation of vehicles etc. Few snapshots are presented below to demonstrate the
ground conditions of the roadway.
In their investigation, the team concluded that besides overloading and underestimation of
the predicted traffic - the main causes of premature failure of the road were deficiencies
in materials, design and construction. Moreover, it is also pointed out in the report that the
bitumen manufactured by the Eastern Refinery in Bangladesh contained a substantial
proportion of volatiles that might have caused premature failure due to accelerated age
hardening as these volatiles evaporated.
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Test result shows that asphalt concrete in both the wearing and binder courses was
deficient in fine aggregate and the filler content. Besides, the bitumen content in asphalt
concrete was found to be about 1 percent less than the approved design mixes. The
percentage of air void in asphalt concrete was also found to be very high. These might be
the plausible other reasons for distress and premature failure of the road, since such
asphalt concrete is prone to rapid oxidation and has high potential for age hardening.
Inferring findings of the report it can reasonably be concluded that though the pavement
was constructed using modern construction equipment viz. batch plant and paver, the
construction of flexible pavement is very susceptible to the quality of materials, design
and most importantly quality control of the construction process.
5.6.2 Project : Dhaka Bypass Road
Investigation carried out by a group of BUET Consultants on the failure of road
embankment and pavement in the National Highway from Joydebpur to Debogram-
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Bhulta-Nayapur Bazar up to Madanpur of Dhaka-Chittagong Highway (Dhaka Bypass,
N-15) [BUET, 2007]. Construction of this National Highway (N-15) was taken up on an
emergency basis to provide a road bypassing the city of Dhaka and link the Jamuna
Bridge for traffic movements from the east and south-east districts of Sylhet and
Chittagong Divisions to the western parts of Bangladesh and vice versa. The project
commenced in FY 1997-98 and was expected to be completed in FY 2005-06. Investment
cost (revised) of the project was estimated at Tk. 281.6 crore. But concerned for quality of
works was raised even before the formal opening of the road to traffic in 2006.
During the field inspection, the Consultants assessed the condition of the Bypass road and
observed that pavement distress in the form of alligator or fatigue cracks, existence of
frequent pot holes, depression, raveling of pavement surface and areas of disintegration of
the top granular sub-base layer were present at few segments of the 48 km bypass road.
The roadway surface condition can be assessed visually from the following few
photographs.
106
It was gathered that only 15 mm thick pre-mixed bituminous seal coat had been provided
at some portions while pre-mixed bituminous carpeting (Manual) work was done on the
remaining portions of the road.
Though the Dhaka Bypass road is recognized to be an important National Highway
linking the Jamuna Multipurpose Bridge between the eastern and western parts of the
country, but due to formation of frequent pot holes, large depression and areas of
disintegration of the top granular sub-base layer, the vehicles face much difficulty in
travelling along the road and frequently tire burst, broken down of axle rod, overturn type
accident are occurring particularly with the commercial vehicles.
The main findings of the causes of premature failure of the pavement were identified as:
1. Use of poorly graded sub-base materials with high proportion of sand than specified,
on the entire stretch of the Bypass Road, caused the coarse aggregates merely to float
in the fine aggregates and resulting lower stability and load supporting characteristics.
2. Use of poor quality construction materials, particularly sub-base, and lower thickness
of pavement layers than specified.
Therefore, it can be seen that in the construction of flexible pavement, quality control of
subsurface layers is also of vitally important. If the weaknesses exist within the sub-
surface layers of the pavement structure then with time they reflect through the surface
course and eventually it becomes very difficult to rectify the problems often without
reconstruction. It is well recognized that the reconstruction of road is inherently very
expensive and time consuming.
5.6.3 Other Roadway Projects with Premature Failure
(a) Dhaka-Chittagong Highway
It is observed that some portions of the Dhaka-Chittagong Highway become unusable
only within three years of its restrengthening work. It is to be noted here that the
restrengthening work in the form of applying pavement overlay was constructed using
plant mix and paver in 2004-06. But due to poor quality of construction, immediately
107
after the overlay work, heaping, raveling, frequent potholes and surface undulation
have started to occur particularly after Chaddagram up to Chittagong end and made
the highway hazardous. Now, due to bad shape of the road often vehicles, particularly
heavily loaded trucks are getting overturned and creating huge traffic congestion to
this very busy economic corridor. The following snapshots are presented to show the
conditions of the highway as well as to show the level of quality control that was
maintained during the construction works.
Source : The Daily Prothom Alo
From the following snapshots it can be seen that the overlay works were performed by
using plant mix and paver based system. It is also learnt from the concerned RHD
officials that in order to rectify the pavement distresses before laying the overlay, at some
segments of Dhaka-Chittagong Highway the damaged surface was reclaimed and reused
by applying recycling method. This application of recycling method in pavement
rehabilitation work was the first time in Bangladesh. Even after application of this costly
and modern rehabilitation work, the pavement did not render services properly. The
reclamation process of asphalt pavement, from the road segment near Feni area can be
seen from the photograph presented below.
108
109
Reclaiming Asphalt Pavement (RAP) by using Excavator
Pavement Surface after Removal of Wearing Course in Dhaka-Chittagong Road
110
(b) Dhaka-Tangail Road
The Dhaka-Tangail Road was rehabilitated in January 2008 applying Double
Bituminous surface Treatment (DBST). But it is reported that in the following
summer season, the road surface become so sticky due to melting of binder materials
that out of control type accident is occurring frequently. Again, poor quality of
construction is blamed for the cause of this bleeding problem. The RHD engineer also
confirms that as the DBST work was constructed during the winter season, excessive
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amount of bitumen was applied to hold the key aggregates. The road is now has
become virtually a death trap for the road users.
(c) Sylhet-Sunamgaj Road
It is reported that the Sylhet-Sunamgaj road has developed widespread potholes of
different sizes within 6 months of its construction. It is alleged that the poor quality of
construction work is the main reason for this premature failure of the road. The
following photograph is showing the present condition of the road segment near
Sylhet BDR Head Quarter.
(d) Jamuan Bridge Access Road
The Jamuna bridge access road has shown distress condition within 3 years of its
construction. Now, the riding quality of this road has become very unacceptable level.
This can be seen from the photographs presented below. It is to be noted here that like
Nalka-Hitikamrul-Bonpara road, this bypass-cum-access road was also constructed on
the new embankment and using plant mix and paver, even then it did not last long.
Theoretically, if the flexible pavement was built properly it should not be required any
major rehabilitation work before 10-15 years. From the literature review, it is found
that now-a-days in developed countries the flexible pavement is designed for more
than 30 years service life. But in order to achieve this perpetual type of flexible
pavement there is a need for proper design, scientific method of construction
112
involving automated smart equipment and most importantly compliance of stringent
specifications.
113
(e) Approach Road of 1st
China-Bangladesh Friendship Bridge
It is observed that in every rainy season, the East approach road of 1st
It is observed that though the main reason for the development of large potholes is
drainage problem, but every year the repair work has to undertake on an urgent basis
without correcting the cause of the problem.
China-
Bangladesh Friendship Bridge become unusable particularly at Postogola point due to
formation of pond size depression. The depth of depression become so high that
frequently vehicles particularly loaded trucks get overturn due to tilting problem. One
of these kinds of incident can be seen from the following photograph.
It is to be noted here that one of the inherent weaknesses of the flexible pavement is
that though most of the damages of the flexible pavement usually occur during the
rainy reason but proper maintenance work cannot be done until the road has become
completely dried. This unwanted delayed maintenance work results enormous
sufferings to the road users. The following photographs are collected to depict the
effect of moisture on flexible pavement and suffering of people due to deferred
maintenances work. It is to be worth remembering here that the maintenance work
114
become more critical during the winter season than the summer period due to high
degree of temperature loss potential. In reality, relatively more careful attention and
field coordination are warranted for ensuring quality of flexible pavement during
construction in cold weather. In contrast, the construction of rigid pavement is less
susceptible to the season as compared to the flexible pavement particularly in the
advent of ready mix and various kinds of admixtures.
115
5.7 Observations on the Adhesion Problems of Flexible Pavement
Field observations on the modes of failure of the flexible pavements revealed that lack of
bonding between new and old layers is one of the most common modes of failure. The
observation is made both on manually and mechanically (i.e. using plant mix and paver)
constructed overlay projects. It is often argued that poor quality of asphalt concrete in the
wearing course along with the presence of significant number of grossly and illegally
overloaded vehicles, particularly 2 axle trucks, resulted in high deflection of pavement
and consequently high tensile and shear stresses in the thin wearing course causing in the
failure of bond between the wearing course and binder course and resulted in distress of
the pavement.
116
In addition, field observation revealed that to some extend bonding problem is related to
level of cleaning of the existing surface before laying the tack coat. From the field
observation, it was found that when carpeting work is performed in the active and busy
road, to expedite the progress of the work often tack coat is applied without proper
cleaning of dust/mud/loose aggregates from the existing road surface. It is also identified
that surface cleaning work is also compromised particularly when the carpeting work is
done at night time. Besides, application of inadequate amount of tack coat might be a
reason for lack of adhesion between new and old pavement layers.
In the resurfacing work, as thickness of the bituminous carpeting is usually less, cleaning
of loose materials is very important to prevent the bond failure between pavement layers.
The bonding problems due to lack of quality control in resurfacing work are documented
by taking the following photographs. From the photographs it can be seen that different
forms of distresses have developed in the surface layer and it gets completely separated
from the underlying layer, which essentially implies the poor quality of asphalt concreting
works particularly in cleaning the surface and in applying adequate amount of tack coat.
The depressed portions of the roadway thus creating from the bonding failure act as
craters/potholes and they not only cause poor riding quality but also make the roadway
condition hazardous for the motorists.
117
118
5.8 Non-uniform Density of Asphalt Concrete
(a) Due to Aggregate and Temperature Segregations
One of the major problems associated with the production of durable hot mix asphalt
(HMA) pavement is the aggregate segregation and temperature differentials which
usually lead to early pavement failure.
Figure 5.1: Aggregate Segregation in a Stockpile Figure 5.2: Temperature Differentials
Aggregate segregation is the non-uniform distribution of coarse and fine aggregate
components within the HMA mixture. The chief detrimental effects of segregation on
HMA performance are: reduced fatigue life, rutting, raveling, and moisture damage.
In contrast temperature segregations are large mat temperature differences resulting from
placement of a significantly cooler portion of HMA mass into the mat. This cooler mass
comes from the surface layer (or crust) typically developed during HMA transport from
the mixing plant to the job site. These cooler areas cool down to cessation temperature
(the temperature at which no further compaction can take place due to increased HMA
viscosity - commonly taken as 175°F) more quickly than the surrounding mat. Roller
patterns developed based on general mat temperatures may not be adequate to compact
these cooler areas before they cool to cessation temperature resulting in isolated spots of
inadequate compaction. Thus, temperature differentials can cause isolated areas of
inadequate compaction resulting in decreased strength, reduced fatigue life, accelerated
aging/decreased durability, rutting, raveling, and moisture damage (Hughes, 1984;
119
Hughes, 1989). Generally, temperature differentials greater than about 25°F can
potentially cause compaction problems (Willoughby et al., 2001).
Aggregate segregation and construction-related temperature differentials display the same
symptoms and result in the same types of damage, which can cause them to be confused
with one another. However, the ultimate damage mechanism, excessive air voids (often
expressed as "inadequate density"), is the same in both cases. Due to these problems, the
United States spends $25 billion annually on pavement maintenance and traffic services
to maintain four million miles of highway. This expenditure is about 27% of the $90
billion spent each year on US highways. Annual pothole patching costs for state highway
agencies in the United States are estimated at $300 to $400 million. Money spent on the
local level is twice that amount [FHWA, 2006].
Currently, there are several patching techniques applied to roads and highways to abate
pavement deterioration: sealing cracks in pavements, patching potholes with cold mixes
and spray injection, and resealing joints in concrete. All of these methods are expensive
and labor-intensive. Although maintenance treatments may provide temporary relief, they
do not cure the problem. As potholes are caused by excessive air voids in the pavement,
excessive air voids are caused by non-uniform density in the compaction process; non-
uniform densities are caused by the temperature and aggregate segregation – recently a
Note : Green spots Indicate relatively cooler paving mix
120
Shuttle Buggy material transfer vehicle (MTV) is designed to ‘Shuttle’ between the hot
mix asphalt haul truck and paver.
The MTV is introduced by recognizing the fact that during the paving process, trucks
dump hot asphalt directly into the hopper of the paving machine. Heat loss begins
immediately around the perimeter of the truck and during haul-time or delay-time at the
job site. Traditional paving equipment does not completely reblend the hot asphalt,
therefore thermal nonuniformities can exist in laid asphalt. The Shuttle Buggy material
transfer vehicle (MTV) incorporates a reblending hopper system that mixes the hot
asphalt before it is laid. Proper reblending of hot mix asphalt before placement is critical
to temperature consistency throughout the laid asphalt. Uniform asphalt pavement
temperatures lead to consistent road densities, thus preventing premature failures in
asphalt roads. The paving process involving the MTV can be seen from the following
photographs.
Shuttle Buggy Material Transfer Vehicle (MTV)
121
(b) Due to Mix Spreading Problem
Field observations revealed that if flexible pavement is constructed by using manual
method then the pavement often shows a ‘strip pattern’ distress on the surface. The strip
could be in the longitudinal as well as transverse directions. Close observation of the
manual method of construction revealed that as the rake is used (as shown in the
following photograph) to spread the paving mix it creates successive ridges and valleys in
the loose mix and thereby later on when the mix is compacted, the density differential
contours are developed. Usually these contour lines are aligned with the raking operation.
The density differential contours can easily be seen from the following photographs in the
form of successive wet and dry pattern. Wet lines indicate less densified pavement with
high void content and more absorbed water as compared to relatively highly densified
adjacent pavements. In course of time this inconsistent density profiles cause loss of
materials from the lesser densified portions of the pavement and eventually create strip
pattern distress. This special mode of pavement distress can be seen from the following
photographs. It is to be noted here that all the photos are collected from the pavement
construction projects that were built manually.
122
123
5.9 Assessment based on the Questionnaire Survey
5.9.1 Introduction
As good quality of pavement construction in the field largely depends on the full
understanding of the scientific method of construction by the concerned engineers, a
questionnaire survey was designed to know the level of understanding of the filed level
staffs both from Clients and Contractors. The outcome of the survey is presented below.
5.9.2 Designing Questionnaire Survey
In order to assess the level of understanding regarding the proper way of constructing
flexible pavement, all together 12 Engineers in the rank of Sub-
Assistant/Assistant/Executive Engineers from Government Organizations like RHD,
LGED and DCC as well as from the Contractor’s side were interviewed. In addition to
that 15 field staffs including three Diploma Engineers particularly from the Contractor’s
side were also interviewed. In this regard a questionnaire survey form is designed which
was comprised of 25 questions, including 3 open ended questions regarding what are the
underlying reasons behind not selecting rigid pavement in road construction. A sample of
the questionnaire survey form is appended in the Appendix B.
The questions were, if the respondent knows:
1. The standard method of flexible pavement construction.
2. Why temperature is to be controlled at every stage of construction?
3. How to heat bitumen?
4. What are the consequences if bitumen is heated improperly and burnt during mix
operation?
5. At what temperature mix ingredients need to be heated, mix should be prepared, laid
and compacted.
6. Before compaction, what should be done if mix temperature is found to be lower than
the specified temperature?
7. Why does batch mix plant need calibration?
8. How to determine mix temperature in case of plant mix?
124
9. What extra precautions are to be needed during pavement construction in the winter
season?
10. Why carpeting/resurfacing typed maintenance work of flexible pavement need dry
roadway condition?
11. Why drainage condition is so sensitive for the flexible pavement?
12. Ideally what traffic management measures should be taken while roads are in under
submerged condition?
13. Why aggregate gradation is so important for flexible pavement construction?
14. Why maintaining % void in the mix is so important?
15. What is the standard requirement of % void in the mix?
16. How to maintain the quality of flexible pavement construction?
17. What is the normal design life of flexible pavement?
18. What are the reasons behind the premature failure of flexible pavement?
19. Why construction of subsurface layers is so important?
20. What are the tests required for checking the quality of ingredients, level of
compaction of subsurface layers, density of wearing course?
21. Do you think frequent maintenance of flexible pavement cost a lot and there is a
scope of pilferage as there is no working drawing for maintenance job?
22. How flexible pavement does differ from rigid pavement?
23. Present practice of selecting pavement type.
24. When do you construct rigid pavement?
25. What are the underlying reasons behind not selecting rigid pavement as a good
alternative of flexible pavement?
5.9.3 Assessment on the Level of Understanding of the Engineers
During the interview with the concerned personnel involved with the construction of
flexible pavement, in general it is observed that Engineers belongs to the Government
organizations were found to be grossly indifferent about the standard method of
construction. In contrast, field Engineers of the Contractor side is found to be have
relatively better understanding in the proper way of constructing flexible pavement
though they candidly mentioned that usually they do not voluntarily comply with the
quality control requirements of the construction works unless they are forced do so by the
owner.
125
Form the questionnaire survey, it is found that out of 12 respondents 10 do not exactly
know how to heat the ingredients of the flexible pavement, what are the consequences of
improper way of heating the binder. 100 % respondents failed to tell the specified limits
of heating, mixing, laying and compaction temperatures. Moreover, it was observed that
in general their understanding regarding in maintain the correct temperatures in different
stages of flexible pavement construction is very poor. Most interested to found that 90%
respondents from the Government organizations and 70% from the Contractor side told
that it is not a big problem if the mix compaction temperature is found to be lower than
the specified temperature and they also believed that if needed by reheating cold mix can
be used in the construction. They have also shown their ignorance regarding the necessity
of ensuring exact or optimum amount of bitumen content in the mix. They think it is a not
sensitive issue rather if they add more bitumen it is good for the paving mix. It was also
found that they have also poor idea about how overheating and burning of asphalt can
affect its binding properties.
It was surprising to found that all the respondents have shown ignorance regarding the
importance of aggregate grading as well as void content in the paving mix. Similarly, they
also have not got any clear idea about the importance of proper way of constructing
subsurface layers. It was also surprising to know that 70% of the respondents told that the
design life of flexible pavement is 5-7 yrs. Most of the interviewees have identified that
overloading, poor drainage and flooding conditions are the main reason for premature
failure of flexible pavement in Bangladesh.
Regarding the present practice of selecting pavement type, it is learnt that by default the
pavement system is always the flexible pavement. Usually the decision of selecting
pavement type is made following the long time tradition rather than based on the
comparative analysis. The common mindset with the engineering community is that the
rigid pavement is very expensive to construct, though they admitted that the performance
of rigid pavement would be better than the flexible pavement. Therefore, it can be seen
that at present underlying reasons behind not selecting rigid pavement as a good
alternative of flexible pavement is the notion that the rigid pavement is costlier to
construct. Moreover, during the interview it is understood that even if rigid pavement is
found to be a cost-effective alternative of the flexible pavement system, but no one is
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ready to take the decision by changing a long time tradition particularly for major road
construction works. Most of them think that the construction of rigid pavement would be
possible only if it is recommended by the foreign consultants particularly in the aided
project.
5.9.4 Rigid Pavement Roads Constructed by DCC, LGED and RHD
From the questionnaire survey it is learnt that DCC, LGED and RHD is constructing rigid
pavements in a limited scale. The organizational initiatives and their own assessment on
the performance of rigid pavements are discussed bellow.
(a) Rigid Pavements Constructed by DCC
During the last couple of years, the city corporation is constructing local streets
particularly lane/bi-lane of old town and in other unplanned residential areas of Dhaka
city by using rigid pavement because of its construction simplicity and most
importantly strong demand from the community people. Few examples of rigid
pavement road constructed by DCC can be seen from the following photographs.
Considering the better performance of already completed rigid pavement, the DCC
Engineers are also interested to construct more roads with rigid surface. Though, they
also pointed out that the main problem with the rigid pavement is difficulties in laying
the utility lines. They have identified that if the main sewerage line can be constructed
beforehand and conduit for other utilities can be laid, the rigid pavement would be the
best option particularly for narrow road.
The DCC officials noticed that if rigid pavement is constructed in place of flexible
pavement it increases effective width of the carriageway due to its better surface
quality particularly at the pavement edges and thereby increase roadway capacity.
Smooth surface is also helpful for the manually driven vehicles where drivers can
maintain desire speed. Most importantly, they also observed that as the drainage
problem is very acute in all the unplanned areas, the flexible pavement requires
frequent maintenance works which seriously disrupt the normal traffic operation and
causes enormous suffering to the community people. In the narrow streets,
maintenance work of the flexible pavement is very difficult due to the need for
heating, mixing arrangement and most importantly need to allow roller to get into the
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narrow road for compaction purpose. That is why now a days both local people as
well as DCC personnel prefer construction of rigid pavement for the local street and
therefore it is gaining popularity day by day. Side by side it is also become clear that
at present rigid pavement would not be suitable for the main roads of urban area due
to the problem associated with the laying of utility lines with their ever increasing
demand.
It is to be worth mentioning here that no published statistic regarding the length of
rigid pavement constructed by the DCC and unit cost of the rigid pavement could be
obtained from the city corporation because of their poor documentation practice.
Though, from the DCC’s Citizen Charter it is found that the demurrage fees of cement
concrete pavement that is to be paid by the utility agencies for the road cutting and
digging operation is 30 – 43% lower than that of the unit rate of flexible pavement.
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The demurrage costs published by the DCC for flexible and rigid pavements are
presented in the Table 5.8.
Table 5.8 Road Cutting Demurrage Fees
Type of road
Road Cutting Demurrage Fees (per sqm) Up to 1.20 m
depth 1.20 m to 2.50 depth
2.50 m to 4.00 m depth
Over 4.00 m depth
(in BDT) (in BDT) (in BDT) (in BDT) Bituminous Road 1335 1476 1801 2046 Cement Concrete Road 874 1008 1147 1147 RCC Road 1431 1570 1570 1570
From the above Table, it can be seen that even the demurrage fees of RCC road is much
lower than that of flexible pavement for depth over 2.5m and only slightly higher for
depth under 2.5m, which essentially suggests that the reconstruction cost of rigid
pavement is lower than the flexible pavement at least according to this published Table.
Moreover, from the questionnaire survey it is confirmed that so far DCC has constructed
about 200 km concrete road, which is nearly 11% of 1868 km total road network.
(b) Rigid Pavements Constructed by LGED
Based on the questionnaire survey it is observed that LGED has also started constructing
rigid pavement particularly at the flood prone areas. At present, the Local Government
Engineering Department (LGED) is implementing a project named “Community Based
Resource Management Project (CBRMP)” funded by IFAD (International Fund for
Agriculture Development) for the period of 2003-2014 at nine upazillas of Sunamgonj
district [IFAD, 2008]. The infrastructure component of the Sunamgonj community based
recourse management project
has focused on building
village roads to connect
communities with the main
road network. Local
community roads have often
been overlooked impacting
tremendously on the
livelihoods of village
communities. In Sunamgonj,
roads are underdeveloped Flood-proof concrete road built to provide sustained
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partly because of the seasonal flooding in the most of the district. Lack of roads prevents
people from bringing their product to market, children from attending school, people from
getting to hospital and often farmers from bringing harvested crops home.
Considering the daily submergence of the land areas, the roads of the project are built by
using concrete rather than bituminous. The above photograph shows one of the
submerged roads of the project. The roads that are constructed in 2004 are found to be
performing well under severe moister condition. The project is now supporting the
construction of two types of reinforced roads i.e. 2.6 m wide and 2 m wide. Other added
benefit of these constructed roads were by being submersible they did not require high
embankment, resulting reducing cost from removing the need to acquire more land, slope
protection works and not disrupting the flow of flood water. This approach also avoids
construction problems related to the need to compact soil on new embankments. The
following Photographs are presented to show the current initiative of constructing rigid
pavements by LGED at rural areas of Bangladesh.
i. Block Pavements
ii. Rigid Pavements
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iii. Cement Concrete Pavements
iv. Rigid and Block Pavements
According to LGED and IFAD publication [LGED, 2005 and IFAD, 2008], so far LGED
has constructed nearly 760 km concrete road, which is about 2% of the total 40,000 km
paved road.
(c) Rigid Pavements Constructed by RHD
Questionnaire survey as well as field observations revealed that the RHD is constructing
rigid pavement road of both CC and RCC categories particularly at the highway segments
adjacent to the Bazar areas, bus bays/waiting areas, level crossing approaches, bridge
approaches and standing areas of toll plazas. The following few snap shots are presented
to demonstrate the RHD initiative in constructing rigid pavement.
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From the close observation of the following pictures, it can be seen that at few occasions
the serviceability of flexible pavements have deteriorated significantly as compare to the
rigid pavement portions of the road. This evidence essentially indicates that with the same
foundation, traffic and climatic loading conditions - the performance of rigid pavement is
far better than that of the flexible pavement. During the field observation, the same
evidence is invariably found in all most all the cases where flexible and rigid pavements
are constructed side by side.
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(d) Rigid Pavement Constructed by Private Initiatives
As flexible pavement construction works need heating of bitumen and aggregates, mixing
of ingredients, laying & compaction of mix at appropriate temperatures, involvement of
heavy roller in compaction work - it is obvious that the construction of flexible pavement
road for small length by community or individual initiative would be very difficult. That
is why it is found that at local level now-a-days people prefer the rigid pavement in place
of the flexible pavement. From the field survey it is observed that most of the alley,
lane/bi-lane, driveway and local streets particularly those are outside municipal
jurisdiction are being built by neighborhood people or often individual initiative by using
rigid pavement. From the interview survey, it is revealed that people prefers rigid
pavement as its construction is hassle free, does not require involvement of any special
contractor, roller, construction is environment friendly and most importantly they think
the pavement is durable and maintenance free. A few examples of rigid pavements built
by individual initiatives can be seen in the following photographs.
From the informal interview with the Engineers of BUET Engineering Section, it is found
that the campus rigid pavement roads are performing better than the flexible pavement.
According to the concerned Engineers, though the main campus rigid pavements were
built in mid 1980s, they are still in good shape and working fine. Considering the past
history of the maintenance works of both the flexible and rigid pavements the Engineers
are in the opinion that the rigid pavement is more or less fit and forget type perpetual
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pavement system. In the following photographs, two segments of main campus roads
made of rigid pavement can be seen with good riding condition.
According to their observations, it is learnt that though the traffic load is not so high- only
light vehicles ply on the campus road even then if not every year, after every alternative
year the flexible pavement needs carpeting/resurfacing work to restore its serviceability.
They have identified that the main reason for poor performance of the flexible pavement
is the campus drainage problem. Observing the time dependent performance of both the
rigid and flexible pavements side-by-side, now a day the engineers have started to replace
the flexible pavement by rigid pavement. According to their cost estimates, the
construction cost of rigid pavement is becoming at par with the cost of flexible
pavements. Most importantly for the construction of rigid pavement the engineering
section does not need any Contractor; they can build the pavement using their own
resources. The concerned engineers also mentioned that due to high overhead involved
with the construction of flexible pavement it is difficult to find Contractors for the
construction of small amount of flexible pavement works. Moreover, often maintenance
work has to be delayed due to unavailability of bitumen. The DCC, LGED and RHD
engineers expressed the same observation, which further reflects the complexity of the
construction of flexible pavements.
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5.10 Overview
A number of field tests and laboratory experiments are performed in order to make
understand the quality control that is currently practiced in the construction of flexible
pavement in Bangladesh. It is found that due to improper way of heating and mixing
bitumen, its properties have changed significantly particularly with the manual method of
construction. Aggregate gradation is hardly maintained in the preparation of pavement
mixtures and thereby lower Marshall flow values along with higher void contents are
obtained in the laboratory investigation.
Also temperature measurements in the field at different stages of construction process
show that bitumen quality is deteriorated significantly at the time of heating and mixing
with aggregates. Overall, it is observed that in every stage of pavement resurfacing/
carpeting works there is a serious lack of quality control particularly in maintaining
appropriate temperature of aggregates and bitumen as well as of placing and compaction
of mixture. In reality, there is a serious ignorance exists both with the field engineers and
contractors related to pavement construction works. They have little ideas about the
compliance of maintaining specific temperature at a particular step of pavement
construction/rehabilitation works.
Form the questionnaire survey it is found that at the community level rigid pavement is
the preferred type of pavement due to its better riding quality, performance, construction
simplicity and most importantly headache free due to its minimum maintenance
requirement. Field observation revealed that where both flexible and rigid pavements are
built side by side by different organizations, the performance of rigid pavements is
relatively found to be better. Rigid pavement as constructed by LGED in Sunamganj
district has found to performing well under daily tidal submergence cyclic loading
pattern.
From the evaluation of different completed projects it is revealed that though overloading
and drainage are the main causes of premature pavement failure in Bangladesh but
manifestation of lack of poor quality of work, use of excessive binder, bonding problem
between new and old layers are also found to be contributory factors for premature failure
of flexible pavement. From the questionnaire survey it is observed that the persons
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concerned with the construction of flexible pavements, both the client and contractor’s
side, have poor understanding on the proper way of doing the construction of flexible
pavement job. As such, there is a need for pavement construction method which is simple
and requires no heating requirement, compaction work and above all not so sensitive to
the quality control, which essentially suggests that rigid pavement construction would be
the most appropriate method of road construction for the local conditions.
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CHAPTER 6
CONCLUSIONS AND RECOMMENDATIONS
6.1 Introduction
In Bangladesh, the current practice for pavement construction is flexible asphalt
pavement, without undertaking any real attempt for any comparative analysis of
pavement types, any engineering and economic considerations and selection of suitable
type for Bangladesh situation. During the last few decades, government of Bangladesh
through its leading organizations like RHD, LGED and DCC or consultants of donor
countries have chosen flexible pavement for this country for some sort of mis-
conceptualized mind-set that are totally unanalyzed and unexamined. As a result
recurrence damages of flexible pavements under submerged condition and annual
maintenance of these roads has become a common practice. In contrast, considering
performance, durability, life cycle cost, construction time, soil condition, submersible
condition, and availability of local materials, the concrete pavement is more suitable and
justified as compared to the flexible pavement in Bangladesh.
In this research work, comparative analysis of both types of pavements on various factors
(like equipment, life cycle cost, availability of materials), case studies on two different
projects and economic analysis for both type of pavements on a particular road section
were done to show acceptably of rigid pavement construction in Bangladesh instead of
going traditional flexible asphalt construction. Also, a through field and lab investigations
were undertaken to find out the problems associated with the construction of flexible
pavement.
This chapter has presented the summary of findings obtained from the comparative
analysis, field investigations and experimental results carried out in the previous
Chapters. It is expected that these findings would help in changing the traditional mindset
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of the pavement designer, policy makers in choosing appropriate type of pavement in the
context of Bangladesh. This chapter also contained recommendations of the study.
6.2 Summery of the Findings
6.2.1 Findings from Comparative Analysis
Detailed description about various factors comparing flexible and rigid pavement is
presented in Chapters 4 and 5. The findings based on that comparative analysis are
summarized below.
6.2.1.1 Requirement of Equipment and Materials
A fleet of heavy equipment including costly asphalt batching plants, pavers and a set of
rollers comprises of three wheel or tandem rollers and pneumatic rollers are required for
the construction of flexible pavement whereas comparatively lesser number of costly
heavy equipment are required for the construction of concrete pavement particularly with
3,000 psi strength which is common in most of the rigid pavement construction works.
Moreover, for concrete pavement the usage time of machineries and equipment are
almost round the year, whereas, the idle hours of machineries and equipment for the
construction of asphalt pavement are exorbitantly high due to weather conditions.
Cement concrete requires less thickness as compared to the flexible pavements for the
same loading and soil conditions. It was observed that for per km construction of a
standard 2-lane width road, material requirement is almost 2 times higher in case of
flexible pavement as compared to the rigid pavement. Material requirements for flexible
pavement increases further with weaker soil condition as the thickness of the cement
concrete pavement are marginally affected by the support condition. Moreover, flexible
pavements unlike rigid ones also need road materials for regular maintenance. It is
definitely suggests that the cement concrete pavement conserves road construction
materials significantly, which is very important for the road construction in Bangladesh
where there is a dearth of construction materials and their available is limited to only few
remote border areas of the country.
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6.2.1.2 Availability of Binding Materials
For construction of new flexible pavement or rehabilitation of existing pavement, there is
a dependency on foreign country for procuring bitumen (the chief binding material for the
construction of flexible pavement) and estimated yearly expenses is Tk. 9,00,00,000/=
which is paid in foreign currency and thereby burdens the economy. Besides, bitumen is
one of the derivatives of crude petroleum, whose supply worldwide is gradually shrinking
and price is going high. It is also learnt from the questionnaire survey that in Bangladesh
often the construction of flexible pavement disrupts due to short supply of bitumen and
thereby delay the project completion time and also increase the cost of construction. But
considering availability (now in Bangladesh there are 60 cement factories having annual
production capacity of 21 million tonnes) and price, cement for rigid pavement
construction would be available in abundant quantities in future to meet the requirements
of the road construction.
6.2.1.3 Methods
of Pavement Construction
From the discussion presented in Chapter 4, it is appeared that
• The selection of proper ingredients and their proportioning are very vital to ensure
the quality of flexible pavement.
• The quality of flexible pavement is also very sensitive to the heating process. In
order to maintain the recommended stringent guidelines in heating binder,
aggregates and preparing mix, there is a need for continuous recording of asphalt
and aggregate temperatures and most importantly use of batch plant is of utmost
important, which are very difficult to ensure in majority of pavement construction
works in Bangladesh.
• Proper sweeping and cleaning of the old surface and application of tack coat are
absolutely essential to promote perfect bond between old and new layers, which
often is not done properly in the field.
• For proper compaction of the paving mixture, the minimum temperature
requirement has to be maintained as well as standard rolling operation using
different types of rollers has to be followed in a planned manner.
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• Flexible pavements require more layers than that of rigid pavements and naturally
for the new construction, performance of flexible pavement structure largely
depends on the quality of sub-surface layer construction particularly in
maintaining proper gradation of aggregates, lift thickness, optimum moisture
content and most importantly on proper and uniform compaction of the layer.
Moreover, uniform support condition is one of the main prerequisites for ensuring
even surface of the flexible pavement. Since, post quality control checking of the
subsurface layers is not easy to perform with the multilayered flexible pavement
structure there is an ample opportunity for the contractor to compromise with the
specified specifications unless the sincere and honest field engineers supervise it,
which is very scarce in Bangladesh.
Analyzing the complete method of construction it was observed that the construction of
heat based flexible pavement involves a series of operations, which need very careful
planning and coordination so that the construction proceeds with a minimum loss of time.
Each of the separate steps must be done carefully and preciously so that the completed
pavement meets the stringent standard specifications. In contrast it is revealed that rigid
pavement construction requires fewer steps and relatively quite straight forward.
Reasonably, it is easier to maintain the quality in pavement construction except for proper
functioning of rigid pavement, joints need to be constructed as well as maintained
properly throughout the service life.
6.2.1.4 Distresses
due to Submergence and Hot Climatic Condition
Comparative analysis as presented in Chapter 4, revealed that one of the common causes
of flexible pavement failure in Bangladesh is due to weather conditions mainly hot
climatic condition and excessive moisture coupled with poor drainage condition and most
importantly unrestricted movements of over loaded vehicles during the periods when the
pavement goes under submerge condition. Moreover, it is to be noted that one of the
inherent weaknesses of the flexible pavement is that though most of the damages and
distresses of the flexible pavement usually occur during the rainy reason but proper
maintenance work cannot be done until the road has become completely dried. This
unwanted delayed maintenance work results enormous sufferings to the road users. Even
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if maintenance work is done on wet surface condition premature failure of the pavement
occurs in a short span of time.
It is therefore evident that climate with high rainfall and recurrent flood demands high
performance pavement system particularly which is not susceptible to water. As
inherently cement concrete is not so susceptible to the temperature and can withstand
high temperatures without any softening simultaneous effects of high temperature and
rainfall/flood do not deteriorate the cement concrete pavement much, t
his property is
likely to be of great value in tropical countries like Bangladesh.
6.2.1.5 Safety Aspects of Pavements
From the comparative analysis as presented in the previous Chapter it has evident that as
concrete pavement provides better visibility, skid resistance, enhances cross drainage over
pavement, better road environment and surface condition etc. it significantly improves the
roadway safety and thereby reduces road accidents risks. Due to its better light
reflectance, it has the potential to improve road safety at night time by providing better
driving queue, particularly for the roads and highways in rural or suburban areas with no
proper road marking and street light which is very common in Bangladesh.
6.2.1.6 Life Cycle Cost
From the comparative analysis, regarding the life cycle cost of pavements it was found
that though the initial cost of concrete pavement is almost equal than the flexible
pavement, but with longer design period the cost of concrete pavement becomes cheaper.
Case studies undertaken for Debogram-Progoti Sharani Link Road project revealed that
the unit cost of 4-lane wide reinforced concrete pavement for 30 years design period is
Tk. 40.86 million (excluding the land acquisition and embankment costs) which is found
to be 48% lower than that of the unit cost of flexible pavement (Tk 78.01 million).
Similarly, for the Dhaka-Sylhet Highway project, the cost per km for concrete pavement
of standard 2-lane wide for 30 years design period is Tk. 22.25 million, which is 47%
lower than that of the unit cost of flexible pavement (Tk 41.79 million).
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In consideration of these, it is high time to construct cement concrete pavement for major
roads and highways of Bangladesh.
6.3.1 Findings from Field Investigations
In order to assess the level of slackness in the construction of flexible pavements, field
investigations were undertaken in the form of critically observing the construction
procedures and measuring associated deviations from the specified standards, comparing
strength parameters between samples prepared in the field using job mix and samples
prepared in the laboratory with the materials collected from the construction sites. This
article presented the results of these field investigations.
6.3.1.1 Qualitative Observations
The important observations that were documented during the field investigation on the
manual method of flexible pavement works are listed below:
• Though ideally bitumen should not be heated continuously for more than one and
half hours but it was observed that the bitumen was heated above fire point and
without any stirring action till the construction work has completed
• Burning of bitumen was observed during mixing operation
• Though cleaning of aggregates is an important prerequisite to reduce stripping
potential of the paving mix, it was observed that before use the aggregates were
not cleaned up at all
• To maintain mix proportion properly no weighing device or volume measuring
unit was found; aggregates and asphalt were poured in the tray by using head
basket and container
• No thermometer and timer were found to be used to control temperature and time
of mixing
• The mixture was transported to the construction site without any protection
against heat loss
• Tack coat was sprayed long before paving mix is laid
• Tack coat was sprayed on old surface without proper cleaning of the surface
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• Distresses in the form of potholes, undulation, alligator cracks etc. that were
present on the existing pavement were not repaired properly before placing the
new surface course
• Mix spreaded by using rack shows successive ridges & valleys and uneven spread
of mixture
• Long waiting before start of the compaction work; even at one site (Kafrul, Dhaka
Cantonment) the compaction started after 5 hr. of laying the paving mix
As such, the present practice of flexible pavement construction particularly the manual
method can be regarded as totally an unscientific method of construction.
6.3.1.2 Quantitative Observations
Laboratory investigations conducted on paving mix and ingredients collected from Site-1
at Khigaon area and Site-2 at Shahabug area revealed that:
Bitumen Content
The range of bitumen content in the paving mix for Site-1 and Site-2 were 5.1 – 5.6% and
5.4 – 5.5% respectively, which implies that variation of bitumen content was relatively
higher for Site-1 than that of Site-2. This may be due to the fact that at Site-1 paving mix
was prepared in the field manually without much control on adding exact amount of
ingredients in the mix where as at Site-2, mix was prepare by using batch plant.
Properties of Virgin and Extracted Bitumen
In general all the properties describing the quality of binder have found to be deteriorated
significantly with the extracted bitumen. For instance, penetration and ductility values
which indicate consistency of the binder shown that these two properties of extracted
bitumen have decreased significantly, from 91 to 77 and from 100+ to 95 respectively, as
compared to that of virgin bitumen. These changes essentially suggest that the
consistency of the binder has decreased due to improper way of heating the bitumen in
the field. Besides, Sp. Gr. as well as Flash & Fire points of extracted bitumen have
increased significantly, which implies that the density of bitumen has increased due to the
excessive loss of volatile substances. Obtaining decreased softening value (480C) for
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extracted bitumen as compared to that of original bitumen (550
C) also suggests that
binder’s susceptible to temperature in a way its softness has deteriorated significantly.
It appears that bitumen properties of Site-2, where plant mix was used, have also changed
as compared to the virgin material. Test results for both Sp. Gr. and Flash & Fire point
show that values for extracted bitumen have increased though not as much as that of Site-
1. Similarly, Penetration and Ductility values have also decreased for extracted bitumen;
89 to 83 and 100+ to 98 respectively. These experimental results revealed that for Site-2
even if paving mix is produced by using batch plant, the properties of binder material
have changed though not so significantly as compared to the amount of changes occurred
for Site-1. This definitely suggests that manual method of pavement construction causes
more age hardening of binder than that of machine made paving mix.
Gradation of Aggregates
For the Site-1, aggregate gradation was found to be deficient at 4 sieves and for the Site-2
gradation of aggregates went beyond the specified limit at three occasions. Moreover,
from the gradation results it was observed that both the field gradations that were used in
the preparation of paving mixtures were gap-graded instead of well-graded.
Strength Properties of Mixes
The Marshall test results for Site-1 revealed that though the stability values for both the
field and laboratory specimens satisfied with the design criteria but in all other respects
i.e. flow, % air void, % voids in VMA and % VFA have failed to meet the limiting
values. Obtaining lower flow value 6.5 for the specimens prepared using paving mixture
collected from the job site as compared to the flow value 15.9 for the laboratory
specimens that were prepared by using the raw ingredients collected from the same
construction sites, indicates excessive age hardening of the bitumen with the field mix.
Higher percent-air-voids for both the laboratory (8.63%) and field specimens (10%) as
compared to the design criteria (3-5%) essentially imply poor grading of aggregates. Non
compliance of VMA and VFA results also indicated weakness in aggregate gradations.
Getting relatively higher % air voids (10%) with the field specimen as compared to the
laboratory specimen (8.63) might be due to low compaction temperature of the mix.
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Marshall results for the Site-2, where plant mix was used in the construction, showed that
both stability and flow values for field as well as laboratory specimens satisfied the
Marshall design criteria. Though, like the Site-1, % air voids, %VMA and %VFA did not
fulfill the design criteria for both the specimens, which also indicated that the problem
lies with the aggregate gradation.
Temperature Measurement at Different Stages of Construction
For the Site-2 as the paving mix was prepared by using batch plant it was not possible to
measure the temperatures of dry aggregates as well as bitumen. Due to the same reason,
the mixing temperature was also could not be measured for Site-2 though it was learnt
from the batch plant operator that the AASHTO specified temperatures for different
stages of mixing process was set initially and maintained throughout the mix production
operation. It was also gathered that after installation of the batch plant in 2004, no
calibration of the machine has been performed.
The temperature measurements showed that at Site-1, temperature of the aggregates was
found to be much lower (72°C) than that of the temperature specified (163°C) by
AASHTO. The temperature of the bitumen in the drum was found to be more than 300°C,
which was not suppose to be more than 163°C. The temperature of bitumen before
pouring into the tray was found to be 199°C which was much lower than the temperature
(300°C) of the bitumen observed in the drum, this is due to the fact that the bitumen was
transferred from the drum to the mixing tray by using a container which was often found
to be kept aside for a long time before pouring it in the mixing tray.
The significant difference in temperatures between aggregates and bitumen is not good at
all for obtaining homogeneous bituminous mixes. For uniform mixing, it is utmost
important that both ingredients must be heated at the same temperature.
The compaction temperatures for both the construction sites were found to be as low as
50°C and 75°C respectively as compared to the specified 100-120°C.
Field Observations on the Completed Roadway Projects
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It is found that serious distresses in flexible pavement have occurred at some portion of
the Nalka-Hatikamrul-Bonpara Road within one and half years of its construction. At
present the road is virtually become unusable and hazardous for the road users. The main
causes of premature failure of the road were found to be deficiencies in materials, design
and construction.
Construction of Dhaka Bypass, N-15 was taken up on an emergency basis to provide a
road bypassing the city of Dhaka and link the Jamuna Bridge for traffic movements from
the east and south-east districts of Sylhet and Chittagong Divisions to the western parts of
Bangladesh and vice versa. But concerned for quality of works was raised even before the
formal opening of the road to traffic in 2006. The main findings of the causes of
premature failure of the pavement were identified as:
Use of poorly graded sub-base materials with high proportion of sand than specified,
on the entire stretch of the Bypass Road, caused the coarse aggregates merely to float
in the fine aggregates and resulting lower stability and load supporting characteristics.
Use of poor quality construction materials, particularly sub-base, and lower thickness
of pavement layers than specified.
Therefore, it can be seen that in the construction of flexible pavement, quality control of
subsurface layers is also of vitally important. If the weaknesses exist within the sub-
surface layers of the pavement structure then with time they reflect through the surface
course and eventually it becomes very difficult to rectify the problems often without
reconstruction. It is well recognized that the reconstruction of road is inherently very
expensive and time consuming.
It is observed that some portions of the Dhaka-Chittagong Highway become unusable
only within three years of its restrengthening work. It is to be noted here that the
restrengthening work in the form of applying pavement overlay was constructed using
plant mix and paver in 2004-06. But due to poor quality of construction, immediately
after the overlay work, heaping, raveling, frequent potholes and surface undulation have
started to occur particularly after Chaddagram up to Chittagong end and made the
highway hazardous.
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The Dhaka-Tangail Road was rehabilitated in January 2008 applying Double Bituminous
surface Treatment (DBST). But it is reported that in the following summer season, the
road surface become so sticky due to melting of binder materials that out of control type
accident is occurring frequently. Again, poor quality of construction is blamed for the
cause of this bleeding problem.
It is reported that the Sylhet-Sunamgaj road has developed widespread potholes of
different sizes within 6 months of its construction. It is alleged that the poor quality of
construction work is the main reason for this premature failure of the road. The Jamuna
bridge access road has shown distress condition within 3 years of its construction. Now,
the riding quality of this road has become very unacceptable level.
6.3.2 Findings from Questionnaire Survey
In order to assess the level of understanding regarding the proper way of constructing
flexible pavement, all together 12 Engineers in the rank of Sub-Assistant/Assistant/
Executive Engineers from different Government Organizations like RHD, LGED and
DCC as well as from the Contractor’s side were interviewed. In addition to that 15 field
staffs including three Diploma Engineers particularly from the Contractor’s side were
also interviewed.
From the questionnaire survey it was observed that in general Engineers belongs to the
Government organizations are indifferent about the standard method of construction. In
contrast, field Engineers of the Contractor side were found to have relatively better
understanding in the proper way of constructing flexible pavement though they candidly
said that usually they do not voluntarily comply with the quality control requirements of
the construction works unless they are forced do so by the owner.
It was found that out of 12 respondents 10 do not exactly know how to properly heat the
ingredients of the flexible pavement, what are the consequences of improper way of
heating the binder. 100 % respondents had failed to tell the specified limits of heating,
mixing, laying and compaction temperatures of paving mix. Most interested to found that
90% respondents from the Government organizations and 70% from the Contractor’s side
told that it is not a big problem if the mix compaction temperature is found to be lower
147
than the specified temperature and they also believed that if needed by reheating cold mix
can be used in the construction. They have also shown their ignorance regarding the
necessity of ensuring exact or optimum amount of bitumen content in the mix. They think
it is a not sensitive issue rather if they add more bitumen it is good for the paving mix. It
was also found that they have also poor idea about how overheating and burning of
asphalt can affect its binding properties.
It was surprising to found that all the respondents have shown ignorance regarding the
importance of aggregate grading as well as void content in the paving mix. Similarly, they
also have not got any clear idea about the importance of proper way of constructing
subsurface layers. It was also surprising to know that 70% of the respondents told that the
design life of flexible pavement is 5-7 yrs. Most of the interviewees have identified that
overloading, poor drainage and flooding conditions are the main reasons for premature
failure of flexible pavement in Bangladesh.
Regarding the present practice of selecting pavement type, it is learnt that by default the
pavement system is always the flexible pavement. Usually the decision of selecting
pavement type is made following the tradition rather than based on the comparative
analysis. The common mindset with the engineering community is that the rigid
pavement is very expensive to construct, though they admitted that the performance of
rigid pavement would be better than that of the flexible pavement. Moreover, during the
interview it is understood that even if the rigid pavement is found to be a cost-effective
alternative of the flexible pavement system, but no one is ready to take the decision by
changing a long time tradition particularly for major roadway construction works. Most
of them think that the construction of rigid pavement would be possible only if it is
recommended by the foreign consultants particularly in the aided project.
Regarding the availability of contractor and bitumen, the concerned engineers mentioned
that due to high overhead involved with the construction of flexible pavement it is
difficult to find Contractor for the construction of small amount of flexible pavement
works. Moreover, often maintenance work has to be delayed due to unavailability of
bitumen. The DCC, LGED and RHD engineers also expressed the same observation,
which further reflects the complexity of the construction of flexible pavements.
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6.3.3 Findings on Rigid Pavement Roads Constructed by DCC, LGED and RHD
6.3.3.1 Rigid Pavements Constructed by DCC
During the last couple of years, the city corporation is constructing local streets
particularly lane/bi-lane of old town and in other unplanned residential areas of Dhaka
city by using rigid pavement because of its construction simplicity and most importantly
strong demand from the community people. Considering the better performance of
already completed rigid pavement, it is learned during the interview survey that the DCC
is planning to construct more local roads at neighborhood level with rigid surface.
The DCC officials have noticed that if rigid pavement is constructed in place of the
flexible pavement, it increases roadway capacity due to improved riding quality vis-à-vis
higher operating speed of the traffic stream which is important for NMV and other
manually driven vehicles. Most importantly, they also observed that as the drainage
problem is very acute in all the unplanned areas, the flexible pavement requires frequent
maintenance works which seriously disrupt the normal traffic operation and causes
enormous suffering to the community people. In the narrow streets, maintenance work of
the flexible pavement is very difficult due to the need for heating, mixing arrangement
and most importantly need to allow roller to get into the narrow road for compaction
purpose. That is why now-a-days both local people as well as DCC personnel prefer
construction of rigid pavement for the local streets. From the questionnaire survey it was
confirmed that so far DCC has constructed about 200 km concrete road, which is nearly
11% of 1868 km total road network.
6.3.3.2 Rigid Pavements Constructed by LGED
The questionnaire survey revealed that considering the merits of rigid pavement LGED
has also started constructing rigid pavement particularly at the flood prone areas. In
Sunamgonj, roads are underdeveloped partly because of the seasonal flooding in the most
of the district. Lack of road prevents people from bringing their product to market,
children from attending school, people from getting to hospital and often farmers from
bringing harvested crops home. Considering the daily submergence of the land areas, the
roads of the project are built by using concrete rather than bituminous. The roads that are
constructed in 2004 are found to be performing well under severe moister condition. Is
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was found that by 2005 LGED has constructed nearly 760 km concrete road, which is
about 2% of the total 40,000 km paved road.
6.3.3.3 Rigid Pavements Constructed by RHD
Questionnaire survey as well as field observations revealed that the RHD is constructing
rigid pavement road of both CC and RCC categories particularly at the highway segments
adjacent to the Bazar areas, bus bays/waiting areas, level crossing approaches, bridge
approaches and standing areas of toll plazas. Field observations revealed that in most of
the cases where flexible and rigid pavements are constructed side by side relatively the
serviceability of flexible pavements have found to be deteriorated significantly as
compare to the rigid pavement portions of the road. This evidence essentially indicates
that with the same foundation, traffic and climatic loading conditions - the performance of
rigid pavement is far better than that of the flexible pavement.
6.3.3.4 Rigid Pavement Constructed by Private Initiatives
As flexible pavement construction works need heating of bitumen and aggregates, mixing
of ingredients, laying & compaction of mix at appropriate temperatures, involvement of
heavy roller in compaction work, the construction of flexible pavement was found to be
not suitable for the small scale job particularly initiated by the community or individual
level. That is why it was found that at local level now-a-days people prefer the rigid
pavement in place of the flexible pavement. From the field survey it was observed that
most of the alley, lane/bi-lane, driveway and local streets particularly those are outside
municipal jurisdiction are being built by neighborhood people or often by individual
initiative using rigid pavement.
6.3.3.5 Price Escalation of Binders and Mixes
From the unit rate analysis of binders, it was found that over a period of four years the
unit cost of bitumen has increased by two and half times as compared to the unit cost of
cement, which has increased by nearly one and half times during the same period of time.
Most importantly it was found that in 2004 the unit cost of flexible paving mix was lower
than that of the cost of cement concrete paving mix and after that its price has increased
150
very rapidly and crossed the price of concrete paving mix by 2006. Now, the unit cost of
bituminous pavement is more than one and half times as compared to the unit cost of
concrete mix. Though in the PWD rate of Schedule 2008, the unit cost of bituminous
premix for wearing course is shown as Tk. 8637/= per cu.m, but in reality currently the
cost is more than that of the Schedule rate. Review of Bill of Quality of the 4-laning
Dhaka-Chittagong highway, which has recently been tendered, shows that the estimated
unit cost of bituminous concrete is Tk. 12,436/=. This essentially suggests that with time
the cost of flexible pavement is increasing at unusually very high rate as compared to the
concrete pavement.
6.4 Recommendations
Based on the above findings of the study the following recommendations may be made :
In the road construction, rigid pavement may be given preference over flexible
pavement due to the following reasons:
Because of higher requirement of aggregates as compared to the cement concrete
pavement and other environmental and ecological advantages.
The chief constituent of flexible pavement, bitumen is an imported material and its
long-term availability is going to be difficult with time. In contrast, cement is local
material and its availability is ensured.
Considering local weather conditions with high intensity of rainfall, recurrent flood,
high temperature during summer time as well as rampant over loading conditions.
In consideration of life cycle cost, adoption of cement concrete pavement construction
policy will optimize the utilization and investment of financial resources available to
road sector.
Longevity of flexible pavement requires careful design, implementation, and
supervision by qualified contractors under continuous supervision of expert engineers
associated with the skilled labors in each step of construction. In Bangladesh,
continuous supervision of construction works by competent, honest and sincere
engineers is seldom seen and unskilled labors are often engaged in the construction
works resulting serious deterioration of the quality of works.
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In the absence of working drawing, traditionally maintenance of pavement works
means pilferage of money due to difficulties in qualifying the volume of works vis-à-
vis bill of quantity, which further justifies the use of fit and forget type perpetual rigid
pavement in Bangladesh, inherently which has the potential to reduce the frequency
of maintenance and thereby to reduce pilferage of money.
Simultaneous effect of high temperature and rainfall/flood do not deteriorate the
cement concrete pavement. Cement concrete is practically impervious to water and
does not allow water to reach the sub grade. As a result, cement concrete pavements
perform better under adverse conditions caused by water and poor drainage. Moreover
Considering the higher reflectance potential of fare colored rigid pavement and the
inherent property of providing continuous visual queue in night time driving, it would
be the safer pavement system for the roads and highways of Bangladesh where
marking is hardly used and headlight glaring is a serious problem.
construction of cement concrete pavement is not a ‘high-tech’ matter and the present
level of engineering and technological know-how level in Bangladesh is quite capable
of adapt easily.
Therefore, in order to get durable as well as safer roadway system, it is the high time to
consider the use of cement concrete pavement for the construction of roads and highways
of Bangladesh. In this regard it is imperative that the pavement design engineers and road
engineers in Bangladesh as well as road authorities have to decide on the preference of
type of pavement appropriate and cost-effective for Bangladesh. Undoubtedly, concrete
pavement will get preference over asphalt pavement for road improvement and upgrading
in Bangladesh provided right pavement engineering practices are adopted. It is now the
time that RHD, LGED and DCC as leading organizations of Bangladesh associated with
road construction should take positive initiatives to adopt the right policy for cement
concrete pavement.
Though it would be difficult, if not impossible, to use rigid pavement in the urban areas
due to the need of frequent road cutting and digging for laying different utility lines to
meet the ever increasing demand of these facilities, but in the rural and suburban areas the
prospects of its application is bright. Besides this, other prospective areas of applying
cement concrete pavement is listed below.
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Special preference for the cement concrete pavement should be given in the
construction of road at the following areas
(a) Where extra performance is needed
-
-
Roads through towns, villages, bazaars where there are poor or no drainage
arrangements, with the road itself acting as a drain at times
-
Pavement of submersible causeways
-
Roads in delta regions (riverrine rural areas)
Roads in flood plains prone to
-
flush flood
-
Roads in high rainfall areas
-
Roads in water logged area
-
Bus bays and bridge/level crossing/toll plaza approaches
-
Pavement with heavily loaded traffic like national highways
Heavy duty pavements like runway, port, container yards
(b)
Narrow roads and streets where access of paver machine, dump trucks and rollers etc.
are limited
(c)
At any small scale paving work where batch plant based construction work is difficult
to justify
(d)
At remote areas where batch plant is not feasible
(e)
Where stage construction is needed, CC block based semi-rigid pavement could be a
favorable alternative
(f) Experimentally
the rigid pavement can be tried with the roads which have failed
prematurely due to poor quality of construction particularly with the sub-surface
layers defects like Dhaka bypass and Hatikamrul road; where pavement
reconstruction is anticipated.
6.5 Limitations of the Study
153
While conducting the research works the following issues could not be covered due to
time, economic constrains and scope of the study.
• Field investigation was made only on resurfacing or carpeting works. It would be
complete and comprehensive if investigation could have been made on the
construction of new road where, besides pavement works construction of subsurface
layers are also involved.
• In order to assess the quality of construction that is practiced in the field, observations
were made only on the pavement works undertaken by DCC (Dhaka City
Corporation). The assessment should be made on the road works implemented by
other large organizations like RHD and LGED.
• The questionnaire survey was limited in terms of the number of respondents. It should
be made more comprehensive by increasing the number of respondents as well as
covering more organizations and contractors.
• The analysis of rigid pavement construction that is presented in this research work
was only qualitative and empirical; no field investigation was performed due to
unavailability of job site.
• It would be better if a long term observations could be made by constructing two
successive segments of a road; one by using flexible pavement and other by rigid
pavement.
The above issues could be the potential topics for further research in this area.
154
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1. RRD (2006), Pavement Design Guide, Ministry of Communication, Roads and
Railways Division.
2. Yoder E.J and Witczak M.W. “Principles of Pavement Design“, 2nd Edition, Jhon
Wiley & Sons, Inc, New Work, USA.
3. Finn road Limited (2004), “Cement Concrete Pavement for Better and Safer Roads in
Bangladesh – A Concept Analysis Report”, Consultant SRNDP, Dhaka, Bangladesh.
4. World Highways (2001), “Concrete Pavement – Netherlands Experience”, January
issue.
5. World Highways (2004), “Concrete Pavement Around the world”, January issue.
6. Internet documents (2006), “Thickness Design for Concrete Pavements”.
7. Internet documents (2008), “Design of Concrete Pavement for City Street”.
8. Internet documents (2007) “Sub grades and Sub base for Concrete Pavements”.
9. World Highways (2000 & 2002), “Concrete Pavement”, March/April 2000,
July/August 2002 issues.
10. World Highways (2004), “Road Technology”, April issue.
11. Khan A. Rahman (1992), “Concrete and Asphalt Construction Practice”, First Edition,
Dhaka, Bangladesh.
12. Thomas, A.V. (1999), “Risk Perception Analysis of BOT Road Project Participants in
India” http://www.mlit.go.jp/sogoseisaku/inter_e/project/ /pdf/bot_ summary_e.pdf
13. David, G. Peshkin, Todd E. Hoerner, Kathryn A. Zimmerm (2000) , “Optimal Timing
of Pavement Preventive Maintenance Treatment Applications
14. Barry P. Hughes (2006), “Optimum Design of Sustainable Concrete Pavements”.
”.
15. PCA (1984); Portland cement Association-A Guide of Thickness Design for Concrete
Highway and Street Pavements.
16. Hyde Flippo (1996), “The German Way and More”, http://en.wikipedia.org/wiki/
German_Autobahns.
17. Matt Rosenberg (2001), “The Largest Public Works Project in History”,
http://en.wikipedia.org/wiki/Interstate_Highway_System
155
18. Annual Report (2008) on “Florida Concrete Product Association (FCPA)”,
http://www.ajfroggie.com/roadpics/fl/fl-other.htm
19. Project Report (2005), Trans-European North-South Motorway (TEM),
(http://www.unece.org/ trans/main/temtermp/docs/TEMconsolidated.pdf)
20. ASCE Report (2007), Journal of Materials in Civil Engineering, Vol. 19, No.3, March
Issue.
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Financing, A Case study: The Mumbai Pune Expressway”
22. Daily Business Line, The Hindu Group of Publication, Internet Edition, 22 July, 2000.
23. FHWA Report (2007) of International Program on “Long-Life Concrete Pavements in
Europe and Canada”.
24. Highway Statistics 1997 (1999), Office of Highway Information Management and
Office of Policy Development, Federal Highway Administration (FHWA).
25. Final Report (2005), TA-4516 (BAN) : Preparing the Second Rural Infrastructure
Improvement Project (RIIP-2), Financed by Asian Development Bank, LGED.
26. Parry, J.D. (1985), “Concrete Roads in Developing Countries”,
(http://www.unece.org/ trans/main/temtermp/docs).
27. Annual Report (2006) of Local Government Engineering Department (LGED).
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Railway Division, Infrastructure Development Component (IDC3), Ministry of
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29. George P.D., (2006), A report on “Life Cycle Cost Analysis and Discount Rate on
Pavements for the Colorado Department of Transportation” in Association with
FHWA.
30. Khan A.R. (2004); A concept analysis report on “Concrete Roads- for Better and
Safer Roads in Bangladesh” in association with FINNROAD Limited.
31. FINNROAD Limited (2008); A Technical Paper on “Concrete Roads- for Better and
Safer Roads in Bangladesh”.
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Road safety component, RHD, Ministry of Communication, Bangladesh.
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Road Transport”, Ministry of Communication, Bangladesh.
34. Wright P.H. (1996), “Highway Engineering”, Sixth Edition, John Wiley & Sons, Inc.
156
35. BUET Report (2005) on “Distress in Pavement on Nalka-Hatikamrul-Bonpara Road :
Their Causes and Remedies”, RHD, Ministry of Communication, by BRTC, BUET..
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Debogram, Bhulta, Nayapur Bazar up to Madanpur of Dhaka-Chittagong Highway”,
RHD, Ministry of Communication, by BRTC, BUET.
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Mixes”, BSc. Engg. Thesis, Department of Civil Engineering, BUET.
40. IFAD (International Fund for Agriculture Development) Monthly publication “ Issue
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42. American Concrete Pavement Association, www.pavement.com
43. American Concrete Pavement Association (ACPA) :
http://www.pavements4life.com/QDs/QD010P%20-%20Enlightened.pdf
http://www.pavements4life.com/QDs/QD016P%20-0Natural%20Advantage.pdf
http://www.pavements4life.com/QDs/QD008P%20-%20Precious%20Cargo.pdf
44. http://www.FHWA.ORG/llcp_07_04.cfm.htm
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157
APPENDIX-A
158
APPENDIX B
Location: Date: Time:
Name of Interviewer with designation:
Nome of Interviewer’s Organization:
SAMPLE QUESTIONNAIRE DESIGN
[Please write answer in the blank spaces below questions; if answers are not known or
interviewers are not willing to answer then tick the meaning ‘No Answer’]
1. The standard method of flexible pavement construction. No Answer
2. Why temperature is to be controlled at every stage of construction? No Answer
3. How to heat bitumen? No Answer
4. What are the consequences if bitumen is heated improperly and burnt during mix
operation? No Answer
5. At what temperature mix ingredients need to be heated, mix should be prepared, laid
and compacted? No Answer
6. Before compaction, what should be done if mix temperature is found to be lower
than the specified temperature? No Answer
159
7. Why does batch mix plant need calibration? No Answer
8. How to determine mix temperature in case of plant mix? No Answer
9. What extra precautions are to be needed during pavement construction in the winter
season? No Answer
10. Why carpeting/resurfacing typed maintenance work of flexible pavement need dry
roadway condition? No Answer
11. Why drainage condition is so sensitive for the flexible pavement? No Answer
12. Ideally what traffic management measures should be taken while roads are in under
submerged condition? No Answer
13. Why aggregate gradation is so important for flexible pavement construction? No
Answer
14. Why maintaining % void in the mix is so important? No Answer
15. What is the standard requirement of % void in the mix? No Answer
16. How to maintain the quality of flexible pavement construction? No Answer
17. What is the normal design life of flexible pavement? No Answer
160
18. What are the reasons behind the premature failure of flexible pavement? No Answer
19. Why construction of subsurface layers is so important? No Answer
20. What are the tests required for checking the quality of ingredients, level of
compaction of subsurface layers, density of wearing course? No Answer
21. Do you think frequent maintenance of flexible pavement cost a lot and there is a
scope of pilferage as there is no working drawing for maintenance job? No Answer
22. How flexible pavement does differ from rigid pavement? No Answer
23. Present practice of selecting pavement type. No Answer
24. When do you construct rigid pavement? No Answer
25. What are the underlying reasons behind not selecting rigid pavement as a good
alternative of flexible pavement? No Answer
161
APPENDIX C1 APPENDIX-C1
162
APPENDIX-C2