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Service Life of Pavements:Context, Review and Definition of Terms

AUSTROADS TECHNICAL REPORT

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Service Life of Pavements: Context, Review and Definition of Terms

First Published 2007

Austroads Inc. 2007

This work is copyright. Apart from any use as permitted under the Copyright Act 1968,no part may be reproduced by any process without the prior written permission of Austroads.


ISBN 978-1-921329-00-5

Austroads Project No: AT1169

Austroads Publication No: AP-T77/07

Project Manager

Bob Peters, MR WA

Prepared by

Tim Martin and Michael Moffatt, ARRB Group

Published by Austroads IncorporatedLevel 9 Robell House287 Elizabeth Street

Sydney NSW 2000 AustraliaPhone: +61 2 9264 7088

Fax: +61 2 9264 1657Email: [email protected]

www.austroads.com.au

Austroads believes this publication to be correct at the time of printing and does not acceptresponsibility for any consequences arising from the use of information herein. Readers should

rely on their own skill and judgement to apply information to particular issues.
mailto:[email protected]://www.austroads.com.au/http://www.austroads.com.au/mailto:[email protected]

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Service Life of Pavements:Context, Review and Definit ion of Terms

Sydney 2007

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Austroads prof ile

Austroads is the association of Australian and New Zealand road transport and traffic authoritieswhose purpose is to contribute to the achievement of improved Australian and New Zealand roadtransport outcomes by:

undertaking nationally strategic research on behalf of Australasian road agencies and

communicating outcomespromoting improved practice by Australasian road agencies

facilitating collaboration between road agencies to avoid duplication

promoting harmonisation, consistency and uniformity in road and related operations

providing expert advice to the Australian Transport Council (ATC) and the StandingCommittee on Transport (SCOT).

Austroads membership

Austroads membership comprises the six state and two territory road transport and trafficauthorities and the Commonwealth Department of Transport and Regional Services in Australia,the Australian Local Government Association and Transit New Zealand. It is governed by a councilconsisting of the chief executive officer (or an alternative senior executive officer) of each of itseleven member organisations:

Roads and Traffic Authority New South Wales

Roads Corporation Victoria

Department of Main Roads Queensland

Main Roads Western Australia

Department for Transport, Energy and Infrastructure South Australia

Department of Infrastructure, Energy and Resources Tasmania

Department of Planning and Infrastructure Northern Territory

ACT Department of Territory and Municipal Services

Australian Department of Transport and Regional Services

Australian Local Government Association

Transit New Zealand

The success of Austroads is derived from the collaboration of member organisations and others inthe road industry. It aims to be the Australasian leader in providing high quality information, adviceand fostering research in the road sector.

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SUMMARY

This project is aimed at improving the understanding of the concept of remaining service life as itapplies to road pavements by developing the following:

uniform definitions of the key terms such as; design life, service life, remaining service life(RSL), economic life, designated level of service and threshold distress values and otherassociated terms

an approach which will allow the service life of pavements to be accurately estimated bypredicting the time for the asset to progress from one condition state to another.

The project is focussed on the following aspects:

a definition of terms document

restricting estimation of the RSL to the next intervention by rehabilitation or replacement

including asset valuation with RSL and clearly integrating RSL with both the accounting and

engineering aspects

the issues that influence the estimation of RSL, including structural capacity, functional andsafety requirements

the development of key performance indicators (KPIs) for pavement management purposesbased on current conditions.

This report develops a broad overview of the RSL topic so that its applications and benefits areunderstood as well as the inter-relationships between key RSL terms. The following key definitionsare proposed for review and discussion in this context:

design life designated level of service

service life maintenance

requisite or functional life maximum service life (MSL)

operational life rehabilitation

economic life reconstruction.

threshold distress values

Estimation of the various definitions of service life depends on resolving the following:

deciding what forms of distress are relevant to limiting the designated level of service of thepavement

assigning threshold values of distress beyond which the pavement is considered to haveexceeded the designated level of service of the pavement

estimating the current, future and optimistic rates of deterioration for each form of distressthat is considered relevant in estimating the service life of pavements and maintenancetreatments.

The above factors are a combination of technical and policy issues and must be resolved within theroad agency responsible for managing the pavement assets. Consequently, estimation of servicelife is not a precise process but it can be improved by rigorous observation of pavementdeterioration of the various road types that comprise the road network. Also required is a clearunderstanding of relevant pavement distresses and their threshold limits, beyond which thepavement performance becomes unpredictable or has exceeded its designated level of service.

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CONTENTS

1 INTRODUCTION................................................................................................................... 11.1 Context and aims................................................................................................................... 11.2 Background............................................................................................................................ 11.3 Document format ................................................................................................................... 22 BROAD OVERVIEW OF REMAINING SERVICE LIFE (RSL) ............................................. 32.1 Scope of definitions ............................................................................................................... 32.2 Asset valuation ...................................................................................................................... 32.3 Influences on estimating RSL................................................................................................ 42.4 Developing key performance indicators................................................................................. 43 DEFINITION OF KEY RSL TERMS ...................................................................................... 53.1 Pavement age and traffic loading .......................................................................................... 53.2 Threshold distress values and levels of service .................................................................... 5

3.2.1 Background.............................................................................................................. 53.2.2 Proposed terminology.............................................................................................. 6

3.3 Design life.............................................................................................................................. 63.3.1 Background.............................................................................................................. 63.3.2 Proposed terminology.............................................................................................. 7

3.4 Service life (related to distress) ............................................................................................. 83.4.1 Background.............................................................................................................. 83.4.2 Proposed terminology............................................................................................ 10

3.5 Requisite life (related to non-distress issues)...................................................................... 113.5.1 Background............................................................................................................ 113.5.2 Proposed terminology............................................................................................ 12

3.6

Operational life..................................................................................................................... 13

3.6.1 Background............................................................................................................ 133.6.2 Proposed terminology............................................................................................ 13

3.7 Economic life ....................................................................................................................... 143.7.1 Background............................................................................................................ 143.7.2 Proposed terminology............................................................................................ 15

3.8 Other definitions................................................................................................................... 154 SUMMARY .......................................................................................................................... 164.1 Definitions............................................................................................................................ 164.2 Estimation of service life ...................................................................................................... 16REFERENCES ............................................................................................................................. 17APPENDIX A DEFINITIONS ASSOCIATED WITH REMAINING SERVICE LIFE ............... 17APPENDIX B EFFECT OF SUBGRADE CBR CHANGES ON DESIGN LIFE..................... 22APPENDIX C OTHER DEFINITIONS ASSOCIATED WITH REMAINING SERVICE LIFE.. 23

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FIGURES

Figure 3.1: Design life .................................................................................................................... 7Figure 3.2: Service life ................................................................................................................. 10Figure 3.3: Requisite or functional life.......................................................................................... 12Figure 3.4: Economic life ............................................................................................................. 14

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1 INTRODUCTION

1.1 Context and Aims

This project is aimed at improving understanding of the concept of remaining service life as it

applies to road pavements by developing the following:

uniform definitions of the key terms such as: design life, service life, remaining service life(RSL), economic life, level of service and threshold distress values and other associatedterms

an approach which will allow the service life of pavements to be accurately estimated byestimating the time for the asset to progress from one condition state to another.

Estimates of RSL for pavements are useful for the following reasons:

to improve the estimation of depreciation for asset valuation purposes that can be applied atproject level and aggregated to the network level for reporting

to estimate the programming and budgeting requirements for major intervention works suchas rehabilitation and reconstruction at a network level

to provide the basis for a key performance indicator (KPI) that is mainly concerned with thestructural life of flexible pavements in a contractual or asset management context. The KPImay or may not be integral for the above estimations.

1.2 Background

This project originated from an earlier Austroads project, BS.AN.009 Remaining life ofinfrastructure assets: an overview, which was completed in 2002 with a report by Robinson et al.(2003) which subsequently became an Austroads (2003) publication. The current projectcommenced with a workshop held with representatives of Austroads member authorities (MAs)and ARRB on 21 July 2005 (Moffatt and Sharp 2005) at ARRB to define the needs and issueswhich should be within the scope of the project and to identify other needs and issues whichshould be excluded from the project. The approach to be followed after the first year of the projectwas also discussed.

It was agreed at the workshop that the project should focus on the following issues:

development of a definition of terms document

the RSL should be restricted in its estimation to the next intervention by rehabilitation orreplacement

asset valuation needs to be considered with RSL as there is a clear interrelationship between

accounting, corporate planning and engineering aspects

the issues that influence the estimation of RSL, including structural capacity, functional andsafety requirements

the development of KPIs for asset management purposes based on current conditions.

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The first aim of this report is to develop a broad overview of the RSL topic so that its applicationsand benefits are well understood as well as the inter-relationships between key RSL terms. Thesecond aim is to provide definitions of key terms such as:

remaining service life

service life

design life

economic life

designated level of service

threshold distress values.

1.3 Document Format

A broad overview of the possible applications for remaining service life calculations is provided inSection 2. Comprising the majority of the document, Section 3provides definitions of terms, and

associated background discussions. A summary listing of all the terms defined is contained inAppendix A.

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2 BROAD OVERVIEW OF REMAINING SERVICE LIFE (RSL)

2.1 Scope of Defini tions

Section 1.2noted that the estimation of RSL should be restricted to the next major intervention that

is either rehabilitation or replacement. This is understood to be the usual practice in Australasiawhere pavement life is considered to cease with either rehabilitation or replacement activitieswhich reset the pavement age to zero. In reality functional pavement life can be considered to beeither substantially extended or renewed by major maintenance intervention, rehabilitation andreconstruction activities. Unlike resurfacing activities, maintenance/rehabilitation/reconstructionactivities have not underpinned the assumed asset lives established via the depreciation policy ofsome road agencies.

Interestingly, North American practice for the design life of some pavements allows for a number ofrehabilitations (Garcia-Diaz and Allison 1984) and the interval between rehabilitations and/orreplacement is regarded as the service life.

The RSL and other associated definitions in this report are confined to the next intervention byeither rehabilitation or replacement. However, there are other maintenance interventions thatoccur before either rehabilitation or replacement, such as surface corrections and thin overlays thatcould be considered to extend the RSL by reducing the subsequent deterioration towards a limitingthreshold value of distress that underpins the assumed asset lives established via the depreciationpolicy of the road agency. These maintenance interventions are often categorised as recurrentcosts rather than capital works costs.

The definition of RSL (see Section 3.4.2) can also be restricted to being the shortest time intervalbetween current conditions and the threshold distress value. This suggests that there may need tobe two possible definitions of RSL; one for the shortest time interval to any designated thresholddistress value, and one for the time taken for the current condition to reach rehabilitation and/orreplacement.

Related to the above definition of RSL is the distinctly different term, remaining surfacelife, whichis confined to the age of the pavement surfacing and the estimation of the number of years thissurfacing is expected to provide an adequate level of service prior to resurfacing.

2.2 Asset Valuation

Asset valuation is seen as useful information for reporting the financial state of the roadinfrastructure and because it has implications for the current condition of the infrastructure.Accounting practice typically bases asset valuation on the age of the asset relative to theprescribed life of the asset in the road agencys depreciation policy; however, some MAs are

considering condition based asset valuations approaches (Austroads 2000). Dowling (2004) notesthat the Department of Main Roads, Queensland has linked asset condition and valuation to thetraffic loading (expressed in terms of Equivalent Standard Axles, ESA) and not simply to age.

Current directions for local government asset valuation practice (LGV 2006) recommend using acondition based approach to determine remaining service life only when the asset is approachingthe nominated end of its life when signs of excessive distress become evident.

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The RSL concept could be a convenient means of linking age and condition based asset valuationbecause current and threshold distress conditions are used in estimating the RSL in years (seeSection 3.2). The RSL could be revised annually based on both current conditions and currentdeterioration rates. However, this implies that by varying the estimated remaining service life ofroads the asset could have a variable economic life which is contrary to the notionally fixed

economic life approach used in accounting practice.

2.3 Influences on Estimating RSL

As discussed in Section 3.4.2, estimating RSL depends on at least the following factors:

deciding what forms of distress are relevant to limiting the designated level of service of thepavement

assigning threshold values of distress beyond which the pavement is considered not to meetthe designated level of service requirements

estimating the current and future rates of deterioration for each form of distress that isconsidered relevant.

The above factors are a combination of technical and policy issues and must be resolved within theroad agency responsible for managing the pavement assets. Consequently, estimation of the RSLis not a precise process but it can be improved by rigorous observation of pavement deteriorationof the various road types that comprise the road network. Also needed is a clear understanding ofrelevant pavement distresses and the distress limits beyond which the pavement is considered tobe either at high risk from rapid structural failure or does not provide the designated level ofservice.

2.4 Developing Key Performance Indicators

As noted in Section 1.1, the development of KPIs is considered a potential outcome of estimating

the RSL of pavements. There is a definite connection between KPIs and relevant pavementdistress threshold values beyond which the pavement is considered to not provide the designatedlevels of service. This connection assumes that the KPIs are a subset of the threshold distressvalues. There is also a need to consider the risks associated with exceeding the distress thresholdvalues so that the consequences and their assigned probabilities are recognised and taken intoaccount if it is not always possible to limit the distresses to threshold values.

In an asset management context the KPIs need to be set before unacceptable conditions arereached so that appropriate intervention can be undertaken. The KPIs may also be measuresother than limiting distress values. These KPIs could be performance based such as the rate ofdistress increase (i.e. deterioration of condition) which is strongly connected to the estimation ofRSL.

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3 DEFINITION OF KEY RSL TERMS

3.1 Pavement Age and Traffic Loading

As pavement management decisions, economic optimisations, and works programs are concerned

primarily with whenproblems will arise or works will be undertaken, it is common practice toexpress the life of an asset in units of years. There is a danger, however, that such terminologycan obscure the fact that the structural capacity of a pavement is consumed by the application oftraffic (usually expressed in terms of equivalent standard axles, ESA, or heavy vehicle axle groups,HVAGs) in conjunction with environmental effects such as seasonal weather variations,temperature, the movement of moisture and the passage of time.

Most structural design and deterioration modelling approaches describe capacity, and thereforeultimate life where there is no structural capacity to sustain further traffic loading, and thentranslate this loading into units of elapsed time. These translations are based on a series ofassumptions relating to the composition of the traffic fleets (e.g. axle load limits, percentage ofdifferent axle types within the traffic fleet, etc.).

Whilst changes in the predicted traffic mix, without increasing axle load masses, may affect therate at which a pavement is subjected to loads, these changes will not affect the load bearingcapacity of the pavement itself. Only the period of time over which this capacity is consumed iseffected. Potential future changes to vehicle access, traffic spectrum, tyre technology, axleconfigurations and axle mass limits, are expected to lead road infrastructure managers tofrequently re-assess the time periods over which they expect the capacity of their pavements to beconsumed because these changes impact on the structural and functional performance of thepavement.

Knowing the life of a pavement expressed in units of years, and making assumptions about thetraffic loading, enables the life of the pavement to also be expressed in terms of ESA, and viceversa. Various components of the pavement management process are better suited toconsideration of life in terms of years (e.g. net present value analysis) and similarly othercomponents are better suited to using units of ESA (e.g. deterioration modelling).

Consequently, most of the concepts and terms following are expressed both in terms of elapsedtime (in units of years) and in terms of traffic (in units of ESAs). Following traditional use bypavement managers, the term lifehas been exclusively used in relation to elapsed or predictedtime. The term trafficis used in relation to the loading applied to pavements, and it is expressed inunits of ESAs. Unless otherwise indicated, traffic is cumulative, representing the sum of traffic in agiven period of time, rather than the annual current level of traffic.

3.2 Threshold Distress Values and Levels of Service3.2.1 Background

The critical issue here is the establishment of the threshold values that are considered to beinappropriate for each distress type or class of road. The process of establishing the thresholddistress values is one presumably based on risk management, legal duty of care issues,community needs and interaction with budgetary processes. There may also need to be someform of community consultation to do some of this. The threshold values may also be those valuesbeyond which it has been observed that deterioration tends to rapidly increase or become muchmore unpredictable.

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In the context of managing pavements, limits to the designated level of service could be seen asbeing represented by the threshold distress values, or contract service standards, beyond whichpavement conditions are considered to warrant some form of maintenance or rehabilitationintervention on a given type or class of road. Generally, it would be expected that roads would bemaintained and rehabilitated to ensure that they do not exceed their designated level of service

during their service life.

3.2.2 Proposed Terminology

The following terminology is proposed:

Threshold distress values:

Measures of pavement condition that are designated as the maximum distress for eachdistress type beyond which pavement deterioration tends to rapidly increase on a given typeor class of road without the imposition of constraints on road users such as load or speedlimits

Designated level of service:

The level of service for a given type or class of road within the designated servicerequirements based on road user needs for access and levels of pavement conditionappropriate to the designated function of the pavement

3.3 Design Life

3.3.1 Background

In Australasia, pavement design (Austroads 2004a) is conducted using an empirical or mechanisticmethod for granular pavements with thin bituminous surfacings (e.g. spray seals), and amechanistic method for pavement structures containing bound materials (e.g. asphalt and cementtreated materials). The aim of the design process is to enable budgeting and planning of

maintenance and rehabilitation systems over a selected design period and to allow comparisons ofvarious design options on a total life cycle cost basis rather than an initial cost basis. A similarprocess is used for the design of structural rehabilitation treatments (Austroads 2004b). Aseparate mechanistically based method is used for the design of concrete pavements. Thisdocument focuses largely on flexible pavements, although the principles discussed are equallyapplicable to concrete pavements.

The distress criteria used in the pavement design processes are related to the structuralperformance of the pavement, although damage to the pavement from environmental causes, suchas temperature and rainfall are considered indirectly through limiting material strength values. Theprocesses of selection and specification of pavement materials are used to ensure that suitablematerials are used.

Both the empirical and mechanistic design processes determine the pavement structure (i.e.thicknesses of given materials) placed over a subgrade (the strength of which is characterised byits California Bearing Ratio, CBR) and subjected to an estimated design traffic load. As the designprocesses are structural in nature, they consider that a pavement capacity is consumed as loadsare applied and not simply by the passage of time. A pavement that receives no loading during agiven period is considered to have experienced no reduction in capacity over that period.

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The design methods consider that a pavement has reached the end of its design life when thepavement exhibits a 25 mm rut at the surface or when fatigue cracking occurs in bound materials.The design methods aim to ensure that these design stress values are not reached within thedesign period. Importantly, the design methods do not provide any guidance as to the rate ofdevelopment of in-service rutting or cracking. Therefore, the pavement design process can only

place two points in time as follows:

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pavement distress is zero at opening to traffic

pavement distress has reached the design process failure criteria at the end of the designperiod.

This is shown schematically in Figure 3.1.

design

distress

design

life

Distress

Life

(years)

Figure 3.1: Design life relationshi p to dist ress


The following terminology is proposed:

Design traffic:

The cumulative traffic load, expressed in terms of the number of equivalent standard axles(ESA), predicted to use a road over the design life of the pavement.

Design life:

The number of years for which the pavement is being designed.

Design period:

Same as design life.

Design distress:

One or more distress values used by the pavement design process that ensures that thedesign distress is not reached before the cumulative traffic load has reached the designtraffic.

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3.4 Service Life (Related to Distress)

3.4.1 Background

In the context of structures (Byers et al. 1997), pavement design and asset management (Bayleyand Kinder 1984, Scullion 1988, Shoukry et al. 1996, Al Hakim et al. 1996, Loizos and Fatseas

1997, Zaghloul et al. 1998, St-Laurent and Prophete 2002, Stidger 2002) it is often understood thatthe remaining service life is limited simply by the assets structural capacity to withstand the currentand future loadings prior to failure.

Others, however, have taken a different view to defining the limit of useful life considering bothstructural and functional limits (Vepa et al. 1996, Flintsch et al. 1997). The functional life limits areoften roughness values (Williams 1990, Sullivan and Scott 1990) or a weighted surface distress orcondition index value (Baladi et al. 1992, Garcia-Diaz and Allison 1984). This is the approachproposed by this document.

The above approaches are reconcilable. Surface distresses such as roughness, rutting and skidresistance correlate well with road user expectations. However, surface distresses do not

necessarily provide guidance on the risks to road user levels of service arising from structuralfatigue of the pavement. Indexes that mix these levels of service and risk aspects may providemisleading information depending on the weightings used which may not reflect the agencyscorporate planning.

An even broader view to defining the limit of useful life can be taken if potential functionalobsolescence is considered where the pavement may be inadequate due to geometry, alignment,width and other broad functional reasons. This concept is explored in Section 3.5. Remainingservice life could also be seen as the remaining useful life or remaining operational life defined bythe minimum of the remaining service life, remaining requisite or functional life and remainingeconomic life.

Again these alternative approaches can be reconciled. Various triggers may initiate reconstructionor rehabilitation, such as:

1. Existing limits on traffic capacity such as the number of lanes, urbanisation effects oralignment (remaining functional life)

2. Road safety initiatives to improve engineering features such as width, shape, configuration,layout of intersections and alignment (remaining service life)

3. Whole of life financial analysis of agency costs, whole of life micro-economic analysis of userand agency costs and whole of life macro-economic analysis that includes the broaderbenefits from freight productivity, economic development, and land use (remaining economiclife).

Each of the above triggers can have separate threshold values of capacity, distress and cost.

The term total useful life is being proposed for local government use in reporting currentreplacement cost and the depreciated replacement cost. In this instance the total useful life is theactual life between construction or last renewal and the latest rehabilitation or renewal (LGV 2006).Ultimately, the useful life is to be determined by councils taking into consideration other priorities,including risk, cost and service level implications.

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Defining the limits of various forms of distress and distress index values, or threshold values, is adifficult process and one that is probably unique to each road agency (Baladi et al. 2004) due tothe nature of pavement performance in a road network. The remaining life potentially depends ona number of threshold values; consequently there can be a number of estimates of remaining life.It is recommended, however, that the shortest number of years to reach predefined threshold

values of distress be used rather than any weighted distress indices (Baladi et al. 1992).

It is not uncommon for these threshold distress values to be different to the failure criteria (i.e.design distresses) used in the pavement design process. Some of the distress parameters used inthe management process has not been included in the design process at all. By way of example,many Australasian asset management processes incorporate road roughness and yet thepavement design process does not consider roughness in any direct way at all.

In schematic form, Figure 3.2shows a threshold distress to be used for the management ofpavements (dashed horizontal line with highest distress value). Whilst this is arbitrarily shown tobe higher than the design distress (dashed horizontal line in the middle) it need not be in all cases,and in fact, as noted above, the threshold distresses may in fact differ in type entirely from those

used in the design process. The dot with the lowest value of age in Figure 3.2represents thecurrent condition and loading to date of an in-service pavement. In order to estimate when thepavement will reach the threshold distress, some form of prediction model is needed (Novak andKuo 1992a, Baladi et al. 1992, Kuo et al. 2001). For the sake of clarity this model is shown as asimple straight line, although it is unlikely that the distress would accumulate at such a constantrate.

Due to a range of conservative assumptions made during the design process, it is not uncommonfor pavements to outlast their original design lives (seeAppendix Bfor an example). It is also notuncommon that some design assumptions are not well managed in practice and pavements maynot achieve their design life, for example, the maintenance of roadside drainage, pavement cross-falls and re-surfacing treatments to water-proof the pavement.

A distinction is made in the following definition of terms between a parameter and an estimation ofthat parameter. For example, the difference between the service lifeand the estimated service lifeis that the service life is the actual number of years achieved between the immediate postconstruction or rehabilitation/replacement condition to a predetermined threshold value of distresswhen the pavement is likely to exceed the threshold distress value. The estimated service life isan estimate made using the best available data at the time that the estimate is made. The servicelifecould be considered as useful information for re-calibrating or adjusting the deteriorationestimation process used for determining the estimated service lifeand estimated remaining servicelife.

A special case of estimated service life is the initial estimated service life, which represents theestimation of the service life of the pavement using immediate post construction orrehabilitation/replacement data1. As the pavement ages, new assessments of the pavementcondition may allow for refinement of the estimated service life calculation. The initial estimatedservice life, however, will remain unaltered by definition.

1Some sources (Baladi et al. 1992, Novak and Kuo 1992a, CTC & Associates LLC 2004) use the term design to describe the life estimated fromimmediate post construction or rehabilitation/replacement condition (nominally zero age) to a predetermined threshold value of distress when thepavement no longer provides the designated level of service. This document, however, considers the design life of the pavement to be related

solely to the pavement design process, which, as noted in Section 3.3.1, may not directly reflect the policy objectives of the pavement managementprocesses.

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design

distress

threshold

distress

designlife

Distress

Life

(years)servicelife

Remaining service life

age todate

distressto date

Figure 3.2: Service life


The following terminology is proposed.

Age to date:

The number of years from the immediate post construction or rehabilitation/replacement ofthe pavement to a given date.

Traffic to date:

The cumulative traffic loading, expressed in ESA, from the immediate post construction orrehabilitation/replacement of the pavement to a given date.

Distress to date:

The distress that an in-service pavement exhibits at a given date.

Service life:

The number of years from the immediate post construction or rehabilitation/replacement

condition to a predetermined threshold value of a range of distresses beyond which thepavement no longer meets its designated level of service.

Service traffic:

The cumulative traffic loading, expressed in ESA, from the immediate post construction orrehabilitation/replacement condition to a predetermined threshold value of a range ofdistresses beyond which the pavement no longer meets its designated level of service.

Remaining service life:

The shortest number of years from a given date to a predetermined threshold value of arange of distresses beyond which the pavement no longer meets its designated level ofservice.

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Remaining service life= service life age to date

Remaining service traffic:

The cumulative traffic loading, expressed in ESA, from a given date to a predeterminedthreshold value of a range of distresses beyond which the pavement no longer meets its

designated level of service.Remaining service traffic= service traffic traffic to date

Estimated service life:

An estimation of the service life.

Estimated service traffic:

An estimation of the service traffic.

Estimated remaining service life:

An estimation of the remaining service life.

Estimated remaining service traffic:An estimation of the remaining service traffic.

Initial estimated remaining service life:

An estimation of the remaining service lifebased on immediate post construction orrehabilitation/replacement condition data.

Initial estimated remaining service traffic:

An estimation of the remaining service traffic based on immediate post construction orrehabilitation/replacement condition data.

3.5 Requis ite or Functional Life (Related to Non-dist ress Issues)3.5.1 Background

Pavements may be rehabilitated or replaced for reasons other than their structural or surfacecondition.

Examples include:

inappropriate geometry for traffic volumes or vehicle types

changes in road alignment

premature rehabilitations conducted in connection with road widening or shoulder sealing.

There must, therefore, be either a specific traffic level or point in time at which rehabilitation orreplacement of the current pavement configuration will occur regardless of the distress levelexhibited by the pavement.

This limiting road configuration threshold is shown as a vertical dashed line in Figure 3.3to the leftof the service life vertical dashed line limited by the threshold distress. Whilst in this figure thelimiting road configuration threshold is seen to occur to at an age before the threshold distress forthe pavement is reached, this is purely arbitrary. It is expected that in many cases thresholddistress levels will be reached at an age before any non-distress related limiting road configurationor traffic level. In such cases the vertical dashed line for the limiting road configuration would occurto the right of the vertical dashed line limited by the threshold distress.

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The limiting threshold for requisite or functional life has been termed the road configurationthresholdin order to indicate that it is a threshold on the configuration of the road itself, and not athreshold on the performance of the pavement. Therefore, the term requisite life,or functional life,has been selected to reflect that up to this threshold a pavement similar to that currently in serviceis required. Beyond that threshold the current pavement does not meet its designated level of

service with respect to the road configuration, and a new pavement is required.

In some cases, for example, such a limit will be a cap on the level of traffic that can occur before aroad alignment is necessary due to a change in the functional class of the road. In other cases thelimit reflects a known time at which works will be undertaken, for example as part of a larger worksscheme. Using simple traffic growth equations (Austroads 2004a) a relationship between trafficlevel and time can be determined, thus allowing non-distress related limits to be plotted againsteither traffic (as shown in Figure 3.3) or time series.

design

distress

thresholddistress

design

life

Distress

Life(years)

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requisite

life

service

life

road configuration

threshold

age to

date

distress

to date


Remaining requisite life

Figure 3.3: Requisite or funct ional life



Road configuration threshold:

A time or traffic level at which the current in-service pavement will be improved or replaced,regardless of its condition because it does not meet its designated level of service withrespect to road configuration.

Requisite, or functional, life:

The number of years from the immediate post construction or rehabilitation/replacementcondition to a predetermined date at which the pavement will be improved or replaced,regardless of its condition, because it has reached its road configuration threshold.

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Requisite traffic:

The cumulative traffic loading, expressed in ESAs, from the immediate post construction orrehabilitation/replacement condition to a predetermined date at which the pavement will beimproved or replaced, regardless of its condition, because it has reached its roadconfiguration threshold.

Remaining requisite, or functional, life:

The number of years from a given date to a predetermined date at which the pavement willbe improved or replaced, regardless of its condition, because it has reached its roadconfiguration threshold.

Remaining requisite life= requisite life age to date

Remaining requisite traffic:

The cumulative traffic loading, expressed in ESAs, from a given date to a predetermined dateat which the pavement will be improved or replaced, regardless of its condition, because ithas reached its road configuration threshold.

Remaining requisite traffic= requisite traffic traffic to date

3.6 Operational Life

3.6.1 Background

Whilst the concepts of remaining service life and remaining requisite, or functional, life will haveuses in their own right, a combination of the two may be also needed to indicate the absoluteexpected life of a pavement irrespective of whether the end of that pavements life is determined bystructural adequacy (as evidenced by distress) or non-distress related reasons.



Remaining operational life:

The lesser of the remaining service lifeand the remaining requisite, or functional, life.

Remaining operational traffic:

The lesser of the remaining service trafficand the remaining requisite traffic.

Estimated remaining operational life:

An estimate of the remaining operational life.

Estimated remaining operational traffic:

An estimate of the remaining operational traffic.

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3.7 Economic Life

3.7.1 Background

There are many different ways of considering and estimating the economic life of a pavement.One possible definition is to consider the end of economic life to have been reached when the

discounted time stream of additionalroad user costs associated with continuing to operate thecurrent pavement compared to the road user costs associated with a rehabilitated pavement isgreater than the discounted net agency costs of rehabilitating and maintaining the pavement.Alternatively, the economic life of a pavement is reached when the discounted user cost savingsassociated with using a rehabilitated pavement compared with the existing pavement, is greaterthan the discounted net agency costs of rehabilitating and maintaining the pavement. However, inmany cases, particularly when considering low trafficked roads, the additional road user costsassociated with operating the pavement may never exceed the net road agency costs at any stageof the pavements life and the pavement may exist primarily for access purposes, such as for alocal road. It therefore may be more appropriate that economic life be based on the minimisationof life-cycle costs of the pavement, considering both the agency costs of maintenance,rehabilitation and the road user costs of vehicle operating costs, travel time, and accident costs to

achieve a designated level of service.

The ultimate limit to economic life may be when the pavements condition reaches a point where itis no longer acceptable for use. In this case the economic life is the same as the service lifediscussed in Section 3.4. However, for roads with high levels of commercial traffic, the economiclife may be shorter than the service life in order to achieve minimum life cycle costs. In this casethe economic life may be optimal; however, the pavement may not be replaced or rehabilitatedbecause of budget limitations.

design

distress

threshold

distress

design

life

Distress

Life

(years)economiclife

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requisite

life

service

life

road configuration

threshold

current

age

current

distress


Remaining requisite life

Remaining operational life = minimum of remaining service life and remaining requisite life

Remaining economic life

Figure 3.4: Economic life

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Economic life:

The lesser of the following:the estimated number of years from the immediate post construction orrehabilitation/replacement condition, which gives the minimum possible life cycle cost,in present value terms that account for the operational costs of maintenance,rehabilitation and road user costs to achieve a designated level of service

the estimated number of years from the immediate post construction orrehabilitation/replacement condition to reach predetermined threshold values ofrelevant distresses beyond which the pavement no longer meets its designated level ofservice (i.e. the estimated service life).

3.8 Other Definitions

Appendix Cdetails the definitions that are associated and subsidiary to the estimation of remainingservice life, economic life and threshold distress values.

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4 SUMMARY

4.1 Definitions

Definitions of the following terms are proposed for review and discussion:

design life

service life

requisite life

operational life

economic life

threshold distress values

designated level of service.

In addition, definitions associated with the above were also proposed for:

maintenance, maximum service life (MSL) and maximum remaining service life (MRSL)

rehabilitation

reconstruction.

The complete list of definitions is contained inAppendix A.

4.2 Estimation of service life

Estimation of the various definitions of service life depends on resolving the following:

deciding what forms of distress are relevant to limiting the designated level of service of the

pavement

assigning threshold values of distress beyond which the pavement is considered to haveexceeded the designated level of service of the pavement

estimating the current, future and optimistic rates of deterioration for each form of distressthat is considered relevant in estimating the service life of pavements and maintenancetreatments.

The above factors are a combination of technical and policy issues and must be resolved within theroad agency responsible for managing the pavement assets. Consequently, estimation of servicelife is not a precise process but it can be improved by rigorous observation of pavementdeterioration of the various road types that comprise the road network. Also required is a clearunderstanding of relevant pavement distresses and their threshold limits, beyond which thepavement performance becomes unpredictable or has exceeded its designated level of service.

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REFERENCES

Al Hakim, B, Al Nageim, H & Pountney, D 1996, Reflection of interface condition modelling error on back-

calculated moduli and pavement remaining life, Eurasphalt & Eurobitume Congress 1996, Strasbourg,

France, Conference Secretariat, Strasbourg, France.

Austroads 2000, Valuation of road infrastructure assets in Australia and New Zealand, AP-144, Austroads,

Sydney, NSW.

Austroads 2003, Remaining life of road infrastructure: an overview, AP-R235/03, Austroads, Sydney, NSW.

Austroads 2004a, Pavement design: a guide to the structural design of road pavements, AP-G17/04,

Austroads, Sydney, NSW.

Austroads 2004b, Pavement rehabilitation: a guide to the design if rehabilitation treatments for road

pavements, AP-G78/04, Austroads, Sydney, NSW.

Austroads 2006, Pavement design for light traffic: a supplement to Austroads pavement design guide: aguide to the structural design of road pavements, AP-T36/06, Austroads, Sydney, NSW.

Baladi, GY, Chatti, K & Buch N 2004, An excellent asset management tool: the remaining service life,

Proceedings 6thInternational Conference on Managing Pavements, Queensland Department of Main

Roads, Brisbane, Queensland

Baladi, G, Noval, EC & Kuo, WH 1992, Pavement condition index remaining service life, ASTM STP 1121,

Pavement Management Implementation, American Society for Testing and Materials, Philadelphia,

PA, pp.63-90.

Bayley, C & Kinder, DF 1984, The impact on road costs of increased transport of grain by road, ARRB

Internal Report AIR 1129-1A, Australian Road Research Board, Vermont South, Vic.

Byers, WG, Marley, MJ, Mohammadi, J, Nielson, R & Sarkani, S 1997, Fatigue reliability reassessment

procedures: state-of-the-art paper, Journal of Structural Engineering, ASCE, vol.123, no.3, pp.271-

276.

CTC & Associates LLC, 2004, Pavement service life- rev. 2, Transportation Synthesis Report, Wisconsin

Department of Transportation, Wisconsin.

Dowling, LB 2004, Valuation of road infrastructure: what does it mean?, Proceedings 6thInternational

Conference on Managing Pavements, Queensland Department of Main Roads, Brisbane, Queensland

Flintsch, GW, Zaniewski, JP & Delton, J 1997, Expert project recommendation procedure for ADOTs

pavement management system, Arizona Transportation Research Centre, Arizona Department ofTransportation, Phoenix, AZ.

Garcia-Diaz, A & Allison, JT 1984, Estimating the remaining service life of flexible pavements, research

report 325-1F, Texas Transport Institute, The Texas A&M University System College Station, Texas.

Kuo, S-S, Hoffman, LL & Kong, F 2001, Flexible pavement performance prediction model on the basis of

pavement condition data, Proceedings 20thARRB Conference, ARRB Transport Research, Vermont

South, Vic

Local Government Victoria (LGV) 2006, Guidelines for measuring and reporting the condition of road assets,

Local Government Victoria, Melbourne, Vic.

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Loizos, A & Fatseas J 1997, Performance based asphalt mix properties in relation to preventative pavement

maintenance, 8thInternational Conference on Asphalt Pavements,Vol 2, International Society for

Asphalt Pavements.

Moffatt, M & Sharp, K 2005, Workshop report 21 July 2005: service life of pavements, Austroads working

document for REAT1169, ARRB Transport Research, Vermont South, Vic.

Novak, EC & Kuo, W-H 1992a, Role of pavement management system analysis in preservation program

development, Transportation Research Record 1334, Transportation Research Board, Washington

D.C., pp.1-8.

Novak, EC & Kuo, W-H 1992b, Life-cycle cost versus network analysis, Transportation Research Record

1334, Transportation Research Board, Washington D.C., pp.66-74.

Robinson, P, Clayton, B, Alderson, A & Sharp, K 2002, Remaining life of road infrastructure: an overview,

ARRB Contract Report RC1643-1 for Austroads, ARRB Research, Vermont South, Vic.

Scullion, T 1988, Incorporating a structural strength index into the Texas pavement evaluation system,

research report 409-3F, Texas Transport Institute, The Texas A&M University System College Station,Texas.

Shoukry, SN, Martinelli, DR & Selezneva, O 1996, Nondestructive evaluation of pavement layers using

combined dynamic and acoustic testing technique, West Virginia University, Morgantown, West

Virginia, USA.

Stidger, RW 2002, Diagnosing problem pavements, Better Roads,vol.72, no.6, pp.27-33.

St-Laurent, D & Prophete, F 2002, Mechanistic evaluation of the impact on flexible pavement of spring load

restrictions, 2002 Annual Conference & Exhibition of the Transportation Association of Canada in

Winnipeg, Manitoba, Canada, 20pp.

Sullivan, T & Scott, R 1990, Strategic road network management an approach using roughness, 15th

Australian Road Research Board Conference Proceedings, Part 3, Australian Road Research Board,

Vermont South, Vic., pp.105-113.

Vepa, TS, George, KP & Shekharan, AR 1996, Prediction of remaining pavement life, Transportation

Research Record 1524, Transportation Research Board, Washington D.C.

Williams, KJ 1990, Beef road to National Highway, 15thAustralian Road Research Board Conference

Proceedings, Part 3, Australian Road Research Board, Vermont South, Vic., pp.23-35.

Zaghloul, S, He, Z, Vitillo, N & Kerr, JB 1998, Project scoping using Falling Weight Deflectometer testing:

New Jersey experience, Transportation Research Record 1643, Transportation Research Board,

Washington D.C.pp.34-43.

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APPENDIX A PROPOSED DEFINITIONS ASSOCIATED WITHREMAINING SERVICE LIFE

Maintenance:

Activities directed to the preservation and repair of the pavement to at least retain its currentcondition and possibly extend its remaining service life

Rehabilitation:

Activities aimed at restoring the pavement to at least its original designated level of service,capacity or condition, including both safety and operational considerations

Reconstruction:

Removal and replacement of part or the entire pavement so that the reconstructed pavementhas the same initial estimated service lifethat it originally had

Threshold distress values:

Measures of pavement condition that are designated as the maximum distress for eachdistress type beyond which pavement performance becomes unpredictable on a given typeor class of road without the imposition of constraints on road users such as load or speedlimits

Designated level of service:

The level of service for a given type or class of road within the designated servicerequirements based on road user needs for access and levels of pavement conditionappropriate to the designated function of the pavement

Design traffic:

The cumulative traffic load, expressed in terms of the number of equivalent standard axles(ESAs), predicted to use a road over the design life of the pavement

Design life:

The number of years for which the pavement is being designed

Design period:

Same as design life

Design distress:

One or more failure criteria used by the pavement design process that ensures that thedesign distress is not reached before the cumulative traffic load has reached the designtraffic

Age to date:

The number of years from the immediate post construction or rehabilitation/replacement ofthe pavement to a given date

Traffic to date:

The cumulative traffic loading, expressed in ESA, from the immediate post construction orrehabilitation/replacement of the pavement to a given date

Distress to date:

The distress that an in-service pavement exhibits at a given date

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Service life:

The number of years from the immediate post construction or rehabilitation/replacementcondition to a predetermined threshold value of a range of distresses beyond which thepavement no longer meets its designated level of service

Service traffic:The cumulative traffic loading, expressed in ESAs, from the immediate post construction orrehabilitation/replacement condition to a predetermined threshold value of a range ofdistresses beyond which the pavement no longer meets its designated level of service

Remaining service life:

The shortest number of years from a given date to a predetermined threshold value of arange of distresses beyond which the pavement no longer meets its designated level ofservice

Remaining service life= service life age to date

Remaining service traffic:

The cumulative traffic loading, expressed in ESAs, from a given date to a predeterminedthreshold value of a range of distresses beyond which the pavement no longer meets itsdesignated level of service

Remaining service traffic= service traffic traffic to date

Estimated service life:

An estimation of the service life

Estimated service traffic:

An estimation of the service traffic

Estimated remaining service life:

An estimation of the remaining service life

Estimated remaining service traffic:

An estimation of the remaining service traffic

Initial estimated remaining service life:

An estimation of the remaining service lifebased on immediate post construction orrehabilitation/replacement condition data

Initial estimated remaining service traffic:

An estimation of the remaining service traffic based on immediate post construction orrehabilitation/replacement condition data

Road configuration threshold:

A time or traffic level at which the current in-service pavement will be improved or replaced,regardless of its condition because it does not meet its designated level of service withrespect to road configuration

Requisite, or functional, life:

The number of years from the immediate post construction or rehabilitation/replacementcondition to a predetermined date at which the pavement will be improved or replaced,regardless of its condition, because it has reached its road configuration threshold

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Requisite traffic:

The cumulative traffic loading, expressed in ESAs, from the immediate post construction orrehabilitation/replacement condition to a predetermined date at which the pavement will beimproved or replaced, regardless of its condition, because it has reached its roadconfiguration threshold

Remaining requisite, or functional, life:

The number of years from a given date to a predetermined date at which the pavement willbe improved or replaced, regardless of its condition, because it has reached its roadconfiguration threshold

Remaining requisite life= requisite life age to date

Remaining requisite traffic:

The cumulative traffic loading, expressed in ESAs, from a given date to a predetermined dateat which the pavement will be improved or replaced, regardless of its condition, because ithas reached its road configuration threshold

Remaining requisite traffic= requisite traffic traffic to date

Remaining operational life:

The lesser of the remaining service lifeand the remaining requisite, or functional, life

Remaining operational traffic:

The lesser of the remaining service trafficand the remaining requisite traffic

Estimated remaining operational life:

An estimate of the remaining operational life

Estimated remaining operational traffic:

An estimate of the remaining operational traffic

Economic life:

The lesser of the following:

the estimated number of years from the immediate post construction orrehabilitation/replacement condition, which gives the minimum possible life-cycle cost,in present value terms that account for the operational costs of maintenance,rehabilitation and road user costs to achieve a designated level of service

the estimated number of years from the immediate post construction orrehabilitation/replacement condition to reach a predetermined threshold value of a

range of distresses beyond which the pavement is no longer acceptable for use (i.e. theestimated service life).

Maximum service life (MSL):

The estimated maximum number of years before the specified maintenance treatment needsrenewal

Maximum remaining service life (MRSL):

The difference between the maximum service life (MSL) and the current age of thepavement.

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APPENDIX B EFFECT OF SUBGRADE CBR CHANGES ONDESIGN LIFE

The pavement design process used for spray sealed granular pavements is particularly sensitive to

the subgrade CBR assumed. Figure B.1 shows the variation in design life that the design processpredicts would result from minor changes in the subgrade CBR. Assuming a design subgradeCBR of 5% and a design life of 30 years, pavement thickness was determined for each of fivedifferent traffic levels. After determining the pavement thickness for each traffic level, the subgradeCBR was altered and for each traffic level the resulting pavement lives determined and plotted.

It can be seen that for all traffic levels a reduction of subgrade CBR of only 1% (i.e. from a CBR of5% to 4%) results in more than halving the design life. Similarly an increase in subgrade CBRfrom 5% to 6% generally results in a doubling of pavement life to approximately 60 years. Anincrease in CBR of 2% further extends the design life, with the local street exhibiting a newpavement life in excess of 150 years.

Figure B.1 indicates that pavement with in-service subgrade CBRs only slightly higher than thevalues assumed in the design process can be expected to outlast their design life by aconsiderable amount.

Sturt Hwy, Truro, SA

Princes Hwy, Batemans Bay, NSW

Monash Freeway, Greater

Dandenong, VIC

Local access in industrial area

Minor with single lane traffic

0

20

40

60

80

100

120

140

160

2 3 4 5 6 7 8

Subgrade CBR (%)

Design

life

(years)

9

Reference pavement

30 year design life

Subgrade CBR of 5%

Source of traffic levels

Austroads (2004a and 2006)

Traffic growth rates assumed

Local roads: 1%

All other roads: 4%

Figure B.1: Effect of subgrade strength variations on design life

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APPENDIX C OTHER DEFINITIONS ASSOCIATED WITHREMAINING SERVICE LIFE

The definitions outlined below include separate explanatory comments beneath each definition.

C.1 Maintenance

These are operations related to the preservation and repair of the asset to improve its conditionand possibly extend its remaining service life.

Preventative maintenance treatments can be considered to have a separate initial estimatedservice life(Novak and Kuo 1992b) in the context of a pavement management program or amaximum service life(Flintsch et al. 1997). Preventative maintenance treatments usually addresssurface defects.

C.1.1 Maximum service life

The maximum service life is the estimated maximum number of years before the specifiedmaintenance treatment needs renewal (from Flintsch et al. 1997).

The term maximum service life(MSL) is limited to the estimated performance of maintenancetreatments. Different MSLs can be defined for the same type of maintenance treatment ondifferent road types (Flintsch et al. 1997). The MSL for the same type of treatment tends to benominated as being lower for roads with higher functional status as shown in Table C.1.

Table C.1: Maintenance treatment service life statisti cs

Road type Maintenance treatment Average servi ce life(years)

95thpercenti le (years) Theoretical MSL(years)

Freeway Reseal 9 17 18Thin overlay 9 17 18

Medium overlay 10 17 18

Thick overlay 10 16 18

Arterials Reseal 11 23 23

Thin overlay 10 23 23

Medium overlay 11 22 23

Thick overlay 12 22 23

Source: adapted from Flintsch et al. 1997

C.1.2 Maximum remaining service life

The maximum remaining service life (MRSL) is the difference between the maximum service life(MSL) and the current age of the pavement (from Flintsch et al. 1997).

The estimate of MRSL is dependent on the estimate of the MSL for a particular maintenancetreatment. In some instances the computer estimated remaining service life may exceed theMRSLbecause the estimated remaining service life is based on current conditions anddeterioration rates. If this is the case, the MRSL is assigned the same value as the computerestimated remaining service life. Figure C.1 shows the typical relationship between estimatedremaining service life and MRSL.

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Distress

Life(years)

Predicted deterioration

(optimistic)

Maximum service life (MSL)

Maximum remaining service life (MRSL)

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Estimated remaining service life

Current age and condition

Threshold distress value

Predicted deteriorationUnacceptable

condition

Acceptable

condition

Figure C.1: Relationship between maximum remaining service life and estimated remaining service life

C.2 Rehabilitation

These are operations aimed at restoring the pavement to at least its original designated level ofservice, capacity or condition, including both safety considerations and operational improvements.

Rehabilitation resets the pavement age to zero and addresses both surface and structuralconditions with the aim of returning these conditions to close to their original condition immediately

post construction. Significant rehabilitation may be aimed at increasing the structural and spacecapacity if there had been an increase in the traffic load and its volume.

C.3 Reconstruction

Reconstruction involves removal and replacement of part or the entire pavement so that thereconstructed pavement has the same initial estimated service life that it originally had.

Reconstruction also resets the pavement age to zero and addresses both surface and structuralconditions with the aim of returning these conditions to at least their original condition immediatelypost construction. Reconstruction usually occurs when the pavement may have become eitherobsolescent or there has been a significant increase in the traffic load and its volume that warrants

reconstruction.

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INFORMATION RETRIEVAL

Austroads, 2007, Service Life of Pavements: Context, Review andDefinit ion of Terms, Sydney, A4, 32pp, AP-T77/07

Keywords:

estimated remaining service life, operational or useful life, economic life,designated level of service, design life, service life, threshold distress values,asset valuation

Abstract:

The project was aimed at providing an understanding of remaining service lifeas a concept and definitions of key terms such as design life, service life,remaining service life (RSL), designated level of service, and thresholddistress values in the context where RSL is restricted to the next interventionby rehabilitation or replacement. The estimation of RSL was noted not to be aprecise process but it could be improved by understanding the relevantpavement distresses beyond which the pavement exceeds its designated levelof service and rigorous observation of the deterioration of various road types.

Documents

AP-T77-07