Performance evaluation of rigid and flexible pavement in Addis Ababa City Road Authority Projects

Academic Paper , 2022 , 94 Pages

Engineering - Civil Engineering

Transportation plays a vital role in facilitating economic development of a country. In particular, road transport acts as a means for the movement of people and agricultural products. Addis Ababa City Roads Authority executed both, constructing new roads as well as rehabilitate and maintain the existing road pavement. Therefore, a good pavement performance is essential for economic prosperity and industrial development. In recent days, Addis Ababa City Roads Authority is working on increasing the city roads coverage, but the biggest issue is the loss of performance and becoming a problem for the users in various aspects.

The purpose of this study is to assess purposely-selected road stretches that are rigid and flexible pavement type work on defect type extent and severity of the defects in detail and to perform Pavement condition Index calculations. According to ASTM D 6433 – 07, the results from this study show, that the pavement condition rating is considered as a serious case. The study shows, that flexible pavement has lots of potholes and alligator cracking with different severity, but the majority of the area is having active construction of multipurpose mixed-use buildings and the waste of the structure including concrete and other materials is disposed to the main road. Because of this, the manhole inlets cause stagnant water on the pavement and lead to deterioration of the pavement. The side roads are used as business areas, the plots don’t have parking area and almost all the drainages are blocked by the shop owners for the case of bad smell.

For the case of the rigid pavement, only cracking and patching small parts is seen on site and comparatively the rigid pavement does not have that much defect. Addis Ababa city roads Authority practiced pavement making from flexible to rigid and has already become better to minimize pavement deterioration as well as pavement maintenance cost. In addition, the city roads authority road asset departments should have followed and made continuous road evaluations and let the maintenance department take immediate action on the pavement before the deterioration got worse.

TABLE OF CONTENTS

DEDICATION

ACKNOWLEDGMENTS

LIST OF TABLES

LIST OF FIGURES

ACRONYMS

ABSTRACT

CHAPTER ONE INTRODUCTION
1.1 Background
1.2 Statement of the problem
1.3 Research Questions
1.4 Research objectives
1.4.1. General objective
1.4.2 Specific objectives
1.5 Scope and limitation of the study
1.6 Significance of the study

CHAPTER TWO LITERATURE REVIEW
2.1 General Overview
2.2. Functions of a pavement
2.3. Types of a pavement
2.3.1 Flexible Pavement
2.3.2 Rigid Pavement
2.4 Performance Evaluation of Rigid Pavement and Flexible Pavement
2.4.1 Why Measure Performance?
2.4.2 Developing Performance Measures
2.5 Comparison of Rigid Pavement and Flexible Pavement
2.6 Structural and functional differences of these two types of pavements
2.6.1 Layer system:
2.6.2 Load Distribution in Pavement
2.7 Layers within a typical flexible highway pavement
2.8 Causes of Road Deterioration
2.8.1. Environmental Factors
2.8.2. Traffic Volume and Loading
2.8.3. Material Properties and Composition
2.8.4. Construction Quality
2.8.5. Road Maintenance Standards
2.8.6. Age of Pavement
2.9. Pavement Distresses
2.10. Pavement Failure
2.11. Pavement Evaluation
2.11.1. Functional evaluation
2.11.2 Structural evaluation
2.11.3. Surface condition evaluation
2.11.4. Safety evaluation
2.12. Pavement Maintenance
2.12.1 Maintenance Types
2.1.2. Maintenance Strategies
2.13 Research gap

CHAPTER THREE RESEARCH METHODOLOGY
3.1 Research Design
3.2 Research Approach
3.3 Research Method
3.4. Pavement performance evaluation
3.4.1 Pavement condition survey
3.5. Study Area
3.6 Study period
3.7 Population and Sampling Technique
3.7.1 Population
3.7.2. Sampling Techniques
3.8 Data Collection Method
3.8.1 Desk Study
3.8.2 Pavement Condition Survey
3.8.3 Pavement Condition Index (PCI) Determination
3.8.4 Pavement Serviceability Index (PSI)
3.8.5 International Roughness Index (IRI)
3.9 Study variables
3.9.1 Dependent variables
3.9.2 Independent variables
3.10 Data processing and analysis
3.10.1 Software and Instruments
3.10.2 Condition survey
3.10 .3 Condition survey by the Pavement Condition Survey Vehicle (PCSV).
3.11 Data Analysis
3.11.1 Quantifying the distress and calculating Pavement Condition Index (PCI)
3.12 Ethical consideration
3.13 Data quality assurance

CHAPTER FOUR RESULTS AND DISCUSSION
4.1 Pavement condition survey result
4.1.1 Visual Inspection Data Collection Method in AACRA By Mobile Application
4.1.2 Visual Inspection Data Collection Method in AACRA By Manual Method
4.1.3 Pavement Condition Survey Vehicle (PCSV)
4.2 Pavement condition Index (PCI) of the Study Area
4.3 Pavement Serviceability Index (PSI) of the Study Area
4.4 International Roughness Index (IRI) of the Study Area

CHAPTER FIVE CONCLUSIONS AND RECOMMENDATIONS

Conclusion

Recommendation

Suggestions for Further Study

REFERENCES

APPENDICES

DEDICATION

I would like to dedicate my work as well the result to my beloved friendly and lifetime role model Mom, Alemtsehay W/Senbet, & Dad Eshetu Gebre at heaven. May your soul rest in peace.

ACKNOWLEDGMENTS

First, I would like to thank Almighty God, who has graciously blessed me all my life and given me the strength and resolve to complete this work. Nothing would have been possible without him.

Next, I would like to express my heartfelt gratitude to my advisor Prof. Emer T. Quezon, P.E., M.ASCE, PhD©, Dr.-Ing(hc) for the valuable support generosity in sharing his expertise and knowledge encouragement as well as the comments and corrections he has given me from the start till the end of this thesis paper.

Finally, I would like to thank my husband Dawit Getnet and our blessings Wudassie and Zimarie for their encouragement and assistance throughout my school time and those who are not mentioned their name here but assisted me by providing the relevant information that I needed to complete this thesis successfully once more I would like to say you God bless you all.

LIST OF TABLES

Table 1.1 Addis Ababa City Road Coverage type by Surface finish

Table 2.1: Recommended Unevenness Index for New and Old Pavements

Table 3.1 International Roughness Index (IRI) Condition Rank

Table 4.1 Pavement distress identification with respect to location

Table 4.2 Pavement Condition Index (PCI) Deduct Value Calculation Sheet

Table 4.3 Pavement Condition Index (PCI Sheet )

Table 4.4 Rigid Pavement and total Deduct Value (TDV)

Table 4.5 Pavement Condition Index (PCI) for rigid Pavement

Table 4.6 Asphalt pavement PSI Value

Table 4.7 International Roughness Index (IRI) Condition Rank

Table 4.8 International Roughness Index (IRI) Addis Ababa City Roads

Table 4.9 International Roughness Index (IRI) Study Area

LIST OF FIGURES

Figure 2.1 Asphalt Pavement (Flexible pavement)

Figure 2.2 Concrete Pavement (Rigid pavement)

Figure 2.3 Distribution of Load and Deflection of Pavements

Figure 2.4 The layered structure and cross-sections of two types of pavements

Figure 2.5 Load Distribution pavements

Figure 2.6 Distribution of Pressure under Single wheel

Figure 2.7. Categories of Pavement Maintenance

Figure 3.1 Location Map of the Study Area

Figure 4.1 AACRA Road Network Plan

Figure 4.2 AACRA Mobile Pavement Condition Inspection Applications

Figure 4.3 Mobile Filed Reporter Condition Inspection RMMS Processing

Figure 4.4 Shows Pavement deterioration at the Study Area

Figure 4.5 Pavement Condition Survey Vehicles Parts and System

Figure 4.6 Pavement Data Collection by PCSV on the study Area

Figure 4.7 Photo shows the road parking and crowdedness of the study area

Figure 4.8 PCI value designations

Figure 4.9 Total Deduct Value (TDV) curve for rigid pavement

Figure 4.9 Showing difficulties to drive on the study area (Asphalt Pavement)

ACRONYMS

illustration not visible in this excerpt

ABSTRACT

Transportation plays a vital role in facilitating economic development of a country. In Particular, road transport acts as a means for the movement of people and agricultural products. 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. Addis Ababa City Roads Authority (AACRA) executed both constructing new roads as well as rehabilitate and maintain the existing road pavement. Therefore, a good pavement performance is essential for economic prosperity and industrial development.

In recent days, Addis Ababa City Roads Authority is working in increasing the city roads coverage, but the biggest issue is the loss of performance (damaged sooner) and became problem of the users in multi dimension. The purpose of this study is too assess purposely-selected road stretches that are rigid and flexible pavement type work on defect type extent and severity of the defects in detail and performs Pavement condition Index (PCI) calculation

According To ASTM D 6433 — 07,The result from this study shows that the flexible pavement type from Gollagul building to Bole High school through Adey Stadium Has PCI value 22 and the pavement condition rating is considered as serious case and its color representation is Dark Red. While for the rigid pavement PCI value is 56, and the pavement condition rating is within the boundary from 55 — 70 with fair case, and its color representation is Yellow in Addition International Roughness Index (IRI)for the flexible pavement is around 6.423 with having poor status.

From the study flexible pavement has lots of pothole and alligator cracking with different severity range due to many reasons but the majored as the area is having active construction of multipurpose mixed-use buildings and the wastages of the structure including concrete and other materials are disposed to the main road and the manhole inlets these cause stagnant water on the pavement and lead to deterioration of the pavement and the road side are using as business areas the plots doesn't have parking area and almost all the drainage manhole in late are blocked by the shop owners for the case of bad smell from the in late. For the case of the rigid pavement only cracking and patching small due cut for utility is seen on the site and comparatively the rigid pavement does not have that much defect on the pavement.

Addis Ababa city roads Authority if practiced pavement making from flexible to rigid is became better to minimize pavement deterioration as well as pavement maintenance cost. In addition, the city roads authority road asset departments should have followed and made continuous road evaluations and let the maintenance department take immediate action on the pavement before the deterioration got worst.

Key Words (Drainage, Flexible pavement, Pavement Condition Index, Performance, Rigid pavement)

CHAPTER ONE INTRODUCTION

1.1 Background

In the context of Ethiopia's geography, patterns of settlement and economic activity, transport plays a vital role in facilitating economic development as 95% of the movement of people, and goods still carried out by road transport. In particular, road transport provides the means for the movement of peoples and agricultural products from rural areas to urban areas and movement of industrial goods, modern agricultural inputs, and peoples from urban areas to rural areas. Road transport also provides a means for the utilization of land and natural resources, improved agricultural production and marketing, access to social services, and opportunities for sustainable growth¹.

Addis Ababa is located in the central part of Ethiopia. It is the capital city of Ethiopia and the seat of African Union and other international organizations. To give adequate infrastructure service to the occupant's AACRA allocates huge amount of Budget and resource to expand and rehabilitate the existing road performance.

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. Therefore, a good pavement performance is essential for economic prosperity and industrial development.

According to Addis Ababa City Roads Authority Yearly road inventory report, the city is getting approximately 41% of the Paved's flexible type.

Table 1.1 Addis Ababa City Road Coverage type by Surface finish

illustration not visible in this excerpt

Source: - Addis Ababa City Roads Authority 2013 Road Asset Inventory Report

As the demands on the national highway network continue to grow, so does the need for construction and maintenance practices that will help extend the life of pavements. No pavement has been constructed that does not need maintenance. Many community associations find out too late that proper maintenance could have prevented costly replacements.²

Road deterioration due to lack of maintenance has become a growing issue in a number of developing countries. The problem has been discussed and the results of a lack of maintenance have been well defined and quantified. Nevertheless, the extent of the problem is not fully appreciated and the solutions are still not commonly understood. Equally, the measures required to rectify the shortcomings are under­estimated. These include the scale of support and capacity development required, and the time-scale necessary for establishing an effective road management system. Such a system should halt road network deterioration and ensure that financial, material and human investments are made in a manner which maintains the quality and value of the assets and, in addition, improves the network in relation to the demands and priorities of the users².

The pavement structure should be able to provide a surface of acceptable riding quality, adequate skid resistance, favorable light reflecting characteristics, and low noise pollution. The ultimate aim is to ensure that the transmitted stresses due to wheel load are sufficiently reduced, so that they will not exceed bearing capacity of the sub grade. The roads of the earlier times depended solely on stone, gravel and sand for construction and water was used as a binding agent to level and give a finished look to the surface.³

1.2 Statement of the problem

Now a day's AACRA is engaged in increasing Addis Ababa city road coverage to reach 30 % within 2015 E.C³. The headache is what to do after the ribbon has been cut and the projects has started to work. AACRA carries out lots of road maintenance activities every year after evaluating roads of the city. However, the maintenance is not conducted properly; out of the classified 7613.59 km of the road network, only 56% of the roads reported as good³. Therefore, the increasing the road coverage and preserving the existing pavement condition shall be done simultaneously to increase the service life of the road.³

The general objectives of roadway pavement maintenance are to provide a safe roadway surface, preserve the state's capital investments in the pavement and to maintain a riding quality satisfactory to the traveling public. Maintenance is intended to slow down this deterioration and should begin on the first day after the road improvement works are completed. In practice, the effect of regular and timely maintenance is to increase the life of the road by putting off the date at which it needs to be reconstructed.⁴

The type of deterioration present in the pavement should be considered for determining whether it has a functional or structural deficiency³ so that appropriate overlay type and design can be developed. Structural failure arises from the conditions that adversely affect the load carrying capability of the pavement structure. Inadequate thickness, cracking, distortion, and disintegration cause structural deficiency.

Since the study area is in Addis Ababa, Addis Ababa City Roads Authority, the road construction site, the visible gap on the issue will be the main reason of pavement performance failures and the remedies that the organization tries to solve the problem.

1.3 Research Questions

1. What are different stress type severity level and distress extent along the study area?
2. What are the numerical Pavement condition indexes (PCI) according to ASTM D6433-07 of the study area?
3. Which pavement type is better with respect to PCI value?

1.4 Research objectives

1.4.1. General objective

The main objective of this research is to assess pavement performance and its failure in AACRA road projects' long time serviceability by assessing the performance evaluation of rigid and flexible pavement in selected road sections in Addis Ababa work on PCI value based on the ASTM D-6433-07 study type of failure reasons for the failure of the road projects in the city.

1.4.2 Specific objectives

1. To identify the different distress types, severity level and distress extent along the selected road sections.
2. To determine the Pavement Condition Index according to their quantitative measurement and their corresponding numerical indicator according to ASTM D 6433-07 for both pavement types.
3. To determine the pavement with good quality with respect to PCI value and make suggestions for better pavement type.

1.5 Scope and limitation of the study

The study focuses on the evaluation of the performance of two alternative pavement types based on different criteria including ERA and AACRA specifications and actual site visual supervision on the distressed road section of the study working with different parameters like PCI ,PSI,IRI and interpret the results for sustainable road construction projects.

The Study focuses mostly on identification of the different distress types on the study area define the types of failure in AACRA projects study in their respective cases and the measure that the city roads' authority is adopting to minimize or eradicate the case for having sustainable infrastructure provision in the city and observe road construction projects not is fully quantifiable in this study.

This study area is selected due frequently history in maintenance of the road and even the distress type is seen almost throughout the year and gets worst in the rainy season.

1.6 Significance of the study

In the area of road construction, especially in Addis Ababa City Roads Authority proper planning of projects is vitally important to highway organizations (authorities) as their construction program outlines how highway funds are to be spent over time and to be sustainable in its serviceability for the comfort of road users, any deviation from the established program often brings a quick response from the public, the press, and politicians. When this occurs, the highway organization loses credibility. On the other hand, if a highway organization can produce realistic program estimates that it can attain, then the agency's image kept enhanced.

Therefore, it is the Authorities' responsibility to make an accurate project planning in the selection of economical pavement materials for the construction of sustainable roads for allocation of justifying budgets.

It is expected that the research findings would help in a better way of understanding the problems why different pavement projects failed for performance and what the root cause and the remedies that AACRA is adopting associated with the construction of flexible pavement. Besides, it is also expected that the research findings would help explore the governing case of pavement performance cases in pavement construction in Ethiopia, Addis Ababa City Roads Authority (AACRA).

Thus, the beneficiaries of this research area. The public who live and work around the study area. The implementing authorities AACRA road construction department, Consulting and construction firms plus practicing Engineers, Educational institutions, which use the information for academic purposes, Investors to focus on manufacturing of ready mix concrete for pavement works, Other researchers who will work in relation to pavement performance, etc.

CHAPTER TWO LITERATURE REVIEW

2.1 General Overview

The purpose of literature review was to study the theoretical background on performance evaluation of rigid and flexible pavement construction in AACRA projects through the journals, books, references, internet, and articles. This chapter investigates the causes of pavement deterioration, pavement evaluation, and the remedies that AACRA is applying to solve the problem and road maintenance experience of other countries. This investigation is important as it provides baseline for evaluation of present AACRA’S road projects performance by assessing different scientific principles and international experience around the world.

2.2. Functions of a pavement

Pavement is the actual travel surface especially made durable and serviceable to withstand the traffic load commuting upon it. According to South African National Roads Agency, the primary functions of a pavement are to⁷

a) Provide a reasonably smooth riding surface: A smooth riding surface (Low Roughness) is essential for riding comfort, and over the years, it has become the measure of how road users perceive a road.
b) Provide adequate surface friction (skid resistance): In addition to a riding comfort, the other road user requirement is that of safety. Safety, especially during wet conditions can be linked to a loss of surface friction between the tyre and the pavement surface.
c) Protect the sub grade: The supporting soil beneath the pavement is commonly referred to as the sub grade, should it be over-stressed by the applied axle loads it will deform and lose its ability to properly support these axle loads. Therefore, the pavement must have sufficient structural capacity (strength and thickness) to adequately reduce the actual stresses so that they do not exceed the strength of the sub grade.
d) Provide waterproofing: The pavement surfacing acts as a waterproofing surface that prevent the under laying support layers including the sub grade from becoming saturated through moisture ingress. When saturated, soil loses its ability to adequately support the applied axle loads, which will lead to premature failure of the pavement.

2.3. Types of a pavement

2.3.1 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 figure 2.1. These types of pavements 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 this "flexing." A flexible pavement is a structure that maintains intimate contact with, distributes loads to the sub grade (Figure 2.1), and depends on aggregate interlock, particle friction, and cohesion for stability¹⁶.

These images were removed due to copyright reasons.

Figure 2.1 Asphalt Pavement (Flexible pavement)

Road flexible pavements intended to limit the stress created at the sub grade level by the traffic traveling on the pavement surface, so that the sub grade is not subject to significant deformations. In effect, the concentrated loads of the vehicle wheels spread over a sufficiently larger area at sub grade level. At the same time, the pavement materials themselves should not deteriorate to such an extent as to affect the pavement's riding quality and functionality. These goals must achieve throughout a specific design period. Pavements do deteriorate, however, due to time, climate, and traffic. Therefore, the pavement design's goal is to limit, during the period considered, deteriorations that affect the riding quality, such as, in the case of flexible pavements, cracking, rutting, potholes, and other such surface distresses to acceptable levels¹⁶. At the end of the design period, a strengthening overlay would normally be required, but other remedial treatments, such as major rehabilitation or reconstruction, may be required.

The design method aims to produce a pavement that will reach a relatively low level of the deterioration at the end of the design period, assuming that routine and periodic maintenance are performed during that period. It is understandable that what constitutes an “acceptable riding quality” depends on what the users expect. For roads with higher traffic, higher geometric standards, and higher vehicle speeds, consequently, less distress will be expected and considered acceptable. Hence, for instance, trunk and link roads may be expected to offer some higher ride ability than access, collector roads, etc., in a similar design period. Similarly, gravel roads may be expected to offer a lower riding quality. These differences are implicitly considered in the design, although in broader terms rather than in precise measurable economic terms¹⁷.

2.3.2 Rigid Pavement

Rigid pavements (also called concrete pavements), as the name implies, are rigid and very strong in compression. Mainly a concrete slab, unlike flexible pavements where successive layers of the pavement contribute cumulatively, contributes the strength of the pavement. The roughs surface required for an adequate resistance to skidding in wet conditions can be provided by dragging stiff brooms transversely across the newly-laid concrete or by cutting shallow randomly spaced grooves in the surface of the hardened concrete slab. As illustrated in picture 2.2, which is generally used to reduce or eliminate joints. The rigid pavement is a rigid structure that distributes the wheel loads over a wider area to the sub grade and depends on the concrete slab strength for stability¹⁶.

These images were removed due to copyright reasons.

Figure 2.2 Concrete Pavement (Rigid pavement)

Pavement grants friction for the vehicles thus providing comfort to the driver and transfers the traffic load from the upper surface to the natural soil. Pavements usually fall into two broad categories namely flexible and rigid pavements⁸.

Transport and mobility are essential for economic and social development. For this reason, developed countries have devoted considerable resources to the development of high-quality transport networks, which need to be adequately maintained. Current road construction methods lead to significant maintenance requirements, which can only be met at a very high cost. The continued growth in road traffic and axle loads and the pressure to restrain government spending put growing pressure on road authorities to develop new solutions. At the same time, the cost to economies due to congestion and disruption during road works on high volume roads has become unacceptably high⁶.

There are growing pressures for long-life road infrastructures that require minimal maintenance. Pavements are the critical elements of an efficient highway transportation system for moving people and goods. Without well-performing pavements, the transportation infrastructure cannot effectively function, road users suffer (in terms of increased costs, travel time, and unsafe roads) and the overall economy suffers (in terms of higher costs for goods and commodities)⁷.

Modern societies cannot function without mobility, and mobility requires well­performing pavements⁸. In recent years, innovation in the road sector has focused on economic and organizational structures, while changes in road paving techniques have been much less dramatic. Rather, they have at best, been incremental. Yet, in order to optimize national highway budgets, whole-life costing methods are increasingly used to determine how, where and when to best spend budget funding for road construction and maintenance. Within this framework, the shift to full maintenance contracting has helped reduce costs, and the adoption of long-term contracts has helped establish an environment in which the development of more durable pavement types could be stimulated⁸.

From the paved roads in Addis Ababa city, rigid pavement construction is limited whereas the majority of pavements are Flexible pavements. Therefore, focus will be concentrated on flexible pavements performance. Flexible pavements comprised of several layers of carefully selected materials designed to gradually distribute loads from the pavement surface to the layers underneath⁹.

One of the main drawbacks of rigid pavement is the high initial cost of construction. However, in consideration of several functions and operational advantages and above all from the viewpoint of life cycle cost, the cement concrete roads are becoming popular around the world. The advent of modern techniques in the production of durable concrete, price escalation of petrol, and, above all, private sector participation in road infrastructure development made the selection of concrete pavement in many high standard roads 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 the franchise without the need for major repairs, overhauls, or rehabilitation. However carefully constructed, a bituminous pavement 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 ]. Nowadays reduction of maintenance works; particularly on busy roads is one the main concerns of traffic management measures.

There has been a historical difference in whether Hot Mix Asphalt (flexible) pavements are more economical or less economical over time than Portland Cement Concrete (rigid) pavements. Even experienced state highway agencies and highway engineers disagree on the subject⁹.

Ethiopian has been undertaking massive development programs to eradicate the country's poverty problems and to bring up the country to the level of middle income countries in 2025 G.C. Aware of the road infrastructure development as the backbone and the blood artery for all economic, social progress, due emphasis has been given to the implementation of the Road Sector Development program (RSDP) since 1997¹⁰.

In Ethiopia, very few and short kilometer lengths of road projects are constructed with rigid pavement viz; in Oromia (Chancho-Derba-Bocho and Beseka road), Addis Ababa (Rehabilitation projects) and Tigray (Michew -Adigudem), of which Beseka and Addis Ababa rehabilitation projects were completed¹⁰.

Even though there are newly emerging cement and reinforcement production factories in Ethiopia that can avoid foreign currency to buy materials for flexible pavement, only few and small-scale concrete pavement projects have been undertaken in the country. Among these projects, Beseka Road, a one-kilometer long that was considered the first cement concrete pavement in the history of the Ethiopian road construction project. In the last seventeen years (1997-2014 G.C), the total length of rigid pavement constructed was only 2.3 kilometers while about 99.9% or 12,640 kilometers are flexible pavement¹¹.

According to AACRA Road asset yearly road inventory report of 2010 E.C the city pavement coverage is about 41% and accordingly the pavement materials is bituminous and have seen lots of roads are deteriorating and malfunctioned.

2.4 Performance Evaluation of Rigid Pavement and Flexible Pavement

Performance of pavement can be generally defined as to the change in their condition or function with respect to age. It can also be indicative of the ability of a pavement to carry the intended traffic and satisfy the environment during the design life, both functionally and structurally. With the increased economic and development activities in a country, the traffic has increased multi fold during the last 3 decades resulting in the overstressing of road network. The development of higher stresses leads to performance failure of the pavements. If the pavements fail to carry the design loads satisfactorily, then the failure is of structural type. It is of functional type, if the pavement does not provide a smooth riding surface. The uneven surface not only causes discomfort, but also increases the Vehicle Operating Cost (VOC), thus influencing the overall transportation cost. This chapter gives a broad outline of the importance of pavement performance evaluation, type of models, applications of performance models in other countries for their Pavement Management System and the research studies carried out so far.¹²

The performance evaluations of any flexible pavement are analyzed through structural evaluation and functional evaluation. Nondestructive testing methods can evaluate structural or functional condition. The performance evaluation of pavement can cover many aspects including assessment of traffic safety on road, evaluation of road surface condition, structural adequacy of pavement and ride-ability of pavement surface. Thus, the following characteristics are generally used to performance evaluation of pavement.¹³

- Skid resistance
- Surface distress of pavement
- Ride-ability of pavement surface
- Pavement deflection

In the last two decades, interest has grown in the art and science of performance measurement, particularly as it applies to road and transportation systems. The topic is well documented in the literature with significant treatises from many organizations around the world, including the US Federal Highway Administration (FHWA) and the Transportation Research Board (TRB), the Organization for Economic Cooperation and Development (OECD), Austroads and the Transportation Association of Canada (TAC). In general, the available research and practice reports provide perspectives as to why performance measurement is important, how it should be undertaken, and what is typically measured. The following sections summarize information extracted from some key references on the theory of performance measurement."¹⁴

The main deteriorations include cracking, potholes, rutting along wheel path and roughness of road surface. The physical manifestation of the internal damage (cracking, rutting, potholes etc.) is known as distress. Percentage of distress gives an indication of the pavement condition. Different modes of distress occur either independently or simultaneously with mutual interaction. For planning purpose, the distress can be based on distress type and the most important are those, which trigger decisions.

The distresses can be broadly classified as:¹⁰

i. Fatigue Cracking

- Load -Associated cracking
- Thermal cracking (due to freeze and thaw)
- Longitudinal cracking at edges due to moisture movement through shoulder
- Deflection cracking

ii. Load associated pavement distortion

- Transverse distortion or rutting
- Longitudinal distortion or roughness

iii. Non - load associated pavement distortions due to foundation movements

iv. Disintegration (raveling, stripping, potholing etc.)

2.4.1 Why Measure Performance?

The ultimate purpose of measuring performance is to improve transportation services for customers¹⁴. Within that simple statement, two important emphases are contained: one regarding customers and the second regarding improving services. Both of these emphases underlie most of the reasons cited in the literature for the increasing importance of performance measurement to transportation agencies¹⁵. Discussing the customer focus during the 2000 Transportation Research Board conference on performance measures, Pickrell and Neumann (2001) explained that publicly-funded agencies have come under increasing pressure to be accountable to the public the owners and customers of the agencies and the transportation systems they deliver. In fact, the need to be accountable to the public is the reason most commonly offered in the literature for performance measurement. There is a growing expectation that the public should be advised on the performance of the transportation system upon which it depends. As well, there is a need to report how public funds are used to maintain the system and the effect of expenditures upon it. Performance measurement is essential to that process. It is interesting to note that the use of performance measurement is considered useful not only for reporting to the public but also for communicating with the public. It is seen as a tool that can help to educate the public as well as senior decision makers and legislators regarding the importance of transportation and the merits of making appropriate investments in the system (Federal Highway Administration, 2004).

2.4.2 Developing Performance Measures

Transportation departments are fortunate to have a wealth of data available to them regarding the services they provide and the infrastructure they build, operate, and maintain if they try to collect the data extensively. However, in a data-rich environment, the challenge is to determine how best to gather, analyze and present the data so that it is meaningful to stakeholders, and this is especially important for performance measures that are reported to or used by a broad range of audiences. In developing a performance measurement process and implementing it as a management system, the selection of the “right” performance measures is a critical step. When developing performance measures, the research emphasizes that the process should begin by defining an agency's vision, its mission and strategic objectives in our case AACRAs vision is “Modeling Addis Ababa in African cities by providing and maintaining comprehensive and accessible road infrastructure in 2022 .” And its mission is “Building Asphalt roads, Gravel Access Roads, Coble Stone pavement Roads, Drainages, Bridges and concrete roads and making that for residents of Addis Ababa remarkably enhance the regular activities, there of using hi- tech and low cost being constructed by contractors and own force at improving level on time available for public service.” While these may be long-range in focus, performance measures used by an agency must be related to those broad goals. Long­term strategic goals can be translated into specific annual goals, against which performance is measured. Policy-makers and agency staff must be educated to understand the performance measures and to accept the link between them and the agency's goals (Poister, 1997).In the case of AACRA when we state its power and duties some of them are

- Initiate policies and laws with regard to road network, construction, protection and use of roads
- Determine design standards for road and implement same
- Prepare long term, medium and short term plans and programs with respect to the construction of roads and other related activities, and implement same upon approval
- Carry out or cause the carrying out of feasibility study and implement
- Prepare design for the construction of roads or cause its preparation through qualified consultants
- Construct roads on its own or have them construct through contractors
- Determine the criteria for the selection of consultants and contractors for roads to be constructed by other bodies
- Prepare and cause the preparation of work consultancy service contracts, conclude contracts and see to it that there is supervision with (a contractor an ensuring that works are executed as per contracts conclude and supervise same)
- Design or cause the designing of traffic signs with regard to roads, collect information from appropriate government offices and place traffic signs on roads, and inform to concerned offices of that they do follow up and implement accordingly
- Determine the size of land required for pedestrian roads and standards for the construction thereof, and it shall also construct, cause the construction of and protect pedestrian side walks'
- See to it that the personnel necessary for the authority are trained and establish training institutions.

As we observe from the list of duties there are no duties regarding performance evaluation and measures. Performance measures should cover the full range of an agency's strategic objectives, but should nonetheless be few in number. In Japan, for example, the national ministry has established a core set of 17 performance measures (Federal Highway Administration, 2004). Limiting the selection of measures to those that reflect the issues that are important to an agency will simplify data collection and reporting. It will also increase the likelihood the measures will be understood by the public and used effectively by agencies.

In summary, the list of performance measures that could be adopted by a transportation agency to evaluate its road network is essentially limitless. There is no one measure, or one set of Performance Evaluation of Addis Ababa City Road, that could be identified as the “best” for all cases. Furthermore, although there are many common issues to be considered, there is not just one good way to develop a set of performance measures or establish a performance measurement system. In each case, the performance measures used must depend on the specific conditions of an agency, its goals, its resources, and its audience. Therefore, for Addis Ababa case AACRA must consider the above issues and incorporate performance measures in its duties.¹⁵

2.5 Comparison of Rigid Pavement and Flexible Pavement

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 the 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 a cement concrete slabs life is limitless and can be prolonged to almost any desired period. This is achieved by careful design, construction under strictly controlled conditions, careful monitoring of the performance, and adequate maintenance. However, several distinct points differ concrete pavement from 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 a different point of view is described in this chapter. Highways are hard-surfaced structures/pavements that allow vehicles with 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 rigid¹⁶.

2.6 Structural and functional differences of these two types of pavements

2.6.1 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 the sub-base course. Base and sub base courses are usually gravel or stone. These layers rest upon a compacted subgrade (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 subgrade. Figure 2.4 represents the layered structure and cross-sections of two types of pavements¹⁶.

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Figure 2.3: Distribution of Load and Deflection of Pavements

This image was removed due to copyright reasons.

Figure 2.4:- The layered structure and cross-sections of two types of pavements.

2.6.2 Load Distribution in Pavement

Flexible pavement having a 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 the load to the sub grade¹⁵.

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Figure 2.5 Load Distribution pavements

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Figure 2.6 Distribution of Pressure under Single-wheel

Load for Flexible Pavements 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 a 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. Therefore, no surface deformation occurs when wheel load passes over it¹⁵.

2.7 Layers within a typical flexible highway pavement

Surfacing - This is the uppermost pavement layer and will normally consist of a bituminous surface dressing or a layer of premixed bituminous material. Where premixed materials are laid in two layers, these are referred to as the wearing course and binder course.

Road base - This is the main load-spreading layer of the pavement. It will normally consist of crushed rock or gravel, or of gravel soils, decomposed rock, sands and sand-clays stabilized with cement, lime or bitumen.

Sub-base - This is the secondary load-spreading pavement layer underlying the road base. It will normally consist of a material of lower quality, than that used for the road base, such as unprocessed natural gravel, gravel-sand or gravel-sand-clay. This layer also serves as a separating layer preventing contamination of the road base by the sub grade material and, under wet conditions; it has an important role to play in protecting the sub grade from damage by construction traffic. Capping Layer - (Selected or improved sub grade) - where very weak soils are encountered, a capping layer is sometimes necessary. This layer may consist of better quality sub grade material imported from elsewhere or existing sub grade material improved by mechanical or chemical stabilization.

Sub grade - This is the upper layer of the natural soil which acts as the pavement foundation. It may be undisturbed local material or may be soil excavated from elsewhere and placed as fill. In either case, it is compacted during construction to give added strength.

2.8 Causes of Road Deterioration

Road deterioration is caused by the effects of the physical environment, traffic, material properties, and quality of road construction, design standards, and the age of the pavement. The details are discussed in the following paragraphs.

In general speaking road pavement failure is caused by load related and moisture case.

2.8.1. Environmental Factors

Climatic factors such as rainwater, solar radiation, temperature, soil type and terrain may cause roads to deteriorate. Rainwater can alter the moisture balance in the sub grade of a road with clayey and silty soils. This may cause swelling and shrinkage resulting in reflective cracking and heaving in the road surface. Sunlight may cause a continuous, slow hardening action on bituminous surfaces. This can increase the cracking process of the surface chip seal. Seasonal changes in temperature or night and day temperatures may cause expansion and contraction of the carriageway. This may progressively cause fatigue, failures, and reflective cracks in the road surface¹¹.

2.8.2. Traffic Volume and Loading

Roads are structures built to carry and sustain vehicular loads. Therefore, traffic is an important factor that influences pavement performance. The impact of traffic on the deterioration of pavements is caused by vehicle loads and volume. Every vehicle, which passes over a road, causes a momentary but significant deformation in the road structure. This is determined by the magnitude of each of its axle loads, the spacing between the axles, the number of wheels, the contact pressures of the tires and the travelling speed. The passage of many vehicles has a cumulative effect which causes repeated flexing of the pavement leading to fatigue, crazing and structural failure¹².

2.8.3. Material Properties and Composition

The choice of materials used for the construction of pavement layers may also cause road deterioration. This is due to inherent variability in the materials used for road construction in terms of soil properties such as strength or load bearing capacity, gradation, mix properties, elastic and resilience modulus. Poor choice of materials used for pavement layers can have a drastic effect on the strength of the layers and their subsequent performance¹¹.

2.8.4. Construction Quality

The quality of road construction if not built to the desired specifications can also facilitate road deterioration. For example, failure to obtain proper compaction, improper moisture conditions during construction, poor quality of materials and inaccurate layer thickness (after compaction) all directly affect the performance of a pavement¹⁰.

2.8.5. Road Maintenance Standards

The rate of pavement deterioration is directly affected by the maintenance standards applied to repair road defects. When a maintenance standard is defined, it imposes a limit to the level of deterioration that a pavement is allowed to attain. Low maintenance standard therefore causes roads to deteriorate at a faster rate,¹¹.

[...]

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¹ Ethiopian Roads Authority, Sixteen Years Performance Assessment Report of RSDP (third year of Phase IV), October 2013, Addis Ababa, Ethiopia.

² Project Administration Service, Operation and Management Improvement Study, City of Addis Ababa, September 1984.

³ A study on the performance of flexible Pavements on mature soil Subgrades,By SREEDEV B.G,2014

⁴ African Development Fund Project Completion Report Road Maintenance and Rehabilitation Project Ethiopia (Transportation Division Infrastructure Department – North,South and East August-2005)

⁵ Finote Addis ,Addis Ababa City Roads Authority, Meskerem/2011E.C Yearly Magazine.

⁶ Gebeyaw Assefa Cement Concrete as an Alternative pavement material Over Asphalt Concrete in Arterial Roads of Ethiopia; Life Cycle Cost Comparison and Economic Analysis. A Thesis Submitted to the School of Graduate Studies in Partial Fulfillment of the Requirements for the Degree of Master of Science in Civil Engineering (Construction Technology and Management), September 2015.

⁷ Organization for Economic Co-Operation and Development (OECD), Economic Evaluation of Long-Life Pavements, Research Paper Report, Paris, France, 2005.

⁸ South African National Roads Agency Ltd, http://www.nra.co.za

⁹ FHWA, Construction Analysis for Pavement Rehabilitation Strategies (CA4PRS) Website:http://www.fhwa.dot.gov/crt/lifecycle/ca4prs.cfm,Washington,DC,2009www .aboutcivil.org, 2014

¹⁰ ENGINEER, J.N.V.C., Pavement Life-Cycle Cost Studies Using Actual Cost Data. 2005.

¹¹ Yonas Ketema, Prof. Emer T. Quezon, Getachew Kebede. Cost and Benefit Analysis of Rigid and Flexible Pavement: A Case Study at Chancho –Derba-Becho Road Project, International Journal of Scientific & Engineering Research, Volume 7, Issue 10, October-2016 181 ISSN 2229-5518.

¹² Johon Watson,BSc. M.I.C.E, Highway construction and maintenance 2ndedition, (1994)

¹³ Federal Democratic Republic of Ethiopia,Ethiopian Roads Authority Design Manual,2002

¹⁴ Opinion, E. www.ethiopianopenion.com. 2014 [cited 2014].www.iosrjournals.org,

¹⁵ A study on the performance of flexible Pavements on mature soil subgrades,BySREEDEVI B.G ,2014

¹⁶ International Journal of Advance Engineering and Research Development Volume 4, Issue 2, February -2017, A Review on Performance Evaluation of Flexible Pavement Hardik V. Aghera, Jyoti Mandhan, Ravindra V. Solanki

• College: Ambo University (Technology)
• Course: Construction Engineering and Management
• Author: Genet Eshetu (Author)
• Publication Year: 2022
• Pages: 94
• Catalog Number: V1355907
• ISBN (PDF): 9783346875082
• ISBN (Book): 9783346875099
• Language: English
• Tags: evaluation