Interim Guide to Evaluation and Rehabilitation of Flexible Pavements

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Interim Guide To Evaluation And Rehabilitation Of Flexible Road pavements.

Cawangan Jalan, Ibu Pejabat JKR, K.L

IKRAM can accept no responsibility for mis-appropriate use of this manual. Engineeringjudgement and experience must be used toproperly utilise the principles and guidelinesoutlined in this manual taking into accountavailable equipment, local materials and condi-tion.

Photographs and drawings of equipment in thispublication are for illustration only and do notimply preferential endorsement of any particu-lar make by IKRAM.

PREFACE

This guide is written primarily as an interimguideline for practising road engineers andthose who are involved in road maintenanceactivities. An attempt has been made to drawtogether all the information required in theevaluation and rehabilitation of flexible roadpavements within one volume.

It is hoped that the background informationgiven, together with the review of currentresearch work carried out at IKRAM, particu-larly in relation to the pavement behaviour and

performance under Malaysian climatic condi-tions will make it of interest to those engagedin the research aspects of road engineering andin teaching the subject.

Some of the practical experiences on which the guide is based have been gained under

Malaysian climatic conditions. However, dueto limitations, some references were drawnfrom various overseas agencies in particular theTransport and Research Laboratory (TRL),U.K.

Although it is the intention of the authors tomake this guide as comprehensive as possible,it has not always been possible to do so as theperformance of flexible road pavements inMalaysian environment is not yet fully under-stood. However, to facilitate the early under-standing of the present practices, this interimguide has been produced. The authors are

FOR INTERNAL USE ONLY

INTERIM GUIDE TO EVALUATION AND REHABILITATION OF FLEXIBLE ROAD PAVEMENT

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aware of the necessary work still needed tocomplete this guide and are, at present, under-taking research to make this possible.

The chapters have been written so that they canbe read and understood largely independent ofeach another, but where necessary cross-refer-encing to specific paragraphs should make thereader's task easier.

This guide aims to be factual but some expres-sion of opinion is inevitable where gaps inknowledge exist.

ACKNOWLEDGEMENTS

This guide is prepared by the PavementResearch Unit

Head: Ir. Mohamed Shafii Mustafalnstitut Kerja Raya Malaysia (IKRAM).

The authors of this guide are :

- Mohd. Sabri Hasim- Abd. Mutalif Abd. Hameed- Ir. Koid Teng Hye- Ahmad Fauzi Abdul Malek - Ir. Mohamed Shafii Mustafa.

This document forms part of a series of guide-lines on the design, construction and mainte-nance of flexible road pavements which thePavement Research Unit is producing as part oftheir studies.

This guide was reviewed by a Committeeheaded by the Director of IKRAM :

Ir Ng Chong Yuen. Other members of theCommittee were :

- Ir Han Joke Kwang (IKRAM)- Ir. Aik Siaw Kong- Ir. Tai Men Choi- Ir. Zainol Rashid Zainuddin

Of Roads Branch (JKR Headquarters) andIr Abdul Shokri Mohd. Dalian (JKR Selangor).The authors would like to express their heart-

felt thanks to the Director General of PublicWorks Malaysia for his permission to publishthis guide. Thanks are also due to Tan KeeHock and Mooi Jiann Liang for their assistancein preparing this guide. Finally, special thanksare due to C. R. Jones of the Overseas Centre,Transport Research Laboratory, U.K. for hisadvice on specific topics of the guide.

CHAPTER 1 : INTRODUCTION

1.1. BACKGROUND

1.1.1 Brief history of Malaysian road pavements 1.1

1.1.2 The need for engineering evaluation of the roadpavement 1.1

1.1.3 Economic analysis as a part of the engineering decision making process 1.2

1.2 SCOPE OF THE GUIDE 1.3

1.2.1 Limitation of the Guide 1.4

1.3 OBJECTIVES 1.4

CHAPTER 2 : PAVEMENT BEHAV-IOUR AND PERFORMANCE

2.1 PAVEMENT COMPONENTS AND MATERIALS

2.1.1 Surfacing 2.1

2.1.2 Road-base 2.1

2.1.3 Sub-base 2.1

2.1.4 Subgrade 2.2

2.2 FUNCTIONS OF FLEXIBLE PAVEMENT 2.2

2.2.1 Road users requirements 2.2

2.2.2 Engineering requirements 2.2


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Interim Guide To Evaluation And Rehabilitation Of Flexible Road Pavements.


2.3 FAILURE DEFINATIONS 2.3

2.3.1 Failure modes 2.3

2.3.2 Failure manifestation 2.3

2.3.3 Failure mechanisms 2.3

2.4 PAVEMENT BEHAVIOUR 2.3

2.4.1 Behaviour of thin surfacing 2.5

2.4.2 Behaviour of component lavers in a typical flexible pavement 2.5

2.5 PAVEMENT PERFORMANCE 2.9

2.5.1 Terminal condition 2.9

2.5.2 Users requirements 2.9

2.5.3 Engineers and managers requirements 2.9

2.5.4 Empirical interpretation of performance 2.12

2.5.5 Mechanistic interpretation of performance 2.12

2.5.6 Future undertakings 2.15

2.6 REFERENCES 2.15

CHAPTER 3 : PAVEMENT EVALUATION

3.1 GENERAL 3.1

3.1.1 Project initiation 3.1

3.1.2 Physical condition assessment 3.1

3.1.3 Non-destructive testing (NDT)3.1

3.1.4 Analysis and rehabilitation design 3.3

3.1.5 Selection of remedial measures 3.3

3.1.6 Cost analysis 3.3

3.1.7 Implementation 3.3

3.2 INITIALASSESSMENT 3.3

3.2.1 Surface condition assessment 3.4

3.2.2 Drainage assessment 3.4

3.2.3 Prelirninarv analysis, sectioning 3.7

3.3 DETAILASSESSMENT 3.8

3.3.1 General 3.8

3.3.2 Choice of NDT devices 3.9

3.3.3 Choices of NDT analysis techniques 3.14

3.3.4 Test interval, variability and accuracy level for structural assessment 3.24

3.3.5 Surface evaluation 3.25

3.3.6 Other key factors to consider during evaluation 3.26

3.3.7 Detail material investigation 3.29

3.4 REFERENCES 3.31

CHAPTER 4 : TRAFFIC LOADING ASSESSMENT

4.1 GENERAL 4.1

4.2 TRAFFIC CATEGORIES 4.1

4.2.1 Normal traffic 4.1

4.2.2 Generated traffic 4.2

4.2.3 Diverted traffic 4.2

4.2.4 Special traffic 4.2


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4.3 TRAFFIC AND AXLE LOAD SURVEYS 4.2

4.3.1 Specific survey method 4.2

4.4 FORECASTING FUTURE TRAFFIC 4.4

4.4.1 Base data 4.4

4.4.2 Methods of predicting growth and compounding 4.4

4.4.3 Estimating damaging effect 4.4

4.4.4 Sensitivity and accuracy 4.4

4.5 EXAMPLES 4.6

4.6 REFERENCES 4.10

CHAPTER 5 : METHODS OF REHABILITATION

5.1 SELECTION PROCEDURE 5.1

5.2 REHABILITATION OPTIONS 5.1

5.3 RESTORATION 5.4

5.3.1 Rejunevating 5.5

5.3.2 Crack Sealing 5.6

5.3.3 Cutting and Patching 5.7

5.3.4 Thin asphalt overlay 5.11

5.3.5 Surface recycling 5.15

5.4 RESURFACING 5.17

5.5 RECONSTRUCTION 5.20

LIST OF FIGURESFigure 1.1 Elements in pavement

evaluation 1.2

Figure 1.2 Decision making levels in road pavement maintenance 1.3

Figure 1.3 Cross-section of a typical flexible 1.4

Figure 2.1 Typical serviceability require-ments for different class of road (AASHO Road Test) 2.2

Figure 2.2 Stresses and strains in a bitumi-nous pavement (Asphalt Institute) 2.4

Figure 2.3 A typical rate of binder hardening in service 2.7

Figure 2.4 Hardening of binder in the top 3mm of the road surfacing 2.7

Figure 2.5 Typical strain-life relationship for bituminous unixes 2.10

Figure 2.6 Typical strain-life relationship for subgrade (SHELL) 2.10

Figure 3.1 Flow chart of pavement evaluation process 3.2

Figure 3.2 Schematics of Benkelman Beam 3.11

Figure 3.3 Schematics of the Dynamic Cone Penetrometer 3.11

Figure 3.4 Schematics of the Road Rater 3.15

Figure 3.5 Schematics of the Falling Weight Deflectometer arrangements 3.16

Figure 3.6 Reduction in deflection after overlay 3.19

Figure 3.7 Distribution of crackingand rutting 3.19

Figure 3.8 Deflection bowl and materials characterisation 3.20

Figure 3.9 DCP test results 3.23


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Figure 3.10. Typical plot of the DCPresults 3.23

Figure 3.11. Micro and macro-lextUre 3.25

Figure 5.1 General Process for Selecting Appropriate Rehabilitation Alternatives 5.2

Figure 5.2 The Spectrum of Pavement Rehabilitation Alternatives 5.3

Figure 5.3 Replacement of Loss Chemical Constituents by Rejuvenation 5.5

Figure 5.4 Proper methods of cutting and patching 5.9

Figure 5.5 Surfacing Recycling Using Hot Milling Method 5.16

Figure 5.6 Methods of Reducing Reflection Cracks UsingInterlayers 5.18

Figure 5.7 Full ReconstructionOptions 5.23

LIST OF TABLES

Table 2.1 Failure modes, manifestations and mechanisms 2.4

Table 2.2 Examples of formula and coefficients for strain-life relationship 2.11

Table 3.1 Surface condition survey form. 3.5

Table 3.2 Classification of cracks 3.6

Table 3.3 Material conditionintrepetation 3.20

Table 3.4 Estimated values of structural coefficients for various conditionsof asphalt. 3.22

Table 3.5 Estimates of structural coefficients, based on DCPin-situ CBR values. 3.22

Table 4.1 Typical HPU traffic survey results 4.3

Table 4.2 Axle load survey results for direction 1, Southbound. 4.6

Table 4.3 Axle load survey results for direction 2, Northbound. 4.6

Table 4.4 Traffic count results for direction 1, Southbound. 4.7

Table 4.5 Distribution of yearly damaging effect 4.8

Table 4.6 Summary of traffic countsresults obtained from HPU.4.9

LIST OF PLATES

Plate 3.1 Rut depth measurement 3.6

Plate 3.2 Surface condition survey 3.7

Plate 3.3 The Road Rater 3.12

Plate 3.4 The Falling Weight Deflectometer 3.13

Plate 3.5 The Heavy Weight Deflectometer 3.15

Plate 3.6 Pendulum Skid Resistance Tester 3.26

Plate 3.7 The Griptester 3.27

Plate 3.8 Sand Patch test 3.27

Plate 3.9 TRRL Minitexture meter 3.28

Plate 3.10 The Friction Tester 3.28

Plate 4.1 Axle load weighing 4.3


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Plate 5.1 Rejuvenating aged Asphalt Surfacings in Progress 5.7

Plate 5.2 Crack Sealing 5.8

Plate 5.3 Cutting and Patching 5.10

Plate 5.4 Cold Milling 5.11

Plate 5.5 Surface Dressing 5.13

Plate 5.6 Slurry Seal 5.13

Plate 5.7 Application of Geosynthetic Materials 5.19

Plate 5.8 Reconstruction Works 5.21

Plate 5.9 Recycling for Base 5.21

CHAPTER l : INTRODUCTION

1.1 BACKGROUND

1.1.1 Brief history of Malaysian road pave-ments.

Bituminous pavements were first constructed inMalaysia some time before the Second WorldWar. In those years, the road pavements wereconstructed using block stone pitching on sandor laterite sub-bases covered with a layer of taror bitumen stabilized aggregates. Since the war,road pavements have been constructed usingcrushed stones road bases and sand sub-baseswith dense bituminous surfacings. This con-struction method is still being practiced today.

To ensure the smooth operation of the road net-work, the road pavements have been constantlymaintained and upgraded. Invariably, the roadnetworks along the main trade routes weregiven more attention than the others. As suchthe road pavements along these routes arethicker than those along the minor roads. Eventhough the roads were regularly maintained andupgraded, there were, generally, a lack ofrecord keeping, on the conditions of the roadsand the type of maintenance carried out. Most

of the upgrading works carried out were eithernot designed or designed using methodologiesimported from the various western countries.An engineering-based road management sys-tem was only introduced in Malaysia in 1974when a Benkelman Beam survey of 2291 kmof Federal and State roads was carried out by_KAMPSAX International.

1.1.2 The need for engineering evalu-ation of the road pavements.

In order to ensure that the road network is ableto satisfy the ever increasing demand placed onit due to increased traffic, there is a need for asystematic approach to the maintenance of theroad network. The lack of proper engineeringrecords on past construction and maintenanceworks now . necessitates the need for fullengineering evaluation to be carried out beforethe design of further road improvements orrehabilitation.

By using definitive and sound engineeringdecisions, appropriate solutions for pavementmaintenance problems can be found.Comprehensive evaluation on distressed pave-ments can fulfill this requirement. This allowsthe most appropriate method of rehabilitation tobe selected thus nninimising long term totalexpenditure.

After a new pavement is constructed, bothenvironmental and traffic stresses will cause itto deteriorate. The rate of deterioration willdepend on the severity of the traffic loads andthe variability of the road materials. In the eval-uation process, the identification and classifica-tion of the type of failure is necessary if correctremedial treatments are to be undertaken.

Pavement engineers are faced with the difficulttask of evaluating pavements that have beensubjected to varying traffic loads under variableenvironmental conditions and material proper-ties (Figrure 1.1). Field measurements are valu-able practical tools in the evaluation of roadperformance and in the identification of thecauses of failure. The task becomes more diffi-cult if the pavement has gone through a series


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Figure 1.1 Elements In Pavement Evaluation

Fugure 1.2 Decision Making Levels In Pavement Maintentenance

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of previous unrecorded maintenance treat-ments.

1.1.3 Economic analysis as part of engi-neering decision malting process.

To ensure a good return on the investment inroad construction, a cost benefit analysis isneeded to ensure that the most cost effectivemethod of maintenance is employed. If thefuture performance of the road is not correctlypredicted, then large sums of money may bewasted.

The details to which the engineering and eco-nomic needs are considered are dependent onthe level at which decisions are made (Figure1-2). The considerations on economic needs aremore important at the Network Level than atthe Project Level.

In most cases, road improvement projects areidentified after due economic consideration aretaken at the network level. At all levels of deci-sion making, a simple, systematic and work

able solution is necessary.

The introduction of the BS(M) ManagementSystem in 1983 was an attempt by the govern-ment to use engineering-based criteria to main-tain and upgrade the road networks. With theintroduction of the Pavement Appraisal andManagement Suite (PAMS) in 1992, this wasextended to balance the engineering and theeconomic needs of the country.

1.2 SCOPE OF THE GUIDE

This guide covers the processes needed in car-rying out an engineering evaluation on flexiblepavements that allows a better decision to bemade at the Project Level. It incorporates briefand relevant discussions of behaviour, perform-ance and deterioration of flexible pavementssubjected to local climatic and traffic conditions. It subjected the evaluationprocess and discusses the most appropriatesolutions in rectifying pavement deficiencies.This guide should be used in conjunction with other


Fugure 1.3 Cross-section Of A Typical Flexible Road Pavement

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IKRAM guidelines on road pavements and existing JKR Standard Specifications forRoadworks.

1.2.1.Limitations of the Guide

Even though it is the intention of the authors toprovide comprehensive and accurate informa-tion in this guide, the users are cautioned thatthe procedures and remedial measuresdescribed in this guide are interim. On-goingresearch work at IKRAM in this field will beable to add more information to the guide inthe next revision. The behaviour and perform-ance of the pavements addressed in this guideis for flexible pavements only. A typical flexi-ble pavement is as shown in Figure 1.3.

1.3 OBJECTIVES

The aim of this guide is to provide a procedurefor the engineering evaluation of flexible roadpavements. The objectives are :

(i) To provide a systematic method of pavement evaluation.

(ii) To assist engineers in identifying primary modes of pavement deterioration.

(iii) To assist engineers in selecting appropriate methods of rehabilitation.

This guide is structured in a manner to providesimple, systematic and workable solutions tothe users. It is aimed at engineers at the project level.

CHAPTER 2

PAVEMENT BEHAVIOUR AND PERFORMANCE

2.1. PAVEMENT COMPONENTS ANDMATERIALS

A flexible pavement is a layered structure con-sisting of the sub-base, road-base and the sur-

facing overlying the natural ground or sub-grade.

2.1.1 Surfacing

]The surfacing is the upper layer of the pave-ment which fulfils the following requirements :

a) To provide an even, non-skidding and good riding quality surface

b) To resist wear and shearing stress imposed by traffic

c) To prevent water from penetrating into the underlying pavement layers

d) To be capable of surviving a large number of repeated loading without distress

e) To withstand adverse environmental condi-tions

The form of bituminous surfacing commonlyused can either be thick or thin. Thick bitumi-nous surfacings nornally consist of crushedmixed aggregates. bitumen and filler. Mostcommon types of plant mixed surfacings inMalaysia are asphaltic concrete or bituminousmacadam. Currently constricted thin surfacingsare surface dressings and slum seals.

Thick bituminous surfacings provide additionalstrength to the pavement and seal the pavementfrom water ingress. Thin surfacings do not givedirect additional strength. They merely protectthe pavement from water and provide a skidresistant riding surface.

2.1.2 Road-base

The road-base is the main structural layer ofthe pavement which spread the load fromheavy vehicles thus protecting the underlyingweaker layers. Its functions are to reduce thecompressive stress in the subgrade and the sub-base to an acceptable level and to ensure thatthe magnitude of the flexural stresses in thesurfacing will not lead to cracking. Unboundcrushed mixed aggregate has been widely usedas a road base material throughout the country.Granite and limestone are readily available inmost areas in Malaysia and have historicallybeen the major sources of aggregate for road-


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bases.

2.1.3 Sub-base

The sub-base is the secondary load-spreadinglayer underlying the road-base. It will nornallyconsist of lower grade granular material as

compared to that of the road-base. Sand andlateftes are commonly used and are easilyavailable. This layer also serves as a separatinglayer preventing contamination of the road-base by the subgrade and also acts as a prepara-tory layer for road-base construction. It canalso act as a drainage layer.

2.1.4 Subgrade

The subgrade refers to the soil under the pave-ment within a depth of approximately 1 meterbelow the subbase. It is the upper layer ofearthworks prepared for subsequent construc-tion of the pavement layers described above.Itcan either be natural undisturbed soil or com-pacted soil obtained from elsewhere and placedas fill material. The strength of the subgradelayer is important as the thicknesses of theupper layers are dependent on it.

2.2. FUNCTIONS OF FLEXIBLE PAVEMENT

The general function of a road pavement is to

provide a safe and comfortable riding surfacefor the road users. Its condition with respect tothese characteristics is normally assessed bytwo groups of people, namely the users and theroad engineers.

2.2.1 Road user requirements

A safe and comfortable riding surface is whatthe road users nontially require. The aestheticaspect of it is also a concern but will receiveconsiderable attention only on heavily traf-ficked pavements. The life of the pavementperceived by the users will be primarily relateto its riding quality. Road pavements that donot provide a safe and comfortable riding sur-face will trigger the road users' awareness as tothe increase in vehicle operating cost.

The users requirement for a road pavement canbe quantified in ternis of serviceability index(1). The terns serviceability was first intro-duced during the AASHO Road Test to repre-sent pavement performance. The road pave-ment was given a rating in terms of ridingcomfort by various drivers, with a value of 5 asthe highest index of serviceability and 0 as thelowest. A terminal serviceability of 2.5 wassuggested as the condition when major roadrehabilitation works. For the rehabilitation ofminor roads, a terminal serviceability of 1.5mvas suggested by AASHO (Figure 2.1).


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2.2.2 Engineering requirements

The engineer is mostly concern with whetherthe road will achieve its design life. The rate ofdeterioration is also a major concern. A rapidrate of deterioration requires immediate inter-vention. The road user may not be aware of theoccurrence of early deterioration since the rid-ing quality may still be acceptable. In contrastthe engineer must be alert to such problems asearly maintenance enhances the road perform-ance.

It is thus necessary to understand the behaviourand performance of road pavement underMalaysian condition. In evaluating and rehabil-itating a road pavement in this country, wherethe environmental factors are different from

Western nations, there are dangers in applyingthose rehabilitation solutions that have beenobtained elsewhere as they may not suit condi-tions in this country without some modifica-tion.

Road user and engineering needs must be prop-erly balanced to suit budget requirements and maximise benefit through appropriate methodsof maintenance. Experience elsewhere has indi-cated that prompt maintenance can indeed saveexpensive reconstruction costs.

2.3 FAILURE DEFINITIONS

2.3.1 Failure modes

The predominant failure modes are fracture,


Mode Manifestation Comman Mechanisms

Frature Cracking Excessive loading Repeated loadingMoisture changes Age hardening

Distortion permanent Deformation Excessive loading Creep DensificationConsolidation Moisture changes

Disintegration Stripping and ravellingLack of adhesion Chemical aggressionAbrasion by traffic Degradation ofaggregate.

Table 2.1. Failure Modes, Manifestations And Mechanisms

Figure 2.2. Stresses And Strains In A Bituminouns Pavement

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distortion and disintegration. Fracture norniallyoccurs in thick bituminous layers. Distortionmanifests itself in any of the pavement layersand will normally appear on the bituminoussurface as netting or other forms of deforma-tion. Disintegration will normally take place onthe bituminous surfacing. Loss of aggregates isa common manifestation of this failure mode.

2.3.2 Failure manifestations

Each component of the pavement layers maycontribute to failures. The most difficult task isto identify which layer is the cause of primaryfailures of the road. Failure in flexible pave-ments most commonly manifests itself ascracking or deformation. These defects canbe visually identified and measured usingappropriate techniques.

2.3.3 Failure mechanisms

Extensive research has established the variousmechanisms that cause road failures. Somecommon mechanisms are :

i) Repeated axle loadingii) Excessive loadingiii) Thermal and moisture changesiv) Material densificationv) Consolidation of subgradevi) Shear in subgradevii) Time dependent deformation (creep)viii)Abrasion by trafficix) Chemical degradationx) Degradation of aggregatexi) Hardening of the bitumen

Early detection of these mechanisms during theevaluation process can help in identifying theprobable remedy. Suitability and accuracy ofevaluation procedures and analysis are depend-ent on accurate identification of actual modesof failure. The relationship between failuremode, their manifestations and probable mech-anisms is as shown in Table 2.1.

2.4 PAVEMENT BEHAVIOUR

Before moving further into pavement evalua-

tion methodology, it is necessary for a roadengineer to understand pavement behaviourespecially under local environmental condi-tions.

Repeated axle loading, the environment, soilcharacteristics and drainage, are some factorsthat affect pavement behaviour. Stresses andstrains are induced in the pavement layers byboth the influences of traffic and environmentalstresses, an example of the latter being diurnaltemperature changes (Figure 2.2).

The bituminous surfacing suffers from tensilestrains at the bottom and the top of the layer(2). The road-base, the sub-base and thesubgrade are mainly subjected to compressivestresses.

Theoretically, pavements will only behave as acomposite material under go ideal condition.This condition exists only when the pavementmaterials are homogenous and isotropic and theadhesion between the component layers is per-fect.

A point on the pavement subjected to a movingload will deflect temporarily. The elastic prop-erties, characteristics of the component materi-als and the loading nature and magnitude willdetermine the size of the deflection. The tem-porary deflection will rebound after the loadhas been moved away from the spot. Thisdeflection is usually referred to as the transientdeflection.

Deflection measurements had been used as anoverall pavement strength indicator. Fieldexperiments from other authorities have shownsignificant relationships between deflection val-ues and pavement life. Deflection test resultscan be used to predict the performance of pave-ment and to design overlay thicknesses.The behaviour of individual pavement layersunder traffic loadings can be very different.Each has its own significant role in the overallbehaviour of a pavement.

2.4.1 Behaviour of thin surfacings


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Surface dressings mid slurry seals are the com-mon types of thin surfacings used to seal roadpavements in Malaysia. These surfacings donot provide direct structural strength to thepavement.

Bituminous sealed road pavements are normal-ly used in Malaysia for roads with low trafficvolumes and axle loads (low class road). Thereis limited field experience and knowledge ofthe behaviour of thin surfacings constructed onhigh volume roads in the country.

Surface dressing have been used by manydeveloped countries for highways and highclass road pavements. Theoretically, if the roadbase layers can be made to spread the loadimposed upon a pavement and meet the expect-ed structural requirement, then a thin layer issufficient to fulfil the functional requirement ofa good riding surface. This is the adopted prin-ciple behind the successful use of surfacedressings in developed countries.

Thin bituminous seals, and in particular surfac-ing dressings, have high bitumen contents thatleads to high bitumen film thickness. They arevery flexible and are able to withstand highpressures from heavy wheel loads if construct-ed properly. Furthermore, they should be ableto withstand environmentally induced stresses.Bituminous surfacings with high bitumen con-tents will have improved resistance against agehardening. These properties cannot be obtainedfrom thick bituminous mixes since stability,skid resistance and texture depth decrease withincreased bitumen content.

Strong adhesion with the road-base is anotherimportant factor which determines the life ofthin seals. The proper application and curing ofthe bituminous prime coat on the road base istherefore vital to its perfornance.

Water can have a deleterious effect on this typeof construction. Serviceability will be reducedif water is allowed to penetrate the surfacing.The condition of surface and side drainage willsignificantly affect the pavement behaviour andperformance. Therefore drainage is a major

area that must be emphasised during evaluationon the performance of this type of road pave-ment.

2.4.2 Behaviour of the component layers in a typical flexible pavement.

Bituminous laver

The deflection experienced by the bituminouslayers due to a loaded wheel induces tensilestrains underneath the bituminous layer. Underrepeated loading this layer is liable to experi-ence fatigue. Permanent deformation of thesubgrade and fatigue failure of the road surfac-ing are the two major characteristics that arenormally used to predict flexible pavement per-formance.

The elastic behaviour of the bituminous mix ismainly governed by the properties of the bitu-men. Bitumen in the mix is visco-elastic and itsbehaviour is highly dependent on temperatureand the rate of loading (3). At low temperaturesand short times of loading they are essentiallyelastic but at high temperatures and long load-ing times the material undergoes viscous flow.The effective modulus is defined as the ratio ofstress to strain at a particular temperature andloading time and is usually referred to as stiff-ness. In practice, high stress areas such asclimbing lanes and junctions suffer long load-ing time at high temperature therefore reducingits modulus value (2). Deformation in the formof shear failure in the surfacing is normallyprominent in these areas.

Laboratory tests have been carried out for vari-ous types of bituminous mixes under repeatedloading to estimate fatigue failure. Apart fromthe test procedures (e.g. testing temperature,loading method or cycles), bitumen type, bitu-men content and air void content in the mixalso influence the fatigue behaviour.

The time lapse between loading cycles is alsoknown to affect the test results. The type ofaggregate used is a secondary variable, and isassumed to have negligible effect. Laboratoryfatigue tests under fully controlled conditions


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can produce more repeatable results comparedto those observed in empirical experiments.

In the field, cracks starting from the bottom ofthe bituminous layer due to repetitive tensilestrain is normally called the traditional fatiguefailure. This form of failure slowly manifestsitself in the form of crocodile cracking in thewheel-path and is easily identified by a surfacecondition survey.

The factors that affect fatigue failure in thefield are loading pattern, channeling and mate-rial properties. Laboratory fatigue values canshift between 20 to nearly 700 times whencompared to those observed in the field (3).This indicates that the behaviour of the individ-ual materials under laboratory conditions isunfortunately not a good substitute for a thor-ough knowledge of the behaviour of the mate-rials when combined within a pavement.Improvement in this area can only come fromthe study of the behaviour of bituminous sur-facings using empirical tests.

Additional compaction under repeated trafficloading contributes to permanent deformationthat is normally manifested as rutting. Mixeswith high bitumen contents and are subjectedto loading at high temperatures are liable toresult in permanent deformation.

Environmentally induced stresses and strainsalso affect bituminous surfacings. Temperaturechanges will cause the bituminous material toexpand and contract. If the material is tempera-ture susceptible, the stresses and strainsinduced will cause thermal cracking.Another common factor that hasten the deterio-ration process significantly within the bitumensurfacing in the tropics is the hardening of thebitumen primarily at the surfacing (4). The toplayer of the bituminous mix can become brittleand may crack easily under traffic loading ortemperature changes. This is common in surmyand hot regions where the oxidation process israpid. The principal causes of bitumen harden-ing are (5) :

i) Oxidationii) Loss of volatiles iii) Physical hardeningiv) Exudative hardening

Oxidation is the main cause of hardening thatcan occur at storage, during mixing and on theroad. The bitumen viscosity of the top fewimillirnetres of the exposed surfacing changesrapidly in our environment (6). Figure 2.3shows a typical rate of hardening of binder inservice. The hardening is more severe in thetop 3 mm of the road surfacing and decreaseswith depth. Figure 2.4 shows that the rate ofhardening is more rapid during the first 20months. After this period, the rate decreasesuntil the binder viscosity reaches approximately6.2 log Poise. At this point, environmental age-ing apparently ceases to have any further sig-nificant effect. Suitable considerations andallowances must be made to deal with this criti-cal problem.

On bituminous roads, cracking and rutting areusually more severe in,the verge-side (near-side) wheel-path compared to the off-side(outer-side) wheel-path. On the other hand, pol-ishing of the road surface by vehicle tyres isnormally seen to be more severe on the off-sidewheel-path.

Unbound layer (road-base and sub-base)

Vertical compressive stresses affect theunbound granular layer. The strength of thislayer is dependent on its elastic properties,thicknesses and subgrade strength. The elasticcharacteristic of this layer under repeated load-ing is difficult to model. The modulus in thevertical direction can be different from that inthe horizontal direction which suggest that it isanisotropic.

The intrinsic properties of the material andproblems in setting up samples for laboratorytests have resulted in the use of the term'resilient modulus' instead of the usual ‘modu-lus' for this material. It is defined as the quo-tient of repeated axial stress in triaxial com-pression divided by the recoverable axial strain.


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In the laboratory repeated loading triaxial testscan be used to studv the individual deformationcharacteristic and resilient modulus of thislayer. The Poisson ratio can also be obtained.

The subgrade strength and the road-base layerthicknesses affect the actual field properties ofthe sub-base. This is common for all pavementlayers. Apart From individual properties,surrounding properties affects actual field per-formance. It was found in the United Kingdomthat nearly two thirds of the total permanentdeformation of the combined layer was con-tributed by the surfacing and the unbound

layer.

Subgrade layer

The subgrade layer bears the final compressivestress. The top one meter is the most criticalsince it suffers almost all the transmitted load.Properly designed and constructed road baseand sub-base layers will spread the load andreduce the stresses induced by the vehicle onthe subgrade. The aim is to limit the compressive stress to an acceptable level so that thesubgrade will not fail or move under repetitiveloading.


Figure 2.4. Hardening Of Binder In The Top 3 mm Of The Road Surfacing

Figure 2.3. A Typical Rate Of Binder Hardening In Service

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The strength of a road subgrade is commonlyassessed in ternis of the California BearingRatio (CBR). New pavements are mostlydesigned using subgrade CBR values as theprimary soil strength indicator. It's popular usein Malaysia has prompted development of rela-tionships to other useful soil-strength indica-tors. The CBR and in general, the soil strengthis dependent on the type of the soil, its mois-ture content and its density.

During pavement evaluation, the moisture con-ditions primarily govern assessment decision. Awell-constructed pavement would have a sub-grade in equilibrium moisture condition mostof the time and there will be no change inbehaviour. This scenario however is not achiev-able in most areas in Malaysia. The subgrade issubjected to variable conditions in theMalaysian environment. Two most commonconditions are :

i) Where the water table is near or possiblyhigher than the formation level. This water table will influence the subgrade moisture content and also the pavement layers above it.

ii) Where the water table is far from the formation level but seasonal variationand drainage efficiency will influence itsmoisture conditions.

Pavements under condition (i) above, will beweakest when the water table is at the highestpoint. This may happen diurnally (tidal change)or seasonally (monsoon season).Nondestructivemeasurements that simulate pavement behav-iour taken at these locations should considerthis. Measurements are best taken at the wettesttime, when the pavement is probably at itsweakest.

Heavy rainfall during wet weather allows mois-ture to enter the pavement layers and the sub-grade through the shoulder and at the edges.This is more pronounced where earth shouldersare used. Sealed road shoulders substantiallyreduce the ingress of water. Drainage is themost important factor that determines the

behaviour of the subgrade throughout its serv-ice life. High standards of drainage provisiongovern the longevity of pavement life at theseareas.

2.5 PAVEMENT PERFORMANCE

2.5.1 Terminal condition

Terminal pavement condition or the end ofpavement life is used to describe its conditionwhen major maintenance is needed. This con-dition is predicted to occur at the end of thedesign period.

The residual life of a road pavement is depend-ent on the definition of the terminal condition.A pavement will have a residual life if its con-dition has not reached terminal level.

In Malaysia, definition of terminal conditionand prediction of residual life were verydependent on experience from other countries.There are no standards on 'end of life' criteriafor Malaysian pavements as yet.

2.5.2 Users requirements

As mentioned in para. 2.1.1, the users' require-ment is for safety and comfort. Only seriouspavement failure can be felt or measured inrelation to this. The AASHO road test in theUnited States suggests a serviceability level of2.5 as the terminal condition (1). At this level,riding on the road will be uneconomical anduncomfortable. However, the choice of thislevel to be used locally needs careful study,taking into consideration local pavementbehaviour.

2.5.3 Engineers and managers requirements

Two forms of distress modes can normally beidentified from the road pavement surface (i.ecracking and rutting). The degree of crackingor rutting or both are normally used as a gener-al indicator of the overall pavement condition.These failure manifestations can be used as acriterion to quantify an empirical terminal con


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dition. One of the empirical terminal conditionknown (7), suggests the existence of both the

initial cracking and ten millimetres rutting asfailure criteria.

Theoretical or mechanistic terminal conditionwill be based on asphalt strain or subgradestrain criteria. The minimum permissible strainlevel is currently based on laboratory findingsthat can be reduced to mathematical formulae.Typical examples are shown in Figures 2.5 and2.6.

Various authorities had perform similar tests

and the formulae adopted are shown in Table2.2. This terminal condition can be accepted if the mechanistic model used depict exact fieldbehaviour.

The effect of age hardening in the field thatinduce top-down cracking is not included inthose models. Allowance for this effect must bemade if the above terminal criteria are to beused. At this juncture, empirical terminal condi-tion seems to be more realistic and therefore itis more reliable.

2.5.4. Empirical interpretation ofperformance


Figure 2.6. Typical Strain-life Relationship For Subgrade (SHELL)

Figure 2.5. Typical Strain-life Relationship For Bituminous Mixes

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Empirical definitions and constraints

Predicting the field performance of visco-elas-tic materials under variable loading patternsand environmental conditions is not a simpleand straight forward task. Material strength andbehaviour are dependent on many variablesand involve the combined effect of other mate-rials. The combinations of bitumen and aggre-gate, on top of other unbound layers makes thematerial difficult to model theoretically.Fluctuations in moisture level within the pave-ment create further uncertainties. Most theoreti-cal models assume an equilibrium moisturecondition.

Empirical experiments are best carried outwhere the variables can be measured and con-trolled. The performance can be monitored andrecorded. The recorded experience can be usedfor future construction work or to assess exist-ing pavement conditions provided similarmaterials and specifications are used.

The empirical approach has been used widelyto design new road pavements and to assessmaintenance needs. The results are absolute butare only applicable locally and its usage is lim-ited to similar materials and construction speci-fications. Adaptation of this methodologybeyond its defined scope needs in-house verifi-cation and modification especially if the envi-ronment and materials used in the experimentare different.

Past experiments and findings

The AASHO Road Test is perhaps the mostcomprehensive pavement experiment everundertaken. Field behaviour and performanceof bituminous material were studied with con-trolled repeated loading pattern under a specificenvironment. Results from this test have beenaccepted world-wide. One of the major find-ings of the road test was the pavement fatiguelife definition in terms of repetition of a stan-dard axle load. This principle had been extend-ed and various other studies on bituminousroad pavements relate to these findings.However, the modes of failure in a particular

local field condition can be very different fromwhat had been experienced in the road test.

Environmental effects

The major constraint in using experimentalresults carried out from other countries is theexistence of different soil types and environ-mental conditions. Local experience is stillregarded as the best guide for the right solution.

These points had been proven from the variousfindings from the AASHO road test. Studiescarried out by TRRL had shown that commonmodes of failure in the tropics are often differ-ent from those encountered in temperateregions. These indicate that pavement behav-iour and performance in Malaysia would bedifferent and require different treatment andemphasis.

Research work carried out at IKRAM showsthat cracking is the major failure mode onasphaltic concrete overlays (8). Rutting is not amajor problem and only occurs on highlystressed areas. Observations made over fouryears on pavement o~7erlays throughout thePeninsular Malaysia have produced sufficientdata to predict pavement performance in thiscountry.

2.5.5 Mechanistic interpretation of performance

The constraints of the empirical designapproach have resulted in other methods beingdeveloped to make it possible to predict othermodes of failure and possible usage of differentmaterial types.

The structural analysis is to consider the pave-ment, consisting of different materials. to becharacterised' by their elastic parameters whichare typical of dynamic load conditions. Thelayered system concept (or multilayer elasticsystem) is normally used. Many assumptionsmust be made to model field behaviour to amechanistic model that can be computed math-ematically. The major assumptions used in themodel are (9) :


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Page 20



i. The component layers are homogenous and isotropic (the property at a point is similar to that at another point and is thesame in any direction)

ii. Complete friction between layers at eachinterface

iii. The stress solutions are characterised by the materials Poisson Ratio and modulusvalues

iv. Each layer has a finite thickness and is in ideal condition

v. Surface shearing force are not present at the surface

vi. The material is infinite in the horizontal direction

These assumptions are made clear in this guideto caution users on indiscriminate use of thetheoretical methods. Specialised laboratory testneeds to be undertaken to support its properuse. Field verification experiment governs thevalidity of the approach.

Pavement response and model

The most common model used to date is thethree layer model. The road pavement is divid-ed into three component layers :

i. the bituminous surfacingsii. the unbound granular layer andiii. the subgrade

More detailed four layer models that separatethe unbound layer into two layers can also beused. However, the practicality and accuracyobtained is still very subjective. More effortshould be given in handling variability in theanalysis (thickness of material and subgradecondition) so that the accuracy of theinterpretation can be improved.

In the multilayer model, the pavement acts as acomposite structure. In theory, when the pave-ment is subjected to a wheel load it will

respond and produce a temporary deflectionknown as transient deflection. The deflectioncan be measured in the field by various meanswhich will be discussed later in Chapter 3.

If the measured deflection is similar to the the-oretical deflection, then the elastic properties ofthe material in the model could be used as anestimate of its actual values in the field. Theanalyses use the method of equivalent thick-ness, normally required to analyse compositestructures under loading. Comparing the theo-retical deflections to the actual field deflectionvalues is normally ternied 'backcalculation'.This is an iterative process. Convergence accu-racy of the iteration can be chosen as required.The initial elastic properties for each laver haveto be estimated. The elastic properties of com-ponent layers obtained are then used to esti-mate the condition of the material.

It must be emphasised that the theoreticalmodel must be able to predict the actual failuremode in the field for it to be used with reason-able confidence. Failure to do so may result inerroneous predictions.

Material fatigue problems have been investigat-ed in great detail in the laboratory by variousauthorities and attention has now been directedto the relationship between these results and thefatigue performance of bituminous materials onthe road. It has been found that the fatigue lifeof the bituminous materials under traffic condi-tion in flexible pavements is considered longerthan that found in the laboratory. It is believedthat these resulted from the. differencesbetween conditions in the road and the test pro-cedure adopted in the laboratory. As an exam-ple, it has been suggested that a factor of 100times is appropriate for condition in the U.K.i.e. the field fatigue life is 100 times that in thelaboratory.

It is also very difficult to model climate relatedfailure in this approach. At this juncture, practi-cal application of this approach may remainconjectural.

Theoretical modes of failure


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The most common theoretical mode of failureadopted in the model are fatigue failure at thebottom of bituminous laver and deformationfailure on top of the subgrade. Additional fail-ure on top of the unbound base is often includ-ed. Theoretical deflections, stresses or strains atthese locations can be calculated using themethod of equivalent thickness. Research in thelaboratory can be used to measure stresses andstrains .at which pre-detennined failure condi-tions occur and relationships established.

These failure modes were considered based onexperience overseas. Care must be taken inaccepting these as the only failure criteria.Local research work carried out shows that thetop of the bituminous surfacing exposed toenvironmentally induced deterioration shouldbe considered. On-going research at IKRAM islooking into this problem.

Materials characterisation

In multilayer analysis the material characteris-tics namely Poisson Ratios, thicknesses andelastic moduli are the main parameters to beconsidered. The Poisson Ratio can be assumedto be of a certain value based on laboratory andengineering experiences. Layer thicknesses canbe obtained from construction as built drawingsor measured directly in the field. The Elasticmodulus of each liver is the property that nor-mally needs to be predicted.

Mechanistic terminal condition

In the mechanistic approach the terminal condi-tion will be based on the calculated stresses andstrain levels. The terminal conditions are pre-determined from laboratory experiments. Thestresses and strains described in para 2.-1.2 aremeasured by repeated loading cycles applied inlaboratory conditions. The relationship betweenrepeated load cycles and strain level at failureis plotted. Equations for the strain-life relation-ships of the particular material can be obtained.Residual life is determined by comparing thestrain estimated from the interpretation ofdeflection measurement with the allowablestrain obtained from the laboratory relation-

ships. The strain level closest to the allowablestrain for a given type of material will indicatethe critical residual life.

Most stress-strain relationships available are formaterials that were obtained overseas. Thereare many different variables in the Malaysianenvironment that must be simulated in order topresent actual loading and material conditions.A recent research finding indicates a rapidchange in asphalt properties for the top layerthat are exposed to the environment. Theseimpose another consideration in the testing.Laboratory fatigue test should also simulatefield loading frequency, otherwise a discrepan-cy of the length of rest period between loadingwill distort simulation.

Uncertainty

The major uncertainties using the mechanisticapproach are :

i. The validity of predicted failure conditions,

ii. The discrepancy between conditions in laboratory experiments compared to those in the field,

iii. The limitation and validity of the assumptions used,

iv. The deficiency in the model that may ignore actual field condition.

The above uncertainties can be overcome byfull-scale experiments under local conditions.

Computerised solutions

The mechanistic approach demands extensivecalculations and iterative computations whickrequire time. Many computer programs exist inthe market. However, in principle almost allwill use the method of equivalent thickness andback calculation procedures to estimate themodulus values. Some packages haveadvanced with full mechanistic bituminousoverlay design. The accuracy and reliability ofestimates from the computerised solution stillremain conjectural unless the problems inmechanistic interpretation as described earlier


Page 22



can be overcome.

JKR currently have a number of computer pro-grams undergoing tests. Recent developmentshave found that the use of PHOENIX can pro-duce reasonably practical estimation of modu-lus values. These values are sensitive to pave-ment layer thicknesses. A study carried out byTRRL found that the moduli estimations usingback-calculation procedure by four pavementconsultants were nearly similar. However, sub-stantial differences in treatment recommenda-tions and bituminous overlay thicknesses indi-cate a general uncertainty over the evaluationconcepts.

Verification of mechanistic interpretation

Controlled field experiment is the best methodto verify mechanistics performance predictionmethods. Such work is now being undertakenby IKRAM. The task is to develope a realisticmodel depicting actual field conditions.

2.5.6 Future undertakings

There is understandable interest in the fullmechanistic approach that will result in greaterflexibility in the choice of materials. However,this demands comprehensive laboratory andfield experiments for Malaysian materials andenvironment. Suitable field deflection testingequipment has been identified. Improvementsin the interpretation and modelling methodolo-gy coupled with field verification is still inprogress.

2.6 REFERENCES

1. AASHTO Guide for Design of Pavement Structures 1986, American

Association of State Highway and Transportation Officials,

Washington D. C.

2. SHELL PAVEMENT DESIGN MAN-UAL, Shell Petroleum Company Inc., London, 1978.

3. DAVID CRONEY, The Design and

Performance of Road Pavements, Department of Environment, Department of Transport, Transport and Road Research Laboratory, HMSO, London 1977.

4. ROLT, J. 'Flexible Pavement Design Methods' Overseas Unit, Transport and Road Research Laboratory, Crowthorne,Berkshire, United Kingdom, 1987.

5. THE SHELL BITUMEN HANDBOOK, Shell Bitumen U.K., 1990

6. PUBLIC WORKS DEPARTMENT, The Deterioration of Bituminous Binders in Road Surfacings, Research Report 5, Institute of Training and Research, PWD Malaysia, 1991.

7. KENNEDY, C.K. and N.W. LISTER. Prediction of pavement performance andthe design of overlays. Department of the Environment, Department of Transport, TRRL Report LR 833. Crowthorne, 1978 (Transport and Road Research Laboratory).

8. PUBLIC WORKS DEPARTMENT, Long Term Performance Study of

Overlays, Institute of Training and Research, PWD Malaysia, 1989.

9. YODER. ,E.J, WITCZAK. M.W., Principles of Pavement Design, 1975.

CHAPTER 3 :

PAVEMENT EVALUATION

3.1 GENERAL

The pavement evaluation processes practised inthe JKR road pavement maintenance are atthree levels. These was described earlier inChapter 1 as the System Level, Network Leveland Project Level. For the network level, pave-ment evaluation requires a different methodolo-gy and equipment. The scope of evaluationmethodology is described in detail elsewhere.


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This chapter deals with pavement evaluation atproject and detail level. The choice of equip-ment, information quality requirement, accura-cy, methods of analysis and techniques used aregiven.

The main steps of the evaluation can be sum-marized as follows :

i) To divide the road into suitable lengths of design sections

ii) Predict the mode of failureiii) Identify failure causes and delimit the

failure areaiv) Select suitable short or long term reme

dial solutions

The above can be carried out efficiently bydividing the tasks into two assessment tiers, ini-tial and detail assessments. The scope of workin the process is shown in Figure 3.1. Briefdescription of the flow of the work is givenbelow.

3.1.1 Project initiation

There are two normal mechanisms that initiatepavement evaluation at the project level :

i) From network level priority listing ii) Specific evaluation request when a

pavement requires upgrading due to special reasons

After a specific budget has been allocated for aproject in a network priority list, a detailedpavement evaluation is normally required tooptimise the budget. This evaluation exercise isnecessary as the condition of the pavementmay have changed since it was evaluated dur-ing the network level pavement survey. Foraccurate results, the time lapse between theevaluation exercise and the commencement ofthe rehabilitation construction must be min-imised. 3.1.2 Physical condition assessment

Simple physical condition assessment of thepavement at the beginning of the evaluationexercise helps efficient organisation of this

task. This can be done visually or using a sim-ple and cheap methods. A general condition ofthe pavement is recorded. A decision should bemade at this juncture whether the pavement issuffering from structural or non-structural fail-ure. If it is structurally sound, its functionalcondition should be queried. If the pavement isboth structurally and functionally adequate thenthe pavement is considered sound, otherwisedetail testing will be needed.

3.1.3 Non-destructive testing (NDT)

Non-destructive testing is currently the state-ofthe-art method for detailed pavementinvestigation. The selection of NDT devices isdescribed in para 3.3.2. NDT allows more datacollection along the road and provides a moreconfident representation of the pavement con-dition. It is necessary not to miss any weakareas at this level of testing. This testing willprovide the base data for analysis and rehabili-tation design.

3.1.4 Analysis and rehabilitation design

The base data from the NDT tests together withother information that was taken previously iscompiled and analysed at this stage. Additionaltests may be required if the information is notsufficient. Suitable methods of analysis areapplied to produce recommendations of reme-dial measures and the procedure of choosingthe appropriate method is described in para3.3.3.

3.1.5 Selection of remedial measures

This can be the most important part of the eval-uation exercise. A detailed description andinterim guide for this task is explained inChapter 5. The first step is to understand anddiagnose the pavement problem. This will thenhelp to provide the solution. The correct solu-tion is not always easy to achieve. Longtenn

engineering solution should be chosen at thisjuncture. It must be assumed that budget is nota constraint at this stage.


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3.1.6 Cost analysis

With budget constraints, the balance betweenengineering or non-engineering driven solutionmust be considered carefully. This scenerio is common in Malaysia. A simple costing analysis

of the remedial measures may provide suffi-cient answers to the problem.

The costing analysis should provide informa-tion to ascertain the budget requirements. If thecost of actual rehabilitation requirement exceed


Page 25



tire allocated budget, the rehabilitation solution may require changes. Short terns and long termremedial measures are selected depending onthe allocated budget. Staged constriction isanother option worth considering in order toreduce initial rehabilitation costs but still fulfills the engineering requirement.

The feasibility of various remedial measuresmay involve discussions with the appropriateauthorities before the final options are selected.Other feasible remedial methods can be appliedif the conventional method are not appropriateor slow.

3.1.7 Implementation

Projected actual time of implementation of theevaluation proposal should be considered dur-ing the evaluation exercise. The estimates ofremedial works normally increase if the timelapse between the evaluation period and theimplementation phase is expected to be long.This is common in Malaysia. where contractualarrangements are often lengthy. Allowance forthis problem should be considered in the evalu-ation exercise.

3.2 INITIALASSESSMENT

Pavement evaluation at project level starts bycarrying out an initial assessment of the physi-cal condition of the pavement. The principle isto use cheap equipment and simple method ofassessment. More expensive and detailed testscan be scheduled if and when required.Engineers nonually carry out or supervise thiswork. The scope of work involves two maintasks :

i) Surface condition assessmentii) Drainage assessment.

Other information related to the surroundingsof the pavement helps to ensure a comprehen-sive evaluation work. Historical data of thepavement would be very useful if available.However, it is not mandatorv to have this datato accomplish the pavement evaluation task.

The results from this initial assessment will beused to :

i) Decide preliminary lengths and locations of `design sections'

ii) Plan for the frequency and interval of detailed tests

Optimum and economical data collection andsampling can be carried out following theselection of the design sections. The final rec-ommendation of rehabilitation measures shouldbe adiusted to suit these individual sections.

A minimum length of a selected design sectionshould not be less than one kilometre to allowfor efficient construction operation. Preliminarydesign sections are chosen first from the initialassessment results. At a later stage, other infor-mation such as soil type, topography, hydrolo-gy, deflection and traffic data can influence thefinal selection of the design sections. The engi-neer should carefully review all the availabledata to judge whether a particular treatment issuitable over the entire project length orwhether shorter design sections using separatetreatments are necessary. Changing remedialtreatments too frequently may result in difficultand expensive construction.

3.2.1 Surface condition assessment

The surface condition survey provide a meansof quantifying the failures of the pavement,shoulder and drainage. Using appropriate tech-niques, the extent of the failures can be classi-fied and quantified. A standard surface condi-tion survey method has been used in JKR. Themain parameters recorded are cracking and rut-ting as well as shoulder and drainage condi-tions. Details of the information recorded isshown in Table 3.1.

Visual assessment of cracks using a classifica-tion system simplified in Table 3.2 provide suf-ficient information for further analysis. It iseasier to divide each section into short 10metres block for accurate and efficient data col-lection. Alternative lengths of sections can beused. A straight edge and a wedge are used to


Page 26



measure the rut depth within the block(late 3.1). The maximum rut depth in the blockis measured. The location of the maximum rutdepth is estimated visually. The condition ofshoulders and side drainage facilities are initial-ly assessed by visual judgement. A full assess-ment of the drainage condition can be madeseparately if necessary. This will be describedin more detail in para. 3.2.2.

The personnel needed to carry out the surfacecondition survey vary depending on the trafficintensity of the site. Plate 3.2 shows the com-mon personnel layout on a low volume roadwith fast traffic. Four persons are required tocollect the data and two persons are needed tocontrol the traffic flow. Safety requirementsvary from site to site. Safety jackets must beworn. Police assistance is recommended atlocations with very heavy traffic.

Surface condition surveys must be carried outduring the day time. It should not be carried outat night unless proper lighting is provided.

3.2.2 Drainage assessment

The condition of surface and side drainage ofthe pavement will contribute significantly to itsperformance. A classification of its conditionwill indicate whether this is the primary or con-tributory cause of damage to the pavementstructure. Some existing road pavements havebeen upgraded from previous construction thatmay not have emphasised on drainage provi-sion. Sometimes the drainage has disappearedthrough sequence of widening work. It isimportant to remedy drainage problems beforeany pavement rehabilitation work is imple-mented. Water is the most important environ-mental factor that influences pavement per-formance. Prediction of moisture conditionand the resulting variation in pavementresponse is still a major unsolved problem thathas not deen defined precisely in any pavementdesign method.Adequate provision of drainage facilities willminimise this area of uncertainty. Keepingwater away from pavement materials is still thebest solution especially where heavy rainfall is

expected.

Surface drainage is judged by the ability of thepavement surface to drain water rapidly, notallowing water to pond either on the bitumi-nous surfacing or on the road shoulder.Observation is best carried out after or duringrainfall when the road surfacing is still wet. Theresults of these observations should provide anindication whether it is necessary to improvethe cross section profile of the pavement andthe road shoulder. This is critical if the probablemaintenance measures would only need minortreatment such as sealing or cut and patch.

The structural drainage condition is more diffi-cult to assess. Past construction records will behelpful if available. This assessment is morecritical in hilly areas where the pavement isconstructed on cut slopes. The engineers needto judge with reasonable confidence by obser-vation whether a particular area requires sub-soil drainage, side drains or interceptor drainsor whether existing drains are sufficientand functioning properly to safeguard the pave-ment. Failure as a result of drainage deficiencywould have been very obvious by the time thepavement undergoes investigation. Comparisonto similar pavement construction on adjacentareas that have good drainage provision canassist on the judgement of the drainage condi-tion.

3.2.3 Preliminary analysis, sectioning

The existing pavement construction and theunderlying condition of the pavement structuregovern the initial selection of homogeneoussections within a road length having a uniformtraffic loading. Visual surface condition dataand deflection results can be used to refine thesections. Statistical analysis can be used todefine representative characteristics and homo-geneity of key parameters within the sections.


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Page 28



Confidence level of 85%,


Crack Type Crack Width Crack Extent

0 - No Cack - -

1 - Single crack < 1 mm < 1 m

2 - Many cracks 1 - 3 mm 1 - 5 m

3 - Interconnected cracks > 3 mm > 5 m

4 - Crocodile cracks > 3 mm and spalling -5 - Crocodile cracks and

spalling - -

Table 3.2 Classification of cracks

Plate 3.1. Rut Depth Measurement

Plate 3.2. Surface Condition Survey

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or more is recommended for statistical representation. Adjacentsections must not contain significantly similarattributes. Significant tests should be carriedout to resolve this problem.

The distribution and population mean of thedeflection, rutting, cracking and other quanti-fied failures highly influence the proposedmethod of treatment. The primary mode of fail-ure often dictates preliminary sectioning.

Sectioning by evidence of cracking

Cracking suggests that predominant failure mode is either by traditional fatigue or agehardening. If the road has been overlaid thecracking can often be reflective cracking froman overlaid surfacing. Pavement strength that ismostly defined by the layer thicknesses caninfluence the degree of cracking and its distri-bution. Information on pavement layer thick-ness will help in the selection of the sections.This method of sectioning is not suitable for aroad pavement that has been inadequatelymaintained and has extensively failed.

Sectioning by rutting severity

Severity of rutting can sometimes be used toassist preliminary sectioning. Areas with uni-form problems of material stability can be iden

tified. Rutting normally indicates evidence ofasphalt instability or weak underlying layers.Rutting alone is not the predominant failuremanifestation where weak underlying layerexists. Cracking and rutting normally appearsin this area. Sectioning by rutting alone willsuggest the predominant role of asphalt insta-bility.

Sectioning by formation type

The contribution of the strength of the subgradeto road failure can result in variations in eithercracking or rutting or both. Distinct formationtypes exist in hilly areas and are common inthis country. Fill areas are prone to construction deficiency where quality of imported subgrade

may effect the pavement performance.Drainage and ground water condition influencethe performance and stability of cuttings.Drainage deficiency could provide further evi-dence to justify division into sections. Distinctdifferences in failure at different formationtypes indicates the suitability of sectioning byformation types.

3.3 DETAILED ASSESSMENT

3.3.1 General

The next stage in the evaluation process is thedetail assessment of the road pavement. Theassessment can be either the structural condi-tion or the surface characteristics of the roadpavement. In most project level assessmentsthat lead to major rehabilitation, the structuralcondition assessment is vital. The surface func-tional requirement may not be critical sincemajor reconstruction requires the existing sur-face to be removed.

The strength of the existing pavement needs tobe measured. The results from those tests willassist in identifying the mode of failure.

The current interest world-wide is to use NonDestructive Testing (NDT) devices. NDT is apreferred approach that is fast and reduces oreliminates laborious and expensive destructivetesting (1).

Destructive testing can give a more accurateindication of the condition and performance ofpavement materials at a specific location.However, it is likely that high variability ofpavement layer thicknesses and material condi-tions over a long stretch of road exists. This is acommon situation along most roads inMalaysia. It is therefore more important to con-centrate the evaluation effort in achieving accu-rate true mean characteristics of the materialsfrom adequate sampling over the stretch con-cerned. Putting emphasis on achieving an accu-rate single sample characteristics could distortthe overall scenario.

NDT surveys for the structural assessment


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should be conducted at the time of the yearwhen the pavement is at its weakest due to sea-sonal environmental condition. Relationshipsbetween environmental factors and deflectionsneed to be established to know when the pave-ment will be at its weakest. For a start anassumption can be made that the pavement is atits weakest after the monsoon season. Diurnaltemperature variation must be considered aswell. Deflection reading is best taken close tothe standardised temperature of 40°C to reducetemperature correction error. Proper tempera-ture correction relationships for different typesof surfacing should also be established.Temperature susceptibility of bituminous mixesvaries with mix types and conditions. Differenttemperature corrections are required for differ-ent mixes. Temperature correction becomesmore significant as the pavement gets hotterduring the day whereby the deflection responsebecomes more sensitive as the surfacing getssofter. It is not significant if the surface hasseverely cracked.

NDT equipment is available in many forms.Broadlv, they can be divided into two majorgroups :

i) Deflection-based equipment ii) Non-deflection-based equipment

There are three mechanised deflection-basedsystems most commonly used in Malaysia.Non-deflection based systems are equipmentusing radar sensors, nuclear devices, ultrasonicdevices, laser sensors and penetrometers suchas die Dynamic Cone Penetrometer.

Currently JKR uses four types of NDT equip-ment to evaluate structural condition of pave-ment. The sophisticated machines are theFalling Weight Deflectomcter (FWD) and theRoad Rater. The simpler devices are theDynamic Cone Penetrometer (DCP) and theBenkelman Beam. Description of this equip-ment and its usage is covered in para. 3.3.2below.

The background to the NDT approach of stnic-tural assessment was explained in Chapter 2. It

must be emphasised here that the accuracy ofthe results will depend on the experience of theuser in handling all evaluation informationdescribed earlier including the NDT results. Noin-house study has compared the results pro-duced by each device and its approach.Preference in the choice of equipment willdepend on speed of test, safety, cost of equip-ment, maintenance, reliability and case of use.Another factor that could be important is theauthority's requirements and emphasis for spe-cific aspects of testing. Safety of the publicduring any testing on the road is of paramountimportance. Test vehicle sometimes may bedisallowed from stopping on the road. A mov-ing test equipment (such as Deflectograph)could be preferred for such case. However, thistype of equipment can be very, expensive andnot easily maintained.

Comprehensive understanding of the elementsinvolved in the detailed pavement assessmentis critical. Over-emphasizing certain aspects ofthe elements can lead to uneconomical deci-sions. It inav be necessary to carry out cost-benefit analyses when choosing the most suit-able NDT equipment for the pavement evalua-tion.

3.3.2 Choice of NDT devices

Benkelman heam.

This is the original NDT deflection device andwas developed in the United States. The princi-ple used by this device is to iueasure the maxi-mum relative pavement surface deflectionunder a moving wheel load. Direct measure-ments using an aluninium beam and dial gaugeare made (Figure 3.2).

This equipment is included in this manualbecause it is accepted world-wide and had beenuse extensively over 30 Nears. JKR had usedthis equipment for the last 1 years. Because ofits simplicity. the confidence in its results ishigher than others. The portability of the equip-ment is also an added advantage. The latestversion can be modified such that it measuresthe complete dellectionn bowl.


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There are two ways io measuring the ntaxim-turt dellection using the Benkelman Beam.namely the 'rebound' and the 'transient' method.The transient method is recommended.Maximum deflection is measured on the near-side wheeltrack. Temperature, rut depth meas-urement and visual inspection is also carriedout simultaneously. The deflection is then cor-rected to a standard temperature of 40°C.

Deflection tests should be carried out at regularintervals. 20 to 50 metre intervals can be cho-sen. The deflection values at those intervals canthen be plotted along the test chainages tocheck the deflection profile. Simple stastisticalcalculations can be used to find a representativedeflection over a selected section. This deflec-tion value is then compared to a prerecordeddeflection history of similar pavements in simi-lar environments. The residual life of the pave-ment can then be predicted and the requiredsurfacing overlay thickness can also be deter-mined.

The use of Benkelman Beam is recommendedin places where expensive equipment cannot bejustified such as small rehabilitation projects.

Where traffic is light the deflection beam canalso be used to assess in-situ pavementstrength. However, it may not be suitable fortesting on a busy road. Some fatal accidentsinvolving the beam operators have occurredwhen using the Benkelman Beam on suchroads in Malaysia. This is the main reason forJKR preference for other deflection devices.

The cost of a Benkelman Beam ranges fromRM10,000-00 to RM50,000-00. A loaded lorryis needed which add to another RM50,000-00to RM10O,00O-00 for a complete and opera-tional equipment cost. Maintenance cost is lowdepending mostly on the lorry efficiency. Infull operation, 1 skilled staff and 3 unskilledstaff are required. Minimum of 2 moreunskilled staff is needed to control traffic.

Dynamic Cone penetrometer (DCP)

Before a DCP test is carried out coring of the

asphalt layer is required. Therefore in principle,the test could be considered as destructive.However, it can be accepted as an NDT sincethe damage caused by coring is minimal.

The DCP can be used to establish :

i) the strength of the granular pavement layers

ii) pavement layer thickness

The DCP is a penetrometer, suitable for roadpavements with unbound granular bases. Asteel rod with a 60° cone is driven through theunbound pavement layers by using a steel ham-mer applied at constant force (Figure 3.3).

The rate of penetration is inversely proportionalto the strength of the material. The relationshipbetween the rate of penetration and CBRenables the strength of granular pavement to bedetermined.

A complete set of DCP costs betweenRM1,00000 to RM3,000-00. Maintenance costis low. Only the cone needs frequent replace-ment. A coring machine and a light truck areneeded if testing is done on existing asphaltpavement. The cost of a fully operationalequipment costs ranges between RM50,000-00to RM70,000-00.

In a typical 8 hours day work on asphalt pave-ment more then 10 points can be carried out.Cost of testing per point is estimated betweenRM50-00 to RM150-00.

Road Rater

The Road Rater is a vibratory NDT device(Plate 3.3). A steady state harmonic vibration isapplied to the road pavement by a dynamicforce generator through a circular loading plate.The frequency of the force function remainsconstant with depth. A static pre-load is appliedto the pavement to provide a reaction duringthe vibratory phase. The transient deflectionsare measured during the steady-state loadingphase.


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Four velocity transducers are placed at the cen-tre of the circular loading plate, and at offsetdistances of 300, 600 and 900 millimetres. Ananalogue computer is used to convert the out-put of the velocity transducers into deflectionsusing a measuring technique normally referredas inertial system. This measuring system does

not require an external reference point for themeasurement of deflection that is needed forFWD or Benkelman beam (Figure 3.4).

The Road Rater produces a steady state har-monic loading and a static preload. It induces astiffened response of the pavement subgrade


Figure 3.2 Schematics Of A Typical Benkelman Beam

Figure 3.3 Schematics Of The Dynamic Cine Penetrometer

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system and can possibly overestimate its truestrength. Allowance for this can be made withengineering judgement and field experience inusing the device. Previous direct use of theRoad Rater has shown correct results where thedeficient aspects of the pavement has been accurately identified and repaired.

The Road Rater deflections and the FWD deflection are highly correlated. For this reasonand for the purpose of standardising proceduresit is recommended to convert the Road Rater

deflection into an equivalent FWD deflectionwhich is then used for the evaluation analysis.The relationship to convert the Road Raterdeflection values is :

FWD = 0.0246 + 6.87 Road Rater

At the time of writing, the Road Rater is notwidely manufactured and has become less pop-ular as compared to the FWD. Moreover it ischeaper and faster than most FWDs and hasthe advantage of low operation cost. Similar tothe FWD it must stop when taking measure-ments. Therefore adequate traffic control mustbe provided during testing for maximum safety.

Falling Weight Deflectometer

The FWD uses an impulse loading system. Atransient force is delivered to the pavement sur-faces. The transient pavement response isrecorded electronically.

The force is applied by a mass falling on a cir-cular plate that is connected to a baseplate bya set of rubber springs. There are three waysof changing the force amplitude :

i). Changing the massii). Changing the drop heightiii). Changing the spring constant (a linear

spring constant is assumed)

The force amplitude is measured by a load cellplaced at the baseplated sandwiched betweentwo steel plates.

The transient deflection is measured by geo-phones. A geophone has an internal mass thatmoves relative to the casing. The mass velocitygenerates an output signal that is integrated toobtain a deflection. One geophone is normallyplaced at the centre of the loading plate. Theother offset geophones can be adjusted accord-ing to one's own preferences or the manufactur


Plate 3.3. The Road Rater

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er specifications (Fir ure 3.5).

The pavement deflection induced by the FWDis typical of that produced by a single heavyvehicle which passed through a point on thepavement surface. However. this fact must notbe confused with the final requirement of thetesting that the device must indicate accuratecondition of the existing material. It is not nec-essary that accurate simulation of actual vehicleprovide accurate indication of materials condi-tion.

The results from the FWD are used to estimatethe pavement layer moduli. The estimatedmodulus values may indicate the currentcondition of the pavement materials.

Bituminous overlay can be design from theseestimated parameters. Various approaches usingthe FWD deflection readings have been devel-oped to design bituminous overlays. None ofthese has been verified in the field or supportedwith sufficient laboratory test for confident usein the Malaysian environment. However, exten-sive work by SHELL laboratories have present-ed a more convincing approach in the analysiswhich was supported by extensive laboratorytestings. Other researchers have carried outfield tests to verify the approach. The resultshows that reasonable estimates of the fatiguelife of asphalt can be obtained from the SHELLfatigue curves incor

porating suitable allowance factors.

Heavy Weight Deflectometer

The principle behind this model is similar tothat of the FWD except that it has been specifi-cally designed to fully meet the needs of bothhighway and airfield pavement deflection test-ing, up to and including the effect of veryheavy aircraft loads. This model is called theHeavy Weight Deflectometer (HWD) (Plate3.5).

The HWD spans a loading range of 30 - 240kN, thus covering the half-axle load imposed by a moderately heavy truck upwards throughthe single wheel load of a loaded BOEING 747aircraft.

HWD generalised data, combined with otherrelated parameters can be used in structuralanalysis to determine such informations as thebearing capacity of a pavement.

Availability of equipment in Malaysia.

The equipment described above is available atthe Pavement Unit, Research Centre, PublicWorks Institute Malaysia (IKRAM). TheInstitute is currently undertaking pavementresearch and evaluation prgjects. There are 2sets of Benkelman Beams, 3 units of RoadRaters, six sets of the DCP and 3 units of the


Plate 3.4. The Falling Weight Deflectometer

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light weight Falling Weight Deflectometer. Aheavy duty version of the FWD is also avail-able for further research and the evaluation ofairport pavements.

A Benkelman Beam test costs ranges betweenRMIO-00 to RM40-00 per test point. RoadRater testing costs between RM30-00 toRM5000 per point for an estimated 300 pointsper day work. The FWD testing costs normally

range between RM30-00 to RM80-00 per testpoint and is capable of covering an estimated250 points daily in a normal 8 hours workingday. Comparatively the FWD is the more cost-ly to operate and maintain. However, it is gain-ing popularity world-wide with the growing interest in using the mechanistic engineeringapproach of pavement analysis.


Figure 3.4. Schematics of the Road Rater

Plate 3.5. Heavy Weight Deflectometer

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3.3.3 Choices of NDT analysis technique

An interim evaluation method using the FallingWeight Deflectometer or Road Rater and theDCP is given below. The mechanistic or empir-ical approaches will bo improved by furtherresearch. It is anticipated that changes to this methodology will be necessary in due course when comprehensive field test results are avail-able.

Empirical structural assessment using the

Standard deflection refers to FWD centraldeflection at the verge-side (near-side) wheel-path under 700 kPa pressure on a 150 mmradius plate at 40°C pavement temperature.

The temperature is taken at 40 mm depthbelow the riding surface. Deflections obtainedfrom Benkelman Beam and the Road Raterrequires conversion of their maximum deflec-tion to standard deflection.

Standard deflection had been used as a basis ofpavement performance prediction. Pavementswith similar deflection levels and application ofrepetitive axle loading will reach terminal con-dition at the same time. High deflections indicate weak pavements whilst low deflectionsindicate strong pavements.

Deflection-life relationship can be developedfrom field experiments and historical measure-ments. The observations and measurements ofall failure manifestations take into account allthe failure modes by default. Terminal condi-tions can be chosen that balance both users' andengineers' requirement. It can also followexactly the basic concept of overlaying; that itis only applicable for non fractured or seriouslydeformed road conditions.

Long term monitoring of pavement overlays inJKR roads has successfully resulted in thedevelopment of a deflection based performanceprediction. Several design curves have been developed by IKRAM. The curves depict realfield situation of current material and construction standard of asphaltic concrete overlaysthroughout the country. Terminal condition isdefined as crack type 2. Pavement with crack-ing more serious than this is deemed unsuitable for resurfacing. These areas can easily be iden-tified from the surface condition survey.

The reduction in deflection before and afteroverlay indicate the improvement of strength ifasphaltic concrete or similar overlay is used.The required strengtening overlay for theexpected design traffic can be derive from therelationship as shown in Figure 3.6.The steps to be adopted for this approach are :


FWD, Road Rater or Benkelman Beam maximum deflection readings.

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Step 1. Deflection survey

Deflection measurement is first carried out inthe field using the FWD, Benkelman Beam orthe Road Rater. The reading must be reduced tothe standard deflection values. The frequencyand interval of tests may depend on the prelim-inary sections. Deflection measurements shouldnot be restricted to specific testing intervals.Simple checks on the variability of the deflec-tions should be made by comparing groups often consecutive values. The maximum andminimum values in the group should not differfrom the mean by one-third of the mean. Thisprocedure may reveal all possible weak andhighly variable areas. More tests may be need-ed at highly variable areas.

Step 2. Sectioning

The road can be divided into representativesections with respect to the deflection levelsand checked with the preliminary sections. Thestandard deflection data is plotted against thechainage. Confidence level at 85% is normallyused to select representative mean deflectionvalues within a selected section. Mean deflec-tions from adjacent sections must not be signif-icantly similar at 95% confidence level or elsethey have to be merge to make up a longer sec-tion.

Step 3. Traffic estimates

Past traffic information provides estimates ofthe number of axle loadings that have traversedthe pavement since the last major rehabilitationexercise. This requires a review of past trafficdata collected by the Highway Planning Unit(HPU), Ministry of Works. Traffic surveyrecords dates to more than 10 years back and issufficient to estimate accurate past traffic load-ing. Estimates of the load equivalency factorcan be made using procedures described in Chapter 4.

Step 4. Estimate residual pavement life

Estimate the pavement residual life from thedeflection life curve. The residual lives define

structural adequacy of the pavement respectiveto terminal failure conditions. The pavement issuitable for application of bituminous overlay ifit nearly reaches its end of life. Other methodsof treatment should be selected if the pavementhas significantly past its life (Chapter 5 .

Summary.

The simple approach of this method had madeit practical and simple for use by engineers.Historical observations ascertain all failuremodes are included for better and more realisticprediction of performance. The accuracy of theresults largely dependent on the accuracy of thehistorical data, the deflection measurementsand the estimates of traffic loading.

Examples

The road between Muar to Tangkak with a con-nection to the North South Expressway is to beupgraded. The last rehabilitation exercise wascarried out five years ago. Surface conditionsurvey was carried out during an initial visit tothe site. The results of cracking and rutting sur-vey was plotted as shown in Figures 3.7.

Preliminary sections were selected from theabove results. The survey was done at the righttime depicted by the level of rutting and crack-ing. Cracking is more prominant than rutting. Itis expected that an application of a suitablethickness of bituminous overlay is a reasonablesolution provided pre-treatment is carried out inareas which have localised failure.

Traffic is similar throughout the length of theroad since there are no major intersections inbetween. Traffic loading estimations have beenexplained in Chapter 4. Traffic would not influ-ence the earlier selected sections.

Deflection survey was carried out at 50 and100 metres intervals depending on the condi-tion of the pavements.

Inspection and statistical analysis of the deflec-tion data normally result in a revision of thepreliminary sections. The representative deflec-


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tion is estimated over a section by statisticalcalculation. The required overlay thickness canbe design for each section from this deflectionvalue.

Mechanistic structural assessment using theFalling Weight Deflectometer or the RoadRater

The deflection readings at the various offsetswhen plotted, produced a bowl shape diagramshown in Figures 3.8, normally termed as thedeflection bowl. This response from the load-ing system is the basis of a theoretical approachthat leads to the estimation of pavement layermoduli and residual life described earlier in

Chapter 2.

The materials characteristics, such as the mod-uli of each layer, Poisson ratios, layer thick-nesses are first estimated. A deflection bowl ispredicted using the multi-layer elastic theory.The predicted deflection bowl is compared tothe actual deflection bowl measured by theFWD. When they are equal or within a prede-termined identical range, the layer moduli satis-fying this condition is taken as the estimatedmoduli of the layer. These modulus values canbe used to estimate the condition of the materi-als in the pavement. The ratio of moduli of dif-ferent layers in the pavement (modular ratio)may also be used to interpret its condition. Themoduli values can be translated to CBR using arelationship given by :

CBR = E/10 ...... (after SHELLInternational)

Where, CBR = California Bearing RatioE = Modulus of material

The modulus of asphalt surfacing may varyfrom as low as 500 MN/mm- to more than10,000 MN/mm-. For the Federal RouteNetwork it may be assumed that asphalt modu-lus greater than 3500 MN/mm- is sound. Easierand clearer interpretation can be made if thereare available relationship between modulus ofasphalt against traffic damage. Research workby IKRAM is currently studying this aspect of

the interpretation with respect to the othershortcomings of the mechanistic modeldesribed earlier. An interim condition criterionis given in Table 3.3.

The stresses and strains in the pavement layerscan also be calculated. The tensile stress belowthe surfacing and the compressive stress on thesubgrade are the two critical stresses normallyconsider. The calculated stresses in the analysisare compared to their respective allowablestresses pre-determined in the laboratory toestimate their residual life. The material withthe lowest residual life is normally assumed torepresent the residual life of the pavement. Thiscalculation also requires traffic loadinginformation that provides an estimate of thenumber of repeated axle loading.

In summary, the steps involved in determiningthe moduli are as follows :

i) Input parameters are measured deflections, layer thicknesses and loading characteristics and geophone arrangements

ii) Estimate the moduli of surfacing (El), base (E2) and sub-base (E3) and the sub-grade.

iii) Transform the layers to equivalent homogeneous structures using the Method of Equivalent Thickness (MET)

iv) Calculate a set of deflections.v) Compare computed and measured

deflections.vi) If the differences in deflections are less

than + 5 %, then the moduli values can be accepted, otherwise repeat iteration from step 4 onwards.

Many computer programs are available in deal-ing with the above computation. Currentlythere are more than 10 available packages.These programs need proper evaluation andverification for correct use and interpretation. Itis important to bear in mind that the pro-grammes demand full understanding of itsinput and output procedure. Most importantly,its approach must be correct for local environ


Page 39



ment and its limitations are clearly outlined.

JKR is currently using the PHOENIX programthat was purchased with the FWD and is fullydocumented. This program was design com-plete with moduli estimation, residual life pre-diction and overlay design. The output modulusvalues was found to be reasonable and practicalfor pavements in Malaysia. Further develop-ment and verification of the program are inprogress.

Areas related to local temperature, moisture,

loading and actual field conditions are covered.At IKRAM, specific focus is given on thedevelopment of a cornputer package calledSERF (System for Evaluation andRehabilitation of Flexible Pavements) using local performance models. These models arederived from research at IKRAM and are veri-fied against established computer packages.This package has two main modules on evalua-tion and rehabilitation. The evaluation moduleis currently in use while the rehabilitation mod-ule is being designed to incorporate the expertsystem.


Figure 3.6. Reduction in deflection after overlay

Figure 3.7. Distribution of cracking and rutting

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The PHOENIX program produces estimatedmodulus values of each pavement layer andsuggests an overlay thickness. A reasonable andpractical overlay thickness can be obtained bythis method. However, it is still not certainwhether the overlays can achieve the designlife when age hardening effect govern the per-formance. There are lack of fatigue studies ofMalaysian pavement materials that closely

simulate field behaviour. This is a subject offurther research at IKRAM on the applicationof the multi-layer model.

There are several precautionary measures to be taken when using the multi-layer elastic theoryto estimate pavement residual life. This theorycan be used to estimate the dynamic behaviourof relatively stiff pavement. However, devia-tions occur under high temperature conditions


Pavement Layer Strength Indication Rating Estomated StructuralCoeffecient

SubgradeCBR < 5% (50MN/m2)5 - 10 %> 10 % (100 MN/m2)

PoorSatisfactory

Sound

0.100.200.23

Sub-base

Modular ratio (E3/Esg)< 1.51.5 - 2.0> 2.0

PoorSatisfactory

Sound

0.230.300.32

Gramular Base

Modular ratio (E2/Esg)< 1.51.5 - 2.0> 2.0

PoorSatisfactory

Sound

0.250.300.32

BituminousSurfacing

Modular value (MN/m2)< 15001500 - 25002500 - 3500> 3500

Very poorPoor

SatisfactorySound

0.600.700.850.95

Table 3.3. Material condition interpretation

Figure 3.8. Deflection bowl and material characterisation

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where it is difficult to establish an effective modulus for biturninous materials and forpavements that derive a large part of their structural stiffness from granular materials (2).Non-linear behaviour of pavement material isan added problem (3). The limitation of usingmulti-layer theory must be rnade clear and theengineer must not rely exclusively on resultsfrom the analysis alone. Reasonable results areachievable if four major areas listed below arecovered and supported with adequate laborato-ry or field testings :

i) Laboratory fatigue testing on various type of materials

ii) Major evidence of failure indicated by traditional fatigue failure

iii) Temperature effect on modulus values can be adjusted according to local conditions

iv) Field verification of fatigue performance.

The first three areas are covered in the SHELLmethod. Accelerated field fatigue testing hasbeen carried out elsewhere. The results suggesta factor of 10 or 20 is used when using theSHELL fatigue curves for estimating residualpavement life (4). However, there is evidencethat age hardening may dominate actual fieldbehaviour in hot climate (5). If these modes offailure are dominant the isotropicity and homo-geneity of bituminous materials will slowlycease to exist thus distorting the multi-layer model. Cracked pavements also alter the aboveconditions. Application of the multi-layer theo-ry to estimate residual life under this conditionmay deviate frorn the original assumptions andmust be treated with caution. These problemsare now under study at IKRAM. At present, thePHOENIX program is considered applicablebut it should be supported by adequate engi-neering judgement.

Structural assessment using the DCP

The DCP is portable and lightweight and canbe operated easily. It is a penetration test equip-ment that directly measures the ability of thematerial to resists penetration thus indirectly

indicating its strength. Detailed methods ofoperating the DCP are given in a Guidelinebeing prepared by IKRAM. The penetrationresistance is measured in millimetres per blow(DCP number). The DCP number is often cor-related to other established strength parameterscommonly used in pavement engineering. Suchparameters are the CBR values, structural num-ber and unconfined compressive strength. It isnecessary to calibrate the parameters to theDCP number for local condition. DCP Numberrelationship with in-situ CBR had been estab-lished for use in Malaysia. The following rela-tionship was developed for quick estimate ofthe CBR at each layer :-

CBR = 269/DCP

This estimate is limited for subgrade strengthbetween 5 to 100 % CBR (6, 7, 8). Research indeveloping specific a DCP evaluation method-ology for local use is still in progress. In thisguide, the approach using the structural numberto evaluate structural strength is considered.The procedures outlined below make use of thecurrent Arahan Teknik (Jalan) on pavementdesign which uses a similar technique.

The steps are :

Step l.The road stretch is first divided into uniformsections determined by the visual survey resultsfrom the initial assessment. The test locationsand intervals should be representative of thesections.

Step 2.DCP tests are carried out on the near-sidewheel track. The frequency of tests depends onthe length of sections and the uniformity of thepavement. A typical DCP test result and DCPplot is shown in Figure 3.9 and 3.10.

A summary plot of the results will show thevariability of the pavement thickness and esti-mated strength. Similar simple variabilitycheck procedure can be used as described earli-er in para. 3.3.3.


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Step 3.

Laboratory test need to be carried out on theasphalt layer. A 100 mm size core is normallyextracted at the verge-side wheel-path. Theasphalt core can be tested to estimate its exist-ing structural coefficient. Resilient modulustest, if available, is recommended to estimatestructural coefficients. The condition of thecore sample can also be used to estimate thelayer coefficient. This coefficient can be usedto calculate the structural number of the pave-ment (Table 3.4 . If the above method is used, it is best to include an estimate or a measure ofthe void content in the mix. High void contentmay reduce the

Step 4.Estimate the existing layer thicknesses and therespective CBR values. The procedures givenin the IKRAM DCP guideline, includes meth-ods of determining the layer thicknesses andCBR values. A uniform section consists of sig-nificantly similar layer thicknesses. If the layerthicknesses are significantly different, the sec-tioning may be adjusted. Pavement layer thick-nesses are normally critical in selecting theremedial measures.


Condition StructuralCoefficient

1. Sound, stable, uncracked.Little deformation in thewheel path.

0.6

2. Crack type 1 and < 5mmrutting. 0.7

3. Crack type 2 - 3, 5 -10 mmrutting 0.5

4. Crack type 4 or greater,> 10 mm rutting. 0.4

CBREstimated of

structural coefficients

Sub-base> 30 %20 - 30 %< 20 %

0.30.20.1

Road-base> 100 %80 - 100 %< 80 %

0.320.300.25

Table 3.4. Estimated values of structuralcoefficients for various conditions of asphalt

Table 3.5. Estimates of strictural coefficients,based on DPC in-situ CBR values.

NoNo.BlowsBlows

(sum)BlowBlow

PenPen.( mm )

NoNo.BlowsBlows

(sum)BlowBlow

PenPen.( mm )

NoNo.BlowsBlows

(sum)BlowBlow

PenPen.( mm )

0 0 0 10 90 180 10 180 42010 10 20 10 100 190 5 185 44310 20 50 10 110 200 2 187 48610 30 90 20 130 220 2 189 52510 40 90 10 140 250 1 190 59010 50 105 5 145 280 1 191 64310 60 120 5 150 320 1 192 69510 70 140 10 160 350 1 193 74810 80 160 10 170 380 1 194 800

Figure 3.9. DPC test results

ROUTE NUMBER : 1SECTION NUMBER : 238DIRECTION : UP

DATE : 1/1/1993METREAGE : 50CORE THICKNESS : 120 mm

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Step 5.Estimate the base and sub-base structural coef-ficient based on the in-situ CBR values fromthe DCP test. Their in-situ CBR obtained isindicative of the structural coefficient of thebase and sub-base layers. Available estimatesare based on overseas research. Verificationof the values suiting localmaterial is inprogress. The estimate can be made usingTable 3.5.

Step 6.Calculate the existing pavement structuralnumber. The structural number of the existingpavement can be found by using structuralnumber equation as follows :SN = h I x C I + h2 x C2 + h3 x C3 Where hl,h2 and 10 are the thicknesses of the asphalt,base and sub-base respectively. Cl, C2,and C3 are their respective structural layercoefficient.

Step 7.

Calculate the desired design traffic level. Thedesign traffic loadings for the required designperiod should follow the examples given inChapter 4.

Step 8.Estimate the design subgrade CBR that isexpected to represent the worst condition the

pavement will experi-ence within the design period. The CBR valuesfrom the DCP tests can be used as a basis ofselection.

Step 9.Estimate the required structural number andoverlay thickness using the design chart inArahan Teknik (Jalan) on pavement design.The required structural number should be high-er than the existing pavement structural num-ber. The difference is converted to asphalt layerthickness taking" structural coefficient of asphalt as 1.0.

The accuracy of this approach relies very muchon the accuracy of the structural number con-cept and estimation of the structuralcoefficient of each material. Field testing of thematerial has an advantage of determining actu-al condition of each layer. A low CBR valuesindicates a weak layer. This evidence providevaluable clues in determining the deficiencyand failure causes of the pavement.

3.3.4 Test interval, variability and accuracylevel for structural assessment

The frequency and accuracy level needed forthis assessment is primarily based on the resultsfrom the initial assessment. Poorly deterioratedpavements may require closer intervals of datacollection compared to a sparsely deteriorated


Figure 3.10. Typical plot of the DPC results

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pavement. The final selection of sampling fre-quency depends also on the uniformity of fail-ure conditions. Less samples need be takenfrom a more uniformly failed pavement.Sampling interval of 10 to 100 metres are nor-mally selected. Each preliminary sectionrequires a uniform interval of testing. A varia-tion in sampling interval allows more data col-lection at uncertain areas with dominant failuremanifestations. Simple variability checksdescribed earlier allows variation of test fre-quency.

The engineers need to employ suitable statisti-cal technique to analyse the data and make use-ful interpretation of the information. The select-ed testing interval will determine the samplesizes that should be sufficient to produce atunbiased estimate of the population mean ofparameters under study. Extravagant tests fre-quencies could result in wasted expensivedeflection or other NDT testings. Useful basicstatistical calculation such as mean, standarddeviation, variance and range improve interpre-tation of each parameter along the road understudy.

The accuracy of the structural assessmentdepends on the engineers experience in han-dling and interpreting available data. Eachlength of road under study may have uniqueproblems. The variable standards of previousconstruction method could pose further diffi-culties. The choice of assessment approachmust be made with due regards to these prob-lems.

3.3.5 Surface evaluation

General

Pavements without structural deficiency or donot need crack sealing require only surfaceevaluation. Slipperiness of the surface is theguiding criteria for road surface evaluation. Theroad surface can be assessed by testing twoattributes of the surfacing that relates to slipper-iness :

i) The wet skidding resistanceii) The surface texture

The micro-textures of the surfacing contributelargely for skidding resistance at low speed.Both the micro and macro texture are relevantfor high speed skid resistance, but the role ofrnacro texture is critical under wet conditions.Figure 3.11 shows the micro and macro-tex-ture.

To date, the skid resistance of a road surfacecan be assessed by using the Pendulum SkidResistance Tester (PSRT) developed by TRRL(8) (Plate 3.6 . The tester yields Skid resistancevalues (SRV) standardised at 35°C for local in-service pavement condition. This value simu-lates the wet tyre resistance of a vehicle travel-ling at 50 kph. The other device that is avail-able to meet this need is the Griptester (Plate3.7 Studies in U.K. have shown that theGriptester could produce accurate results ifused correctly. However, it has limitations inaccuracy of testing at difficult road geometries(9).

Surface texture

It is important for the engineer to know thatskid resistance is critical not only for low speeddriving but also for high speed driving. Surfacetexture of the surfacing plays a more importantrole for high speed driving under wet condi-tions. Adequate surface texture is needed toprovide channels for the bulk water trappedbetween the road surface and tyre to drainquickly to reinstate contact between the tyreand road surface. If this is not achieved a phe


Figure 3.11 Micro and macro-texture

Page 45



nomenon called aquaplaning is highly likely tooccur and will cause skidding. There is at pres-ent no mandatory minimum surface texturerequirement for new or in-service road surfac-ings in Malaysia. A review of the subject isbeing undertaken by IKRAM whereby aninterim specification will be prepared.

Surface texture can be measured conventional-ly using the Sand Patch method (Plate 3.8 orthe more advanced TRRL Minitexture meter(Plate 2.9). The sand patch is cheaper, easilyavailable and simple to use.

The texture measurements define indirectly the probability of the removal of bulk watertrapped between the tyres for safe high speeddriving under wet condition. There are circum-stance where the water film thickness under theMalaysian condition can reach a level whereeven the best surface texture will still be flood-ed with water. Heavy rainfall would normallylead to this phenomenon. Direct skidding testsimulating this condition at high speed may berequired. The Friction Tester is an example ofsuch equipment that can measure skid resist-ance under such conditions (Plate

Figure 3.11 Micro and macro-texture Skidresistance3.10). IKRAM will be equiped with this equip-ment in the near future which can measure the

slipperiness of both highways and airport run-ways (10).

3.3.6 Other key factors to consider during pavement evaluation

Moisture variation; drainage and shoulder,rainfall intensity, seasonal variation

Pavement cross section should be design toeliminate water from entering the componentpavement layers at any time. In Malaysia, newroad pavement would normally have these fea-tures. However, for old pavement, this seldom happens and consideration of moisture varia-tion in the pavement layers during the evalua-tion period should be noted. Seasonal variationplays a major part in the estimation and predic-tion of performance. Investigation measure-ments have to be corrected for seasonal varia-tions.

Environmental effects; rainfall, tempera-ture, humidity

The main environmental elements perculiar toeach country that can affect pavement perform-ance are temperature, rainfall and humidity.Bituminous material is known to be sensitive totemperature and other environmental factors.Most laboratory standards of testing for thismaterial are at 25°C depicting moderate service


Plate 3.6 Pendulum Skid Resistance Tester

Page 46




Plate 3.7 The Griptester

Plate 3.8 Sand Patch Test

Plate 3.9 TRRL Minitexture Meter

Page 47



temperature conditions. This should have been35°C or 40°C that realistically depicts localconditions. Research findings by TRRL haveshown that there is a significant increase in therate of pavement deterioration during the sum-mer period. However there is insufficientrecorded experience in field performance pre-diction above 35°C, covering the Malaysianrange of pavement service temperature. Withthis difficulty in hand the use of the simplifiedapproach must be carefully reviewed withexperience in the field.

The average yearly rainfall in Malaysia is 2000millimetres, higher than any other countryknown to have full research in pavement per-formance. Within the country itself there aredifferences in rainfall intensity. Hilly areas andthe eastern region of the country are knownto have high rainfall especially in the monsoon.Due recognition of this must be made.Accelerated deterioration of the surfacing inthese areas can be expected with the presenceof more water. The rate of change of deteriora-tion is also expected to be faster especiallythose related to cracking.

Little is known of the effect of humidity onpavement performance. However it is predictedthat the effect of heavy rainfall and temperatureare more to performance rather than humidity. Ultra Violet (UV) radiation is an additional fac-tor contributing to pavement deterioration. UVradiation is thought to accelerate the rate of

bitumen hardening at the surface. Research isstill in progress to understand and quantify itsrole. However, at this juncture the combinedeffect of environment in relation to ageing isthe best and most practical to consider.Hardening by oxidation plays a more critical role in the ageing process.

3.3.7 Detailed Material Investigation

General

Direct material assessment is only necessary if the non-destructive approaches fail to providesufficient information that confidently guidestreatment selection. This scope of works fallsunder the category of detail material investiga-tion that usually arise from premature pave-ment failures or very serious failures.

The usual approach to this is to dig a test pit inthe pavement at selected locations determinedfrom results of the initial assessment. Thematerials are sampled for laboratory testing.Insitu tests that could indicate actual materialcondition on site can also be carried out. TheJKR Standard Specifications for pavementmaterial govern the suitability criteria of exist-ing material. Detailed requirements of materialstandard should also follow this specification.

Surfacing

The strength and weakness of bituminous sur-


Plate 3.10 The Friction Tester

Page 48



facing are its behaviour sensitivity with temper-ature. The bitumen used in the mix is the maincontrolling factor that determine the propertiesof the mix. The primary functions of the bitu-men are :

i) Binding agent ii) Waterproofing iii) Stableiv) Durability and oxidation resistance

The condition of the existing mix may indicatedeficiency of some of the above requirements.Bitumen penetration grade 80/100 is normallyspecified for use in JKR road pavements.Laboratory tests can be carried out to investi-gate the condition of the bitumen in the exist-ing mix. The viscosity and the penetrationvalue of the bitumen can provide sufficientinformation on the condition of existingasphalt.

Apart from bitumen, the aggregates used in thesurfacing mix should be sufficiently strong towithstand traffic loading and construction oper-ations. It should also have adequate polishingresistance. Requirements of the StandardSpecifications should be met.

In summary, the key information related to thesurfacing that may be required during evalua-tion are: -

i) Type and composition of mixii) Thicknesses of each layeriii) Properties and percentage of bitumeniv) Temperature adjustment conditionsv) Fatigue or deformation relationship with

repeated loadingvi) Hardening characteristics of the mix vii) Aggregate grading, properties and pol -

ishing resistance

The condition of the existing pavement and thechoice of evaluation techniques govern thenecessity of the above information.

Road base

The primary function of the road base is for

spreading the traffic load. It must be strong andsufficiently thick. Unbound crushed stone, dry-bound macadam and wet-bound macadamhave been the major types of granular roadbase materials used in Malaysia. The specifica-tions and requirements for strength have beendescribed fully in the standard specifications.The thickness of the road-base layer is the mostimportant information that must be known inpavernent evaluation. It is mandatory if amechanistic analysis is used.

Granite and limestone has been the major typeof aggregates used for road construction inMalaysia. There has been no experimental evi-dence stating the better types for use as a road-base. Compliance to the requirements laiddown in the Standard Specifications is suffi-cient to judge the suitability of the material.During the evaluation, investigation of the den-sity and aggregate grading of the material maybe sufficient to check the quality of the road-base material used.

In-situ density test can be carried out to meas-ure the field density of the road base layer.Adequate samples should be taken for laborato-ry CBR test to check the material properties.DCP tests provide a simpler and cheaper alter-native to estimate the in-situ bearing capacityof the road-base.

Sub-hase

As a secondary load-spreading layer, thicknessis important, apart from other requirementsgiven in the standard specifications. In-situCBR Of the sub-base can provide an accurateindication of its existing strength. Laboratorytests could indicate its properties and suitabilityas a sub-base material. DCP tests can also beused to estimate the bearing capacity of the subbase layer.

Subgrade

The subgrade material that mainly consists ofcompacted soil is best studied using conven-tional soil testing procedures. In-situ tests suchas density determination, CBR and the DCP


Page 49



test may not be sufficient to asses the quality ofthe soil. Laboratory compaction test, moisturecontent, soil classification and CBR provide aclearer indication of the soil compliance torequirements in the Standard Specification.

Samples for moisture determination can betaken at various depths below the formationlevel to check for the existence of any moisturegradient. Bulk samples can be taken for labora-tory tests. The testing procedure and the qualityrequirements are stated in the JKR StandardSpecifications.In-situ measurements

hi-situ density of the soil indicates the fieldcondition of the compacted soil. The field den-sity can be compared to the maximum densityachieved in the laboratory. Poorly compactedsoil can be found by this method. Soil densitymeasurement by the sand replacement methodis normally used.

In-situ CBR is slow an expensive. The DCPcan be used to measure the penetration resist-ance of the subgrade. The CBR values can beestimated using established DCP in-situ/CBRrelationship.

Laboratory measurements

Undisturbed samples can be taken to the labo-ratory for density tests or the CBR tests.Disturbed sample should undergo compactionand the CBR test for better representation ofthe soil condition. Determination of theAtterberg's limit will further reveal the trueproperties of the existing soil. These propertieswill indicate the current condition of the soil.Selection of appropriate remedial action shouldconsider the condition of the existing soils. Fullreconstruction normally requires justification toproof that existing soil is unacceptable andneeds replacement.

Summary

Detailed material investigation is only neces-sary when NDT has failed to provide answersto remedy the ailing pavement. Sufficient engi-

neering judgement is required before digging atrial pit which is normally not recommended.Localised reconstruction area could be identi-fied from experience and historical evidence.Rutting and cracking intensities are best usedas a guiding criteria. This will be explained fur-ther in Chapter 5.

3.4 REFERENCES

1. M.S HOFFMAN, M.R THOMPSON. Mechanistic interpretation of nondestruc-tive pavement testing deflections. Transportation Engineering Series No. 32. Illinois Cooperative Highway and Transportation. Illinois 1982.

2. N.W LISTER, The transient and long term performance of pavements in relation to temperature, Proceeding of the 3rd Int.

Conference on the Structural Design of Asphalt Pavements, Vol. 1, London, 1972.

3. OVERSEAS UNIT. Deflection mesure-ments and road strengthening. Department of Transport, Overseas Unit Information Note. Crowthorne 1986. (Overseas Unit TRRL)

4. G.WJAMESON, K.G.SHARP, N.J. VERTESY, R. YEO. The fatigue performance of asphalt and cement treated crushed rock under accelerated loading. Proceedin,,16th ARRB Conference, (Part 2). Australia1992.

5. HASNUR I. The Deterioration of Bituminous Binders. M. Phil Thesis, University of Birmingham. 1990.

6. SABRI M., ZAIN A., SHAFII M. Quick in-situ CBR for Road engineering from Insitu-CBR/DCP relationship developed in

Malaysia. Proceeding 6th REAAAConference, Kuala Lumpur 1990.

7. FAUZI A, SHABRI S, DCP/CBR Relationship for soft soils in Malaysia. Proceeding, 7th REAAA Conference, Singapore 1992.


Page 50



8. ROAD RESEARCH LABORATORY. Instructions for using the portable skid resistance tester. Ministry of Transport, Road Research Laboratory, Road Note 27, London 1969 (H.M.S.O).

9. SABRI M. Skid Resistance and Surface Texture of Wearing Courses. MSc. Thesis, University of Birmingham 1991 (unpub-lished).

10. SAAB Friction Tester, Workshop Manual. SAAB Car Division. S-61181 Nykoping. 1993.

BIBLIOGRAPHY

1. DAVID CRONEY, The Design and Performance of Road Pavements, Department of Environment, Department of Transport, Transport and Road ResearchLaboratory. HMSO, London 1977.

2. YODER E.J., WITCZAK M.W. Principles of Pavement Design. 1975.

3. THE SIIEL1, BITUMEN HANDBOOK, Shell Bitumen U.K.1990.

CHAPTER 4 :

TRAFFIC LOADING ASSESSMENT

4.1 GENERAL

The assessment of pavement performance andmaintenance needs requires the use of trafficinformation. Pavement behaviour and perform-ance are dependent on repeated axle loadingsthat can be derived from traffic and axle loadinformation. It is most desirable to have bothcurrent and historical traffic data. This manualcovers structural and surface evaluationaspects, therefore the main focus will be givento heavy vehicle traffic.

The magnitude and number of individual wheelload passes both cause deterioration to the roadpavement. Research elsewhere has found thatlight vehicles weighing less than 1500 kg

(gross weight) will not cause any significantdamage to the road pavement. Heavier vehiclesnormally fitted with large axles will cause thedamage. The weight of an individual axle iscalled an axle load. A standard axle has beendefined as having an axle load of 8 160 kg(8.16 Tonne). The repetition of this standardaxle is used as the quantitative measure ofdamaging effect to the road pavement.

The extent of the final rehabilitation measuresrecommended depends on the expected usageof the improvement. Accurate traffic assess-ment is needed to study and forecast the impactresulting from the road improvement. Thechanges in traffic movements will determinethe future life of the pavement. Effects of traf-fic volume and loading to the pavement servicelife have been established since the AASHOroad test. It was shown that the pavement life isdependent substantially on the amount of heavyaxle load passes. Prediction of the accumulatedstandard axle load requires high degree ofaccuracy. The number of axle loads depends onthe commercial vehicle activities and types ofgoods transported along the road.

4.2 TRAFFIC CATEGORIES

It is highly likely that due to change in land useand other factors, the traffic using the road willchange once the pavement is upgraded.Origindestination surveys coupled with axleload surveys are the best methods that can beused to predict the traffic volume and type andalso the axle load spectrum within the studyarea. Although it is expensive and time con-suming to perform this task, it is necessary toachieve an accurate prediction of future pave-ment service life and performance. It should becarried out if resources are available.

Apart from normal traffic using die road, therewill also be generated and diverted traffic.Normal traffic can be counted by traffic survey.Origin destination surveys can be used to esti-mate the amount of generated and diverted traf-fic.


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4.2.1 Normal traffic

This category of traffic will pass along existingroad even if no improvement is carried out.The existing traffic count by the HighwayPlanning Unit (HPU) consists primarily of thiscategory of traffic.

4.2.2 Generated traffic

Road improvement will increase the efficiencyin transportation and would result in additionaltraffic. This category of traffic is difficult toforecast accurately. It will only be significant ifthe reduction in transport cost is high. In manycases, generated traffic on the existing Federalroad networks can be ignored.

4.2.3 Diverted traffic

When the pavement condition has improved,there will be traffic diverted from another route(or mode of transport) preferring to use theimproved facility. This isan important consid-eration in the design. Most traffic survey wouldnot only measure normal traffic, it includes theamount of possible deviated traffic. In this case,it is necessary to carry out origindestinationsurveys that could provide data on the trafficdiversions likely to take place. This surveyshould be carried out for projects with largesums of money allocated for improvements.Assumptions can be made that all vehicles willdivert to the improved facility if time or moneycan be saved, otherwise they will remain usingthe same route or mode. In Malaysia, changingmodes of transport as a result of road improve-ment is negligible since the choice of othermodes of transport is limited. It can be signifi-cant if other main transportation modes, espe-cially railways, are improved. Rail serviceshave the capacity to carry heavy loads and pos-sibly reduced pavement loadings. However, inview of the higher quality of service providedby road, only small allowance can be made.

4.2.4 Special traffic

In Malaysia, there has been cases where neweconomic development has introduced extra

road transportation activities. Heavy materialsor goods in transit have significantly increasedthe damaging effect to the pavement. If thedevelopment can be forecast or known earlier,it is best to include some of this future effectsin the design. In certain cases, a specific direc-tion of travel has a very large difference indamaging effect compared to the other direc-tion. Rehabilitation design must consider thisphenomenon especially if the probable damag-ing effect is very significant.

4.3 TRAFFIC AND AXLE LOAD SURVEYS

The Highway Planning Unit (HPU) carries outtwo traffic counts yearly at designated roadlinks throughout the whole country in themonths of April and October. Results of thecounts can be obtained in the following year.However, axle loading and origin-destinationinformation are not included. For immediateand effective traffic information for pavementevaluation, specific surveys need to be carriedout. These specific surveys may include origin-destination surveys and axle weighing.However, if generated or deviated traffic is pre-dicted to be small, the origin-destination surveycan be ignored.

4.3.1 Specific survey methods

To reduce errors in estimating traffic and axleloading, it is recommended that for specificsurveys, consecutive seven-day counts orweighing during normal period be carried out.The 24-hour count is preferred since heavyvehicles are more active after dusk. If this istoo difficult or costly, a 16-hour count orweighing can be carried out coupled with atleast a full 24-hour count or weighing so thatadjustments can be made to gross up the 16-hour values. More accurate results can beobtained if this procedure is repeated severaltimes during the analysis year. A representativedaily traffic volume or loading can be calculat-ed from this method of sampling.

For specific surveys, traffic counts can be car


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Plate 4.1 Axle load weighing

16 HOUR TRAFFIC COMPOSITION BYVEHICLE TYPE OCTOBER 1990

Percentage Vehicle CompositionsSection No. 16-IIr Peak Hr (Period) Cars & S. Vans & Medium Heavy Buses M'cycles Heavy(Old) (New) Trailic Traffic Trucks Utilities Lorries Lorries Vehicles

DISTRICT BATU PAHAT

OS29 (JR105) 9630 845 (1700 - 1800) 18.3 13.3 15.0 6.2 3.1 14.1 24.3S28R (JR107) 18121 1703 (1300 - 1400) 38.4 14.2 10.0 4.0 6.5 26.8 20.5OS29 (JR105) 11510 1381 (0700 - 0800) 45.3 11.3 12.8 6.1 3.5 21.0 22.4

DISTRICT KELUANG

0042 (JR305) 12100 1024 (1800 - 1900) 42.6 10.4 16.8 14.8 3.5 12.0 35.1F54R (JR306) 26695 2111 (1700 - 1800) 44.2 12.7 8.4 5.0 2.9 26.8 16.30043 (JR304) 1164 7878 (1700-1800) 43.5 8.5 19.7 17.2 4.0 7.1 40.9

DISTRICT MUAR

F42R (JR61 I) 6016 452 (1800 - 1900) 51.3 9.8 12.0 6.0 3.0 17.9 21.0OF-41 (JR601) 10596 881 (1700 - 1800) 50.4 9.8 12.7 2.5 2.8 21.8 18.0S26R (JR609) 5055 410 (1500 - 1600) 39.6 8.7 23.8 7.6 3.1 17.3 34.5

DISTRICT SEGAMAT

0038 (JR801) 6444 488 (1400 - 1500) 40.3 12.9 10.9 12.3 2.1 21.6 25.30052 (JR802) 5614 442 (1700 - 1800) 43.4 15.4 11.2 12.9 2.0 15.0 26.10039 (JR803) 6583 556 (1400 - 1500) 44.7 11.8 10.2 18.3 1.6 13.4 30.1OS22 (JR804) 4444 416 (1900 - 2000) 42.3 12.5 9.2 4.7 1.5 29.8 15.4

Table 4.1 Typical HPU Traffic Sutiey results

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ried out manually using hand-held traffic coun-ters. The counting operation can be divided intoa few groups to count specific vehicle types inboth directions of travel.

Portable axle weighing devices can be used toweigh the axle loads of heavy vehicles Plate4.1 Weigh-in-motion technique is also availableand this could be a better choice since full sam-pling of heavy vehicles can be made. Bothtypes of equipment normally measure thewheel load of each axle. The axle load will betwice the wheel load.

4.4 FORECASTING FUTURE TRAFFIC

4.4.1 Base data

The base data for forecasting future traffic canbe taken from the specific traffic and axle loadsurvey results. If this is not available, trafficinformation from the HPU can be used (Table 4.1)

4.4.2 Methods of Predicting growth and Compounding

The year of survey is normally taken as thebase year. Refering to past historical traffic data, the growth rate of normal traffic can beestimated. The baseline traffic can be calculat-ed after making allowances for possible gener-ated and diverted components. From the base-line traffic, future traffic can be accumulatedover the design period using the standard com-pounding formula.

CESA = YESA x {( 1 + r )" - 1 }/r

Where CESA = Cumulative equivalent standard axles

YESA = Equivalent standard axle of base yearr = Growth rate n = Design life

4.4.3. Estimating Damaging Effect (Load equivalent factor)

The axle load survey data is used to estimatethe damaging effect of heavy vehicles. The

equivalence single axle load factor for eachaxle weighed is calculated using the relation-ship :

EF = (N/8.16)4.55

Where :N = Axle load (in Tonnes)EF = Equivalent factor of the damaging

effect4.55 is the load equivalency exponent 8.16 is the standard axle load in Tonnes

The axle equivalency exponent of 4.5 can beused as an interim value. This value was rec-ommended for use in Malaysia based on over-seas experience (2). It is sufficient to use thisvalue to assess the damaging effect.If axle load surveys are not possible, estimatesof the damaging effect can be chosen from paststudies of similar survey. The estimates canalso be made using procedures given in ArahanTeknik (Jalan) on pavement design.

4.4.4 Sensitivity and Accuracy

The errors in traffic estimation for pavementevaluation will come from areas describedbelow. To reduce these errors some guidelinesare provided: -

i). Traffic counts

If the method of counting as described in para 4.3.1 is used, then error in obtaining representative daily traffic vol-ume can be minimized especially if it is repeated a few times. A specific survey is better than relying on periodic count.

ii) Axle weighing and estimation

The accuracy in weighing will depend on the type of equipment used. Static weighing is more accurate but slow and only small samples can be obtained. Theweigh-pad must be made level with the surrounding test area otherwise a small tilt of the vehicle could introduce large errors. Weigh-inmotion techniques could


Page 54



be faster and produced more samples but it may not be accurate. Thus, it requires skillful calibration. Any weighing method can be used provided the above considerations with respect to accuracy are carefully noted.

iii). Conversion to damaging effect

The equivalency formula given in para 4.4.3 is subject to changes when more local research results are available. This is the best available estimate of damag-ing effect being used by many countries.Each axle weight should be converted individually using the relationship and totalled for a specific class of vehicles. The mean equivalent factor for each vehicle class can then be determined by dividing the total equivalent factor by the total number of vehicle in that class.

iv). Estimating growth

Estimating the growth rate of heavy vehicles can be the most difficult part and could change the overall estimate drastically. Some economic knowledge of the country is thus helpful. Advice and discussions with economists are invaluable. The growth rate of heavy vehicles is dependent on economic activities and transportation of goods especially for semi-agricultural country like Malaysia. As a broad estimate an assumption can be made that the growthrate is similar or twice the growth in Gross National Product (GNP).

v). Directional difference

On certain roads. traffic flow or damag-ing effect due to heavy vehiclestravelling in one direction can be very different to that of the opposite direction.Lorries using roads connecting logging areas, quarries. docks, steel factories, etc., are heavily loaded when they leaves these areas but are mostly empty when coming in. Special allowances

need to be made for these cases. Using the results from the heavily loaded lane only, can sometimes be adopted. Due consideration must be made if it is too excessive and becomes uneconomical. Staged rehabilitation may be more appropriate in such cases where the risk can be reduced.

6. Seasonal variation

Traffic flow and transportation of goods inMalaysia in general have very small seasonaleffect. The majority of the national agriculturaland industrial products are available throughoutthe year. In most evaluation cases, error withrespect to this can be considered insignificantand ignored. However, in certain regions of thecountry seasonal variation due to the rice har-vest may be significant.

7. Abnormal cases

Malaysia being a multiracial nation has manyfestive seasons the dates of which change year-ly. Care must be taken not to cam, out anystirvev at this time. othenvise, the result willnot be representative. Small allowances can bemade to adjust these effects.

There are cases when upgrading are needed forspecific activities such as the construction ofhuge projects that requires transportation ofheavy materials at using identified routes with-in specific or non-specific periods of time.Information on the quantity of materials to betransported and the type of vehicles to transportthe materials will enable estimates of theincrease in damaging effect to be made. A typi-cal case is shown in Problem 2 of the followingexamples.

4.5. EXAMPLES

Problem 1

In the year 1989, a road stretch from Muartown to Tangkak leading to the North-SouthExpressway was to be upgraded. TheExpressway terminated at the Tangkak inter-


Page 55



change and vehicles travelling southboundwould exit there. The next portion of theExpressway, southbound, was projected to becompleted in late 1992 where 50 per cent ofsouthbound heavy vehicles using the road wasexpected to divert to that part of theNorthSouth Expressway. The expected increasein northbound heavy vehicle traffic was 20 %due to increase activity towards the highway.Estimate the damaging effect for rehabilitationdesign for ten years for each direction takingthe diversion into consideration and comparethe average loading if the diversion wasignored.

Solution 1:

A specific 24 hour classified axle load surveywas carried out where all the heavy vehicleswere weighed. The results obtained were asshown in Table 4.2 and 4.3.

Seven consecutive 24-hours count was carriedout and the summary of heavy vehicles areshown in Table 4.4.

In 1989, the yearly damaging effect of thesouthbound direction was 429,717 standardaxles, 257 °" higher than the northbound traffic.The above table shows that the vehicle loadingis critical in producing the difference in damag-ing effect. In this case commercial vehiclestravelling southbound were more heavilyloaded. It is highly likely that these vehiclescontained raw products that are normally heav-ier than processed products.

A similar trend of loading and damaging effectis assumed in the 10 years' design period. Theexpected growth rate is 5 per cent throughoutthe design period. To calculate the cumulativeloading for that period, the relationship in para.4.4.2 can be used. However, the calculationsshown below are for each year. to sho,,N theeffect of diversion. This method of calculationis also suitable for estimating past traffic wheneach yearly damaging effect will be knownmore accurately.

If the diversions were not considered the fol

lowing traffic will be estimated :-

Southbound :

CESA = 429,717 x { (1 + .05)'° - 1}/0.05= 429,717 x 12.5778= 5,404,934= 5.4 million standard axles (msa)

Northbound :

CESA = 120,337 x 12.5778 = 1,513,586= 1.5 msa.


HeavyVehicleGroup

(sum)Equivalent

Factor

(sum)Vehicle Mean E.F.

A 7.38 225 3.28

B 1000 350 2.86

C 270 125 2.16

D 200 450 1.33

Table 4.2 Axle load survey results fordirection 1, Southbound.

HeavyVehicleGroup

(sum)Equivalent

Factor

(sum)Vehicle Mean E.F.

A 124.32 112 1.11

B 116.10 135 0.86

C 40 80 0.50

D 26.25 75 0.35

Table 4.3 Axle load survey results fordirection 2, Northbound.

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E HEAVY VEHICLES

GROUP A GROUP B GROUP C GROUP D

DirectionsDay

SouthBound

Northbound

SouthBound

Northbound

SouthBound

Northbound

SouthBound

Northbound

1 125 112 212 202 95 76 45 41

2 186 156 255 215 72 82 56 51

3 172 190 189 172 88 98 62 64

4 144 124 156 144 86 66 52 59

5 131 123 178 128 67 67 55 57

6 122 132 119 111 66 56 49 42

7 91 77 120 122 30 43 12 5

AVERAGE VEHICLES 139 131 176 156 72 68 47 46

STANDARD AXLEPER COMMERCIALVEHICLE (SA/CV)

3.28 1.11 2.86 0.86 2.16 0.50 1.33 0.35

CUMULATIVE YEAR-LY S. AXLE 166410 53075 183726 48968 56765 12410 22816 5877

Total yearly Southbond cumulative standard axles = 429.717

Total yearly Northbond cumulative standard axles = 120,337

Table 4.4. Traffic Count Results For direction 1, Southbond

YEARCOMMERCIAL VEHICLE

COMMENTSSouthbond Northbond

1989 429,717 120,337 Base year

1990 451,202 126,354

1991 473,762 132,671

1992 497,451 139,305 North-south Expressway (Completed)

1993 261,162 175,552

1994 274,220 184,300

1995 287,931 193,516

1996 302,328 203,191

1997 317,444 213,351

1998 333,316 224,018

1999 349,982 235,219 End of analysis period

TOTAL 3,548,798 1,827,477

Average cumulative yearly standard axles (CESA) = 2.69 msa

Table 4.5. Distribution Of Yearly Damaging Effect

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Average CESA = 3.45 msa

The average design accumulated loading isnearly 30% higher if the diversion is ignored.

Solution 2 :

Without specific traffic or axle load surveyresults

From the HPU traffic survey results in 1988,the traffic results as shown in Table 4.8 wereobtained from a recent count in April.

If similar count is available in October, theaverage values should be used. The yearlydamaging effect = 1326 x 365 = 483,990 stan-dard axles. This will be the base year traffic.Accumulation procedure can be done similarly as shown in the previous solution

Problem 2: Abnormal traffic

A road is to be upgraded to transport 900,000tonnes of goods yearly, from one end to theother. The estimated maximum gross weightper vehicle that will be used is 45 tonne. Thespecification and dimension of the vehicle areavailable. The vehicle type is a five axle trailer.The distribution ratio of axle loading on thefive wheel arrangement is0.14:0.20:0.20:0.23:0.23 on the five axles andremains similar for lower or higher gross loads.This additional commercial activity willincrease the damaging effect to the existing pavement. Estimate the increase in damagingeffect on the pavement.

The damaging effect will depend on the config-uration of the vehicles and the load that theywill carry. For the purpose of estimating thedamaging effect of this additional commercial

activity, several assumptions were made, aslisted below :-

i. The distribution of load in the trailer is uniform and distributed within the trailer length with no overhang.

ii. The distribution ratio of axle loading on the five wheel arrangement is 0.14:0.20:0.20:0.23:0.23 and remainssimilar for lower or higher gross load.

iii. Only trucks with minimum of five axles will be used and trucks returning are ennpty resulting in negligible damaging effect.

iv. The damaging criteria considered was based on phenomenological theory of cumulative axle load damage only using equation given in para. 4.4.3.

Solution :

The gross weight of each vehicle was found tobe 45 tonnes with maximum axle loads ofmore than 10 tonnes, the loading that may beused.

Amount of goods to be transported yearly is900,000 tonnes.

Gross weight of each vehicle = 45 tonnes payload = 37 tonnes Maximum axle load will be10.35 tonnes.

Therefore number of vehicle trips per year =900,000/(37) = 24,324

The vehicle type is a five axle trailer that willhave an estimated axle load distribution ratio of0.14:0.20:0.20:0.23:0.23 on the five axles. It is


Survey DateTotal Daily

CommercialVehicles

percentageCommercial

Vehicles

Estimatedequivalent Factor

(Table 3.2)

DamagingEffect

April 442 23 % 3.0 1326

Table 4.6. Summary Of Traffic Counts Results Obtained From HPU

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assumed that the distribution of goods in thelorry is uniform and distributed over the fulllength of the trailer, otherwise this figure maychange significantly. For gross weight of 45tonnes , the damaging effect that this lorrywould provide is 9.33 times standard axleweight of 8.16 tons or the nunnber of equiva-lent standard axles per lorry is 9.33. The accu-mulate yearly standard axle is therefore :

24,324 x 9.33 = 226,943or 0.227 million standard axles (msa).

For each year, the additional number of axleloading that will be experienced by the pave-ment is 0.227 msa. This additional loading willincrease the rate of deterioration to the pave-ment. Other factors controlling the rate of dam-age will depend on the current structural condi-tion of the pavement and distribution of thegoods in the trailer. The existing condition ofthe pavement could be evaluated by properpavement evaluation if deemed necessary(Chapter 3).

Existing pavements which have high trafficloading inay not experience significant increasein axle loading or the damaging effect resultingfrom the values calculated above. The normaltraffic using the route is already high, thereforethe percentage increase would be small.However for an existing pavement with lowtraffic loading and weaker pavement, anincrease in the axle loading with the abovemagnitude will accelerate the rate of deteriora-tion. This is not favourable and due considera-tion must be made if the abhormal traffic is toutilise such roads.

4.6 REFERENCES

1. The AASHO Road Test Report, Highway Research Board. Report 5: PavementResearch.Special Report 61E. Washington, D.C., 1962 (National Academy of Science, National Research Council), Publication No. 954. AASHO

2. Transport and Road Research Laboratory (1978) Guide to the measurement of axle

loads in developing countries using a portable weighbridge. TRRL Road Note No 40. Her Majesty's Stationery Office, London.

3. ZAIN ARIFFIN, YOJIRO MIYAOKA, Axle load survey at Jalan Vantooren, Port Kelang, Selangor. Cawangan Jalan Ibu

Pejabat JKR, Kuala Lumpur 1983.

CHAPTER 5 :METHODS OF REHABILITATION

5.1 SELECTION PROCEDURE

In the previous chapters, the sources of pave-ment problems, their failure modes and per-formance forecasting have been described. Inthis chapter, the results of the evaluation carriedout on the pavement are used to establish themost appropriate method of rehabilitation.

The selection procedure depends heavily onengineering judgement but other factors suchas costs, construction feasibility, effects on thegradeline and the road user should be consid-ered as well. The general process of selectingan appropriate treatment is as shown in Figure5.1.

Stage l: Identifying Prohlein

As a first step, the mode of failure of the exist-ing pavement needs to be identified. At thispoint, constraints on the projects such as thedesign life of the rehabilitated section should beidentified.

Stage 2: Identifying Prohahle Alternaties

Based on the results of pavement evaluation. anumber of alternative methods of rehabilitationshould be selected. These are tested against thefeasibility of design, construction constraints,and requirement of service life.

Stage 3: Selecting the Preferred Solution

Those alternatives which pass these criteria are


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further analysed by considering their life-cyclecosts and other non-monetary constraints.Finally, the preferred rehabilitation alternativeis selected for detailed design. The engineershould not rule out using different techniqueson one project. It may be more cost effective todo this than select a common method of reha

bilitation for the whole project.

Each alternative technique is evaluated first on the merit of its design and construction feasibil-ity. Consideration should be given to the prob-lems of construction during monsoon periods, for instance. Care must be taken where roads


Stage 1 IDENTIFICATION OF PROBLEMS

* Conduct pavement evaluation* Identify constraints

Stage 1 IDENTIFICATION OF PROBLEM ALTERNATIVES

* Select possible rehabilitation treatmrnts* Chock design and constuction constraints

Stage 1 SELECTION OF PREFERRED SOLUTION

* Cost analysis* Other constuctions* Select preferred solution* Detailed design * Construction

Figure 5.1. General process For Selecting Appropriate Rehabilitation Alternatives

Figure 5.2. The Spectrum Of Pavement Rehabilitation Alternatives

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pass under bridges. For traffic and safety pur-poses, the vertical clearance underneath abridge should be maintained and this will limitthe allowable overlay thickness. Other factorsto consider include traffic control requirements,disturbance to the public, the need for stagedconstruction, and the availability of plants andmaterials.

5.2 REHABILITATIION OPTIONS

The rehabilitation of flexible pavementsencompasses a broad range of activities whichcould be grouped into three categories namely:

i) Restorationii) Resurfacing (strucl.ural)iii) Reconstruction

The choice of any specific rehabilitation tech-nique depends on the condition of the existingpavement. The conditions which apply for oneproject may be different from another. For thisreason, rehabilitation techniques will changefrom one project to another or within one sin-gle project. Although other factors areinvolved, theperformance and cost-effective-ness of each type of rehabilitation techniquewill depends primarily on the existing pave-ment condition. As a general guide, the differ-ent pavement rehabilitation options can besummarised as shown in Figure 5.2 where theyare related to the life of the road.

In the first phase of the pavement's life, its con-dition is good and its rate of deterioration isnormally low. At this stage, routine mainte-nance should be considered as it may be morecost-effective than carrying out major mainte-nance later in the life of the pavement.

Restoration

As the pavement condition deteriorates further,particularly when distress such as cracking andpolishing of the aggregate become apparent,the restoration rehabilitation option is warrant-ed. Some techniques that maintain the service-ability of the pavement include :

i) rejuvenating the aged surface using chemicals

ii) scaling the cracksiii) blinding polished and flushed surfaces

with hot aggregatesiv) applying thin bituminous overlaysv) cutting affected areas and patching with

new bituminous mixesvi) recycling the affected surface

The surface recycling and cut and patch alter-natives should be considered especially whenthe deterioration of the pavement is moreadvanced but has not reached the stage where astructural overlay is necessary.

Successful restoration work achieves one ormore of the following; it repairs the existingdistress, decreases the rate of increase of rough-ness, and slows down the subsequent pavementdeterioration by arresting the mechanism caus-ing the distress. For example crack sealing willpreN ent water from entering the pavementthus preventing failure in the lower layers.

Resurfacing (Structural)

As the cumulative traffic load increases thefatigue life of the surfacing is exceeded, whicheventually manifests itself in the form of crack-ing in the wheel path (crocodile cracking).When the pavement has suffered severe andextensive structural damage, restoration worksmay not be cost-effective. Structural improve-ment would then become a costeffectiveoption. It is therefore important to determinewhen a pavement requires structural improve-ments as opposed to restorative work. This canbe done by carrying out a pavement evaluationexcercise to determine the structural integrity ofthe pavement.

Resurfacing is currently the most popularmethod of rehabilitating distressed pavementsin Malaysia. It involves the placement of freshmaterial on the existing surfacing whichimproves riding quality and provides additionalstructural strength. It is necessary to design theoverlay thickness in order to achieve thedesired design life.


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The most commonly used resurfacing materialsare: -

i) thick asphalt overlaysii) granular overlays

Resurfacing cm be applied to all types of dis-tressed surfacing, but pre-treatment is some-times necessary before resurfacing isactually carried out.

Reconstruction

A pavement that is allowed to deteriorate fur-ther will eventually reach a state where thedeterioration is so advanced that even a thickoverlay would be less cost effective than thereconstruction option. Reconstruction of thepavement layers will be necessary when any ofthe layers has deteriorated beyond economicalrepair. Depending on the layers needing repair,reconstruction can be categorised into full orpartial reconstruction. Full reconstruction isneeded when the existing subgrade has deterio-rated and become unstable. Partial reconstruc-tion is carried out when only the road base orthe subbase layers have deteriorated.

In order to determine the extent of reconstruc-tion required, the pavement structure will haveto be examined by carrying out an evaluation

of the existing pavement condition. This can bedone using non-destructive methods or by dig-ging trial pits to carry out a more direct exami-nation of the conditions of the lower pavementlayers. However, digging trial pits should beavoided as much as possible because the rein-statement works usually do not bring back thepavement to existing conditions. This willresult in a depression on the road surface.

When the failure of the road base is very exten-sive, the road base can be recycled along withasphalt surfacing either by adding additionalaggregate or cement to stabilise the new roadbase material.

The construction of recycled stabilised roadbases requires specialised machinery. Standardplant are not not suitable for this type of con-struction.

5.3 RESTORATION

Restoration is designed to restore the surface toa suitable condition for placement of an addi-tional stage of construction or otherwise toperform satisfactorily for a substantial period oftime. These techniques include rejuvenation.patching, cold milling, crack sealing and sur-face recycling.


Figure 5.3. Replacement Of Loss Chemical Constituents By Rejuvenation

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The restoration option is suitable for pavementswith good structural integrity of standarddeflection lower than l).5 mm. It is best appliedto pavanents with distress limited to the surfac-ing. Block cracking, stripping, cracks, ravel-ling, polishing, bleeding and aged surfacing arethe typical types of failure suitable for restora-tion techniques.

5.3.1 Rejuvenating

Description: Hardened or aged bituminoussurfacing can be restored by spraying a laver ofbitumen or polymer modified bitumen toimprove its existing condition. Rejuvenatingagents have been introduced as an alternativeas they can restore the original properties of thebitumen. Figure 5.3 shows the constituents ofthe bitumen in the bitumen suffering fromhardening and the effects of adding lost con-stituents. The effect of rejuvenating agents hasnot been studied in the Malavsian environment.Currently the available products claimed thatthe rejuvenating agents could replace the poly-meric constituents lost as a result of oxidationand loss of volatiles. Howevcr the correctchoice of rejuvenating agent depends on care-ful study on the bitumen condition in the exist-ing surface as it will dictate the type andamount of rejuvenating chemicals to be used.

Conditions of use :AgeHardening had been described earlier asa major cootributary factor to deterioration ofbituminous surfacings.

The top few millimeters of the surfacing sufferthe most severe hardening. Thin surfacingswhich suffer from this effect will look dry. Forthick asphalt, cracks may occur from the topwhere rejuvenating chemicals can be applied.Laboratory tests are needed to identify thedegree of improvement and thus the most cor-rect use of rejuvenating chemicals. Excessintroduction of polymeric constituents mayeffect the bitumen properties. As such, precau-tions should be taken to eliminate the possibleintroduction of other problems such as bleed-ing, a slippery surface and weakening of exist-ing asphalt. The cost of rejuvenating agents

should be compared to the increased life ofpavement to establish its cost effectiveness.

Construction : The application of the rejuvenating chemicalsis simple to carry out. There is no specialequipment needed for this work. On a largersize job, it may be economical to use amechanical sprayer (Plate 5.1)

Since the chemicals used tend to-leave a layerof residual oils on the road surface, slowingdown the traffic during the initial period is veryimportant.

Cost :Currently, in Malaysia there are not many reju-venating chemicals being marketed. The pricerange for a rejuvenating job is about RM 2.00to RM 4.00 per square metre depending uponthe area to be rejuvenated.

Reliability :The performance of the rejuvenating chemicalsdepends upon how deep the chemicals aredrawn down into the bituminous layer. This isdependent on the density of the surfacing. Adense mix such as the Asphaltic ConcreteWearing Course will experience little drawdown. Rejuvenating chemicals are useful whenused with other methods such as the surfacerecycling, where the chemicals are used toreplenish the lost chemical constituents in theasphalt.

5.3.2 Crack Sealing

Description: Crack sealing is a cheap restora-tion alternative which would seal the cracksfrom ingress of water. Small or fine cracks (<3mm wide) may be filled with crack fillers. Inaddition, fine sand or fine aggregates may beadded to fill up larger cracks. The major benefitto be gained from proper sealing is that itreduces water infiltration into the cracks.

Conditions of use :Crack sealing is normally carried out forenvironmentally induced block cracks whereenvironment is the major controlling factor of


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such failures. Fatigue related cracks which aresealed only provide short term benefits. Theperformance of crack sealants will depend onthe age of the pavements and traffic loading. Itis also best done where the road is structurallystrong.

There are several different types of cracksealants, and each has its own unique proper-ties. Hot or cold bituminous products are gen-erally used. Sealant materials available includerubber asphalt, low modulus silicone and petro-leumbase sealants. Each of these materials hasdifferent durability, bonding, extensibility andother properties. Only the best available sealantshould be used for long lasting performance.Crack sealing should be carried out as a meansof deterring ingress of water into the pavementlayers.

Construction:Before cracks are sealed it is bet-ter to remove dirt and loose materials from thecracks. These are done using air compressors.Care must be taken to ensure safety of vehiclesbefore opening to traffic. Any loose materialmust be swept away. If sand is used as addi-tional filler, allowing slow moving traffic canhelp the embedment of the small particles intothe cracks. Excess filler material must beremoved since this could reduce the skid resist-ance of the surface (Plate

Cost :The cost of sealing cracks depend on the typeof sealants used and the size of the job. Thecost can range from as low as RM 0.50 toabout RM 3.50 per square metre.

Reliability :Crack sealants will not completely fill the fulldepth of the cracks. Only the top few millime-tres are filled. Because of this, the use of crackseals is limited to those cracks which have notpropogated completely through the surfacing.

5.3.3 Cutting and Patching

Description :

Cutting and patching is the replacement ofdeteriorated asphalt surfacing with suitablebituminous mix, placed and compacted to simi-lar level to adjacent undeteriorated asphalt.There are two types of bituminous patchingmaterials which are commonly used :

i) hot-mix asphaltii) cold mix asphalt

These mixtures vary widely in quality, compo-sition and cost.

Bituminous patching mixtures must have suffi


Plate 5.1. Rejuvenating Aged Asphalt Surfacings in progress

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ciently good properties. The required propertiesare :

i) Stability - to resist shoving and rutting ii) Cohesiveness - should stick to host

materialiii) Resistance to water - impermeableiv) Durable - resist wearv) Workability - easily handled and con-

structedvi) Storageability - can be stored xvithout

deteriorating for immediate works

The performance of a bituminous patchdepends on quality of the materials and con-struction techniques.

Conditions of use :For pavements with localised surface failures,cutting out the failed areas and patching it withnew bituminous mix should restore the pave-ment. The 'cut and patch' method is also ameans of pre-treating the existing pavementsbefore a resurfacing work. It is designed toremove the existing cracks and thereby elimi-nate reflection cracks. However, the crackshave to be removed totally as cracks in thelower layers will eventually cause reflectioncracks on the new layer.

For pavements with rutting caused by the insta-bility of the wearing course mix, the 'cut andpatch' alternative is also suitable. This type of

failure is mostly found on climbing lanes and atjunctions. The unstable layer must be removedprior to being replaced with a stiffer mix.

Construction :Even though the construction of patching doesnot require special equipment, proper construc-tion technique is still important. On many ocas-sions, the construction is not carried out proper-ly causing the patched area to fail early. Thecorrect construction method is described below.See also Figure -5.4.

MarkingThe boundaries identified to be patched shouldbe marked. Straight line markings are prefered.All deteriorated areas should be included withallowance for joints. These boundaries can bechanged during cutting to allow for initiallyundetected damage.

CuttingThe area marked for patching should be neatlycut and removed using a proper asphalt cuttingtools. A vertical unbroken cut will enhanceadhesion and promote efficient compaction.

Cleaning and dryingThe surface under the new patch must be clean,dry and free from loose material. Air blowingfollowed by vacuum cleaning is recommendedfor efficient cleaning and drying.


Plate 5.2. Crack Sealing

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Tack CoatingA thin bituminous layer is normally sprayeduniformly on the prepared surface prior topatching hot-mix to promote adhesion betweenthe new layer and the cut surface. For smalljobs, low pressure hand sprayer can be used,whereas a bitumen sprayer is suitable for largeareas. Tack coat materials available include :

i) cut-back bitumenii) bitumen emulsioniii) synthetic resin

Tack coating should not be applied if cold-mixasphalt is used, unless the patch surface ismade of concrete. The tack coat can soften thecoldmix and promote shoving and stripping.

Filling

The material can be placed in several lifts. Asingle lift should not exceed 100 min thick.Filling is normally carried out manually.Shovels should be used and raking is not advis-able to reduce segregation. Hand tamping atedges and corners can also be carried out witha hand rammer. The surrounding surface mustbe kept clean from spilled filling material.

CompactionVibratory rolling is the best method for com-pacting patched area. By rolling the edgesfirst the filling will pinch into the hole. Thecentre of the patch is rolled first, moving out-wards towards the edges with each succeedingpasses. This will tighten the adhesion aroundthe edges. The roller should rest completely onthe patched area and not partly on the old pave-ment.

Cleaning up and checking joints

Cleaning up is essential for a comprehensivepatching ,job. Checking the finished productespecially the joints should be carried out. Theedge or joints of the patch should be sealedusing bituminous material similar to cracksealants described earlier. The life of thepatch is often dependent on how well the jointsare made.

Cold Milling

If extensive patching is required or if the pro-posed patches are too close to each other, thencold milling can be considered as an option. A


Figure 5.4. Proper Methods For Cutting and Fatching

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milling machine is required for this work. Thismachine can cut the deteriorated surfacing tothe depth and width as required. The maximumdepth and width depends on the machine typeand specifications. The milled material can besalvage or recycled. Patching should then becarried out using an asphalt paver.

Cost :

The cost of cutting and patching pavements isnoNN- competitive. The cost ranges betweenRM 8.00 to RM 10.00 per square metre.

Reliability :

The performance of a patched area dependsheavily on the type of mix used and the con-struction standard. If constructed properly, thisalternative would be able to last the life of theuntreated sections. But if poorly constructed,this alternative can increase the roughness ofthe road section.

5.3.4 Thin Bituminous Overlays

Thin bituminous overlays provide a feasiblealternative for low cost pavement surfacerestoration. It improves the surface riding con-dition and can extend the service life of a pave-ment. It can also be used as a short term meas-ure to address specific distress condition. Mostcommonly used thin asphalt overlays are :

i) Surface Dressingsii) Slurry Seals (Thin seal mixtures)iii) Thin Hot Mix Overlays.

Surface Dressings

Description :

A surface dressing is an application of bitumenfollowed with an aggregate cover in a single ormultiple application. In double surface dress-ings the larger sized stones are place in the firstapplication with the smaller sized stones in thesecond application to fill in the voids in the firstlayer. The aggregates used have to be cleanedand free from dust. This will facilitate cohesionbetween the aggregates and the bitumen. Ifdusty aggregates are used, then pre-coatingthem first is more suitable.

Conditions of use :

Surface dressing has been commonly used as awearing course on low volume roads. It hasalso been used as a resurfacing technique totreat surface failure on these types of roads.The potential use of the surface dressings torestore distressed bituminous pavement has notbeen fully demonstrated in Malaysia, eventhough it is greatly used in Australia and theUnited Kingdom. Apart from being able torestore the riding quality of the road surface, ithas other advantages. The high bitumen contentof a surface dressings layer means thicker bitu-men film will be coating the aggregates. Thiswill improve resistance to ageing making thesurfacing more durable. At present, limitedlocal experience in the use of surface dressingson asphaltic concrete surfaces restricts its appli-cation on high volume roads because of the


Plate 5.3.Cutting And Patching

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worry that loose stones may pose hazards tothe traffic. Furthermore, the long constructionperiod may cause traffic distruption. As such itis proposed that the use of surface dressings onasphaltic concrete surfaces be limited to lowvolume roads with Average Daily Traffic(ADT) < 5000.

When using surface dressings on asphaltic con-crete surfaces, a proper design needs to be car-ried out. The design guideline from theTransport Research Laboratory Overseas RoadNote 3 specifies the rate of spray of the binderand the aggregates as important to the perform-ance of the surface dressings. The hardness ofthe existing asphaltic concrete surface and theflakiness of the aggregates are important con-siderations too. The hard surface will not allowany penetration of the aggregates for embed-ment and because of this, a suitable binder isneeded to ensure the stones are not whipped offby traffic.

The use of modified bitumen, fibres or specialaggregate may improve the construction proce-dure and. enhance the performance of surfacedressing. This improved performance willincrease its applicability on high volume roads.

Construction :The construction of the surface dressings

requires the binder to be sprayed using amechanical sprayer and the aggregates to bespread by a specially designed chipping spread-er. These are inexpensive and are easilyavailable locally.

Traffic control immediately after the surfacedressings have been applied, is important. Thisis due to the loose chippings which still needkneading by the traffic tyres. During this peri-od, at least 2 hours after application for normalbitumen, the speed of the traffic have to be low.This period may be reduced if modified bindersare used.

Cost : The cost of construction of surface dressings onlaterite surfaces (usually in the rural areas) isless than half that for Asphaltic Concrete. Butto construct it on existing bituminous pave-ments may cost more since the binders are dif-ferent and the traffic control is more elaborate.At present, the cost ranges from RM 3.00 toRM 8.00 per square metre.

Reliability :If the surface dressings is constructed on a roadthat is structurally sound,it will last a long time. The thicker bitumenfilm thickness ensures the flexibility of thelayer and would reduce age hardening. Because


Plate 5.4. Cold Milling

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of this, the use of surface dressings as a restora-tion alternative should be encouraged. InMalaysia where the intense sunlight does createproblems with the rate of ageing, the surfacedressings wearing course may last longer thana thin asphaltic concrete layer.

Slurry Seals

Description: Slurry seals are a mixture ofaggregates, water and filler (usually cement) bound with bitumen emulsion, and mixed insi-tu prior to laying using specialized equipment.

It has potential for both corrective and preven-tive maintenance of asphalt surfacings.However, it is not a structural layer.Application of slurry seal is known to retardthe hardening process of the top portion ofasphaltic concrete surfacing.

There are three types of slurry seals, namely.Type 1, 11 and III as specified by the interna-tional Slurry Seal Association (ISSA).

The aggregate size, filler and the residual bitu-men from the emulsion govern the classifica-


Plate 5.5. Surface Dressing

Plate 5.6. Slarry Seal

Page 69



tions. Nominal 4.75 mm aggregate size is spec-ified for Type I whilst size 9.5 mm for Type 11and 111. The emulsion specified should bechecked for compatibility with the aggregateand the desired setting time. Slow settingcationic emulsion is normally used.

Conditions of use :The nature of the existing surfacing and theexpected traffic level govern the appropriateuse of slurry seals. It is not suitable for shapecorrection or for use at heavily loaded pave-ments with interconnected cracks or moreadvanced cracks. Slurry seal should not beapplied on structurally, weak areas.Conventional slurry seals using slow settingemulsion need a long curing time, thereforeapplication is not advisable when rain isexpected. Rain water can wash away the emul-sion, breaking aggregate bondage and destroy-ing the slurry. Localized pavement defects suchas cracks, nits, humps, low pavement edgesmust be repaired before applying the slurryseals.

Modified emulsion, fibres or special aggregatescan improve the properties and performance ofslurry seals. Their conditions of use is similarto the surface dressings described above andmay be extended to higher class of roads.

Construction :Constriction of the slurry seals require a specialpaving equipment. A more powerful and fastermixer is required if the modified emulsions areused. It is also desirable to have experiencedcontractors to do the job.

The long curing tirrnc of about 3 to 4 hours forthe normal slurry seal makes it necessary forthe provision of proper traffic control. This isespecially difficult to carry out in built-upareas. Usaull_v, sand is used to blind the areaswhere traffic may be travelling over the wetslurry. The inclusion of modifiers to the emul-sion usually shortens the curing time to about30 minutes.

Cost :The normal slurry seals costs about RM 2.00 to

RM 4.00 per square metre, whereas the modi-fied slurry seal costs about RM 4.00 to RM8.00 per square meter depending on the size ofthe job.

Reliability :Slurry Seals are effective in areas where theprimary problem is excessive oxidation andhardening of the existing surface. They mayalso be used to improve the friction characteris-tics of polished surfaces at low traffic levels.However, when used in areas where the pave-ment deflections are high and the surface issuffering from cracks (block and crocodilecracks), the slurry seal will crack very quicklyand should not be used.

Thin Hot Mix

Description :Thin hot mix asphalt is an asphalt mix which isnormally less than 40 mm thick. Any type ofhot asphalt mix or modified mix can be used.The thin asphalt layer is mainly to correct sur-face deficiencies and will not add much struc-tural strength to the road.

Apart from the normal asphalt concrete, fibr-ereinforced ultra-thin mix and the porousasphalt mix fall into this category. The fibre-reinforced ultra-thin mix is popularly used inEurope with success. The introduction of thefibres increases the fines in the mix, therebyallowing more binder to be added. This addi-tional binder in the mix will help in preventingageing of the binder.

The porous asphalt mix is also popular inEurope. This mix is designed with high voidcontents to allow for free draining of surfacewater. The high voids are also able to absorbtraffic tyre noise which makes it popular inbuilt-up areas. To ensure stability of the mix,the use of modified binders may be ncccssan-.

Conditions of use.Thin hot mixes can be applied at areas subject-ed to low deflection. It is not meant to correctstructural failures and severe rutting. Surfacingthat suffer from polishing, stripping, bleeding


Page 70



can be overlaid with thin hot mixes. Suitabletack coats must be used prior to laying the thinoverlays. Strong adhesion with the existing sur-face is necessary, otherwise delamination andflaking can occur.

The present practice of providing a thin overlay(up to 40 mm overlay) without giving due con-sideration to the structural needs is not a goodpractice. If laid on top of the existing asphaltlayer without prior treatment to the crackedsurface, the cracks reflect through the newlayer as early as within 3 months depending onthe deflection and the traffic intensity of theroad. It is therefore very important that crackedsurfaces must be treated before overlay.

The fibre-reinforced ultra thin mix and theporous asphalt mix are applicable on road sur-faces with good structural intensity. Thesemixes are usually used to enhance the surfaceproperties of the pavement. In addition, theporous asphalt mix can drain surface water fast.

Construction : No special equipment other than that used inthe construction of normal hot mixes is neces-sary. Traffic can run on the mix as soon as therolling is completed. But in the case of theporous asphalt, it is necessary to leave the mix

for a couple of hours before opening to traffic.

Cost :The cost of constructing the thin hot mix varyaccording to the types and mix design. For thenormal asphaltic concrete thin mix, it costabout RM 5.00 to RM 8.00 per square metre. Tlie fibre-reinforced ultra thin mix costs aboutRM 6.00 to RM 8.00 per square metre. But forthe porous asphalt mix the use of polymermodified binders can increase the cost to aboutRM 10.00 to RM 18.00 per square metre.

Reliability :The aggregate gradings and bitumen type andamount used in this mix will affect the per-formance of the layer. Because of its thinnature, bigger sized aggregates would becrushed by the steel roller resulting in looseaggregates. Apart from that, the bitumen filmthickness will influence the life of the layer.

In Malaysia pavement constructed with porousasphalt have performed very well. Its reliabilitydepends on the design of the mix and the typeof binder used. The clogging of this type ofmix with time may reduce its ability to drainwater.

5.3.5.Surface Recycling


Figure 5.5. Surfacing Recycle Using Hot Milling Method

Page 71



Description: Pavement surface recycling is thereworking of the pavement surface to improveits performance and correct surface failuresparticularly surface cracking. It is a growingfield in pavement rehabilitation but must beused with care. Suitability of its application willdepend primarily on the structural conditions ofthe existing pavement. Normally it can beapplied only when the pavement is structurallysound and the mode of failure is corned to thetop of the surfacing.

In this method, the surfacing material is scari-fied or pulverized by using a hot milling(heater-planer or heater-scarifier) or cold-milling device. The scarified materials aremixed and relaid in a number of ways, either ina continuous single pass or in separate opera-tions (Figure 5.5).

In using the hot milling method, two types ofheating devices are available ie. the open flameheating or the radiant heating. Various manu-facturers have developed equipment for theabove processes, some of which are used as aheating unit on its own, while the more sophis-ticed ones can carry out the heating, remixingand laying in a single pass. The benefit fromthe use of the equipment is subject to fieldinvestigations of their actual pavement per-formance.

Another method of recycling the pavement sur-face is termed as cold recycling. Cold recyclingis the reworking of a pavement surface by pul-verising the top layer using a milling machinefollowed by reshaping and compaction. Thereshaping and mixing can be done in the Fieldor at a central plant. Stabilisers and additionalmaterials can be included. The top 25 mm isnormally recycled. This is the critical portionwhere surface failures such as ravelling, bleed-ing, polishing and weathering occurs. Thismethod is only suitable for correcting surfacedistress. The structure of the pavement must beintact and capable of accepting an overlay witha standard life expectancy.

Conditions of use :Surface Recycling can be applied for all types

of surface failures provided the causes andextent are known. Effectiveness of its applica-tion is highly dependent on the accuracy of thepavement evaluation . Surface recycling doesnot provide a substantial increase in the struc-tural strength of the pavement. It is a methodfor treating the surface distresses.

It is a known fact that heating of fresh bitumenduring manufacture of the asphalt causes agehardening, and re-heating it during hot millingwill induce further hardening. Recycling thepavement surface using the hot milling methodwith the heat application being higher than 200deg C, will cause the condition of the bitumenin the asphalt to deteriorate further. To counterthis, it is advisable to add rejuvenating chemi-cals to the remixed layer apart from the addi-tion of bitumen.

Available equipment in the market today isonly capable of heating and softening the topfew centimetres, which restrict the depth of cutfor a single pass. The usual depth per pass isapproximately 25 mm. With this limitation, themethod would be able to eliminate crackswhich are of the top-down nature and have pro-gressed to a depth of 50 mm. If the cracks havegone down through the full depth of the surfac-ing layer, and these are not removed, then thereis a possibility the remaining cracks will reflectupwards through the new layer.

Construction : Specialized equipment is necessary for therecycling of the pavement surface. The size andcost of this equipment depend on the nature ofthe operations it can carry out. The most expen-sive would be the plant which is capable of car-rying out the recycling, re-laving and additionof fresh mixes in a single pass.

The use of gases to heat the pavement surfaceand the intense heat generated during the oper-ation may pose a hazardous situation to theroad users. Thus proper traffic control is need-ed during construction. Care should be taken toensure that no pedestrians are allowed to comenear the heating equipment. The operators ofthe equipment need to be specially trained.


ble of carrying increased traffic. It alsoimproves riding quality. The thickness of theasphalt resurfacing depends on the strength ofthe existing pavement and the expected traffic.It is necessary to carry out a proper design toestablish the thickness of the surfacing.

There are two methods of resurfacing popularlyused in Malaysia, namely, thick asphalt over-lays with or without a prior granular overlay.The foriuer involves the construction of acrushed aggregate layer on the existing pave-ment before laying the asphalt layer. The use ofgranular overlays reduces the need for pre-treatment works.

Conditions of use :Resurfacing without a prior granular overlaycan be applied to rectify many types of pave-ment failures. However, pre-treatment workssuch as patching and reconstruction should becarried out at localised failed areas prior toresurfacing. Resurfacing can be applied on sur-facings that are cracked, rutted, polished,

Cost :The cost of recycling the pavement surfacedepends on the type of equipment used and theextent of work involved. It ranges between RM6.00 to RM 13.00 per square metre.

Reliability : Surface recycling is a rehabilitation alternativesuitable for restoring pavement surface distress-es only. If used on full-depth cracked pave-ments and with pavement deflections in excessof 0.5 mm. there is a possibility, of the crackreflecting early.

5.4 RESURFACING

Description :Resurfacing is the placement of fresh materialon an existing surfacing to enhance its structur-al strength. Asphalt resufacing is the most pop-ular method of pavement rehabilitation inMalaysia. When done properly, this method isappropriate since the addition of new layersstrengthens the road pavement making it capa

Page 72




Figure 5.6. Methods Of Reducing Reflection Cracks Using Interlayers

Page 73



raelled, and those that are bleeding. Properevaluation of the existing pavement conditionis neccessary to determine the extent of pre-treatment required. The following paragraphsdescribe some of the aspects that should beconsidered prior to resurfacing.

Resurfacing on Cracked Surfaces

Cracks occur frequently on roads in Malaysia.These cracks should be treated early to stopingress of water into the road base layer there-by weakening it. The common practice of over-laying the cracked pavements without priortreatment to the cracked surface. causes thecracks to reflect through the new layer as earlyas within 3 months depending on the deflectionof the road section and the traffic level. It istherefore very important that cracked surfacesmust be treated before overlay. Alternatively,more expensive techniques such as using inter-layers to absorb the stresses and strains of thecrack tips can be used.

One common pre-treatment method is to 'cutand patch' before overlay. This results not onlyin delaying reflective cracking but it also givesa slight increase in the strengnh of the pave-ment.

The rate of progression of the cracks reflectingthrough the new asphaltic layer depends on thestructural strength of the pavements. Pavementswith higher deflection. causing higher crackmovements, tend to be the first to crack.

Another method of reducing reflection cracksis by introducing a separating layer (Figure 5.6)to absorb the stresses from the crack move-ments. An example of this stress-absorbinglayer is the geosynthetic material. There aremany types of geosynthetic materials available,and most of them claimed to be effective inmitigating reflection cracks. However, the con-struction procedures have to be properly lookedinto to ensure that the geosynthetic materialsare laid in accordance to the manufacturer'sspecifications.

There are basically two types of geosynthetic

materials available in the market, the grid andthe non-woven geotextiles. When using thegrid, care should be taken to reduce thepossibility of the picking up or stretching thegrid by lorry tyres. When this happens, thegrids will warp and the resultant displacementof the grids will lead to poor compaction of theasphalt layer. This leads to cracking. On theother hand, if the non-woven materials areused, care should be taken on the amount andtype of tack coat used. If used in excess, thenonwoven material will become saturated andwill lead to bleeding. If the bitumen tack coat istoo soft the material can slide at the exsitingroad/material interface.

Other types of Stress Absorbing MembraneInterlayers (SAMI) are also available. Thesecan be in the forms of aggregate interlayers(e.g. surface dressings) or modified bitumenwith or without chippings. At 1KRAM studiesare being carried out on the use of some ofthese interlayers. Laboratory experiments arealso being carried out on the manufacture ofSAMIs using natural rubber blended into bitu-men.

Crushed aggregates have also been used as aninterlayer. This method has perform positivelyeven with crack movements of l.5mm. In oneof the trials constricted by IKRAM, the crushedaggregates were laid on top of segmented con-crete pavement where the movements at thejoints were substantial. Previously, asphaltoverlays without prior treatment Nvould onlylast about 2 months. But with this method, thecracks from the concrete.joints have vet tocome through after a couple of years.

Resurfacing on Rutted Surfaces

Resurfacing ou existing pavements with sur-face nits require special considerations. Densebituminous surfacings nit when it loses its sta-bility properties. These usually occur in areaswhere there are prolonged loading periodsof slow moving or stopped heavy vehicles,namely at climbing lanes and at intersections.The high stresses imposed on the asphalt layercauses it to densify and with the reduction in


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voids in the mix, the mix becomes unstable.This layer must be removed by milling prior tooverlaying it with a fresh asphalt layer.

Bituminous mixes designed by the Marshallmethod have been shown to perform poorly inhigh stress areas. To counter this, polymermodified bitumen can be used in asphaltic con-crete on climbing lanes and junctions. The rateof rutting of these mixes are slower than thenormal asphaltic nixes. However, the use of thepolymer modified bitumen can increase thecost of the asphalt to double its normal cost.

In an effort to find a cheaper solution to theabove problem, IKRAM has introduced a newmix for the surfacing, called the HCMBituminous Surfacing. The mix was tried in atrial at the Bukit Tinggi climbing lanes alongthe Kuala Lumpur - Karak Highway. In thesame trial, other mixes using polymers andadditives were also tried. After nearly 3 yearsin service, the HCM Bituminous Surfacing hasperformed on par to the more expensive poly-mer modified wearing courses.

Resurfacing on Bleeding Surface

If the existing pavement surface which needsstrengthening is suffering from bleeding, it isadvisable to consider the possibility of theexcess bitumen migrating into the new layer.The application of hot sand should be consid-ered.Resurfacing on Corrugated Surface

If corrugations are the result of unstable surfac-ing materials, it should be replace before resur-facing. If it is due to unstable granular pave-ment layers then partial reconstruction will be abetter solution.

Resurfacing on Ravelling orWeathered Surfaces

If the existing surface is experiencing ravellingand loss of aggregates, no pre-treatment is nec-essary.

Cost :A major portion of the cost in carrying out astructural resurfacing job goes to the pretreat-ment works. The cost of the asphaltic concreteitself is around RM 10.00 per square metre,whilst the costs of pre-treatment such as the useof grid geosynthetic materials may push thecost up by between RM 8.00 to RM 20.00 persquare metre. The use of fabric geosyntheticmaterials would reduce the total constructioncost as the fabrics may add about 30-40% moreto the cost.

Reliabilitv :Structural resurfacing can last the design life ifproper pre-treament work is carried out. Mostof the resurfacing works which show earlysigns of distress are due to improper pre-treat-ment works.

5.5 RECONSTRUCTION

Description: Reconstruction is the removaland rebuilding of all (including subgrade) orpart of the road pavement using fresh materialand new construction specifications. Pavementsthat have failed Beverly are usually thosewhere deterioration has been allowed to occurwithout maintenance. The condition of thee


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lower granular layers of the pavement is bestdetermined by destructive testing.

There are two types of reconstruction, namely,full reconstruction and partial reconstruction.Full reconstruction is needed when the sub-grade layer as well as the pavement layers hasdeteriorated beyond repair. In full reconstruc-tion, the rebuilding includes the subgrade.Partial reconstruction is needed when the roadbase has been contaminated and it has lost itsinherent stability. In this case the rebuildingdoes not include the subgrade.

In the case where the failure of the road base isextensive and conventional partial reconstruc

tion method is uneconomical, it is advisable tocarry out recycling. Recycling of the road baseis a partial reconstruction alternative where theexisting surfacing and/or part of the road baseis pulverised, and replaced as a new road baselayer. The process breaks up the existingasphalt layer into small pieces thereby remov-ing existing cracks and at the same time allow-ing addition of road base thickness. It thereforecan be used to eliminate reflective crackingproblems and correct thickness deficiencies.

Base recycling is suitable where the deteriora-tion of the surfacing has become so extensivethat partial reconstruction option will not beeconomical. The deterioration can be due to a


Plate 5.8. Reconstruction Works

Plate 5.9. Recycling For Base

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poor road base layer or insufficient base thick-ness. Additional aggregates and stabilisers canbe included in the mix to improve its perform-ance.

Among the common stabilisers suitable forbase recyling are :

i) cut-back bitumenii) cementiii) bitumen emulsion

The correct choice of stabilisers will depend onthe existing pavement material type, its condi-tion and compositions.

Condition or Use :Identifying areas needing reconstructionrequires evaluation of the pavement conditions.However, experience has shown that the fol-lowing rule-of-thumb to be reasonably accept-able in identifying localised reconstruction

areas:

Identifying full reconstruction

Full reconstruction may be needed for the fol-lowing combination of failures.

i) Pavement surface which suffer from crocodile cracks with rut depths of morethan 25 mm, without shoving.

ii) Pavement surface which suffers cracking with rut depth of more than 15 mm and deep shoving.

Identifying partial and base reconstruction

Partial reconstruction may be needed for thefollowing failures or combination of failures.

i) Spalling and crocodile cracking withrut depth of less than 15 mm.

ii) Shoving with rut depth less than 15 mm.


Figure 5.7. Full Reconstruction

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iii) Crocodile cracking with block size less than 100 mm with shoving.

Confirmatory test using the Dynamic ConePenetrometer (DCP)

If the site engineer is not certain of the extentof reconstruction required, the DCP can beused to estimate the pavement layer strengthand thus identify which materials needs to beremoved. Partial reconstruction can be carriedout if it is not necessary to replace the subgradeor the sub-base.

Construction :Reconstruction requires more lane closure timethan resurfacing, since the work includesbreaking up the pavement, removal andrebuilding of existing layers. The time taken fora partial reconstruction is less than that for thefull reconstruction.

Allowances should be made for the possibilityof secondary compaction of the reconstructedareas by opening them to traffic for a period oftime before applying the final overlay.

Particular attention should be given to the pro-vision of adequate drainage when reconstruct-ing roads with high water table.

Marking the areas to be reconstructed

Marking of the areas to be reconstructed is bestdone a few days before construction.Temporary marking can be used if contructionis to follow immediately otherwise permanentmarking can be carried out. It is advisable toextend the area needing reconstruction beyondthe area over which it occurs. Marking is bestcarried out by experienced personnel in identi-fying serious pavement defects. This task iscritical in optimising the probability of successof the rehabilitation job.

Construction of Base Recycling

The construction ol` recycled stabilised basenormally requires specialised machinery.Standard construction method may not be suit-

able and can be expensive. The works involvedin base recycling are:

Pulverisation or ripping

Mechanical pulverisors can break up any of thethe pavement layer and reduce it to uniformsizes. The pulverised materials should beinspected where all large pavement chunks andorganic substances should be removed.Addition of stabilisers may_ be introduced atthis stage.

Stabiliser distribution

Cement stabilisers can be spread by a bulkspreader or manually depending on the jobsize. The spread rate, water content and mixingprocess is critical for efficient stabilisation.Bituminous stabilisers are mechanically spreadand are seldom used for base recycling.

Compaction

Compaction can be carried out using normalvibratory rollers. The number of roller passes iscritical, as over-compacting cement stabilisedbase may overstress the surface. Bitumen sta-bilised road base do not have this problem.

Cost :Reconstruction is an expensive option andshould be considered only if the pavement hassuffered beyond economic repair. Partial recon-struction can cost between RM 35.00 to RM45.00. Full reconstruction is more costly. It canrange between RM 40.00 to RM 50.00.

Reliability :Reconstruction work done to a high construc-tion standard will have a life surpassing allother rehabilitation options. In fact, it can bedesigned to any desired performance period.However, it is expensive and should only becarried out where necessary.


Documents

Interim Guide to Evaluation and Rehabilitation of Flexible Pavements