Development of an Asphalt Pavement Distress Evaluation Method for Freeways in China

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1 Techncal Paper ISSN Int. J. Pavement Res. Technol. 7(2): Chnese Socety of Pavement Engneerng Development of an Asphalt Pavement Dstress Evaluaton Method for Freeways n Chna Lan Zhou 1, Fujan N 1+, and Zhen Leng 2 Abstract: Reasonable evaluaton of the asphalt pavement dstress condton s a very mportant part of the pavement management system. The objectve of ths research s to develop an effectve method to evaluate asphalt pavement dstress condtons n Chna. Three sngle evaluaton ndexes were proposed, namely the Transverse Crackng Evaluaton Index (TCEI), Pavement Patchng Condton Index (PPCI), and Pavement Surface Dstress Condton Index (PSCI), to assess the severty of asphalt pavement dstresses. The pavement dstress condton ndex (PDCI) was then developed as a general evaluaton ndex by usng the analytc herarchy process (AHP). The feasblty of ths evaluaton method was valdated usng the feld dstress data collected from Nng Hang freeway and Fen Guan freeway n Jangsu Provnce, Chna. The results showed that the PDCI could reasonably represent the dstress condton n asphalt pavements. The ndex value correlates well wth the actual condton of the pavement. Therefore, a scentfc and ratonal method has been establshed to evaluate Chnese asphalt pavement dstress condtons. DOI: /jprt.org.tw/2014.7(2).159 Key words: Analytc herarchy process; Asphalt pavement; Evaluatng method; Pavement dstress; Transverse crack. Introducton 12 Wth the rapd development of freeway constructon n Chna, ts total freeway mleage s the hghest n the world. In Chna, most of the asphalt pavement structures use sem-rgd base. However, because of the nfluence of traffc and the envronment, dstresses of varous forms and severty levels occur on asphalt pavement, ncludng ruttng, cracks, potholes, subsdence, etc. Many asphalt pavements have to be repared prematurely because serous dstresses occur even before the end of desgn lfe. Pavement dstresses not only damage the ntegrty and contnuty, but also reduce the pavement structural capacty. Thus, they can affect the servce level and servce lfe of freeways and threaten drvng safety as well. Investgaton and reasonable evaluaton of the dstress condton of asphalt freeway pavements s a very mportant part of pavement mantenance evaluaton [1]. It s the bass for evaluatng and predctng pavement performance, whch then can be used to determne the preservaton plan, make decsons on nvestment, and provde strong support for pavement decson makers. It s also sgnfcant for the constructon and mantenance of freeways n the future. The objectves of ths study are to develop an effectve method to evaluate the dstresses condton of asphalt freeway pavements n Chna based on the damage mechansm and data analyss, and then perform an analyss on the mantenance treatment approach. Ths paper ams to provde reference and gudance for freeway mantenance management n Chna. 11 College of Transportaton Engneerng, Southeast Unversty, 2# Spalou, Nanjng, 296, P.R.Chna. 22 Department of Cvl and Structural Engneerng, The Hong Kong Polytechnc Unversty, Hung Hom, Kowloon, Hong Kong. + Correspondng Author: E-mal nfujan@gmal.com Note: Submtted Aprl 25, 2013; Revsed October 17, 2013; Accepted October 28, Exstng Evaluaton Methods of Pavement Dstresses In the early 1960s [2], buldng a pavement evaluaton model was one of the most essental achevements of the U.S. AASHTO road tests. The evaluaton model had a profound mpact on the development of pavement management technologes around the world. In the early 19s [1], many other countres such as Canada, Brtan, and Japan began to establsh ther own pavement performance evaluaton models wth n-depth study and extensve applcaton of Pavement Management System (PMS). AASHTO Present Servceablty Index (PSI) Present Servceablty Index (PSI) s the frst ndex establshed by usng the expert evaluaton technology based on the practcal engneerng n the pavement management ndustry [2-3]. Road nspectors nvestgate the damage level of each expermental secton, and conduct multple regresson analyses to establsh the relatonshp between the damage stuaton and the Present Servceablty Ratng (PSR) value based on experts gradng, whch s the Present Servceablty Index (PSI). For asphalt pavement: 2 1 SV 0. 21RD 0. C P PSI g 01 where PSI = Present Servceablty Index; SV = dscrete degree of the longtudnal smoothness at the wheel track; RD = ruttng depth, cm; C = crackng degree, m 2 /0m 2 ; P = patchng degree, m 2 /0m 2. The model contans four varable parameters, namely smoothness, surface crackng, pavement patchng degree, and ruttng. Of the four factors, surface crackng and ruttng take very small proporton, (1) Vol.7 No.2 Mar Internatonal Journal of Pavement Research and Technology 159

2 meanng ther varaton has lttle mpact on the PSI. On the contrary, the smoothness has a sgnfcant nfluence on the PSI, especally when the SV s below 10. The PSI model s actually a rdng qualty model whch s manly related to the smoothness from the perspectve of parameter weghts. ASTM Pavement Condton Index (PCI) The Pavement Condton Index (PCI) for roads s a sngle ndex value used to quantfy all forms and severty levels of pavement dstresses, developed by the U.S. Army Corps of Engneers and further verfed and adopted by the Department of Defense (DOD) and Amercan Publc Works Assocaton (APWA) [4]. In the Standard Practce for Roads and Parkng Lots Pavement Condton Index Surveys (D ), asphalt pavement dstresses are classfed nto 20 types, n whch the typcal dstresses are cracks, ruttng, and weatherng of the pavement surface. The PCI s determned by the followng equaton. For asphalt pavement: PCI = - max (CDV) (2) where PCI = Pavement Condton Index; CDV = the corrected deduct value (DV) obtaned from total deduct value and q by lookng up the approprate correcton curve for AC pavements; DV = the deduct value (DV) for each dstress type and severty level combnaton obtaned from the dstress deduct value curves. The PCI s a numercal ratng of the pavement condton that ranges from 0 to, wth 0 beng the worst possble condton and beng the best possble condton. Snce the deduct value curves and correcton curve are obtaned accordng to the crcumstances of asphalt pavements n USA, the PCI ndex may not be sutable n Chna. Japanese Management Conservaton Index (MCI) Researchers from the Japanese mnstry of cvl engneerng have developed the Management Conservaton Index (MCI) by modfyng the PSI model accordng to the Japanese stuaton [2]. Unlke the Amercan PSI model, the MCI model emphaszes pavement surface crackng and ruttng, whle the smoothness only accounts for a small proporton, as shown n Eqs. (3) to (6). MCI = C D σ 0.2 (3) MCI 0 = C D 0.7 (4) MCI 1 = C 0.3 (5) MCI 2 = D 0.7 (6) where MCI = mantenance and management condton ndex, 0-10; C = crackng rato, %; D = ruttng depth, mm; σ = smoothness, mm. In order to accurately characterze dfferent pavement condtons, the MCI model actually contans four relaton models. So t s reasonable that Eq. (4) only contans two parameters: crackng rato and ruttng. For the pavement sectons wth severe ruttng dstress but lttle crackng, Eq. (4) provdes a relatvely hgh value, whereas Eq. (6) provdes more reasonable value for ths knd of pavement condton. For modellng purposes, dfferent equatons have been developed to deal wth dfferent pavement condtons, whch confuse the users occasonally. Ths s the defect of multple regresson analyss technques, as t s dffcult to adapt one sngle set of formula to evaluate dfferent road condtons due to the mmutablty of the regresson coeffcents. Chnese Pavement Condton Index (PCI) In the most recent Chnese pavement mantenance specfcaton, Hghway Performance Assessment Standard (JTG H ) [5], the Pavement Condton Index (PCI) model s recommended for evaluatng pavement surface dstress condton by usng Eq. (7): PCI DR (7) 21 1 A DR (8) A where PCI = pavement surface condton ndex; DR = pavement dstress rato, %; A = dstress area of dstress type, m 2 ; A = area of the nvestgated pavement sectons, m 2 ; ω I = weght of dstress type ; and = severty of dstress type. The PCI model does not consder the nfluence of pavement smoothness. It s only a functon of pavement surface dstress. The advantage of ths method s that t can accurately calculate the overall extent of damage caused by a varety of dstresses. Therefore, the PCI model overcomes the defect of the MCI model. Analyss of Exstng Evaluaton Models Investgatng the prevous pavement condton evaluaton models of dfferent countres shows that the AASHTO PSI model s actually a smoothness related rdng qualty model. Gven the specfc stuaton of the freeway pavements n Chna, where crackng and ruttng are the two man types of dstresses, the PSI model s not sutable for the evaluaton of the asphalt pavement dstress condton n Chna. In the Chnese specfcaton, the PCI model covers 21 types of dstresses. Although relatvely comprehensve, t s too general to put all the dstresses together [6]. In fact, the causes of these dstresses are dfferent, and ther nfluences on pavement performance are dfferent. As a result, hgh PCI values may not represent good pavement condtons, and vce versa. Dfferent pavement dstresses should be consdered separately accordng to the specfc crcumstances. To explan the lmtaton of the Chnese PCI model, the dstress data obtaned from Jng Hu freeway n Jangsu provnce n Chna was collected and analyzed. The calculaton results are summarzed n Table Internatonal Journal of Pavement Research and Technology Vol.7 No.2 Mar. 2014

3 Table 1. Example of the Dstress Condton Evaluaton Method n Chna. Pavement Secton Length of the Investgated Transverse Crack Length of Crack Transverse Crack PCI PCI Level Number Pavement Secton (m) Amount (m) Spacng(m) 1 0 Excellent Excellent Good Good Excellent Excellent Excellent Good Fg. 1. Proporton of Each Pavement Dstress Numbers to the Dstresses Amount n 2011 n Jangsu Provnce. The PCI values of all sectons are above n Table 1, ndcatng that the pavement sectons are n good condton. But the results are nconsstent wth the actual condton. For example, the PCI values of secton 4 and secton 8 are the same, but the extent of transverse crackng n secton 8 s much more than that of the secton 4, whch means the crack condton of secton 8 s actually more severe than that of secton 4. In other words, the PCI couldn t accurately reflect the dfferent severty levels of transverse crackng condton. Therefore, the evaluaton method needs mprovement. Only usng PCI ndex to evaluate pavement dstress s too general. It s not reasonable, nor scentfc. Because pavement dstress s an mportant part of pavement performance, t s necessary to develop a sutable evaluaton model of pavement dstress condton n order to provde gudance for developng a mantenance plan. Development of New Sngle Evaluaton Indexes for Pavement Dstress Condton As of 2011, the total mleage of freeways n Jangsu provnce has reached 4,121 km. The pavement structure of all freeways n Jangsu s an asphalt concrete pavement wth sem-rgd base layer, whch s the typcal pavement structure n Chna. There are varyng degrees of crackng, ruttng, shovng, pothole, etc., n Jangsu freeways each year. The pavement dstresses data used n the paper were collected by vsual nspecton n the feld from 14 freeway sectons that had been n servce over 5 years. Fg. 1 shows the proporton of each pavement dstress to the total n 2011 n Jangsu provnce. It reflects the current dstress condton of the whole Jangsu freeways. As shown n Fg. 1, transverse crackng and patchng are the two major types of asphalt pavement dstresses n Jangsu provnce, whose total proporton s above %, followed by pothole and longtudnal crackng, and the proportons of other dstress types are very small. Table 2 presents the pavement dstress condtons of dfferent freeways n 2011 n Jangsu provnce. The types and severtes of pavement dstress vared n dfferent freeway pavements; however, transverse crackng s stll the major dstress. The proportons of the other dstresses dffered wth the servce tme of the freeway, the degree of severty of the traffc load, and the effects of pavement mantenances. The longer servce tme and the heaver traffc load, the more types and hgher severtes of pavement dstress; whle the shorter servce tme and lower traffc load, the less the amount and types of pavement dstresses. The survey reveals that most of the transverse cracks are reflectve cracks, but fatgue cracks also appear on freeway pavements that are older than 10 years, and longtudnal cracks are manly caused by the dfferental settlement of subgrade. Generally, regardless of the type of pavement dstress, based on the freeway preventve and tmely mantenance requrements n Chna, the dstress, whch s dangerous to hgh-speed drvng, should be repared mmedately. Thus, these dstresses may be patched soon. Vol.7 No.2 Mar Internatonal Journal of Pavement Research and Technology 161

4 Table 2. Pavement Dstress Condtons of Dfferent Freeways n 2011 n Jangsu Provnce. Freeway Name Total Length of Freeway (km) Servce Lfe (Year) Dstress Amount The Proporton of Each Dstress Type to the Total Dstresses (%) 1* Hu Nng Zhen Jang Guangjng-X 52 Cheng Jng Hu Nng Jngyan Nng Hang Nng Suxu Fen Guan Yan Jang X Y Su Huayan Yan Ha Zhen L Nng Chang *Dstress type: 1: transverse crackng;2: longtudnal crackng; 3: block crackng; 4: fatgue crackng; 5: rregular crackng; 6: pothole; 7: ravellng; 8: patchng; 9: scratch; 10: shovng; 11: snkng; 12: bleedng; 13: water bleedng and pumpng; 14: other dstress. Therefore, the area of patchng can reflect the pavement condton ndrectly. Besdes the three dstress types above, pothole s another common type of freeway dstress. At the same tme, because of the danger of potholes to motorsts on the freeways, these damages are patched whenever they appears. Thus, the dstresses n asphalt freeway pavements can be classfed nto three categores: crackng, patchng, and other surface dstress. In addton, the transverse crackng s the most common dstress on freeway n Chna [1, 7]. In order to make the evaluaton results more pertnent, the transverse crackng s lsted separately as an ndvdual evaluaton ndex whle other crackng types are classfed nto surface dstress evaluaton. Based on ths method, n order to overcome the dsadvantage of the Chnese PCI model, three sngle evaluaton ndexes are defned to evaluate the asphalt pavement surface damage condtons n freeways, namely the pavement transverse crackng condton ndex (TCEI), pavement patchng condton ndex (PPCI), and pavement surface dstress condton ndex (PSCI). The detals of each ndex are descrbed n the followng sectons. Pavement Transverse Crackng Evaluaton Index (TCEI) In Chna, the man dstresses of sem-rgd base layer asphalt pavement are crackng and ruttng. The ruttng depth ndex (RDI) has already been a sngle evaluaton parameter n the 2007 Chnese standard; as another typcal dstress, the crackng has not yet receved enough attenton. The asphalt pavement surface cracks n Chna are mostly transverse reflectve cracks due to the sem-rgd base layer. For ths reason, the transverse crack evaluaton ndex (TCEI) was developed to ndcate the severty of the transverse crackng n asphalt pavements [8]. The calculaton method s shown as follows. TCEI = { e TCCI nocrackng TCCI > 1 TCCI 1 (9) TCS TCCI (10) TWR L TCS (11) TCN TCTL TCL (12) TCN TCL TWR (13) B where TCCI = Transverse Crack Index, dmensonless; TCS = Average Transverse Crack Spacng, m; TWR = Transverse Crack Wdth Rato, dmensonless; If the TWR value s more than 1.0, the TWR should be consdered to be 1.0. TCL = Transverse Crack Average Length, m; TCN = Number of Transverse Crack n Pavement Secton beng evaluated; TCTL = Transverse Crack Total Length, m; L = Total Length of the Pavement Secton beng evaluated, m; and B = Wdth of the Pavement Secton beng evaluated, m. Transverse Crack Spacng (TCS) ndcates the longtudnal dstrbuton of transverse cracks and transverse Crack Wdth Rato (TWR) presents whether the transverse crack s full wdth or less, representng the severty level of the crack. The TCEI ndex characterzes the transverse crack damage condton comprehensvely n asphalt pavements, whch can be used to determne the proper mantenance tmng and methods. The transverse crackng condton s more serous when the TCS s smaller and the TWR s bgger. The pavement crackng s one of the mportant factors aggravatng pavement roughness, and often causes pavement structural falure. The TCEI s dvded nto fve performance levels: excellent (TCEI ), good ( TCEI < ), 162 Internatonal Journal of Pavement Research and Technology Vol.7 No.2 Mar. 2014

5 moderate (70 TCEI < ), nferor (60 TCEI < 70) and poor (TCEI < 60). The pavement crackng severty can be assessed through the TCEI, and then the causes of the pavement damages can be analyzed, whch then can be used to select proper treatments. Pavement Patchng Condton Index (PPCI) The pavement patchng s the result of the pavement dstress treatment, but not the dstress tself. However, the pavement patchng reflects the hstorcal condton of pavement dstresses. Wth the ncrease of the pavement servce lfe, the performance of the pavement structure layers descends, and the patchng area may ncrease rapdly. When the patchng area exceeds a lmtaton, the pavement ought to be rehabltated. The patchng also affects the drvng experence and the pavement appearance. It s related to the drvng qualty and safety n freeways. The patchng has been treated as one of the pavement dstresses n the recent Chnese specfcaton, whle ts severty s gnored [13]. Therefore, t s necessary to devate the patchng from the PCI model and develop a sngle evaluaton ndex to evaluate the pavement hstorcal damage condton more specfcally. As shown n Eq. (14), the Pavement Patchng Condton Index (PPCI) has been proposed by ths study to evaluate the pavement patchng. a1 0PPR (14) PPCI a n A 1 PPR (15) A where PPR = Pavement Patchng Rato, %; A = area of pavement patchng type (m 2 ); A = the nvestgated pavement area (m 2 ); a 0 = calbraton coeffcent, ; a 1 = calbraton coeffcent, ; n = the patchng numbers. The PPCI s dvded nto fve performance levels: excellent (PPCI ), good ( PPCI < ), moderate (70 PPCI < ), nferor (60 PPCI < 70) and poor (PPCI < 60). Pavement Surface Dstress Condton Index (PSCI) In addton to the patchng and transverse crackng, there are stll other types of surface dstress n freeway asphalt pavement, for example, shovng, bleedng, shavng, and longtudnal crackng etc. The other pavement surface dstress can be evaluated by pavement surface dstress condton ndex (PSCI). The surface dstress reflects the damage condton of the current pavement. Thus, t can also be named as pavement current damage condton ndex. Refer to the evaluaton method of pavement damage condton ndex PCI n Standard 2007, the mark reducng method s utlzed to make the evaluaton n PSCI as follows. 0 a1 PSCI - a SDR (16) n 1 A SDR * (17) A where SDR = Pavement Surface Dstress Rato, t s defned to be the proporton of the damage total areas to the pavement nvestgaton areas (%). A = the surface damage area of type, except the patchng and transverse crackng (m 2 ); A = the nvestgated pavement area (the product of nvestgaton pavement length and the effectve pavement wdth)(m 2 ); ω = the weght of the type pavement dstress. a 0 = calbraton coeffcent, 15.0 s adopted; a 1 = calbraton coeffcent, s adopted; n = the total number of damage types ncludng the damage severty. The PSCI s dvded nto fve performance levels: excellent (PSCI ), good ( PSCI < ), moderate (70 PSCI < ), nferor (60 PSCI < 70) and poor (PSCI < 60). Evaluaton of the New Sngle Evaluaton Index In order to test the feasblty of the new sngle evaluaton ndex, seven pavement sectons that cannot be successfully evaluated by the old PCI model were selected from Jng Hu freeway n 2008 for analyss. Table 3 summarzes the evaluaton results of TCEI, PPCI, PSCI, and PCI. As shown n Table 3, the PCI values were all above, whch means the pavement performance condtons were excellent. However, whle usng the TCEI to evaluate, the scores of some pavement sectons were below, even less than 70. Accordng to the TCEI evaluaton standard, the TCEI ndex was under the moderate level. The transverse crackng condton was serous, whch s consstent wth the actual pavement performance. And the TCEI can approprately reflect the pavement transverse crackng condton. The PSCI values were larger than PCI values n Table 3. Accordng to dstress data, the surface dstresses of these 7 pavement sectons were not serous except for the transverse crackng. Ths result s consstent wth the actual surface dstress effectve area condton. PPCI s used to evaluate the hstorcal condtons of pavement dstresses. Accordng to the PPCI, the patchng areas of these 7 pavement sectons were secton 2 > secton 6 > secton 7 > secton 1 > secton 4 > secton 3 > secton 5 before Development of General Pavement Dstress Condton Evaluaton Model The three sngle ndexes, TCEI, PCCI, and PSCI, as mentoned above, can be used to ratonally characterze the pavement damage condton. However, sngle ndexes are not good at evaluatng macroscopcally. Therefore, a general evaluaton ndex, Pavement Dstress Condton Index (PDCI), s developed to evaluate the pavement damage condton entrely by combnng the three sngle ndcators TCEI, PPCI, and PSCI. Buldng reasonable and feasble pavement dstress general Vol.7 No.2 Mar Internatonal Journal of Pavement Research and Technology 163

6 Table 3. Evaluaton Results of the New Evaluaton Indexes. Pavement Secton Pavement Secton PCI TCEI PSCI PPCI 1 K K K K K K K K K K K K K K evaluaton ndex and determnng the weghts of each sngle ndex are the keys to solve the problem. However, the relatonshps between each sngle ndex are qualtatve; t s dffcult to determne the weghts. Analytc herarchy process (AHP) [10-11] can avod ths problem effectvely by consderng the quantty and qualty effects comprehensvely and determnng the weghts of each sngle ndex. AHP s one of the most typcal systems engneerng approaches that ntegrate the quanttatve and qualtatve analyss. Ths approach s sutable to cope wth the problems whch nvolved complex structures, many decson crtera, and dffculty on quantfyng. It also can help people to keep the consstency of thought process. Therefore, AHP s wdely used n determnng the factor weghts [10-11]. Ths study selected AHP to determne the weght of each sngle ndex to obtan a general ndex to evaluate the whole pavement dstress condton. Basc Prncples of Analytc Herarchy Process Analytc herarchy process was frst presented by Amercan operatons researcher T. L. Saaty. Ths method can make the decson thought behnd a complcated system herarchcal, and make an organc combnaton of qualtatve and quanttatve factors n the determnaton process. AHP can calculate the weghts of each factor whle the quanttatve and qualtatve factors are both ncluded. And t can reduce the probablty of the contradcton between subjectve judgments and actual problems. The process of AHP modelng and weght calculaton contans four steps: 1) buldng the herarchy model; 2) buldng the judgment matrx; 3) sngle level sortng and consstency check; and 4) herarchy total level sortng and consstency check [12]. Development of Pavement Dstress Condton Index (PDCI) The PDCI was the weghted average of three ndexes, TCEI, PPCI, and PSCI. The PDCI s defned n the followng equaton. PDCI = a*tcei + b*ppci + c*psci (18) Through analyss, t s rather ratonal to determne the weghts of sub-ndexes through AHP and obtan the comprehensve ndex on such a bass. In ths case, the PDCI wll be defned as target layer A. The analyss of the PDCI s based on two prncples, ratonalty and feasblty, whch are defned as two elements of crteron layer named C 1 and C 2. The PDCI s calculated from three ndexes, TCEI, PPCI and PSCI, whch are defned as three elements of scheme layer named P 1, P 2 and P 3. The herarchcal structure model s graphcally shown n Fg. 2. Monolayer Judgment Matrx A-C was bult on two elements, the ratonalty and feasblty. These elements were determned by comparng ther mportance, and Matrx A 2*2 was bult on such a bass. Then, matrx C-P was bult, whch ncluded three elements, the TCEI, PPCI, and PSCI. Matrx (C 1 ) 3*3 and (C 2 ) 3*3 were bult through multple comparson and assgnment of these three elements. 1 1 A C C Frst, matrx A should be checked for consstency. A s a two order matrx, and t fts the consstency prncple. The maxmum egenvalue λ max s equal to 2, and ts correspondng egenvector W s shown as W = [W 1, W 2 ] T = [0.25, 0.75] T. Then, a consstency check was made to the matrx C 1 and C 2, and the weght of each element was calculated. The results of Monolayer Judgment Matrx are summarzed n Table 4. Monolayer matrx C 1 and C 2 pass the consstency check from the results of CR n Table 4, whch means they are avalablty matrx. Fnally, a consstency check was made to the herarchy total sort [9]. A: General evaluaton model: Pavement Dstress Condton Index C 1 :feasblty C 2 : ratonalty P 1 :TECI P 2 :PPCI P 3 :PSCI Fg. 2. Herarchcal Structure Model of Weght Analyss for Sngle Evaluaton Index. 164 Internatonal Journal of Pavement Research and Technology Vol.7 No.2 Mar. 2014

7 PDCI value PCI value PDCI value PCI value Zhou, N, and Leng Table 4. Results of Monolayer Judgment Matrx. Element Weght W 1 W 2 W 3 λ max CI RI CR W C W C PDCI PCI (a) PDCI PCI (b) Fg. 3. Varaton Curve of PCI Value and PDCI Value along (a) East Bound Drecton, (b) West Bound Drecton. The correspondng weght W P of target layer of factors P 1, P 2 and P 3 s equal to W P = [W P1, W P2, W P3 ] T = [0.6179, 0.25, ] T, where W P1 s correspondng to a, W P2 s correspondng to b, and W P3 s correspondng to c n Eq. (19). Therefore, Eq. (18) can be descrbed as follows. PDCI = *TCEI *PPCI *PSCI (19) The PDCI s dvded nto fve performance levels: excellent (PDCI ), good ( PDCI < ), moderate (70 PDCI < ), nferor (60 PDCI < 70) and poor (PDCI < 60). In summary, the new pavement dstress condton evaluaton model conssts of three sngle evaluaton ndcators, namely TECI, PPCI, and PSCI, and one general evaluaton ndcator PDCI. The process of calculatng the PDCI s as follows: Frst, the data of pavement dstresses should be collected, ncludng the quantty and the area or the length. Second, calculate the three sngle ndcators TCEI, PPCI and PSCI by Eqs. (9), (14), and (16). And fnally, calculate the PDCI accordng to Eq. (19). The general gudelne of determnng the pavement mantenance method s dvded nto three key steps: 1) calculatng the PDCI ndex of each secton and choosng the sectons wth PDCI values less than 75 as the mantenance sectons; 2) comparng the correspondng sngle ndcators (TCEI, PPCI, and PSCI) of these mantenance sectons and fndng the man dstress type of each mantenance secton; and 3) determnng the proper mantenance method for each mantenance secton based on the type and severty of the dstress. Engneerng Applcaton In order to valdate the evaluaton method proposed n ths study, data were collected from Nng Hang freeway (open to traffc n 2003) and Fen Guan freeway (open to traffc n 2002) n Jangsu Provnce. Both freeways have asphalt concrete surface on top of sem-rgd base layer, wth two traffc lanes n each drecton. The surface thcknesses of Nng Hang freeway and Yan Jang freeway are 18 cm and 17 cm, respectvely. Both freeways use cement stablzed macadam n the base layer. The base layer thckness for Nng Hang freeway s 36 cm and for Yan Jang freeway s 38 cm. The traffc volumes of the two freeways have ncreased every year snce they opened to traffc, and the proporton of the trucks also ncreased contnuously. The overloadng condton on the two freeways s also very serous. Applcaton of PDCI on Evaluatng Pavement Dstress Condton of Nng Hang Freeway To valdate the performance of the PDCI model, the data were collected from Nng Hang freeway n The statstcal results of some pavement sectons are analyzed usng PCI and PDCI. Fg. 3 shows the varaton curves of comparson results of PCI and PDCI. As shown n Fg. 3, when the pavement dstress condton s not serous, there s no sgnfcant dfference between PDCI and PCI wthn the scope of to. However, n some sectons where the PDCI values were below, the PCI values were above. These sectons may mss the key approprate mantenance opportunty f the PCI model s used to evaluate pavement dstress condton. Fve Vol.7 No.2 Mar Internatonal Journal of Pavement Research and Technology 165

8 PDCI value PCI value PDCI value PCI value Zhou, N, and Leng Table 5. Statstcs of Actual Pavement Dstress Condton of Fve Sectons. Transverse Crackng Condton Patchng Condton Surface Dstress Condton Secton PCI PDCI Average Average Average Number Amount TCEI Amount PPCI Amount PSCI Length Area Area (a) (b) Detecton tme Fg. 4. (b) Development Trend of Pavement Dstress Condton along (a) South Bound and (b) North Bound Drecton over Tme PDCI Detecton tme PDCI PCI PCI pavement sectons wth PDCI lower than and PCI hgher than were chosen for further analyss, and these sectons are K2097-K2098, K2101-K2102, and K2119-K2120 n the east bound drecton, and K2101-K210 and K2118-K2119 n the west bound drecton. These fve sectons were named secton 1, secton 2, secton 3, secton 4, and secton 5, respectvely. Table 5 summarzes the statstcs of the actual pavement dstress condton of the fve sectons. As shown n Table 5, the transverse crackng condtons of the fve sectons are serous wth the TCEI around, whch means the approprate mantenance method should be taken to prevent further deteroraton. The PDCI values are all less than, ndcatng that the overall dstress condton s not bad. However, the PCI values are all more than meanng the pavement s n good condton. The reason for the dfference between PDCI and PCI s that the transverse crackng condton s serous, but other types of pavement dstress were rare. Compared to PDCI, PCI s much more general and t reduces the mportance of transverse crackng by mxng t wth other pavement dstresses. In concluson, t s more reasonable to evaluate the asphalt pavement dstress condton based on PDCI nstead of PCI. Applcaton of PDCI on Evaluatng Pavement Dstress Condton of Fen Guan Freeway The pavement secton chosen from Fen Guan freeway has never been mantaned except for routne mantenance, lke fllng the cracks, snce t opened to traffc. Therefore, by evaluatng the hstorcal condton of pavement dstresses from 2004 to 2011, the dstress development trend can be obtaned by the PCI model and PDCI model respectvely, as shown n Fg. 4. Fg. 4 shows that when usng the PCI model to evaluate the pavement dstress condton, the PCI value dropped from to from December 2004 to Aprl The PCI changed n eght years, and t could not capture the development of the pavement dstress 166 Internatonal Journal of Pavement Research and Technology Vol.7 No.2 Mar. 2014

9 development trend. However, the PDCI value dropped from to 70, whch clearly reflected the development of pavement dstress. Takng the actual dstress condton of Fen Guan freeway nto consderaton, the TCEI of the secton n the south-bound drecton n Aprl 2011 s 51.1, whle the TCEI n the north drecton s Thus, the transverse crackng condtons n both drectons are very serous, and the secton s n urgent need of specfc mantenance. Correspondngly, the PDCI s below 75, ndcatng a moderate pavement dstress condton. However, the PCI s around whch means the condton s excellent, and the PCI s unable to reflect the serous transverse crack condton. Thus, t can be seen that the PDCI model s more approprate and reasonable than the PCI model n the pavement dstress evaluaton system for the Chnese freeways. Conclusons The prmary objectve of ths study s to establsh an effectve method to evaluate asphalt pavement dstresses on Chnese freeways. Based on the current stuaton of asphalt freeway pavements and exstng research n Chna, a scentfc pavement dstress condton evaluaton method has been developed. The evaluaton method s establshed based on three sngle evaluaton ndexes and one general evaluaton ndex. The sngle evaluaton ndexes are the TCEI, PPCI, and PSCI. The general evaluaton ndex PDCI enables a comprehensve descrpton of the pavement damage condton n asphalt pavements. Based on the analyss of pavement dstress condton on Jangsu freeways n 2011, the three sngle evaluaton ndexes were proposed to evaluate dfferent stuatons of pavements. The feasblty of the three sngle ndexes was also valdated by the data from other freeways n Jangsu provnce. The three sngle ndexes are adoptable to reflect the dfferent pavement condtons of freeways accurately. AHP was used to develop the general evaluaton ndex, PDCI, whch s composed of three sngle ndexes (TCEI, PPCI and PSCI). The valdty of ths ndex was proved by the data obtaned from Nng Hang freeway and Fen Guan freeway n Jangsu. The results ndcated that the PDCI model s better, more approprate and reasonable than the PCI model for Chnese pavement management purposes. In summary, the establshment of a pavement dstress condton evaluaton model s valuable for the pavement mantenance decsons. Ths paper provdes a very potental model for asphalt freeway pavement dstresses research. Acknowledgements The authors would lke to thank the managers of Jng Hu Freeway Company, Nng Hang Freeway Company, and Fen Guan Freeway Company n Jangsu Provnce for provdng wth the detecton data of pavement dstresses. References 1. Zeng, J., Xu, J. (2009). Evaluaton Methods for Breakdown Condton of Expressway Asphalt Concrete Pavements. Journal of Changsha Unversty of Scence and Technology (Natural Scence), 6(2), pp (n Chnese). 2. Haas, R., Hudson, W.R., and Zanewsk, J. (1994). Modern Pavement Management. Kreger Publshng Company, Malabar, Florda, USA. 3. Washngton State Department of Transportaton, Pavement Interactve. Accessed ASTM Desgnaton : D (2011). Standard Practce for Roads and Parkng Lots Pavement Condton Index Surveys, ASTM Internatonal. 5. Mnstry of Communcatons (2008). Hghway Performance Assessment Standards (JTG H ). pp , People Transportaton Publshng House, Bejng, Chna (n Chnese). 6. Wu, C. (2007). Shortcomngs and Improvement of Evaluaton Methods for Breakdown Condton of Expressway Asphalt Concrete Pavements. Hghway, No. 5, pp (n Chnese). 7. Mller, J.S. and Bellnger, W.Y. (2003). Dstress Identfcaton Manual for Long-term Pavement Performance Program (fourth revsed edton). Report No. FHWA-RD FHWA, U.S. Department of Transportaton, Washngton, DC, USA. 8. Zhou, L., N, F.J., and Zhao, Y.J. (2010). Study of Evaluaton Method to the Transverse Crack for Freeway Asphalt Pavements, Transportaton Research Record, No. 2153, pp Zhou, L. and N, F.J. (2011). Research of Asphalt Pavement Performance Evaluaton for Freeways n Jangsu. Report. Nanjng, Chna (n Chnese). 10. L, H.Y., L, F.Z., Fan, H.H., and He, Y. (2012). Evaluaton for Damaged Condton of Asphalt Pavement Based on Fuzzy-AHP Method, Hghway Engneerng, No. 6, pp (n Chnese). 11. Zhou, L. and N, F.J. (2011). Study on Pavement Roughness Evaluaton Model for Freeway Sem-rgd Base Asphalt Pavements. Proceedngs of the 11th Internatonal Conference of Chnese Transportaton Professonals, Nanjng, Chna. 12. Xu, S.B. (1998). Practcal Decson-makng Method : Prncple of Analytc Herarchy Process. Tan Jng Unversty Publshng House, Tan Jng, Chna (n Chnese). 13. Statstcal Package for the Socal Scences (2002). Tutoral for Wndows 2: Regresson Analyss. SPSS, pp Vol.7 No.2 Mar Internatonal Journal of Pavement Research and Technology 167