Arab J Sci EngDOI 10.1007/s13369-014-1216-2

RESEARCH ARTICLE - CIVIL ENGINEERING

Creep Compliance: A Parameter to Predict Rut Performanceof Asphalt Binders and Mixtures

Imran Hafeez · Mumtaz Ahmed Kamal

Received: 24 December 2012 / Accepted: 30 June 2013© King Fahd University of Petroleum and Minerals 2014

Abstract Highway agencies have been using polymers inasphalt binders to reduce rutting-associated distresses inasphalt pavements. Rheological parameters like complexshear modulus (G∗) and phase angle (δ) in the form ofG*/Sinδ were used to predict rut resistance of asphalt binders,which have been replaced by a new parameter called non-recoverable creep compliance. The present study investigatesthe creep compliance of straight run (neat) and polymer-modified asphalt binders, at their high performance gradetemperature (58, 64, 70, and 76 ◦C), using a multi-stress creeprecovery test. The test data are used to assess the tempera-ture and stress sensitivity of asphalt binders at different per-centages of polymer. Asphalt mixtures, prepared using fourasphalt binders, are tested in a wheel tracker to arrive at arelationship between creep compliance and rut resistance ofasphalt mixtures. This study has revealed that creep compli-ance depicts the temperature and stress sensitivity of asphaltbinders and asphalt binders’ polymer modification. Basedon the stress sensitivity and creep compliance data, the suit-ability of asphalt binders for different traffic loadings is sug-gested. The present study proposes a reasonable relationshipbetween creep compliance at 3.2 kPa and rut depth of asphaltmixtures, obtained from a wheel tracker test. This labora-tory study may be extended in the future for field validationand development of asphalt mixtures performance-relatedspecifications.

I. Hafeez (B) · M. A. KamalDepartment of Civil Engineering, University of Engineeringand Technology, Taxila, Pakistane-mail: imranhafeez783@yahoo.com

M. A. Kamale-mail: drmakamal@yahoo.com

Keywords Asphalt binders · Creep compliance ·Polymer-modified asphalt · Rut depth

1 Introduction

Strategic highway research program (SHRP) developedsuperpave specifications of high temperature performancecharacterization of asphalt binders. These specifications werefollowed in different research studies, and efforts were madeto relate superpave specifications of asphalt binders’ high per-formance parameter G*/Sinδ (at w = 10 rad/s) with its rutresistance [1,2]. Superpave defines complex shear modulus

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Table 1 Grading of asphaltbinders

Sr. No. Penetrationgrade

Mean penetrationvalue (1/10 mm)

Modified/neat Performance grade(AASHTO M320-05)

1 60-70 67 Neat PG 58-16

2 60-70 65 Modified with 1.35 % Elvaloy PG 70-22

3 60-70 64 Modified with 1.7 % Elvaloy PG 70-19

4 60-70 61 Modified with 2 % Elvaloy PG 76-16

5 80-100 92 Neat PG 58-22

6 80-100 85 Modified with 1.7 % Elvaloy PG 64-22

7 80-100 83 Modified with 2 % Elvaloy PG 70-16

(G*) and phase angle ( δ): two principle rheological parame-ters of asphalt binder that can be measured using a dynamicshear rheometer. The former indicates stress-to-strain ratio,and the later shows the phase difference between correspond-ing stress and strain in an oscillatory system [3,4]. The para-meter G*/Sinδ (at w = 10 rad/s) in dynamic shear rheometer(DSR) is used to determine the high temperature performancegrade (PG) of an asphalt binder. According to AASHTOM320 [5], the asphalt binder should attain a minimum valueof 2.2 kPa at this temperature under a rolling thin-film oven(RTFO)-aged condition as per ASTM D2872 [6]. The fre-quency (w = 10 rad/s) represents a traffic speed of approx-imately 90 kilometer per hour [7]. Since the last decade, itseems that this parameter fails to capture creep or permanentdeformation behavior of modified asphalt binders [8,9]. Anew parameter called non-recoverable creep compliance wasintroduced by SHRP that depicts high temperature binders’performance [10–14]. Different approaches have been usedto correlate rut potential of asphalt mixtures with binder prop-erties [15–18].

The present paper reports on the effects of temperature,stress levels, and percentage addition of a polymer on thenon-recoverable creep compliance (Jnr ) of asphalt binderswithin their linear elastic range. It compares the values ofJnr at a stress level of 3.2 kPa (up to maximum linear rangeof creep compliance) and at a temperature where G*/Sinδ (atw = 10 rad/s) of asphalt binder is 2.2 kPa, which is a SHRPhigh PG temperature selection criteria [13]. An attempt isalso made for specifying asphalt binder grade to tempera-ture and vehicles’ loading condition using Jnr . The goal ofthe study was to find out the suitability of the creep com-pliance parameter for the evaluation of asphalt mixtures’ rutpotential.

2 Experimental Program

2.1 Asphalt Binders

Seven asphalt binders were chosen for this study. Two neat(60/70 and 80/100 penetration grade) and five modifiedasphalt binders from the same neat asphalt binders with

different percentages of Elvaloy polymer were selected. Elvaloypolymer is a high-molecular-weight polymer having elas-tomeric and plastomeric modifiers, and commonly been usedin asphalt binders’ modification. It is also classified as eth-ylene inter-polymer alloy, and it acts as a stiffener in asphaltbinders that increases asphalt mixtures’ rut resistance com-pared to other types of polymers [19]. Elvaloy polymer chem-ically reacts with asphaltenes fraction of asphalt and oxidizedvolatile components rapidly, resulting in an increase in stiff-ness of asphalt binder. Relatively low creep compliance andhigh complex modulus values of polymer-modified asphaltbinder, obtained from a DSR, are indicators of its better per-formance in the field as compared with neat asphalt binder.The asphalt binders selected in the present study were uti-lized on different highway projects in hot climatic regionsof Pakistan. Different percentages of Elvaloy polymer, whenadded to asphalt binders, produced different PGs. Conven-tional tests of penetration grade are also conducted on thesame asphalt binders. Penetration grade of neat and modi-fied asphalt binders is measured at standard test conditions(100 g, 5 s, and 25 ◦C) in accordance with AASHTO T 49[20] and reported in Table 1.

Table 1 also shows the information of asphalt binder’sperformance grading [21]. Short-term aging was performedusing standard rolling thin-film oven (RTFO) test [6]. TheRTFO-aged samples were subjected to multi-stress creeprecovery (MSCR) test and are reported in the sections tofollow.

2.2 Multi-Stress Creep Recovery (MSCR) Test

Multi-stress creep recovery test, using the dynamic shearrheometer, was run on RTFO-aged samples. Anton Paar DSRwith its parallel-plate geometry loading device and a controland data acquisition system were utilized for conducting theMSCR test in the present study. This DSR can maintain thetest temperature from −30 to 120 ◦C by its Peltier systemand capable of measuring the dynamic shear modulus from100 Pa to 10 MPa. Specimens were tested in replicates using a25-mm disc and with 1-mm gap setting at temperatures of 58,64, 70, and 76 ◦C (PG of asphalt binders) and at a stress rang-

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ing from 0.025 to 25.6 kPa. The tests were performed at theselected temperatures using a constant stress creep of 1.0 sec-ond duration and a relaxation period of 9 seconds. The testswere performed at multiple stress levels of 0.025, 0.05, 0.1,0.2, 0.4, 0.8, 1.6, 3.2, 6.4, 12.8, and 25.6 kPa, for ten cyclesat each stress level. Percent recoverable and non-recoverablecomponents of creep compliance were determined at the endof 10 cycles [22]. A typical schematic diagram of stress appli-cation and accumulation of strain in response to applied stressmay be found elsewhere [17].

Initial strain (εo) value at the beginning of creep portionof each cycle and strain value at the end of creep portion (εc)

of each cycle were determined. The difference in both strainsis known as adjusted strain (ε1). Similarly, strain values (εr )

at the end of recovery portion of each cycle, and adjustedstrain value (ε10) at the end of recovery portion of each cycle,were computed. The adjusted strain value (ε10), percentagerecovery, and non-recoverable compliance were calculatedfor ten cycles at each constant stress level using the followingformulae

ε10 = εr − εo (1)

Percentage Recovery = (ε10 − ε0)

ε1× 100 (2)

Jnr = avg.γu

τ, (3)

whereas non-recoverable creep compliance (Jnr ) in unitsof kPa−1, as noted in Eq. 3, measures the residual strainin a specimen after a creep and recovery cycle divided bythe stress applied, and indicates the resistance of an asphaltbinder to permanent deformation under repeated load [22].Where γ u is the unrecovered strain from the end of the 9-seconds recovery portion of the creep and recovery test, τ isthe shear stress applied during the one-second creep portionof the creep and recovery test. Creep and strain measurementswere recorded for different stress levels. Creep recovery testdetermines the mechanical properties of asphalt binders andcreep compliance of asphalt cement and can be used to pre-dict rutting of asphalt mixtures [17].

3 Results and Discussions

Non-recoverable creep compliance (Jnr ) and percentagerecovery values were calculated. Creep compliance valuesof asphalt binders were then compared at each temperatureand stress level. The stress levels corresponding to linear vis-coelastic behavior of different asphalt binders were noted.The influence of temperature and stress levels on creep com-pliance (Jnr ) was recorded and discussed in the followingsections.

0

10

20

30

40

50

60

70

0.01 0.1 1 10 100

Jnr

(kPa

-1)

Stress (kPa)

PG 58-22 PG 58-16 PG 64-22

PG 70-22 PG 70-19 PG 70-16

PG 76-16

Fig. 1 Influence of stress level on Jnr value of asphalt binders at 76 ◦C

3.1 Non-Recoverable Creep Compliance (Jnr ) of AsphaltBinders

Non-recoverable creep compliance was obtained at eachstress and temperature level. Figure 1 shows a plot of theinfluence of stress levels on Jnr of asphalt binders at76 ◦C.

As expected, Jnr increases with the increase in stress level.Also, creep compliance of an asphalt binder tends to be linearup to a stress level of about 3.2 kPa and then rises gradually. APG of 76–16 asphalt binder shows relatively flatter responseat 76 ◦C. At the same time, an asphalt binder having a PGlower than a testing temperature shows high rate of increasein Jnr .

At all test conditions, higher PGs have relatively low Jnr

compared with low PGs. High PG binders show more ten-dencies to recover upon release of stress than low-gradebinders. This tendency is a function of selected temperatureand applied stress. The higher the Jnr value, the less will bethe tendency of the asphalt binders to return back to theiroriginal shape and vice versa. Figure 1 also shows relativelysmall change in Jnr plot up to a stress level of 3.2 kPa, partic-ularly for higher PGs. One can predict a linear viscoelasticbehavior of asphalt binder up to 3.2 kPa stress level [23,24].It may also be noted from Fig. 1 that creep compliance showschange in asphalt binder’s characteristics, even if they are atthe same superpave performance grading. This is in line withwhat has been reported in the literature [25].

The effect of temperature on creep compliance of singlebinder (PG 58–22) is typically shown in Fig. 2. It may benoted that the rate of increase in creep compliance of asphaltbinder at 58 ◦C is low. This means that the slope of stress–Jnr plot tends to be mild up to the PG temperature. How-ever, beyond the PG temperature, such as 64, 70, and 76 ◦C,this rate increases significantly with the increase in thetemperature.

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0

10

20

30

40

50

60

70

0.01 0.1 1 10 100

Jnr

(kPa

-1)

Stress (kPa)

58°C 64°C 70°C 76°C

Fig. 2 Typical plot showing the effect of temperature on Jnr value ofPG 58–22 at different stresses

0

2

4

6

8

10

12

0.01 0.1 1 10 100

Cre

ep C

ompl

ianc

e (k

Pa-1

)

Stress (kPa)

60/70 neat 1.35% Elv.

1.70% Elv. 2.00% Elv.

Fig. 3 Effect of addition of various percentages of polymer on Jnrvalue at 64 ◦C

It is important to discuss here the effect of asphalt mod-ification by the addition of different percentages of Elvaloypolymer on Jnr value of asphalt binders. The Jnr dataobtained for PG 58–16 (60/70 pen. grade), PG 70–22 (60/70pen. grade with 1.35 % Elvaloy polymer), PG 70–19 (60/70pen. grade with 1.7 % polymer), and PG 76–16 (60/70 pen.grade with 2 % polymer) at 64 ◦C were compared and pre-sented in Fig. 3.

One can observe that the rate of increase in Jnr valuedepends significantly on the percentage of polymer presentin the asphalt binder. With an increase in polymer content, theslope of Jnr -plots reduces. Figure 3 shows some differencebetween Jnr curves of asphalt binder with 1.35 % (PG 70–22) versus 1.7 % of polymer (PG 70–19). It may be notedthat both asphalt binders have the same high performancegrade (PG 70), as determined using SHRP criteria (G*/Sinδ

is 2.2 kPa), but exhibiting different Jnr curve.Stress sensitivity of asphalt binders was determined by

measuring percent increase in Jnr value from 0.1 to 3.2 kPain a multi-stress creep recovery test. The basic purpose was to

ascertain the sensitivity of asphalt binders toward an increasein stress value. According to SHRP criteria, if percentageincrease in Jnr value at 3.2 kPa is less than or equal to 75 %of the Jnr at 0.1 kPa, the asphalt specimen is not stress-sensitive [26].The requirement to keep the percent increasein Jnr value below 75 % was to ensure that the binder wouldnot be overly stress-sensitive under unexpected heavy load,or unusually high temperature [22]. Figure 4 shows stresssensitivity of different asphalt binders at their PG tempera-ture.

Figure 4 shows two binders (PG 58–22 and PG 58–12)that are sensitive to 70 ◦C and four binders (PG 58–22, PG58–12, PG 64–22, and PG 70–22) that are sensitive to 76 ◦C.Three asphalt binders (PG 70–19, PG 70–16, and PG 76–16)are not even sensitive to 76 ◦C. As expected, PG 58–22 isthe most stress-sensitive, and PG 76–16 is the least stress-sensitive asphalt binder. Stress sensitivity of asphalt binderdecreases with an increase in binder PG. Also, no asphaltbinder was found stress-sensitive at its PG temperature.

A relative comparison of creep compliance at 3.2 kPa andat different performance grade temperature of asphalt binderswas carried out as reported in Table 2. The main purposeof this comparison was to investigate the variation of Jnr

of asphalt binders from G*/Sinδ at ω = 10 rad/s (whichis 2.2 kPa). In Table 2, Jnr values at different PG tempera-tures of different asphalt binders are highlighted for ease ofreaders.

One can observe from Table 2 that Jnr values at PG rangefrom 3 to 5 with an average value of 3.99 kPa−1, which isin line with what has been reported by D’Angelo, 2010 [26].Non-recoverable creep compliance is also presented in Fig.5, to ascertain the effect of temperature on Jnr at a tem-perature where G*/Sinδ is 2.2 kPa. Average values of Jnr

for PG 58–22, PG 58–16 (serial no. 1 and 2), PG 70–22,70–19, and PG 70–16 (serial no. 4, 5, and 6) have been usedin the plot. Increasing trends in Jnr values of asphalt binders(at a temperature when G*/Sinδ is 2.2 kPa) have been recordedwith an increase in testing temperature.

3.2 Binder Specification for Grade Bumping

Multi-stress creep recovery (MSCR) test has been used forgrade bumping of asphalt binders for different types of traf-fic levels. Grade bumping generally describes the potentialof an asphalt binder to hold its stiffness at the same SHRPcriteria of performance grading, even after a change in tem-perature by 6 ◦C. The Jnr values at 3.2 kPa stress level usingthe MSCR test were calculated for evaluating the standard(S), heavy (H), and very heavy (V) types of traffic. For aspecific temperature, the Jnr value at 3.2 kPa stress level isrecommended less than 4 (standard traffic), 2 (heavy traf-fic), and 1 kPa−1 (very heavy traffic), and the correspondingvalues of equivalent single-axle loads (ESAL) are less than

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Fig. 4 Stress sensitivity ofdifferent asphalt binders atvarying PG temperatures

30

40

50

60

70

80

90

100

52 58 64 70 76 82Pe

rcen

tage

Sen

stiv

ity

Temperature (oC)

58-22

58-16

64-22

70-22

70-19

70-16

76-16

SHRP 75% Limit

Table 2 Non-recoverable creepcompliance at temperaturewhere G*/Sinδ(at ω = 10 rad/s)is 2.2 kPa

Average Jnr value at PGtemperature (Italic values) =3.99.Coefficient of variation (%)=12.2.Values in italics indicate thenumbers used to take an averageof Jnr at PG temperature

Sr. No. PG of asphaltbinder

G*/Sin δ at PG (kPa) Jnr value at 3.2 kPa and temperature (kPa−1)

58 ◦C 64 ◦C 70 ◦C 76 ◦C

1 58-22 2.2 3.47 6.28 20.05 35.17

2 58-16 2.2 3.15 5.36 17.51 30.70

3 64-22 2.2 2.36 4.0 14.75 24.10

4 70-22 2.2 1.66 2.96 4.48 16.10

5 70-19 2.2 1.52 2.37 4.24 12.38

6 70-16 2.2 1.35 1.64 3.97 8.78

7 76-16 2.2 1.11 1.82 2.11 4.60

y = 0.0682x - 0.53R² = 0.95

2

2.5

3

3.5

4

4.5

5

52 58 64 70 76 82

Jnr

@ 3

.2kP

a (k

Pa-1

)

Temperature at which G*/Sinδ is 2.2kPa

Fig. 5 Non-recoverable creep compliance of asphalt binders at tem-perature where G*/Sinδ value is 2.2 kPa

10 million, 10 to 30 million, and greater than 30 millionESALs, respectively [26]. Multi-stress creep recovery testbinder specifications for different PGs, as a result of presentstudy, are shown in Table 3.

Table 3 suggests the utilization of asphalt binders at dif-ferent temperatures and traffic levels. It may be noted thatfor the same PG asphalt binder, suitable temperature limitsfor different types of loading vary significantly. Each asphaltbinder can be used for heavy loading below its PG tempera-ture. For example, Table 3 shows that PG 76–16 can be usedfor heavy loading up to a pavement temperature of 64 ◦C.Also, PG 70–16 shows different temperature limits than PG70–22 and PG 70–19.

3.3 Asphalt Mixtures

In the second phase of the study, the effect of asphalt binder(Jnr ) and addition of polymer on asphalt mixtures’ rut per-formance were investigated. The main aim of this phase ofstudy was to suggest correlation between the Jnr and mix-tures’ rut values. Therefore, four asphalt binders comprisedof PG 58–16 (neat 60/70 pen. grade), PG 70–22 (60/70 pen.grade with 1.35 % polymer), PG 70–19 (60/70 pen. gradewith 1.7 % polymer), and PG 76–16 (60/70 pen. grade with2.0 % polymer) were selected from Table 1.

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Table 3 Performance gradeselection of asphalt binders fordifferent traffic levels, usingMSCR test

Binder grade Suitabletrafficloading

Upper stresssensitivity limit (◦C)

Suitable temperature limitfor all type of loading

PG 58-22 S 58 58◦C@ standard traffic loading

PG 58-16 S 58 58◦C@ standard traffic loading

PG 64-22 S 64 64◦C@ standard traffic loading

PG 70-22 H 70 64◦C@ standard traffic loading

58◦C@ heavy traffic loading

PG 70-19 H 70 64◦C@ standard traffic loading

58◦C@ heavy traffic loading

PG 70-16 H 76 70◦C@ standard traffic loading

64◦C@ heavy traffic loading

PG 76-16 V.H 76 64◦C@ very heavy traffic loading

70◦C@ heavy traffic loading

0

20

40

60

80

100

0

% P

assi

ng

Sieve Size, mm(raised to power 0.45)

Density Line

Selected Gradation

0.075 0.3 0.6 1.18 2.36 4.75 9.5 12.5 19.0 25.4 37.5

Fig. 6 Aggregate gradation for asphalt mixtures

Single dense graded aggregate gradation with nominalmaximum aggregate size of 12.5mm, as shown in Fig. 6 waschosen for the preparation of asphalt mixtures.

Superpave method of mix design was used to prepareasphalt mixtures at about 4 % air voids [27]. Optimum asphaltcontents (by weight of mix) of different mixtures are shownin Table 4.

Slab specimens of 40.3 cm × 40.3 cm × 5.0 cm sizes werecompacted using a roller compacter at an air void ratio ofabout 6 %. Rut depth of asphalt mixtures was measured for20,000 passes of 700 ± 20 N loaded wheels at 58, 64, 70,and 76◦C. Wheel tracking test was run on the four asphaltmixtures to study the effect of polymer addition to asphaltbinders. A summary of final rut depth of asphalt mixtures ateach temperature level is shown in Table 4.

Data obtained from wheel tracker machine, as shown inTable 4, reveal that the asphalt mix with PG 76–16 offersmaximum rut resistance, and mixture with PG 58–16 showsminimum rut resistance at any temperature. At asphalt binder

PG temperature (at Jnr average value of 3.99 kPa−1), therut depths of four asphalt mixtures were recorded from 5to 6 mm. Rut development of mixtures in wheel trackingmachine at 76◦C has also been shown in Fig. 7, to ascertainthe temperature effect on mixtures. Figure 7 shows that thehigher the PG (that is the higher the percentage of polymer) ofasphalt binder, the more will be the resistance of the asphaltmixtures to rut development.

It may be noted that PG 70 with 1.7 % Elvaloy exhibitsmore resistance than that of 1.35 %, which is exactly in linewith the trends in the Jnr values. This shows that Jnr is agood indicator of rut prediction of asphalt mixtures.

The final rut depth, obtained from the wheel tracker at20,000 cycles, was compared with Jnr (at 3.2 kPa) values,at PG temperature (58, 64, 70, and 76◦C). Figure 8 shows atypical plot of final rut depth (x-axis) and Jnr (at 3.2 kPa ony-axis) of asphalt mixtures prepared with PG 76–16 binder at58, 64, 70, and 76◦C. Figure 8 also shows a strong relation-ship (R2=0.96) between non-recoverable creep complianceof asphalt binder and rut depth of asphalt mix obtained froma wheel tracker test.

The foregoing discussion reveals that non-recoverablecreep compliance of asphalt binder can be used to predictthe rut resistance of asphalt mixtures. Based on this index,asphalt mixtures can be designed using suitable grade ofasphalt binder for different traffic levels and environmentalconditions. It will be a useful index to predict the rut resis-tance of asphalt mixtures in the field. The rut developmentof an asphalt layer, prepared with an asphalt binder of differ-ent Jnr value, measured at different time period and trafficvolume, can be compared and utilized for the validation oflaboratory Jnr –rut resistance relationship. The present studyinvestigates the creep compliance effects of a single type ofpolymer. It would be useful to analyze different types of mod-ifiers for the purpose of obtaining their influence on mixtures’performance. Depending upon the type of modifier (polymer

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Table 4 Rut depth developmentin asphalt mixtures at 20,000wheel passes

Values in italics indicate rutvalue at PG temperature

Descriptionof mixtures

Optimum asphaltcontent (%)

Rut value (mm) (at 20,000 passes of wheel tracker machine)

58◦C 64◦C 70◦C 76◦C

PG 58-16 4.35 5.35 8.62 11.42 14.57

PG 70-22 4.47 4.76 5.51 6.97 10.38

PG 70-19 4.49 4.58 5.10 6.85 9.05

PG 76-16 4.57 2.13 2.95 3.34 4.77

0

2

4

6

8

10

12

14

16

0 5000 10000 15000 20000

Rut

Dep

th (

mm

)

Load Cycles (N)

Mix with PG 76-16

Mix with PG 70-19

Mix with PG 70-22

Mix with PG 58-16

Fig. 7 Development of rut depth in asphalt mixtures at 76 ◦C

Jnr= (1.3506*Rut Depth) - 2.044R² = 0.963

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 1 2 3 4 5 6

Jnr

at 3

.2 k

Pa (

kPa-

1)

Rut depth (mm)

PG 76-16

Fig. 8 Rut depth-Jnr correlation between asphalt mixtures and PG76–16 asphalt binder

or non-polymer), creep compliance may have different influ-ence on the performance of asphalt mixtures. Results of suchanalysis will help in developing the permanent deformationspecifications of asphalt mixes.

4 Conclusions

The following conclusions are drawn from this study:

• Temperature, stress level, and the addition of differentpercentages of Elvaloy polymer have significant effect

on the non-recoverable creep compliance (Jnr ) of asphaltbinders. However, the plots of asphalt binders show thatthe increase in Jnr value tends to be flatter up to a temper-ature, where G*/Sinδ value is 2.2 kPa.

• At PG temperature (where G*/Sinδ is 2.2 kPa), averageJnr value of asphalt binders is 3.99kPa−1, with a coeffi-cient of variation of 12.2 %. However, with an increase inPG temperature, the value of Jnr increases. This increasein Jnr with increasing temperature can be computed usingJnr = 0.068 (temp) −0.53, at R2 of 0.95.

• Percentage sensitivity, obtained from percentage recov-ery and non-recoverable creep compliance at different PGtemperatures, depicts grade bumping of asphalt binders,for different traffic loading conditions.

• The higher the PG of asphalt binder, the higher will be theresistance of asphalt mixtures to rut development. Non-recoverable creep compliance captures rut resistance ofasphalt mixtures. Reasonable relationship exists (R2= 0.96)between the rut depth of asphalt mixtures, obtained fromwheel tracker machine, and Jnr of an asphalt binder.

• Present study may be expanded in the future to validateasphalt mixtures’ field performance with non-recoverablecreep compliance. The rut development of an asphalt layer,prepared with asphalt binders of different Jnr value, mea-sured at different time period and traffic volume, can becompared and utilized for the validation of laboratory Jnr –rut resistance relationship. The present study, also, sug-gests investigating the effect of other types of modifiers onrelationships between non-recoverable creep complianceof asphalt binders and rut resistance of asphalt mixtures.The outcome of the study can be utilized in the develop-ment of high temperature permanent deformation specifi-cations for asphalt mixes.

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