DEPARTMENT OF HIGHWAYS JOINT HIGHWAY RESEARCH PROJECT INFORMATIONAL REPORT JHRP-85-1 PERFORMANCE RELATIONSHIP MODEL FOR HIGHWAYS. Fwa Sinha T.F. K.C.

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1 SCHOOL OF CIVIL ENGINEERING INDIANA DEPARTMENT OF HIGHWAYS 5 JOINT HIGHWAY RESEARCH PROJECT INFORMATIONAL REPORT JHRP-85- A ROUTINE MAINTENANCE AND PAVEMENT PERFORMANCE RELATIONSHIP MODEL FOR HIGHWAYS T.F. K.C. Fwa Sinha UNIVERSITY

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3 JOINT HIGHWAY RESEARCH PROJECT INFORMATIONAL REPORT JHRP-85- A ROUTINE MAINTENANCE AND PAVEMENT PERFORMANCE RELATIONSHIP MODEL FOR HIGHWAYS T.F. K.C. Pwa Sinlia

4 Digitized by the Internet Arhive in 20 with funding frm LYRASIS members and Slan Fundatin; Indiana Department f Transprtatin

5 Infrmatinal Reprt TO: H.L. Mihael, Diretr July 2, 985 Jint Highway Researh Prjet FROM: K.C. Sinha, Researh Engineer File: Jint Highway Researh Prjet Attahed is an infrmatinal reprt entitled, "A Rutine Maintenane and Pavement Perfrmane Relatinship Mdel fr Highways". The researh was nduted by T.F. Fwa under my diretin fr his dtral prgram. The reprt presents an expliit examinatin f the relatinship between highway pavement rutine maintenane and pavement perfrmane. An aggregate damage apprah was emplyed in the analysis f pavement perfrmane and a methdlgy was develped based upn the servieability perfrmane nept. A quantitative measure fr levels f pavement rutine maintenane was prpsed. It is felt that the researh wrk will prvide useful infrmatin t the IDOH, partiularly in the develpment f the Pavement Management System. Respetfully submitted, K.C. Sinha Researh Engineer and Prfessr f Civil Engineering A.G. Altshaef f J.M. Bell W. F. Chen W.L. Dlh R.L. Eskew J.D. Friker W.H. Getz G.K. Hallk J. P. Isenbarger J.R. MLaughl in R.D. Miles P.L. Owens B.K. Partridge G.T. Satterly C.F. R.M. K.C. J.R. C.A. L.E. S.R. Shler Shant eau Sinha Skinne r Venable Wd Yder

6 ACKNOWLEDGMENTS The authrs gratefully aknwledge the assistane f the fllwing individuals: Prf. V. L. Andersn f the Department f Statistis fr his advie n statistial analysis; Dr. E. A. Sharaf, Pst-Dtral Researh Fellw in Civil Engineering, fr his help in preparing the neessary pavement data base; Mr. K. J, Kerher f the Indiana Department f Highways fr prviding pavement rughness data; Mr. J. R. Mlntyre f the Shl f Agriulture fr his help in btaining the l imat lg ial data f Indiana; and Mr. S. R. Yder f the Indiana Department f Highways fr his advie n design and maintenane praties in Indiana. The authrs are, hwever, slely respnsible fr the ntents f this reprt.

7 iv TABLE OF NTENTS Page LIST OF TABLES viii LIST OF FIGURES xi ABSTRACT xv CHAPTER INTRODUCTION. Bakgrund.2 Purpse and Spe f Researh 3.3 Dissertatin Organizatin 6 CHAPTER 2 LITERATURE REVIEW : DISAGGREGATE VERSUS AGGREGATE DAMAGE APPROACH 9 2. Intrdutin Relatinship Between Disaggregate and Aggregate Damage Apprah Review f Disaggregate Distress Funtin Apprah Federal Study M.I.T. Pavement Life Cyle Cst Study TTI Study Cunsel Trans Study Review Summary 2 CHAPTER 3 NCEPTS OF PROPOSED AGGREGATE PERFORMANCE APPROACH Intrdutin The Cnept f PSI-ESAL Lss Appliatin f AASHO Rad Test Results t Perfrmane Analysis AASHO Rad Test Relatinships 32

8 Page AASHTO Perfrmane Equatins Appliability f AASHO Rad Test Results and AASHTO Perfrmane Equatins Measurement f Lad Effets Measurements f Lad-Related, Nn-Lad- Related and Interatin Effets Effets f Rutine Maintenane n Pavement Perfrmane The Need t Cnsider Effets f Rutine Maintenane The Cnept f Zer-Maintenane Pavement Perfrmane Derivatin f Ttal Pavement Damage Determinatin f Lad-Related and Nn-Lad- Related Effets by Prprtinality Assumptin Summary f Prpsed Apprah 50 CHAPTER 4 APPLICATION OF PROPOSED METHODOLOGY : PAVEMENT PERFORMANCE ANALYSIS OF INDIANA HIGHWAYS Intrdutin Data Requirement and Data Base Desriptin Pavement Inventry Data Traffi Data Pavement Perfrmane Data Rutine Maintenane Cst Data Subgrade Sil Data Determinatin f Field Perfrmane Curves Pavement Servieability Index Mdel Cmputatin f Cumulative ESAL Pltting f Field Perfrmane Curves Predure f Pavement Damage Respnsibility Analysis Criteria fr Perfrmane Analysis Establishing N-Lss Line Calulating PSI-ESAL Lsses fr Perfrmane Curves Cmputing Rutine Maintenane Expenditures 84

9 vi Page Deriving PSI-ESAL Lss (A+B) f Zer-Maintenane Curve Damage Respnsibilities f Lad- Related and Nn-Lad-Related Effets.. 86 CHAPTER 5 DAMAGE RESPONSIBILITIES OF LOAD-RELATED AND NON-LOAD-RELATED EFFECTS ON HIGHWAYS IN INDIANA Intrdutin General Desriptin f the Results Identifiatin f Variables fr Damage Respnsibility Crrelatin Analysis Pavement Charateristis Traffi Ladings Envirnmental and Climati Cnditins Damage Respnsibility and Pavement Type Reginal Effets n Damage Respnsibility Reginal Znes in Indiana Statistial Analysis f Reginal Effets Ill Analysis fr Flexible Pavements Analysis fr Rigid Pavements Relating Results t an Earlier Study Develpment f Damage Respnsibility Preditin Mdels Uses f a Damage Respnsibility Mdel Flexible Pavement Damage Respnsibility Mdels Rigid Pavement Damage Respnsibility Mdels Summary Remarks 30 CHAPTER 6 RELATIONSHIP BETWEEN ROUTINE MAINTENANCE AND PAVEMENT PERFORMANCE Intrdutin Quantitative Representatin f Level f Pavement Rutine Maintenane Quantitative Representatin f Pavement Pe rf rmane Psitive Crrelatin f Level f Maintenane and Pavement Perfrmane Suitability f Linearity Assumptin 44

10 vii Page CHAPTER 7 QUANTITATIVE MEASUREMENT OF ROUTINE MAINTENANCE EFFECTS ON PAVEMENT PERFORMANCE Intrdutin A Cnept f Measuring Pavement Rutine Maintenane Effetiveness General Bakgrund Effets f Levels f Rutine Maintenane Effets f Maintenane Pliy and Tehnlgy Appliatin f Pavement Rutine Maintenane Effetiveness Index M Pavement Maintenane Effetiveness Index M fr Indiana Highways Reginal Effets n Maintenane Effetiveness Analysis f Flexible Pavements Analysis f Rigid Pavements Pavement Rutine Maintenane Effetiveness Index Preditin Mdels Uses f a Maintenane Effetiveness Preditin Mdel Mdels fr Flexible Pavements Mdels fr Rigid Pavements Summary Remarks 9 CHAPTER 8 SUMMARY AND NCLUSIONS Summary f Prpsed Perfrmane Analysis Apprah Summary f Findings Limitatins f the Prpsed Apprah Remmendatins fr Further Researh 20 REFERENCES 205 APPENDIX Sme Results f Perfrmane Analysis n Indiana Highways 22

11 viii LIST OF TABLES Ta ble Page Vehile Classifiatin fr Perfrmane Analysis 57 Vehile Class Weight Grup Classifiatin Perent VMT f Vehile Classes n Interstates 6 Perent VMT f Vehile Classes n State Primary 62 Perent VMT f Vehile Classes n State Sendary 63 Perent Axle Weight Distributin f Vehile Classes and Weight Grups n Interstates Perent Axle Weight Distributin f Vehile Classes and Weight Grups n State Primary 65 Perent Axle Weight Distributin f Vehile Classes and Weight Grups n State Sendary 66 Pavement Rutine Maintenane Ativities Sil Supprt Values fr Majr Sil Types in Indiana 72 Present Servieability Index Mdels 76 Values f Cnstants in Equatins (4.2) thrugh (4.4) 79

12 Table Page Lad-Related Pavement Damage Respnsibilities fr Flexible Pavements in Indiana 9 Lad-Related Pavement Damage Respnsibilities fr Rigid Pavements in Indiana 92 Ranges f Independent Variables in Statistial Analysis f Damage Respnsibility Results 95 Pavement Damage Respnsibilities f Indiana Highways by Pavement Types 06 Charateristis f Nrthern and Suthern Regins f Indiana 2 Statistial Analysis fr Mdel in Equatin (5.) Flexible Pavement 5 Statistial Analysis fr Mdel in Equatin (5.2) Rigid Pavement 8 Crrelatin Matrix fr Statistial Analysis f Damage Respnsibilities n Flexible Pavements in Indiana 23 Statistial Charateristis f Damage Respnsibility Mdels fr Flexible Pavements 26 Crrelatin Matrix fr Statistial Analysis f Damage Respnsibilities n Rigid Pavements in Indiana 29 Statistial Charateristis f Damage Respnsibility Mdels fr Rigid Pavements 3 Signifiane Test fr Linear Relatinship between PSI-ESAL Lss and Mean Annual Maintenane Expenditure Per Lane-Mile Perent Cnfidene Intervals fr Ppulatin Crrelatin Ceffiients f Flexible Pavement Cases 5 95 Perent Cnfidene Intervals fr Ppulatin Crrelatin Ceffiients f Rigid Pavement Cases 53

13 Table Page 7. Pavement Rutine Maintenane Effetiveness Indies fr Flexible Pavements in Indiana Pavement Rutine Maintenane Effetiveness Indies fr Rigid Pavements in Indiana Charateristis f Pavement Rutine Maintenane Effetiveness Indies fr Indiana Highways Statistial Analysis fr Mdel in Equatin (7.) Flexible Pavement Statistial Analysis fr Mdel in Equatin (7.2) Rigid Pavement Crrelatin Matrix fr Statistial Analysis f Maintenane Effetiveness n Flexible Pavements in Indiana Statistial Charateristis f Maintenane Effetiveness Index Mdels fr Flexible Pavements in Indiana Crrelatin Matrix fr Statistial Analysis f Maintenane Effetiveness n Rigid Pavements in Indiana Statistial Charateristis f Maintenane Effetiveness Index Mdels fr Rigid Pavements in Indiana 90 Appendix Table A. Results f Crrelatin Analysis between PSI -ESAL Lss and Mean Annual Maintenane Expenditure Per Lane-Mile n Rigid Pavements 23 A. 2 Results f Crrelatin Analysis between PSI -ESAL Lss and Mean Annual Maintenane Expenditure Per Lane-Mile n Flexible Pavements 24 A. 3 Pavement Charateristis Data fr Rigid Pavements in Indiana 27 A. 4 Pavement Charateristis Data fr Flexible Pavements in Indiana 28

14 LIST OF FIGURES Figure Page. Majr Wrk Items within Spe f Study 5 2. Sequene f Testing fr a Pavement Management System 2.2 Sequene f Cst Allatin Analysis 3 3. Pavement Servieability Time Histry Plt A Pavement Perfrmane Plt in terms f Servieability and Cumulative ESAL PSI-ESAL Lss as a Measure f Pavement Deteriratin Shemati Diagram Shwing Field and AASHTO Pavement Perfrmane Curves PSI-ESAL Lsses fr Field and AASHTO Pavement Perfrmane Curves Ttal Pavement Damage as Defined by Zer- Maintenane Pavement Perfrmane Curves Shemati Diagram Shwing Pavement Perfrmane Curves with Different Levels f Rutine Maintenane Shemati Diagram Shwing Lad-Related and Nn-Lad-Related Effets Respnsible fr Pavement Damage Axle Cnfiguratin Charateristis f Vehile Classes Engineering Sil Parent Material Distributin in Indiana 7

15 xii Figure Page 4.3 Relatinship Between Califrnia Bearing Rati and Mdulus f Subgrade Reatin Cmputatin f PSI-ESAL Lsses fr Pavement Perfrmane Curves An Example f PSI-ESAL Lss (A+B) versus Rutine Maintenane Plt Distributin f Mean Freezing Index Distributin f Mean Annual Snwfall in Inhes Distributin f Mean Annual Rainfall in Inhes Distributin f Thrnthwaite Misture Index Distributin f Freeze-Thaw Cyle Index Values in Indiana Distributin f Annual Mean Daily Temperature in Degree Fahrenheit Distributin f Majr Sil Types in Indiana Nrthern and Suthern Regins in Indiana Reginal Fatr Znes fr Indiana Generalized Reginal Fatrs Map f the United States 0 5. Reginal Distributin f Damage Respnsibility fr Flexible Pavements in Indiana Lad-Related Damage Respnsibility n Rigid Pavements Perfrmane Curves f Pavement Setins with Different Pavement Charateristis Perfrmane Curves f Pavement Setins with Maintained with Different Maintenane Pliies and Tehnlgies 4

16 xiii Figure Page 6.3 Distributin f R Values Crrelating PSI-ESAL Lsses and Dllars Maintenane Expenditure Per Lane-Mile f Pavement Distributin f R Values Crrelating PSI-ESAL Lsses and Dllars Maintenane Expenditure Per Lane-Mile f Pavement Distributin f Adjusted R Values Crrelating PSI-ESAL Lsses and Dllars Maintenane Expenditure Per Lane-Miles f Pavement Shemati Diagram Shwing the Effets f Pavement Rutine Maintenane and Rehabilitatin n Pavement Perfrmane Effet f Different Levels f Rutine Maintenane n Pavement Perfrmane Cmparisn f Perfrmane f Pavement Setins Maintained by Different Levels f Rutine Maintenane Effet f Maintenane Pliy and Tehnlgy n Pavement Perfrmane Reginal Distributin f Pavement Maintenane Effetiveness Index n Flexible Pavements In Indiana 77 Appendix Figure A. PSI-ESAL Lss vs. Maintenane Expenditure Plt fr A. 2 PSI-ESAL Lss vs. Maintenane Expenditure Plt fr A. 3 PSI-ESAL Lss vs. Maintenane Expenditure Plt fr A. 4 PSI-ESAL Lss vs. Maintenane Expenditure Plt fr A. 5 PSI-ESAL Lss vs. Maintenane Expenditure Plt fr A. 6 PSI-ESAL Lss vs. Maintenane Expenditure Plt fr SR 3n 226

17 xi v Appendix Figure Page A. 7 PSI-ESAL Lss vs. Maintenane Expenditure Plt fr SR 3s 227 A. 8 PSI-ESAL Lss vs. Maintenane Expenditure Plt fr US A. 9 PSI-ESAL Lss vs. Maintenane Expenditure Plt fr SR A. 0 PSI-ESAL Lss vs. Maintenane Expenditure Plt fr SR A. PSI-ESAL Lss vs. Maintenane Expenditure Plt fr SR A. 2 PSI-ESAL Lss vs. Maintenane Expenditure Plt fr US A. 3 PSI-ESAL Lss vs. Maintenane Expenditure Plt fr US A. 4 PSI-ESAL Lss vs. Maintenane Expenditure Plt fr SR A. 5 PSI-ESAL Lss vs. Maintenane Expenditure Plt fr SR A. 6 PSI-ESAL Lss vs. Maintenane Expenditure Plt fr SR A. 7 PSI-ESAL Lss vs. Maintenane Expenditure Plt fr SR A. 8 PSI-ESAL Lss vs. Maintenane Expenditure Plt fr SR A. 9 PSI-ESAL Lss vs. Maintenane Expenditure Plt fr US 42n 239 A. 20 PSI-ESAL Lss vs. Maintenane Expenditure Plt fr US 42s 240

18 ABSTRACT Highway pavement maintenane and its management are areas f serius nern and study tday. A tpi that deserves a great deal f researh effrt is the develpment f the relatinship between pavement rutine maintenane and pavement perfrmane. This study was undertaken t investigate the feasibility f emplying an aggregate perfrmane/damage apprah in the analysis f highway pavement perfrmane. A methdlgy was develped based upn the servieability perfrmane nept first neived at the AASHO Rad Test mpleted in the early 960s. Several new nepts were intrdued in the press f develping the aggregate perfrmane apprah methdlgy. A new parameter, PSI-ESAL lss, was defined as an aggregate representatin f pavement damage. A nept f zer-maintenane perfrmane urve was adpted

19 xvi t aunt fr the effets f rutine maintenane wrk. This nept permitted an estimatin f the atual ttal damage f a pavement. A quantitative measure fr levels f pavement rutine maintenane was prpsed. This quantitative measure, upled with the PSI-ESAL lss representatin f pavement damage, failitated the establishment f a relatinship between pavement perfrmane and level f rutine maintenane. On the basis f the abve theretial framewrk, a predure fr allating pavement maintenane and rehabilitatin sts in a highway st allatin analysis was develped. This predure was suessfully implemented in a full-sale highway st allatin study at state level. A further develpment f the perfrmane analysis nept invlved a quantitative assessment f the effets f rutine maintenane n pavement. A maintenane effetiveness index was defined whih prvided a means fr quantitative evaluatin f pavement maintenane wrk. The aggregate perfrmane apprah prpsed is simple in nept and easy t understand. The amunt f data required is muh less than that required by a disaggregate distress funtin apprah. The amunt f analysis effrt invlved is als redued nsiderably.

20 CHAPTER INTRODUCTION. Bakgrund In the area f highway pavement st allatin analysis, there is a lng-existing prblem whih still remains unreslved tday. This prblem invlves the determinatin f the relative prprtins f traffi and envirnmental respnsibilities in highway rehabilitatin and maintenane expenditures. In reent years, the majr effrt f mst state highway agenies have been shifted frm building new highways and failities t preserving and rehabilitating the existing system. A sund slutin t the stated prblem is therefre vital t arriving at an equitable and effiient allatin f pavement sts t highway users. The usefulness f the knwledge f traffi and envirnmental effets n pavement perfrmane is nt limited t the field f highway st allatin. A better understanding f these effets wuld have signifiant

21 impliatin in pavement design, mnitring and evaluatin tehnlgy. It wuld als prvide additinal infrmatin fr pavement maintenane and rehabilitatin deisin making, whih is an imprtant press f a pavement management system. The basi nept and methdlgy presented in this dissertatin was riginally develped fr the Indiana Highway Cst Allatin Study [] fr allating pavement maintenane and rehabilitatin sts. There were a number f prblems whih the Indiana study team faed at the beginning phase f the study. Firstly, there was a lak f pavement damage data in terras f individual distress types. Sendly, time and budget nstraints did nt permit a full sale disaggregate distress funtin analysis fr st allatin. As a result, a meaningful analysis based upn nsideratin f individual distress types uld nt be arried ut. It beame neessary that an alternative st allatin methdlgy be develped fr the type f data available in Indiana. A researh was then initiated t investigate the pssibility f emplying the annual rughness data whih were available fr pratially the entire state highway system f Indiana. This had led t the develpment f a perfrmane-based apprah whih frms the theretial framewrk fr the analysis presented in this dissertatin.

22 The situatin in Indiana is nt unique. Due t the limitatin f manpwer and funds, mst states d nt pssess the apability f maintaining detailed rerds f pavement nditins in terms f individual distress types fr the entire rad netwrk. On the ther hand, the experiene f several states (inluding Indiana [2], Utah [3], Kentuky [4] and West Virginia [5]) has indiated that perfrmane infrmatin, suh as servieability, uld be btained n the entire netwrk in a relatively shrt perid f time, thus making peridi and timely evaluatin pssible. The develpment f a perfrmanebased methdlgy fr pavement deteriratin analysis wuld further enhane the value and effetiveness f suh a mnitring apprah by prviding additinal infrmatin nerning pavement perfrmane..2 Purpse and Spe f Researh The basi gal f this researh was t develp a perfrmane analysis methdlgy t evaluate the effets f traffi and envirnmental fatrs n highway pavements. In rder t satisfy the immediate need f highway st allatin study, a majr part f the researh effrt was direted tward develping a sund framewrk fr attributing pavement maintenane and rehabilitatin sts t different vehile lasses based upn the pavement deteriratin impsed by eah individual lass f vehile.

23 A meaningful bjetive f this effrt was t illustrate, thrugh the appliatin f the perfrmane-based methdlgy t a full-sale st allatin study at state level, that suh an apprah wuld be a feasible steffetive alternative t a muh mre elabrate disaggregate distress funtin apprah [8]. In additin t deriving the relative effets f lad-related and nn-lad-related fatrs n pavement deteriratin, further researh was nduted t investigate the effets f rutine maintenane n pavement perfrmane. It was an bjetive f this study t prvide useful infrmatin, by means f perfrmane analysis at bth prjet and netwrk levels, t assist highway agenies in making rehabilitatin and rutine maintenane deisins. In the press f amplishing these bjetives, sme imprtant questins need t be reslved. First f all, sme frm f relatinship between pavement perfrmane and level f maintenane must be established. T ahieve this, an apprpriate quantitative measure f pavement perfrmane was required. In additin, levels f maintenane had t be defined in a manner suh that they uld be related t rutine maintenane sts. These requirements are delineated by the dtted lines in Figure..

24 r -p 0 e 0 > n 0 a. u «- m i M u»* 0 > 0 E _ a u -P «f 3 0 Q E» -P 0 u e u a C 0] p 0 3 p O CC u M-, O Ul V 0 a > u 0 _) ig E 0 V P 4J IB e E 0 m tr «0 U Id C is e - (- 0 *> u in «- (. n ti e a. p» - in ai iq e s a. ai > 0 u u Q. 0. " 0 C 3 C 0 m Oi K E 3 nj 4J m (. U. IK * 3 «u < U -H Oi 0 0 *» u»» <» 6 > ib Uj - - p at 3 - <t- -< «C <t- IB in iu I ai C 0> *» -PC OJ P C 3 <* in a. «e 4J 0 u i- 3 II Ul 6 ) t- 0 r (ftp (- a 0 > a. -p p <n 4* 0 H e -P 0 > HI m 3 a. p IB 0 u in u 0 a (- a. 0 0) in «0 u n a P -P u u 0 Q «- L. 4- U] - H) 0 a > _ CT - T P g <B a IB «Z a 0 IT -.p C 0 n) 0 C E * - at E "I > u ib 0 _l 0. 4* 0i «*. a a.. m -p -P 3 u at ai at : u u * <t- *» IB >B Ul E 0 0 p m -p 0 0 u- 4 C 0 0 E " 0i IB > E m 0 IB -~ * U 0. IB <«. a in ) f P u O O -M - u. (ft 43 P ( u in u 0 IB -*4 -* a. a. (- <*. E i ti- p i-t -p ll u u at 3» IB h- E (. at 3 IB T3 > P C IB Ul (J IB a.

25 The perfrmane-rutine maintenane mdel in Figure. Is the theretial basis fr all the analyses perfrmed in this study. These analyses, as indiated in the figure, inlude (a) the determinatin f the relative effets f lad and nn-lad fatrs n pavement damage fr use in st allatin; (b) the investigatin f the effets f lad and envirnmental fatrs n different pavement types, and the influene f pavement harateristis, limati fatrs and subsil nditins n the relative effets f lad and nn-lad fatrs n pavement perfrmane; () the examinatin f the relatinship between pavement perfrmane and rutine maintenane assumed in the perfrmane-rutine maintenane mdel; (d) the evaluatin f the effets f rutine maintenane n pavement perfrmane; and (e) the study f the effets f pavement, limati and envirnmental fatrs n effetiveness f pavement rutine maintenane wrk.. 3 Dissertatin Organizatin The reprt nsists f eight hapters vering tw phases f the researh. The researh effrt f Phase fused primarily n develping the theretial framewrk fr the entire study. It invlved the develpment f (a) the pavement perfrmane-rutine maintenane mdel depited in Figure., and (b) a

26 methdlgy t determine the relative effets f traffi and envirnmental fatrs n pavement deteriratin. Detailed disussins f this theretial framewrk are presented in Chapters 2 and 3. Chapter 2 disusses differenes between the mmnly emplyed disaggregate distress funtin apprah and the prpsed aggregate perfrmane apprah fr pavement damage analysis. A literature review n existing disaggregate distress funtin apprah methdlgy is als presented in the same hapter. Chapter 3 prvides the theretial basis f the prpsed apprah. The nept f PSI-ESAL lss as a measure f pavement deteriratin is intrdued, and the appliability f AASHO Rad Test perfrmane equatins [9] t pavement deteriratin analysis is examined. These are fllwed by a disussin f the need t nsider effets f rutine maintenane n pavement perfrmane when perfrming a pavement deteriratin analysis. Finally, the predure f relating level f maintenane t perfrmane, and the methdlgy f alulating the relative effets f lad and nn-lad fatrs are presented. In Phase 2 f the study, researh was extended beynd the field f highway st allatin t investigate the effets f traffi ladings, envirnmental fatrs,

27 8 pavement harateristis and rutine maintenane n pavement perfrmane. These analyses were perfrmed with data frm the state highway system f Indiana. Chapter 4 gives an aunt f the type f data required, and hw these data were lleted, derived and used in the analyses. The results f applying the aggregate perfrmane apprah methdlgy t the state highways f Indiana are analyzed in Chapters 5, 6 and 7. Chapter 5 investigates the impats f pavement harateristis, limati and subsil nditins n the relative effets f lad and nn-lad fatrs n pavement deteriratin. In Chapter 6, the relatinship between pavement perfrmane and rutine maintenane is examined. This is fllwed by Chapter 7 whih presents an analysis f the influene f limati and subsil nditins n the effetiveness f rutine maint enane Chapter 8 summarizes majr findings f the study and indiates areas where further researh is required.

28 CHAPTER 2 LITERATURE REVIEW: DISAGGREGATE VERSUS AGGREGATE DAMAGE APPROACH 2. Intrdutin Traditinally, there are tw brad apprahes in the evaluatin f highway pavement nditins. One apprah nsiders the grss perfrmane f pavements by means f an aggregate measure. An example f this apprah is represented by the AASHO Rad Test nept f pavement servieability [9, 0] whih measures the ability at time f bservatin f a pavement t serve highway traffi. The ther apprah defines pavement nditins by speifying the extent and amunt f individual pavement distresses. Examples f this apprah are fund in the pavement rating systems adpted by sme state highway agenies [63,64,65,66]. In pavement damage respnsibility analysis, where an estimate is made t assess the relative respnsibility f lad and envirnmental fatrs n pavement damage, the predures used an likewise be lassified int tw

29 0 apprahes, namely the disaggregate distress funtin apprah and the aggregate perfrmane apprah Relatinship Between Disaggregate and Aggregate Damage Apprah The relatinship between a disaggregate distress funtin apprah and an aggregate perfrmane apprah fr pavement damage analysis may be explained by nsidering the basi bjetives f a pavement management system (PMS). Figure 2. shws a simplified flw diagram whih utlines the sequene f testing invlved in a typial pavement management system [6,7]. The system seeks t prvide, amng ther infrmatin, answers t the fllwing tw questins: (i) where are the defiient setins requiring repair r imprvement? (ii) what are the distress type invlved in these defiient setins? Tw levels f nditin survey may be identified in the PMS in Figure 2.. They are labeled as levels I and II. Level I prvides infrmatin t questin (i), and level II t questin (ii). The pavement damage analysis methdlgy desribed in this dissertatin relies upn level I infrmatin nly and is therefre termed an aggregate perfrmane apprah. Thse methdlgies that nsider impliatin f individual distress types belng t methds f the disaggregate apprah whih requires detailed infrmatin frm level II nditin survey.

30 0) 0 u a E H <4-l -r-l J i-l (- w en &- ) u n 00 Ou 0) <u E 4 0) 0 «H > XI <0 T-l. i-l 4- < u 0 r-l < u Eh <0 u 0) l~> 60 0 z ^ i-l u (0 IS 0) H Pi 0 u D 3 r 4) en 0 i-l > T-l 0) JJ ih U <J_i 0 0) <0 jj ~H C en 0) >» 0) en a *-

31 2 Besides the differenes in the frm f data required, the tw apprahes als differ signifiantly in the predure by whih pavement damage analysis is arried ut. This is best illustrated by nsidering a highway st allatin prblem nerning pavement maintenane and rehabilitatin sts. Figure 2.2 indiates the majr steps invlved in a pavement maintenane and rehabilitatin st allatin analysis fr bth apprahes. The sequene f analysis shwn fr disaggregate distress funtin apprah is based upn the 982 Federal st allatin predure [8], and that fr aggregate perfrmane apprah based upn the predure desribed in this dissertatin. A diret nsequene f the differene in analysis predure is apparent. The use f disaggregate distress funtin apprah wuld require a large amunt f data lletin and handling effrt. In ntrast, the data required fr an aggregate perfrmane apprah are muh less and are mre readily available Review f Disaggregate Distress Funt in Apprah Federal Study The 982 Federal st allatin study [8] was the first suh study t emply nsumptin thery t assess analytially the pavement damage respnsibilities f

32 ' 3 Level I Survey ~ Level II Survey Identify Res pns ible Distress Types Derive Cs t Develp Mathemat ial Mdel fr eah Distress Estimate Imprtane f eah Dis t ress f Respnsibilities f Lad- and Nn-Lad- Related Effets Cmpute Vehile Class Respns ibility fr eah Diss t ress Assign Weight t eah Distress Type Arding t Imprtane Cmpute Overall Cst Respnsibility fr eah Vehile Class Cmpute Maintenane and Rehabilitatin Csts and Allate t Vehile Classes Legend Aggregate Perfrmane Apprah Disaggregate Distress Funtin Apprah Figure 2.2 Sequene f Cst Allatin Analysis

33 4 vehile lasses. A nsultant [] was engaged speifially t develp pavement damage funtins fr st allatin purpse. The analysis predure f the apprah has been utlined in Figure 2.2. A list f distresses whih were imprtant t highway rehabilitatin deisin making was first identified. Mathematial mdels were then develped fr individual distress types. T determine the pavement damage respnsibilities f vehile lasses, it was neessary t alulate the respnsibility f eah vehile lass fr eah individual distress, and t estimate the relative imprtane f eah distress in the deisin t rehabilitate a given pavement. The Federal methdlgy did nt address the issue f lad and envirnmental effets expliitly. T failitate st allatin mputatin, all mathematial damage funtins f lad-related distresses were mdeled after AASHTO servieability lss equatins. Lad equivaleny fatrs fr eah distress type were develped fr vehile ladings t mpute their relative respnsibilities fr the distress nerned. The mdels therefre did nt prvide any infrmatin n the relative pavement damage respnsibilities f lad and envirnmental fatrs. Other limitatins f the Federal apprah inlude the fllwing: (i) interatin f distresses was ignred; (ii)

34 5 the effets f maintenane and maintenane pliy were nt nsidered; and (iii) maintenane sts, whih represent a large perentage f ttal expenditures fr mst highway agenies at state and lal levels, were nt inluded in the analysis M._I.T. Pavement Life Cyle Cst Study A reent researh in the area f pavement damage respnsibility analysis is a study arried ut by Wng and Markw [0]. This was an extensin f the Federal st allatin study mandated by the Cngress. The study fused n the allatin f life-yle pavement sts, enmpassing rutine maintenane and rehabilitatin, but exluding initial nstrutin and renstrutin. Central t this study was the use f an existing simulatin mdel, knwn as the EAR0MAR-2 system [2], t predit highway perfrmane, maintenane and rehabilitatin sts. An extensive amunt f data was required as input t the mdel. The data inluded pavement strutural and materials prperties, existing pavement surfae nditin, traffi vlume, mpsitin and lading infrmatin, envirnmental nditins, maintenane pliies, lal praties f wrk sheduling, unit sts f maintenane labr, equipment and materials. The envirnmental fatrs nsidered were seasnal tempe rature,

35 6 rainfall, freezing index, reginal fatrs, and subgrade sil lassifiatins. The EAROMAR-2 system emplyed a series f pavement distress mdels t predit pavement damage. These mdels were based upn empirial pavement researh r upn lsed-frm apprximatins t theretial mdel preditins. The ttal umulative damage f eah distress type (r damage mpnent) ver the analysis perid was mputed by means f these preditive mdels. The Present Servieability Index (PSI) f the pavement was then estimated as a funtin f the damage mpnents. It is unfrtunate that the st (r damage respnsibility) allatin phase f the study was nt treated with the same details and depth. Instead f examining individual distresses t assess the respnsibility f eah vehile lass, all damage respnsibilities assiated with lad-related distresses were indifferently allated n the basis f equivalent 8-kip single axle lad (ESAL). This limitatin is nt unexpeted nsidering the fat that the EAROMAR-2 system was nt riginally develped fr use in a st allatin study. It is therefre nt surprising that it did nt prvide the neessary infrmatin required fr an equitable allatin f highway pavement sts.

36 7 It is apprpriate at this pint t state that, while many damage funtin mdels are available in the literature, there is hardly any theretial mdel whih uld be used diretly t mpute the relative effets f lad and envirnmental fatrs n pavement deteriratin. Mst mdels, being either regressin based r empirial, annt be used fr suh purpse TTI Study The 98 TTI study [3] was nduted fr the Amerian Truking Assiatin and the Mtr Vehile Manufaturers Assiatin. The predure emplyed t estimate the prprtin f pavement damage attributable t lad invlved the fllwing steps: (i) lassifiatin f pavement distresses int 3 ategries: lad-related, envirnmental and mbined stresses; (ii) determinatin f damage weighting fatrs fr varius distress types based upn pavement rating shemes; (iii) appliatin f distress mdels t predit expeted level f eah distress; and (iv) mbinatin f the weighting fatrs and predited distress levels t determine the prprtins f envirnmental and lad-assiated damage. The assignment f distress type t a partiular ause has a diret impat n the utme f the final results. The assignment in TTI Study, unfrtunately, was made largely by subjetive reasning. Anther ritial area f

37 8 the study is the weighting f eah distress type as t its relative imprtane t ttal pavement damage. As the TT study fund frm a survey f pavement rating shemes frm mre than 40 states, "there exist a variety f praties frm state t state, withut a standard list f distresses that make up a pavement rating sre, and withut a standard weight applied t distress." This suggests that the use f subjetive pavement rating shemes may nt be a reliable means t assess the relative imprtane f different distresses. The TTI study did nt address the st allatin phase f the prblem. N attempt was made t estimate the shares f lad and envirnment effets in mbined distresses. Instead, upper and lwer bunds f pavement damage respnsibility f lad effet were mputed fr different limati znes. First, a ttal dedut pint was established that wuld be subtrated frm a perfet pavement rating sre was evaluated fr a given pavement. This ttal dedut pint was mputed by summing up the dedut pints f 3 main ategries, namely lad, mbined and limati dedut pints. The range f lad damage respnsibility was defined as fllws: Lwer bund lad damage rati Lad dedut pints Ttal dedut pints

38 9 Upper bund lad damage rati Lad + Cmbined dedut pints Ttal dedut pints The predure depended heavily n pavement rating sheme whih was diretly related t deisins t rehabilitate r maintain. It is imprtant t realize, hwever, that the prblem f determining the relative effets f traffi ladings and envirnmental fatrs n pavement deteriratin is nt the same as the subjet f deisin riteria fr maintenane and rehabilitatin ativities. Deisin riteria are likely t vary amng highway agenies that maintain and rehabilitate highway pavements. On the ther hand, damage respnsibilities f lad and envirnmental fatrs are mre a funtin f pavement harateristis, intensity f traffi ladings and severity f limati nditins Cunsel Trans Study Cunsel Trans study [4] was als spnsred by the Amerian Truking Assiatin and the Mtr Vehile Manufaturers Assiatin. The pavement damage data used in the study were lleted by windshield survey at arund nrmal vehile perating speed ver a perid- f ne and a half mnth. The survey vered 87 miles f Interstate

39 20 highways in six states, ut f a ttal f ver 40,000 miles natinally. The study lassified all distress types as either lad related r envirnment related. The nsequenes f traffi lading n pavement already exhibiting envirnment related distresses, and the effets f envirnmental fatrs n pavement with lad related distresses were nt nsidered in the analysis. In determining the relative damage respnsibilities f lad and envirnmental effets, a distress index was first mputed fr eah distress type based upn the severity and extent f the distress. These indies were then gruped tgether withut applying any weighting fatrs. This was equivalent t assigning equal weight t all distress types. In general, the Cunsel Trans apprah is similar t TTI study in nept, but is less refined in many aspets. First f all, it is dubtful if windshield survey data are suitable fr use at all in a sientifi study suh as this. The assumptins f nn-existene f interatin f lad and envirnmental effets, and f equal imprtane f all distress types greatly failitated the data analysis in the study. The validity f these assumptins, hwever, are questinable.

40 Review Summary The disaggregate distress funtin apprah has a sund theretial basis. Hwever, due t the limitatin f ur present day knwledge n the subjet f pavement distresses, and n the relatinships between individual distresses and verall pavement perfrmane, there are unertainties invlved in applying the nept t slving the prblem nerning relative respnsibilities f lad and envirnment n pavement damage. The review f existing disaggregate distress funtin apprah predures indiates that there are 3 majr steps whih are mmn t these predures. These are: (i) identifiatin f the distress types whih affet pavement perfrmane; (ii) develpment f distress mdels t determine lad and envirnment respnsibilities fr eah distress types; and (iii) assignment f weights t distress types based upn their relative imprtane t ttal pavement damage. There exist tw ritial areas in the disaggregate apprah that deserve attentin. Different assumptins used in these tw areas may signifiantly affet the final utme f the analysis. Firstly, it is the identifiatin f the auses f eah distress (i.e., lad versus nn-lad; r lad-related, envirnment-related, and mbinatin f lad and envirnmental auses) and the

41 22 subsequent frm f distress funtin develped t mdel this distress. Sendly, it is the assignment f weighting fatrs t distress types arding t their relative imprtane t pavement damage. Eah f the fur studies [8,0,3,4] disussed in the preeding setin adpted a different list f distress types whih were nsidered t be imprtant auses f pavement damage. All the fur studies were als nt agreeable upn whether a given distress type be lassified as lad-related, nn-lad-related, r mbined effets f lad and envirnment. Furthermre, as there is a large number f distress mdels available in the literature, it is nt surprising that the distress funtins emplyed in the fur studies differ nsiderably in terms f the frm f funtinal equatin and the types f variable inluded. The assignment f relative weights t different distress types has a diret impat n the mputed magnitudes f the relative damage respnsibility f lad and envirnmental fatrs. Unfrtunately, there des nt exist a lear-ut bjetive way t determine the relative imprtane f eah distress type. Sine all the fur studies adpted different weighting shemes in their analyses, there is a wide diversity f reprted respnsibility values fr lad and envirnmental effets. In summary, it an be seen frm the disussin abve

42 23 that althugh the disaggregate distress funtin apprah Is theretially sund in nept, there an be nsiderable variatins in the final results depending upn the type f distress nsidered, the frm f distress mdels adpted, as well as the weighting sheme used t assign weights t distress types. This tends t suggest that, with the present state-f-art knwledge and tehnlgy in pavement nditin mnitring and evaluatin, an bjetive analytial slutin whih is aeptable and agreeable t all annt be ahieved by means f the disaggregate distress funtin apprah.

43 24 CHAPTER 3 NCEPTS OF PROPOSED AGGREGATE PERFORMANCE APPROACH 3. Intrdutin The best knwn and mst widely used aggregate pavement perfrmane mdel is undubtly the relatinships between axle ladings and pavement deteriratin develped thrugh the AASHO Rad Test f the early 960s. These relatinships have been summarized in the AASHTO Interim Guide fr Design f Pavement Strutures [9]. The present study adpted the AASHTO relatinships as a measure f aggregate pavement perfrmane. The general nept presented in this hapter, hwever, is still appliable shuld ther measure f pavement perfrmane be seleted fr use in analysis. 3.2 The Cnept f PSI-ESAL Lss A signifiant ntributin f the AASHO Rad Test was the intrdutin f pavement servieability as a measure f pavement perfrmane. It prvided a means fr quantitative evaluatin f pavement nditin and

44 25 perfrmane. This pavement evaluatin predure has gained widespread aeptane in pavement studies. Pavement servieability is usually expressed as an index number knwn as the Present Servieability Index (PSI). The signifiane f the index is that it establishes relatinships between bjetive pavement nditin measurements and subjetive ratings f rad users. It is based upn the rrelatin f rad user pinins with physial measurements f rad rughness, raking, pathing and rutting. The servieability equatins develped at the AASHO Rad Test are shwn in Equatins (3.) and (3.2). Fr flexible pavements PSI= lg(l+sv) - O.Ol/C+P -.33(RD) 2 (3.) Fr rigid pavements PSI= lg(l + SV) /C+P (3.2) whe re SV = n n 2 f ] E x, - - Z x, \ ± n = l i = *] l n- (3.3) SV = slpe variane x = the ith slpe measurement

45 26 n = ttal number f slpe measurements C = linear feet f majr raking per 000 sq.ft. f pavement area P = bituminus pathing in sq.ft. per 000 sq.ft. f pavement area RD = rut depth in inhes in bth wheel traks measured with a 4-ft straightedge It is imprtant t nte that PSI is a nditin rating f a pavement at the time measurements are taken. N indiatin is given as t pavement harateristis, limati, traffi and subgrade nditins, nr t the prbable behavir f the pavement in the future. T evaluate pavement nditin ver a perid f time, a perfrmane histry may be btained by having servieability measurements at different pints f time in pavement life. A typial pavement servieability time histry is shwn in Figure 3. where PSI is pltted against pavement age in years. At any time t, the nditin f the pavement is given by (PSI), and the rrespnding pavement deteriratin is represented by a term knwn as servieability lss, r PSI lss. The PSI lss at time t is equal t the differene between the initial PSI and the PSI at time t, that is, PSI lss at time t = (PSI) - (PSI)

46 27 a, >> u Q. a. a.

47 28 A mre useful plt is btained by pltting pavement servieability against umulative traffi lading expressed in terms f equivalent 8-kip single-axle lads (ESAL). A typial pavement servieability-umulative ESAL plt is shwn in Figure 3.2. Suh a plt is useful beause it relates pavement perfrmane t traffi ladings whih are ne f the majr nerns f pavement engineers. Mre imprtantly, it permits a mparisn t be made between measured field perfrmane and AASHTO perfrmane preditin, thereby allwing a pavement engineer t estimate, within reasnable limits, the perfrmane trends f an in-servie pavement. Althugh PSI lss uld still be used as an indiatin f the state f pavement deteriratin at any given stage f pavement life as shwn in Figure 3.2, it is nt a nvenient parameter fr pavement perfrmane analysis. This is beause, as disussed earlier, the index PSI prvides a nditin rating f the pavement there and then, with n referene t influenes f lad and envirnmental fatrs. T verme this prblem, an alternative pavement deteriratin measure is needed. A new pavement deteriratin measure was adpted fr use in this researh study fr pavement perfrmane analysis. This quantitative measure is represented by the shaded area in Figure 3.3. It is knwn as the PSI-ESAL lss f the pavement at the time f analysis, designated

48 29 e u J <u <: u w C H CU > U H O U i <0 CU - 3 <u S 3 O «E a u (0 <4-( u s* CU JJ Q- H -H u *-! C XI (8 3) CU O > ^ < > a* u <u < a. a.

49 30 C en H -a 4- tfl -J U < O 03 ^ W L- CD -i u Crt 0) CL. a n n a> <^ 3 60 Q.

50 3 as stage n in the figure. This new measure gives an additinal dimensin t the traditinal measure, PSI lss. While PSI lss is an assessment f pavement nditin at a pint f time in pavement life, PSI-ESAL lss prvides a measure f pavement deteriratin vering the entire analysis perid frm the time the pavement is nstruted, renstruted, r resurfaed thrugh the time f analys is. On the understanding that pavement deteriratin is the result f repetitive atin f traffi ladings and umulative effets f envirnmental fatrs, it is rekned that PSI-ESAL lss prvides a better representatin f pavement deteriratin fr pavement perfrmane analysis than the 'pint-estimatr' PSI-lss des. The use f PSI-ESAL lss greatly failitates the inrpratin f traffi lading and envirnmental effets int perfrmane analysis beause PSI-ESAL lss prvides a means t measure pavement perfrmane quantitatively n the same time frame basis as that used fr evaluating lads and envirnmental effets. The researh nduted in this study als fund PSI-ESAL lss t be a nvenient parameter fr relating pavement perfrmane t levels f rutine maintenane, and fr assessing the effetiveness f rutine maintenane in repairing pavement damage.

51 Appliatin f AASHO Rad Test Results t Perfrmane An al_v s is 3.3. AASHO Rad Test Relatinships At the AASHO Rad Test, pavement damage was defined in terms f PSI lss n a relative sale as fllws: G = P p - P " P t < G < (3.4) whe re G = pavement damage measure initial servieability index P = t P = terminal servieability index present servieability index This pavement damage measure was then related t lad by means f regressin analysis n the AASHO Rad Test data. The general AASHO Rad Test equatin is [5]: WIS -(f) (3.5) whe re W = number f axle lad appliatins p = a nstant equal t the number f lad appliatins at whih the damage G equals.0 6 = a regressin nstant T simplify the slutin t equatin (3.2.2) fr

52 33 mixed traffi, AASHO Rad Test seleted 8-kip single-axle lad as a datum lad level. By means f lad equivalene fatrs (i.e. equivalent 8-kip single-axle lad fatr, r ESAL fatr), all ther axle lads were nverted int ESALs fr alulating the variable W in equatin (3.5). By definitin, the ESAL fatr f an axle lad is the rati f the number f lad appliatins f the 8-kip datum lad t ause a given level f damage t the number f lad appliatins f the axle lad under nsideratin t ause the same level f damage. It is imprtant t nte that ESAL fatrs vary with level f damage, with magnitude f axle lad, with axle nfiguratin, with pavement thikness, and with the stiffness f the subgrade AASHTO Perfrmane Equatins Based upn the 962 AASHO Rad Test relatinships between perfrmane, pavement thikness and traffi ladings, the 972 AASHTO Interim Guide [9] further extended these relatinships t ver pavements built n different subgrade types. Fr rigid pavements, mdifiatin f the general Rad Test equatin was amplished by mparing stresses alulated frm strain measurements n the Rad Test pavement slabs with stresses alulated using the

53 34 theretial frmula develped by Spangler [7]. Fr flexible pavements, a sil supprt sale was established based upn tw types f radbed supprt at the Rad Test. A sil supprt value f 3.0 was assigned t the subgrade sil, and a value f 0.0 t the rushed-rk base material used. A linear sale between pints 3.0 and 0.0 was assumed t inrprate the effets f sil supprt nditin int the AASHO Rad Test relatinships. By heking the linear sale against a number f mmnly used design predures and against results f layered elasti thery analysis, it was fund that the assumptin f the linear sil supprt sale was reasnable. The mdified perfrmane equatins are: Fr flexible pavements, lg W = 9.36 lg(sn+l) (S - 3.0) lg(g) (SN+) 5. 9 (3.6) Fr rigid pavements, lg W = ( P t ) lg (yj-^j) V 75 " fe^f " lg(d+l) lg(g).624x0 (D+l) 8.46 (3.7)

54 35 whe re W = number f 8-kip single-axle lad appliatins SN = strutural number G = pavement damage defined in Equatin (3.4) S = sil supprt value D = thikness f slab in inhes P = terminal servieability index M = mdulus f rupture n nrete J = lad transfer effiient Z = E/k E = Yung's mdulus f elastiity f nrete, psi k = mdulus f subgrade reatin, psi/in Equatins (3.6) and (3.7) are the perfrmane equatins used fr the perfrmane analysis desribed in this dissertatin. It shuld be nted that the rigid pavement perfrmane equatin des nt inlude any adjustment fr envirnmental nditins different frm the AASHO Rad Test nditins. The reasn stated was that it was nt pssible t measure the effet f variatins in limati nditins ver the tw-year life f the pavement at the Rad Test site. An adjustment was inluded fr envirnmental nditins in flexible pavement perfrmane equatin presented in the AASHTO Interim Guide [9]. This adjustment was made by intrduing a reginal fatr whih takes a value f.0 fr the AASHO Rad Test site

55 36 nditins. Unfrtunately this fatr annt be learly defined, and it has n diret relatinship t any testing r measurement predure. AASHTO Interim Guide mentined that "there is n way t determine diretly the reginal fatr fr ther latins and nditins". Van Til et al. [8] fund frm a survey f fifty states that ne r mre f the fllwing were used by the states in assigning a reginal fatr:. Tpgraphy 2. Similarity t Rad Test latin 3. Rainfall 4. Frst penetratin 5. Temperature 6. Grundwater table 7. Subgrade type 8. Engineering judgment 9. Type f highway faility 0. Substane drainage Due t the unertainty and subjetive judgment invlved in the determinatin f reginal fatrs, this adjustment prpsed by AASHTO was nt adpted fr use in this researh, and it was nt inluded in the perfrmane equatin (3.6). It is interesting hwever t nte that by nt making any adjustment fr limati nditins, the perfrmane equatins (3.6) and (3.7) an be used, as explained in the subsequent setins, as a referene fr

56 37 assessing the relative impats f lad and envirnmental effets n pavement damage Appliability f AASHO Rad Test Results and AASHTO Perfrmane Equatins The AASHO Rad Test results and the AASHTO perfrmane equatins prvide very useful relatinships amng pavement perfrmane, strutural thiknesses, traffi ladings and subsil nditins. They have been used widely in the areas f pavement thikness design, pavement nditin mnitring and evaluatin. Hwever, due t the limitatin f the spe f the test and the nditins under whih it was nduted, they annt be applied in a straightfrward manner in ther areas. These areas inlude highway st allatin study and perfrmane analysis t determine the relative pavement damage respnsibility f lad and envirnmental fatrs. The AASHO Rad Test was nduted ver a perid f tw years. This time perid is relatively shrt mpared t an expeted servie perid f 20 years r mre fr mst pavements. Furthermre, during the Rad Test a maintenane pliy was implemented t permit nly minr maintenane s as t keep test traffi perating as muh as pssible [6]. In applying AASHO Rad Test results t pavement perfrmane analysis, ne must therefre be aware f the fllwing ptential differenes between AASHO Rad