J.10_Reformulated_Pavement_Remaining_Service.pdf

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Reformulated Pavement Remaining Service Life (RSL) Framework PUBLICATION NO. FHWA-RD- April 2012

U.S. Department of Transportation Federal Highway Administration

Research, Development, and Technology Turner-Fairbank Highway Research Center 6300 Georgetown Pike McLean, VA 22101-2296

DRAFT

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FOREWORD

The FHWA Office of Infrastructure R&D conducts and oversees research and development programs and projects that address critical highway infrastructure needs and priorities of national importance. Studies focus on the design, materials, construction, operation, and preservation of highway pavements, bridges, culverts, tunnels, and other structures. In addition, the Office of Infrastructure R&D provides expert technical assistance to other FHWA offices, other Federal agencies, State and local transportation organizations, industry and academia.

This study addresses the challenging issue of standardizing nomenclature used by highway agencies related to pavement remaining service or structural life.

This document provides detailed information on the research performed on the issue of remaining pavement life. The many issues which exist with the current remaining service life terminology and resulting numeric’s which confuse, confound, and complicate proper interpretation, interagency data exchange, and use are explored.

Technical references are provided to a plethora of sources from within and outside of the pavement community. While this document focuses on pavements, it is also applicable to other types of transportation infrastructures.

Jorge Pagán-Ortiz Director, Office of Infrastructure Research and Development

Notice

This document is distributed under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for its contents or use thereof. This report does not constitute a standard, specification, or regulation.

The U.S. Government does not endorse products or manufacturers. Trade and manufacturers’ names appear in this report only because they are considered essential to the object of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of the information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvements.

1. Report No.

FHWA-

2. Government Accession No.

3. Recipient’s Catalog No.

4. Title and Subtitle Reformulated Pavement Remaining Service Life (RSL) Framework

5. Report Date April 2012

6. Performing Organization Code

7. Author(s) Gary E. Elkins, Travis M. Thompson, Jonathan L. Groeger, Beth Visintine, and Gonzalo R. Rada

8. Performing Organization Report No.

9. Performing Organization Name and Address AMEC Environment and Infrastructure, Inc.

12000 Indian Creek Court, Suite F Beltsville, MD 20705-1242

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

DTFH61-08-C-00033

12. Sponsoring Agency Name and Address Office of Infrastructure Research and Development Federal Highway Administration 6300 Georgetown Pike McLean, VA 22101-2296

13. Type of Report and Period Covered Final Draft Report, October 2009

– April, 2012

14. Sponsoring Agency Code

15. Supplementary Notes Contracting Officer’s Technical Representative (COTR): Nadarajah Sivaneswaran, HRDI-20

16. Abstract The process of providing and managing a pavement network requires a number of important decisions regarding future budgetary needs to be made. At the heart of this budget process, is the prediction of needed future construction events. One approach to providing a single numeric on the condition of a pavement network is the use of pavement remaining service life (RSL). However, many issues exist with the current RSL terminology and resulting numeric’s which confuse, confound, and complicate proper interpretation, interagency data exchange, and use. A major source of uncertainty in the current RSL definitions is the use of the term “life” to represent multiple points in the pavement construction history. The recommended path to consistency involves adopting terminology of time remaining until a defined construction treatment is required– RSL is replaced by "Remaining Service Interval" or “RSI.”

This terminology has the ability to unify the outcome of different approaches to determining needs by focusing on when and what treatments are needed, and the service interruption created. This report presents the framework for replacing the current RSL terminology with one based upon more exact construction event terms. A companion document provides step-by-step guidelines for implementation of the RSI terminology.

17. Key Words Pavement remaining service life, pavement remaining life, pavement remaining service interval, pavement construction events, pavement construction triggers, pavement threshold limits, pavement performance expectancy curves, pavement data collection, and pavement strategy selection.

18. Distribution Statement No restrictions. This document is available to the public through the National Technical Information Service, Springfield, VA 22161.

19. Security Classif. (of this report) Unclassified

20. Security Classif. (of this page) Unclassified

21. No. of Pages

2. Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized iv

SI* (MODERN METRIC) CONVERSION FACTORS

APPROXIMATE CONVERSIONS TO SI UNITS

Symbol When You Know Multiply By To Find Symbol

LENGTH

in inches 25.4 millimeters mm ft feet 0.305 meters m yd yards 0.914 meters m mi miles 1.61 kilometers km

AREA

in2 square inches 645.2 square millimeters mm2 ft2 square feet 0.093 square meters m2 yd2 square yard 0.836 square meters m2 ac acres 0.405 hectares ha mi2 square miles 2.59 square kilometers km2

VOLUME

fl oz fluid ounces 29.57 milliliters mL gal gallons 3.785 liters L ft3 cubic feet 0.028 cubic meters m3 yd3 cubic yards 0.765 cubic meters m3

NOTE: volumes greater than 1000 L shall be shown in m3

MASS

oz ounces 28.35 grams g lb pounds 0.454 kilograms kg T short tons (2000 lb) 0.907 megagrams (or "metric ton") Mg (or "t")

TEMPERATURE (exact degrees) oF Fahrenheit 5 (F-32)/9 Celsius oC or (F-32)/1.8

ILLUMINATION

fc foot-candles 10.76 lux lx fl foot-Lamberts 3.426 candela/m2 cd/m2

FORCE and PRESSURE or STRESS lbf poundforce 4.45 newtons N lbf/in2 poundforce per square inch 6.89 kilopascals kPa

APPROXIMATE CONVERSIONS FROM SI UNITS

Symbol When You Know Multiply By To Find Symbol

LENGTH

mm millimeters 0.039 inches in m meters 3.28 feet ft m meters 1.09 yards yd km kilometers 0.621 miles mi

AREA

mm2 square millimeters 0.0016 square inches in2 m2 square meters 10.764 square feet ft2 m2 square meters 1.195 square yards yd2 ha hectares 2.47 acres ac km2 square kilometers 0.386 square miles mi2

VOLUME

mL milliliters 0.034 fluid ounces fl oz L liters 0.264 gallons gal m3 cubic meters 35.314 cubic feet ft3 m3 cubic meters 1.307 cubic yards yd3

MASS

g grams 0.035 ounces oz kg kilograms 2.202 pounds lb Mg (or "t") megagrams (or "metric ton") 1.103 short tons (2000 lb) T

TEMPERATURE (exact degrees) oC Celsius 1.8C+32 Fahrenheit oF

ILLUMINATION

lx lux 0.0929 foot-candles fc cd/m2 candela/m2 0.2919 foot-Lamberts fl

FORCE and PRESSURE or STRESS N newtons 0.225 poundforce lbf kPa kilopascals 0.145 poundforce per square inch lbf/in2

*SI is the symbol for th International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380. e (Revised March 2003) v

TABLE OF CONTENTS

CHAPTER 1. INTRODUCTION

INTRODUCTION

PAVEMENT BUSINESS DECISIONS

ROLE OF RSL IN PAVEMENT BUSINESS DECISIONS

ISSUES WITH CURRENT RSL TERMINOLOGY

FRAMEWORK PRESENTED IN THIS REPORT

CHAPTER 2. REFOCUS OF PAVEMENT REMAINING LIFE VOCABULARY

REFORMULATING RSL TERMINOLOGY

FUNDAMENTAL PAVEMENT PLANNING ELEMENTS

CONSTRUCTION EVENT TERMINOLOGY

CHAPTER 3. FUTURE CONSTRUCTION NEEDS ANALYSIS FRAMEWORK

INTRODUCTION

CONSTRUCTION TRIGGERS

THRESHOLD LIMITS

EXPECTANCY CURVES

COLLECTION OF INPUTS

STRATEGY SELECTION

ASSESSMENT AND UPDATE

CHAPTER 4. CONSTRUCTION TRIGGERS

INTRODUCTION

LEVEL OF SERVICE

PAVEMENT SURFACE DISTRESS

STRUCTURAL CONSIDERATIONS

SAFETY

AGENCY TIME-BASED RULES

TRAFFIC CAPACITY

CHAPTER 5. THRESHOLD LIMITS

INTRODUCTION

SUBJECTIVE

ENGINEERING

EMPIRICAL

ECONOMIC ANALYSIS

COMBINATIONS

CHAPTER 6. EXPECTANCY PERFORMANCE CURVES

INTRODUCTION

MODELS BASED ON DESIGN EQUATIONS

EMPIRICAL MODELS

AGENCY TIME-BASED RULES

CHAPTER 7. COLLECTION OF INPUTS

INTRODUCTION

PAVEMENT ROUGHNESS

PAVEMENT DISTRESS

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PAVEMENT STRUCTURAL RESPONSE

TRAFFIC LOADS

CLIMATE

MISSING DATA

MEASUREMENT VARIABILITY

SAMPLING INTERVALS AND FREQUENCY

CHAPTER 8. STRATEGY SELECTION

INTRODUCTION

NETWORK ANALYSIS

PROJECT ANALYSIS

CHAPTER 9. ASSESSMENT AND UPDATE

INTRODUCTION

ASSESSMENTS

UPDATES

CHAPTER 10. SUMMARY

REFERENCES

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LIST OF FIGURES

Figure 1. Illustration. Basic framework of future pavement construction needs Figure 2. Graph. Conceptual relationship between present worth agency repair costs as a function of pavement condition Figure 3. Graph. Basic concept of modern pavement design is based on a predicted pavement design life that drops to a minimum acceptable condition based on functional service considerations

Figure 4. Graph. Illustrated service histories of several trial pavement designs incorporating future overlays from the 1986 AASHTO Pavement Design Guide

Figure 5. Graph. Staged pavement construction design concept which incorporates a planned structural overlay early in the pavement life in order to meet the desired pavement design life

Figure 6. Graph. This perpetual pavement design concept is based on construction of a pavement so that distresses occur in the pavement surface layer, which can be removed and replaced at intervals to provide a long-lasting and possibly perpetual pavement structure

Figure 7. Graph. Multiple distress based pavement design is based on consideration of when one of the distresses will reach a maximum threshold limit. In this illustration since distress type 2 reaches the maximum threshold first it is used as the basis of the pavement design life

Figure 8. Graph. Applicable maintenance, repair and restoration treatments tend to be most effective before pavement condition reaches a point when rehabilitation treatments need to be used. At some point, pavement condition can reach a level where reconstruction is the best option. Typically reconstruction is required after pavement condition falls below a minimum acceptable functional condition

Figure 9. Graph. In concept, pavement construction costs increase in proportion to the pavement’s capacity to resist detrimental structural and environment loads. In contrast, maintenance, repair, and restoration costs decrease with increased pavement resistive capacity. Optimum occurs at the point of minimum total cost

Figure 10. Graph. Concept of increasing repair cost as a function of pavement deterioration. (8) ... 54 Figure 11. Graph. Classical bathtub curve of component failure rate versus time. The MTBF statistic is commonly based on the minimum failure rate

LIST OF TABLES

Table 1. Role of RSL models in levels and types of pavement management business decisions Table 2. PSR threshold values used in the HPMS analytical process for minimum tolerable conditions for overlay and reconstruction viii

LIST OF ACRONYMS

Acronym - Definition

AASHO - American Association of State Highway Officials AASHTO - American Association of State Highway and Transportation Officials AC - asphalt concrete ADT - average daily traffic ANN - Artificial Neural Network APT - Accelerated Testing program ASR - Alkali Silica Reaction AWS - Automated Weather Station BLCCA - bridge life cycle cost analysis CAPM - Capital Preventive Maintenance CDF - Cumulative Distribution Function CDOT’s - Colorado Department of Transportation’s COST - Cooperation of Scientific and Technical Research CPR - concrete pavement restoration CRCP - continuously reinforced concrete pavement DOT - Department of Transportation ECC - Engineered Cementitious Composites ESAL - Equivalent Single Axle Loads ETR - Effective Thickness Ratio FACS - Fatigue, ASR, Cracking, and Spalling FN - friction number FHWA - Federal Highway Administration FWD - Falling Weight Deflectometer GAPEMS - Geospatial Airfield Pavement Evaluation and Management System GHG - greenhouse gas GPR - Ground Penetrating Radar HERS - Highway Economic Requirements System HMA - hot-mix asphalt HPMS - Highway Performance Monitoring System HRI - Half-car Roughness Index IRI - International Roughness Index INDOT - Indiana Department of Transportation JPCP - jointed plain concrete pavements KDOT - Kansas Department of Transportation LCC - life cycle costs LCCA - life cycle cost analysis LTPP - Long Term Pavement Performance MDOT - Michigan Department of Transportation MDOT - Mississippi Department of Transportation M-E - Mechanistic-Empirical MEPDG - Mechanistic-Empirical Pavement Design Guide MoDOT - Missouri Department of Transportation ix

M&R - Maintenance and Rehabilitation MR&R - Maintenance, Rehabilitation, and Repair MTBF - Mean Time Between Failures NAPCOM - National Pavement Cost Model NCHRP - National Cooperative Highway Research Program NCDC - National Climate Data Center NDT - Nondestructive Deflection Testing NHS - National Highway System NIST - National Institute of Standards and Technology NOS - network optimization system PaveCARE - Pavement Condition Assessment & Rehabilitation Effectiveness PCC - portland cement concrete PCI - Pavement Condition Index PCR - Pavement Condition Rating PDF - Probability Density Functions PDF - portable document format PFS - Pooled Fund States PH - proportional hazards PHT - Pavement Health Track PMS - Pavement Management System POP - Pavement Optimization Program PPP - Public-Private Partnership PSR - Pavement Serviceability Rating RSI - Remaining Service Interval RSL - Remaining Service Life RI - Roughness Index ROCOF - Rate of Occurrence of Failures RN - Ride Number RQI - Ride Quality Index RWD - Rolling Wheel Deflectometer SAS - Statistical Analysis Software SHA - State highway agencies SHRP - Strategic Highway Research Program SNeff - effective Structural Numbers TxMLS - Texas Mobile Load Simulator

EXECUTIVE SUMMARY

The “remaining service life” or “RSL” concept has been around for decades and is well entrenched in the pavement community. It is used at all levels of the pavement management decision process to plan for future field construction events. However, there is no single, clear and widely accepted definition of RSL. Moreover, there is a great deal of uncertainty associated with the definition, especially with the use of the term “life” to represent different points in a pavement’s construction history. In addition, when communicated, the meaning of “life” is lost and it is interpreted differently by stakeholders.

To overcome the RSL shortcomings, this framework introduces terminology that removes the word "life" from the lexicon since it is the basis for confusion. Instead of “life,” the new terminology introduces the concept of time remaining until a defined construction event is required. Pavements are comprised of interrelated structural parts which can be maintained, preserved, restored, rehabilitated, or reconstructed to serve the intended transportation need.

The RSI concept does not provide an alternative to assessing the health of the network or making decisions about where to spend the available funds. It simply provides a clear terminology and a logical process that will move us away from erroneous statements such as "this pavement has only 5 remaining years of life” and moves us toward a consistent construction event-based terminology and understanding -- types of construction events and the timing of those events within the concept of life cycle cost (LCC), risk analyses, and other prioritization approaches based on streams of future construction events and benefits to facility users.

CHAPTER 1. INTRODUCTION

INTRODUCTION

The prediction of future pavement preservation, repair, rehabilitation, and reconstruction requirements is the fundamental basis of engineering design and management of pavement structures. Pavement design methods are based on provision of a pavement structure predicted to remain in acceptable condition under anticipated traffic loads and environmental conditions for a specified number of years. After construction, planning the timing of maintenance, preservation, resurfacing, rehabilitation, and reconstruction activities that take into account the material and structural "as-constructed" pavement characteristics become important. Life terminology has been developed and used in various ways to describe the expected period of time it will take for a pavement to reach an unacceptable condition state.

The term pavement remaining life or remaining service life (RSL) is the time from the present to when a pavement reaches an unacceptable condition requiring construction intervention. While some make the distinction that remaining life is the time until major rehabilitation and remaining service life is the time until a service threshold is reached, both type of events require some type of construction treatment to correct.

The purpose of this report is to provide a framework to replace current pavement life terminology with one based upon more exact construction event terms. In the remainder of this chapter we start the discussion with pavement business decisions and the role that current RSL terminology serves in these decisions. This is followed by a discussion of issues with current RSL terminology.

PAVEMENT BUSINESS DECISIONS

The process of providing and managing a pavement network requires a plethora of decisions to be made. A common method to classify these decisions into groups with common characteristics is through the notion of hierarchal levels within the business management process. The pavement management business processes impacted by these decisions are most often described as network and project level decisions.

The purposes and goals of network-level pavement management are normally related to the budget process. (1) Decisions at this level are made by higher level management positions within an organization with resource allocation authority.

Network level decisions have many strata starting at the local level and progressing to the national level. In local municipal agencies, network decisions start at the city or regional level depending on size and governmental organization. Decisions on pavement networks managed by State agencies can start at a district level but ultimately are made centrally. National level decisions on funding for roads included in the National Highway System (NHS) are made by Congress based on information supplied by the Federal Highway Administration (FHWA), which is based on data submitted from State Highway Agencies (SHA). A primary result of network level pavement/asset management decisions is the amount of funding allocated to the pavement infrastructure. At other network level strata, decisions are made on which segments of the road network are scheduled for future construction interventions requiring project level plans to be prepared.

Because of the economics of pavement condition field data collection, data requirements to support network level business decisions must be more aggregated and contain fewer details, as one progresses from local to national level network strata.

The purpose of decisions at the project level is to provide the most cost-effective, feasible, and original design, maintenance, rehabilitation, or reconstruction strategy possible for a selected section of pavement within the available funds and other constraints. (2) The data needs at the project level are the greatest since they result in engineering plans and specifications on treatment activities to be applied to individual projects.

Alternative contracting mechanisms such as design-build-operate and warranty construction are subsets of the more general project level business decisions and could be classified as a contract administration level type of business decision. Because the acceptance conditions must be specified in the contract, data support for these project level contracts have an additional burden of withstanding the test of potential contractual challenges.

ROLE OF RSL IN PAVEMENT BUSINESS DECISIONS

The prediction of the remaining life of a pavement is a fundamental aspect of pavement management planning. Knowing or estimating the future condition of pavement segments is the rational basis of all informed pavement infrastructure planning decisions. A goal of modern pavement management systems is to optimize agency resource expenditures while minimizing impacts on facility users and the ecosystem.

Pavement infrastructure budget optimization techniques require prediction of the change in pavement condition within a defined set of time frames, which then predict what is needed under the following action scenarios:

• The do nothing alternative. This is defined as no physical road construction event is needed within the planning horizon since the pavement structure is expected to still be in acceptable condition.

• Applications of routine reactive maintenance to correct spot deficiencies.

• Application of preventive maintenance and preservation activities designed to extend pavement service life without significant pavement structural changes prior to the time when reactive maintenance treatments are required.

• Application of alternative rehabilitation treatments.

• Pavement reconstruction.

Table 1 presents a summary of the role of RSL models in business decisions at different levels of pavement management, contract construction, and pavement operation mechanisms.

Table 1. Role of RSL models in levels and types of pavement management business decisions.

Decision

Level Decision Pavement RSL Model Role

Project Design Rehabilitation treatment selection

Time until pavement structural and functional limit thresholds are reached or exceeded

Service life prediction of candidate treatments

Project Design Overlay thickness design

Service life prediction of candidate overlay design thicknesses

Project Design Non-overlay rehabilitation treatments

Time until pavement structural and functional limit thresholds are reached or exceeded

Service life prediction of candidate treatments

Project Design Noise mitigation treatment selection

Prediction of increase in noise as a function of pavement age, surface texture, traffic volumes, and vehicle speed

Project Design Friction mitigation treatment selection

Prediction of changes in friction as function of predicted change in surface texture characteristics and age

Pavement Network Planning

Needed pavement maintenance budget

Time until pavement functional limit threshold are reached or exceeded

Predicted pavement condition as a function of funding allocation

Pavement Network Planning

Needed pavement rehabilitation budget

Time until pavement structural and functional limit thresholds are reached or exceeded

Changes in pavement condition for non-treated projects Change in pavement condition for rehabilitated projects

Pavement Network Planning

Needed pavement reconstruction budget

Time until pavement structural and functional limit thresholds are reached or exceeded

Change in pavement condition for non-treated projects Change in pavement condition of reconstructed projects

Pavement Network Planning

Budget optimization

– allocation of resources to projects

Change in pavement condition for non-treated projects

Change in pavement condition for rehabilitated projects

Change in pavement condition of reconstructed projects

Decision Level Decision Pavement RSL Model Role

Contract Maintenance Management

Contractor award fees /penalties

Structural and functional service life prediction as a function of applied maintenance treatments

Contract Design-Build- Operate

Acceptance by public agency at end of contract – decisions based upon contract terms

Time until pavement functional need thresholds are reached or exceeded

Predicted maintenance free life

Time until rehabilitation required

Predicted performance of pavement until rehabilitation required

Warranty construction contract

Acceptance by public agency at end of contract – decisions based upon contract terms

Time until pavement functional need thresholds are reached or exceeded

Predicted maintenance free life

Time until rehabilitation required

Predicted performance of pavement until rehabilitation required

As described in Table 1, the central role of RSL models in all of these pavement management business decisions is predicting the change in pavement condition as a function of time, traffic loading, and environment. The basic difference in the RSL models used at the project, network and contract administration levels are data requirements related to level of technical detail, extent, quality, precision and accuracy of the model inputs. Project and contract level models require the greatest amount of input data to satisfy statistically based inferences. Ideally models used at the project level are expected to be calibrated to local conditions, use better and more data, and thus are perceived to be more accurate than models used at network levels since actual engineering decisions are based on their results. Network level decisions typically result in allocation of resources, which must be subsequently programmed down to the project level.

Since pavement network condition is only one input into this process, data requirements do not currently justify the intensity of project level data collection.

When the promise of fully automated pavement data collection technology is finally reached, project and network level decision making can converge to use of a common set of RSL model inputs. Then the basis of the decisions made at the network planning level will converge with information used at the project implementation level. Since simplified models are currently used for network level planning, the assumptions made during the optimization process on the type of future treatments to apply to each pavement segment may not match the actual pavement treatments designed using detailed project level data. Until the disparity between assumptions used in network level budget optimization algorithms are matched to the resulting project level treatment decisions, true network budget optimization will not be achieved. While this vision of merging network and project level pavement management modeling may be somewhat optimistic at this point in time, efforts to reduce network level data collection costs while providing more information are continuing to be pursued.

ISSUES WITH CURRENT RSL TERMINOLOGY

While the prediction of time until a corrective or preventative construction treatment should be applied is an established critical component at all levels of pavement management decisions, many issues exist in the current RSL terminology and resulting numeric’s, which confuse, confound, and complicate proper interpretation, interagency data exchange, and use.

One common RSL definition is the time until the next rehabilitation or reconstruction event.

Rehabilitation and reconstruction are two very different events in terms of pavement condition at the time of construction and construction costs. The rule of thumb is that rehabilitation treatments should be applied before a pavement has suffered too much structural damage, otherwise the rehabilitated pavement structure will not last very long. Reconstruction treatments are generally warranted after a pavement has reached an advanced degree of deterioration;

typically in the planning process an agency decides to apply a rehabilitation treatment to extend the time until reconstruction is required. Attempting to interpret combined RSL estimates from mixed rehabilitation and reconstruction "units" can cause confusion for decision makers.

Another common RSL definition is the time until a condition index threshold limit is reached.

This approach shares the same issues as rehabilitation and reconstruction RSL units, but also introduces other service and safety condition indices, which further complicate the meaning of RSL. Setting threshold limits for pavement conditions which are not based on human subjective ratings, such as cracking, can be complicated to justify. Moreover, interpretation of a single RSL number gets even more complicated when it is based upon multiple condition states. For example, if the RSL for roughness is 2 years, RSL for cracking is 5 years, RSL for friction is 7 years, and the RSL for rutting is 20 years, saying the current pavement RSL equals two years can lead to faulty construction decisions since the construction treatment to correct roughness may ignore the more serious cracking issue expected to occur soon after the roughness threshold is reached. Since there are many construction treatments that can be used to correct excessive pavement roughness that can be classified as pavement preservation, this approach adds maintenance type activities to RSL units.

Another intriguing aspect of RSL based upon threshold limits is negative RSL. When a pavement condition index limit is reached, from a numerical standpoint, the years it remains in service after this time could be considered a negative service life which is counterintuitive. One approach is to set negative values to zero; thus, not allowing a negative RSL value to be provided by the process. Another approach is to consider negative RSL as overdue needs, in which case the number of years overdue can be considered as information content to decision makers, if they know the basis of the condition in need of attention.

Another approach to RSL is based upon agency management rules on the time between applications of corrective pavement construction treatments. For example, a state agency with a relatively small number of interstate highway lane-miles might establish a policy that every 8 years a resurfacing, rehabilitation, or reconstruction treatment is applied to each construction segment unit on their system. Some agencies consider this as a proactive approach to keeping their highest level functional class pavements in the best condition. The RSL becomes the difference in time between the policy construction frequency and how long it has been since the last treatment was applied. While this approach can work for agencies with enough budget to satisfy all pavement repair needs within its system, it typically does not provide for optimal distribution under a limited funds constraint scenario of budget planning.

One unintentional consequence of using current RSL terminology, which is defined as the time to reconstruction or major rehabilitation, is that it tends to promote "worst-first" approaches to correcting pavement deficiencies. By expressing pavement condition in terms of RSL, laymen and politicians expect that pavements in the worst condition get treated first. Construction treatments on pavements in the worst condition tend to cost the most. Applying a "life" extending corrective rehabilitation treatment before the pavement condition gets too bad, tends to cost less than reconstruction treatments. Optimum allocation of annual pavement resurfacing, rehabilitation and reconstruction budgets will be a mixture of pavements with differing remaining lives and not based solely on a worst first approach.

FRAMEWORK PRESENTED IN THIS REPORT

The framework presented in this report is intended to provide a common definition that may be referred to by anyone attempting to evaluate the remaining life or service life of a pavement structure. The report will discuss the updated vocabulary in chapter 2. In chapter 3, it will cover the framework associated with RSL development and construction needs assessment. The remaining chapters will cover each step of the process including construction triggers, threshold limits, expectancy curves, inputs, strategy selection, and assessment and update. The final chapter will summarize the report.

CHAPTER 2. REFOCUS OF PAVEMENT REMAINING LIFE VOCABULARY

REFORMULATING RSL TERMINOLOGY

A primary objective of this document is to provide a definition of pavement remaining life that will promote consistency in the use of the terminology. A great variety of RSL definitions are currently used in the pavement community to describe different events in the construction history of a pavement. Construction related history best describes the use of RSL models in all levels of the pavement management decision process because the primary purpose for predicting remaining pavement service life, or life within the context of modern pavement management, is to plan for future field construction event(s), whether it be the application of maintenance, preservation, rehabilitation, reconstruction, or other treatments to correct some attribute of the pavement structure. Regardless of the name given to different treatments, these are all construction events that cost the highway agency to provide and impact facility users. Ideally, the definition of RSL should be independent of business decisions.

The major source of uncertainty in the current RSL definitions is the use of the term “life” to represent multiple points in the construction history. In the pavement design context, "life" is used to represent the time until the hypothetical pavement structure reaches an unacceptable condition, since the pavement designer must make assumptions on the pavement properties. In the pavement management context, after construction of the pavement structure, the "as-constructed" properties become more important in pavement life expectations than the assumed inputs into the original design process. A pavement structure can be thought of as a system whose components include subgrade treatments, subsurface drainage features, base layers, shoulders, bound structural load bearing layers, and surface layers. As a repairable system, the life of the system is not defined by correctable component failures.

The proposed solution to the problem is to remove the word "life" from the lexicon since it is the basis for confusion. Instead of using remaining service life or structural life, a path to consistency appears to be adopting terminology of time remaining until a defined construction treatment is required to replace the generic ill-defined RSL term. This terminology has the ability to unify the outcome of different approaches to determining needs by focusing on when and what treatments are needed, and the service interruption created. Perhaps "Remaining Service Life" is replaced by "Remaining Service Interval" (RSI).

Moreover, adoption of a definition related to construction treatments opens up the vocabulary to treatments related to other factors besides pavement condition. For example, if a construction cycle is defined in terms of time until the next construction event requiring lane closures, then capacity improvements, shoulder widening, utility construction, and realignment construction activities can be included in the construction event. In turn, this provides for broadening the application of the definition in the future. In some situations, for example, capacity issues can have more of an effect on the service provided by a pavement structure than condition of the pavement surface. Or the pavement has reached a level that the next utility cuts and resulting repairs can be performed within a defined time window. This shifts the emphasis on the life remaining in a pavement structure to the time remaining until the next planned construction lane closure is required or future type of defined construction treatment is needed.

FUNDAMENTAL PAVEMENT PLANNING ELEMENTS

The fundamental elements required to unify RSL terminology include:

1. Development of a high order "controlled" vocabulary used to define pavement construction events. The objective of this vocabulary is to uniquely define the "what" in the type of predicted future construction event need.

2. A common basis for "when" the future construction event is needed.

3. "How" future needs are determined is the decisive differentiation between different levels of business decisions.

4. "Where" defines the location and extent of the needed treatment.

The logic of this structure is based upon separating the definitions of what future construction event is needed from how the need is determined. Although project level prediction methods require more intensive engineering data than network level models, they are used for the same purpose in determination of similar types of future treatment needs.

Another need for a fundamental RSL model is to incorporate the service interruption concept.

Drawing from the concept of a repairable system used outside of the pavement industry, incorporating service interruption into the model and quantifying the effect on user experience is critical. Thus, some form of user experience (analogous to functional condition percepts) should be a part of a fundamental RSL definition. In addition, there is the need to model life from an engineering standpoint and this primarily involves integrating a structural component into the model. Each of these perspectives must be accounted for as part of fundamental pavement planning activities.

CONSTRUCTION EVENT TERMINOLOGY

The proposed replacement for remaining service life or remaining structural life is terminology to time until a construction treatment is required; i.e., remaining service interval or RSI. This terminology requires three attributes - time when a treatment is needed, type of construction treatment, and reason for the construction treatment.

Time is being specified since this is the basis of budgeting decision making. This is meant to replace prediction models based upon traffic applications. Traffic application rates used in the modeling process need to be converted to a time basis. Conversion of traffic application rates to a time basis is a complex process based upon consideration of the “design lane” which receives the most truck loadings, on multilane facilities, “damaged lane” which is the lane in worst condition since it is not always the design lane, and other local factors which influence pavement damage from vehicle and environmental effects.

A controlled vocabulary is needed to describe the construction treatments. A common vocabulary promotes database integration and increases the level of aggregation at local, district, state, and national levels. The following are example definitions of construction events based on the expanded paradigm of common pavement improvements included in many modern pavement management systems:

• Crack sealing – application of sealants in surface cracks.

• Joint sealing – application of sealants in preformed joints.

• Surface treatment – application of a layer of material of intended uniform thickness less than 12 mm (0.5 in.) thick.

• Thin overlays – application of a material layer of intended uniform thickness greater than 12 mm (0.5 in.) and less than 50 mm (2 in.) in thickness and which does not increase the thickness of the bound material layers by more than 25 percent.

• Thick overlays – application of a material layer of intended uniform thickness greater than 50 mm (2 in.) in thickness or increases thickness of bound pavement layers by more than 25 percent.

• Concrete Pavement Restoration – application of full-partial depth joint repairs, slab replacement, dowel bar retrofit, or other restoration treatment not covered in another definition.

• Grinding – removal of portions of the surface layer of a pavement without placement of a new material layer.

• Grooving – cutting of grooves in the surface of a pavement without application of a new material layer.

• Milling – removal of bound portions of a pavement that is associated with placement of a new material surface layer.

• Undersealing – injection of cementitious material underneath bound pavement layers.

• Reconstruction - removal and replacement of all bound layers of an existing pavement.

• Addition of lanes – construction of additional lanes to the facility designed to permit greater traffic capacity.

• Addition of tied shoulders – removal and construction of Portland Cement Concrete (PCC) shoulders tied to adjacent PCC pavement structures.

• Shoulder widening – extending the width of the existing shoulder with use of similar materials.

Note that the above definitions only attempt to describe what type of construction treatment is being applied to the pavement.

An indication of the reason(s) why a future construction event is predicted is needed to complete the definition since pavement improvements are based on different needs. The following are examples of controlled vocabulary that can be used to explain the basis of predicted time to a threshold event.

• Roughness exceeds y IRI. The y value is the generally accepted limiting value for pavement roughness in terms of IRI.

• Cracking exceeds limit requiring major rehabilitation.

• Cracking exceeds limit requiring reconstruction.

• Rut depth correction requires major rehabilitation.

• Rut depth correction requires reconstruction.

• Skid resistance reaches safety limit.

• Pavement Condition Index reaches threshold x. For systems based on a PCI based index, x represents the various thresholds between rehabilitation and reconstruction.

• Pavement Serviceability Rating reaches x. For systems still using the PSR/PSI concept, x is the terminal serviceability value considered by the agency appropriate for the route classification.

Typically an agency will develop some sort of decision matrix to use as part of their pavement management. This matrix will relate reason(s) for construction with types of construction. For example, if the roughness exceeds the IRI threshold, then one typical approach would be placement of an overlay to correct the roughness.

CHAPTER 3. FUTURE CONSTRUCTION NEEDS ANALYSIS FRAMEWORK

INTRODUCTION

A more refined construction activity needs analysis terminology is proposed to reduce potential confusion over the use of the remaining service life nomenclature. General guidelines on how to formulate future pavement construction needs analysis are presented in the remainder of this report. The construction needs addressed in this report are those associated with correcting pavement surface and structural deficiencies, although many of these concepts could be adapted for construction related to other needs such as capacity and shoulder improvements.

The basic process to determine future pavement construction needs is illustrated in Figure 1.

Most pavement construction activity planning is based on an annual fiscal time cycle used by the agency. The steps in this figure are cyclical and depend on the time cycle appropriate to the type of pavement asset. In this figure, the process starts with input data. Input data are fed into the expectancy models, which produce prediction of future change in the construction trigger models. The outputs from the predictions are used to select the most appropriate construction strategy, which is used to develop construction plans and specifications. The feedback cycle starts with documentation of the actual condition observed over time as well as the actual construction activities performed. Monitoring measurements are performed to provide updated inputs for the next planning cycle.

Figure 1. Illustration. Basic framework of future pavement construction needs.

Because the basic framework illustrated in Figure 1 starts with inputs, and input requirements are based upon the model used for construction triggers, the following framework discussion starts with construction triggers. Construction triggers are the basis for setting threshold limits and establishing expectancy curves to those factors used to select corrective construction strategies.

The following topics must be addressed to develop, implement, maintain, and update a construction needs analysis methodology. The methods should be tailored to individual agency requirements related to budgeting process, types of pavements in use, common types of pavement deficiencies requiring correction, construction contract instruments, and other considerations.

CONSTRUCTION TRIGGERS

A critical step in the construction needs analysis process is determining the most appropriate pavement factors that should be used to indicate application of pavement construction treatments. The selected set of construction triggers constitutes the basis for all of the other activities used in the construction needs analysis.

These construction triggers equate to the reason(s) for construction identified in chapter 2. These triggers may be distress related – identifying specific target levels of cracking, roughness, rutting, or friction – or related to capacity of the roadway involving addition of lanes to handle increased traffic levels.

THRESHOLD LIMITS

The next step in the process is to set threshold limits on the pavement factors selected as construction triggers. Crossing a threshold limit can indicate the need for a construction treatment. Pavement condition assessment is complicated with the use of hierarchical thresholds limits of construction needs for the same condition factor.

EXPECTANCY CURVES

Because the goal of this activity is to plan for future construction events, some form of expectancy curve is needed to forecast the change in each construction trigger since the last condition measurement. Expectancy curves on the rate of change in pavement condition can never be static due to changes in traffic loadings, climate effects, construction techniques and materials, and technology advancement. Keeping pavement expectancy curves updated with current technology is an apparent intractable problem since long-term observations are generally required to understand how newly introduced technology performs.

COLLECTION OF INPUTS

Ideally, pavement management agencies should only collect data needed to support their decisions. Inputs needed to support future pavement construction needs include condition states of construction triggers, explanatory variables used in expectancy curves, basis of threshold limits, and construction costs.

STRATEGY SELECTION

The strategy selection process is based on the indication of future construction needs when the expected condition state of a construction trigger exceeds a threshold limit. Secondary processes include estimation of construction costs and pavement performance expectation after application of each alternative construction treatment so that cost/benefit based optimization calculations can be performed.

ASSESSMENT AND UPDATE

All management processes require a formal system that documents current procedures, provides for an independent assessment of adequacy and compliance with established procedures, and includes an improvement update process to keep them relevant and technologically current. The formal quality management standards developed by national and international agencies can be used as the basis to develop agency specific protocols.

CHAPTER 4. CONSTRUCTION TRIGGERS

INTRODUCTION

Construction triggers are measureable aspects or other aspects of a pavement’s condition that can be used to indicate the need for application of a corrective treatment. The selection of construction triggers is the basis for development of field data collection programs to measure the condition state of each pavement segment.

Some of the considerations in the selection of construction triggers include:

• Historical practice. This is the starting point for most agencies since development of time-history pavement condition data is needed to develop and modify expectancy curves discussed later in this report.

• Related agency practice. Piggybacking on practices of related pavement management agencies is a strategy that can be used to potentially reduce field measurement, engineering, development, and software costs. Related pavement agencies are those located in the general geographical area, use similar materials, and have commonality in construction practices / pavement contractors. For example, there may be areas of overlap between city, regional, and state transportation authority’s managing pavements with common attributes that forms a basis for information and technology interchange.

• Extent of the pavement network being managed. The greater the number of lane-miles being managed the greater the need for automation to reduce condition measurement costs. Manual pavement condition measurements performed by human crews typically cost more, is slower, and introduces greater safety considerations than automated methods.

• Data collection budget. The majority of construction triggers are based upon some type of field pavement condition measurement. The type, extent, and frequency of condition measurements are based on the data collection budget and incremental cost/benefit of the data collected relative to the construction decision process.

• Required measurement accuracy, precision, and detail. The required accuracy, precision, and detail of pavement condition measurements are related to the use of the information. Project level measurements, which are used to develop construction plans and specifications or used for contractual acceptance purposes, require the best available standard of accuracy, precision, and information detail content. Network level measurements, which are used to provide a coarse filter of the condition of all pavements included in the system that should be subjected to project level scrutiny, generally require less detailed information content and lower levels of precision.

• Functional class of pavements in the network. Functional classification of pavements is primarily based upon the routes location, role, volumes and governmental classification in the pavement transportation system. Location is rated as urban/rural. Role is rated as local, collector, arterial, and interstate.