COMPARISON OF LOW TEMPERATURE FIELD PERFORMANCE.pdf

7/28/2019 COMPARISON OF LOW TEMPERATURE FIELD PERFORMANCE.pdf

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COMPARISON OF LOW TEMPERATURE FIELD PERFORMANCE AND

LABORATORY TESTING USING TEN TEST SECTIONS IN THE MIDWEST

Submission date: August 1, 2008

Word count: 3924 plus 3 tables and 10 figures

Adam Zofka (corresponding author)Assistant Professor

Department of Civil and Environmental Engineering

University of Connecticut

261 Glenbrook Road Unit 2037, Storrs, CT 06269-2037Tel: (860) 486-2733, Fax: (860) 486-2298, Email: [email protected]

Andrew BrahamGraduate Research Assistant

Department of Civil and Environmental EngineeringUniversity of Illinois at Urbana-ChampaignB226 NCEL, MC-250, 205 N Mathews Ave, Urbana, IL 61801

Tel: (217) 244-5526, Fax: (217) 333-1924, Email: [email protected]

Submitted for Presentation and Publication at the 88th

Annual Meeting of the

Transportation Research Board

TRB 2009 Annual Meeting CD-ROM Paper revised from original submittal.


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Zofka, Braham 2

ABSTRACT

When evaluating asphalt mixtures for low temperature performance, current standards are based

heavily on asphalt binder properties. This approach does not take into account interaction

between the binder and aggregate, both chemically and physically. This interaction has been

shown to have significant influence to the cracking resistance of asphalt mixtures. This paperinvestigates three laboratory tests that evaluate cracking resistance of asphalt mixtures at low

temperatures. The first test is the traditional tensile strength test, the Indirect Tensile Test (IDT).The two other tests are fracture tests: Semi-Circular Bending (SCB) and Disk-Shaped Compact

Tension [DC(T)]. Field cores were obtained from ten pavement sections in Minnesota and

Illinois for testing in the lab. Results from the three laboratory tests were compared and

correlated with field performance data. Results showed that the tensile strength from the IDT didnot vary significantly for the ten mixtures. The SCB and DC(T) correlated relatively well to

each other depending on the test temperature. The SCB showed the best correlation and highest

Spearmans rank correlation coefficient when comparing to the observed quantity of cracking inthe field. It was concluded that the laboratory fracture tests, either SCB or DC(T), are better

suited for qualitative cracking performance predictions at low temperatures compared to the IDT.For quantitative predictions, it is recommended to apply advanced analytical and/or numericalmodels that take into account material properties, environmental conditions, and loading

conditions. It is also recommended that additional studies comparing laboratory fracture

parameters with the field performance should be conducted.



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Zofka, Braham 3

INTRODUCTION

Low temperature thermal cracking can cause major damage of asphalt pavements in cold climate

regions. In order to minimize the damage and reduce user-delay costs, asphalt mixtures should be

designed and constructed with materials that are able to sustain the stresses induced by the

combination of the cold temperatures and traffic loads. When evaluating asphalt mixtures for lowtemperature performance, current standards are based heavily on asphalt binder properties. This

approach does not take into account interaction between the binder and aggregate, bothchemically and physically. The Indirect Tension Test (IDT) is the only test widely used for

evaluating asphalt mixtures at low temperatures. The IDT measures bulk material properties,

such as dynamic modulus and creep compliance, and also the separation of asphalt mixtures.

Bulk properties measure how the material acts as a whole, while separation properties focus onthe asphalts response to coming apart.

Recent research demonstrated that fracture tests are able to capture low temperature

properties of asphalt mixtures [1]. Low temperature properties can be categorized as separationproperties, which can be captured through fracture tests. This study reviewed the results from

two fracture tests, the Semi-Circular Bend Test (SCB) and the Disk-Shaped Compact TensionTest [DC(T)], and compared these tests to IDT results and field performance on ten pavementsections in Minnesota and Wisconsin.

OBJECTIVES

There were three objectives to this study:

Compare the results from three low temperature cracking testing procedures Compare field performance of ten pavement sections with results of laboratory testing

from asphalt mixtures from the ten pavement sections

Identify the laboratory procedures that can be used as practical indicators of low

temperature cracking performance in the field.

MATERIALS AND TESTING

Materials

The materials used in this study were a part of a National Pooled Fund Study on low temperaturecracking in asphalt pavements [1]. This study focused on materials collected from ten pavement

sections. Five of the sections were MnROAD test sections: Cell 3, Cell 19 and Cells 33-35. The

other five sections came from two sections of CSAH-75 in Minnesota, two sections of US-20 inIllinois, and one section of I-74 in Illinois. The details on these ten sections are presented in

Figure 1.



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Zofka, Braham 4

HMA PG58-28

crushedgranitebaseclass5

HMA PG58-34

crushedbaseclass5

HMA PG58-34

recycledmix(32B)

4 (1999) siltyclaysubgrade,constructedin1994Cell33

12

HMA PG58-34crushedgranitebase

class5


HMA PG58-40

crushedgranitebaseclass5


12

HMA 120/150

crushedbaseclass5

6.3 (1992) siltyclaysubgrade,constructedin1992Cell3

4

crushedsubbaseclass3 33

Cell3

4

33

HMA PG AC-20

crushedbaseclass3

7.8 (1992) siltyclaysubgrade,constructedin1992Cell19

28

2 (1996) sand-gravelsubgradeconstructedin1955CSAH75WB 2

2.5

~12

HMA PG58-34

crushedbaseclass5

recycledmix(32B)

2 (1996) sand-gravelsubgradeconstructedin1955CSAH75EB 2

2.5

~12

recycledmix(42B)

AC-10, AC-20

AC-10, AC-20(19mm)

1.5 (1986)US-20,IL

w/rock-nodrainsw/soilhasdrains

11.5

varies

AC-20

AC-20(19mm)

1.5 (1992)I-74,IL

lime-stabilizedsubgrade

15.5

12

FIGURE 1 Structure and material of ten pavement sections.

Cells 33-35 were located in Low Volume Road (LVR) loop, were constructed in 1994

and rehabilitated with the top asphalt layer in 1999. These three cells from the LVR loop had

identical pavement structures. During rehabilitation, the same Superpave mix design for the top



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asphalt layer was used, with the grade of the asphalt binder as only difference. Cells 3 and 19

from MnROAD were originally constructed in 1992 as a part of the mainline MnROAD.County State Aid Highway (CSAH) 75 in Minnesota was originally constructed in 1955

and it underwent major re-construction in 1996. At that time, it was one of the first local projects

in Minnesota that used Superpave mix design combined with polymer modified binder. The top

asphalt layer in the westbound section was constructed with 19.0mm Nominal MaximumAggregate Size (NMAS) mix while a 12.5mm NMAS mix was placed in the eastbound section.

The two pavement sections on Illinois US-20 were a part of a demonstration project in1986 that evaluated a mechanistically-based pavement design procedure. These two sections

were built in series, with identical pavement structure except for the asphalt binder used. Both

mixtures used a 19.0mm NMAS, one with an AC-10 binder and the other with an AC-20. The

third mixture from Illinois was a section of I-74 running through Champaign-Urbana. Thispavement section was constructed in 1990-1991 as a full depth asphalt pavement that replaced a

poorly performing Continuously Reinforced Concrete Pavement. The samples were taken

immediately before a 4-inch mill and overlay in 2006. Since then, the pavement structurecontinues to perform very well. More information on these ten test sections can be found

elsewhere [2, 3, 4].

TestingAfter obtaining field cores from the ten pavement sections, each core was measured for density

and processed in the laboratory to prepare specimens for testing. Specimens from each sectionwere tested in three different experimental configurations: the Indirect Tensile Test (IDT, creep

and strength), the Semi-Circular Bending (SCB) test, and Disk-Shaped Compact Tension

[DC(T)] test. All ten asphalt mixtures from the pavement sections were tested in each

experimental configuration at three different temperatures. These three test temperatures wererelated to the low PG grade of the binder used in each mixture. For example, the mixture from

Cell 34 with PG 58-34 binder was tested at -12C (Hlevel), -24C (Ilevel) and -36C (L level).

There were 3 replicates at each temperature level for all mixtures for a total of 90 tests in eachtesting configuration, and 270 tests total. The identification system used in this research, the

binder grade, and the final test temperatures are shown in Table 1.

TABLE 1 Field sections and test temperatures.

SiteDesignation

name

Original

binder

grade

Equivalent

binder

grade

Test

temperatures

(IDT, SCB)

Test temperatures

(DCT)

Temperature1

-> H I L H I L

MnROAD Cell 03 MnROAD 03 120/150 PG 58-28 -6 -18 -30 -6 -18 -30

MnROAD Cell 19 MnROAD 19 AC-20 PG 64-222

-12 -24 -36 0 -12 -24

MnROAD Cell 33 MnROAD 33 PG 58-28 PG 58-28 -6 -18 -30 -6 -18 -30



MN CSAH-75,

section 2 EBMN75 2 PG 58-28 PG 58-28 -6 -18 -30 -6 -18 -30



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MN CSAH-75,

section 4 WBMN75 4 PG 58-34 PG 58-34 -12 -24 -36 -12 -24 -36

IL US-20,

section 6IL US20 6 AC-10 PG 58-28

3-6 -18 -30 -6 -18 -30

IL US-20,

section 7IL US20 7 AC-20 PG 64-22

2,3-12 -24 -36 0 -12 -24

IL I-74 IL I74 AC-20 PG 64-222,3 -12 -24 -36 0 -12 -241

H high (PG+10)+12, I intermediate (PG+10), L low (PG+10)-122

test temperatures (for SCB and IDT) based on PG 64-343IDT not performed due to thin AC layer

The IDT setup was used to perform the 1000sec creep test and the tensile strength testaccording to AASHTO T322-03 [5]. A schematic of the IDT test is presented in Figure 2.

During the creep test, a constant load was applied to the specimen for the 1000sec while vertical

and horizontal displacements were measured around the center of the specimen using transducersmounted on both faces of the specimen. The creep compliance was determined from

displacements using appropriate identification procedure from AASHTO T322-03. In a separate

device, the coefficients of thermal contraction for each mixture were measured usingdilatometric method [6]. Next, measured creep compliance and coefficients of thermal

contraction were used in thermal stresses calculations using similar approach to TCMODEL

which is a part of Mechanistic Empirical Pavement Design Guide [7, 8]. After the nondestructiveIDT creep tests were conducted, the destructive tensile strength was run. The tensile strength

test used a 12.5mm/min loading rate until specimen failure.

ACspecimen

Transducers

FORCE

FIGURE 2 IDT creep and strength experimental setup.

Semi Circular Bending (SCB) test was performed to determine fracture toughness KICand fracture energy G of the asphalt mixture [9, 10]. The computation of fracture toughness

implies that the material tested does not have softening characteristics. Some researchers believe



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that at low temperatures, asphalt mixtures do not have softening characteristics, while other

researchers believe that asphalt mixtures have softening characteristics at all temperatures. Forthe SCB, it was assumed that these asphalt mixtures did not have softening characteristics.

Therefore, KIC was measured in the SCB testing configuration. The load was applied vertically at

the top of the semi-circular specimen and the load line displacement (LLD) was measured using

a vertically mounted transducer, as seen in Figure 3. The samples were 150mm wide, 75mm tall,25mm thick, with a ligament length of 60mm. The load applied during the test varied to sustain

a constant rate of the crack mouth opening displacement (CMOD) gauge mounted at the bottomof the specimen, 0.03mm/min. The fracture toughness was calculated through Equation 1 [9]

=ICK k

PaY

DB Equation 1

Where KIC = fracture toughness (MPa m0.5

)P = applied force (N)

D, B = specimen dimensions (diameter, thickness) (m)

a = crack length (m)Yk= dimensionless stress intensity factor which is a function of the dimensionless

crack length, a/D.

The fracture energy is found through Equation 2

lig

fA

PduG

= Equation 2

Where Gf= fracture energy (J/m2)

P = load (kN)

u = CMOD opening (m)Alig = area of ligament (m2).

ACspecimen

LLDTransducer

CMODTransducer

FORCE

FIGURE 3 SCB experimental setup.

The Disc-Shaped Compact Tension test, DC(T), was recently adopted for asphalt

mixtures to determine low-temperature fracture properties of cylindrically-shaped specimens [11,



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12, 13]. The specimen is 150mm tall, 145mm wide, 50mm thick, with a ligament length of

82.5mm. The DC(T) test was performed under tensile loading at the loading holes. The crackmouth opening displacement (CMOD) was measured with a clip-on gage at the face of the crack

mouth (Figure 4). The test was controlled through a constant CMOD rate (1 mm/min) to provide

a stable post-peak fracture. The fracture energy is calculated by determining the area under the

load-CMOD curve normalized by initial ligament length and thickness.

CMODTransducer

FORCEACspecimen

FIGURE 4 DC(T) experimental setup.

The SCB and DC(T) tests output was recorded as a plot of the load versus the crack mouth

opening displacement, or the CMOD. Figure 5 shows an example plot of the output of the

fracture tests at high, medium, and low testing temperatures. As the temperature increased, thefracture energy increased because the softening curve was more shallow.

0 1 2 3 4 5 60.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

CMOD [mm]

Load[kN]

Lowest Test Temp.

Intermediate Test Temp.

High Test Temp.

FIGURE 5 Typical fracture curves at high, intermediate, and lowest test temperatures.



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RESULTS

The results of this study are presented in two parts. The first part shows the direct comparison of

the three low temperature laboratory testing procedures on the ten asphalt mixtures. The second

part shows the comparison of the laboratory results and field performance for from the ten

pavement sections in Minnesota and Illinois.

Comparison of Low Temperature Laboratory ResultsThe correlation between fracture energy determined from SCB and DC(T) tests depended on the

test temperature level, as seen in Figure 6. Better correlation was obtained at the intermediate

and low temperatures. It is believed that this discrepancy was primary due to different CMOD

rates as well as due to different specimen shape and dimensions used in both tests. For example,the ligament area for the SCB was 1500mm2, while the ligament area for the DC(T) was

4125mm2. Since asphalt mixtures are very heterogeneous, the placement of aggregate within

this ligament area could significantly effect the resulting fracture energy. The correlationbetween the two tests could also be slightly improved if the potential outliers were removed. In

addition, it appeared that with an increase of testing temperature, the fracture energy increasedand the spread of the replicates increased. This could occur because at lower temperatures, theasphalt cement and aggregate had similar stiffness, which caused a brittle failure with a small

softening curve. However, at warmer temperatures, the asphalt cement is more ductile, which

causes the cracks to move through the softer material, and increase the softening curve.However, since asphalt mixtures are heterogeneous, that indicates that the cracks will probably

have to move around the aggregate, giving less consistent results.



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0 200 400 600 8000

200

400

600

800

DC(T) Fracture Energy [J/m2]

SCBFractureEnergy[J/m2]

Lowest Test Temperature

R2=0.5146

100 500 900 1300 1700100

500

900

1300

1700


SCBFractureEne

rgy[J/m2]

High Test Temperature

R2

=0.1932

300 600 900 12000

300

600

900

1200


SCBFractureEnergy[J/m2]

Intermediate Test Temperature

R2=0.6063

FIGURE 6 Correlation between fracture energy from DC(T) and SCB tests.

The correlation between the IDT strength test and the two fracture tests was weak

regardless of the temperature level. Figure 7a shows a correlation between IDT strength and

DC(T) facture energy at low temperatures. The range of IDT strength results is relatively smalland the test poorly differentiates between various sites. The IDT strength value provides only a

snapshot of the material toughness whereas fracture tests captured material crack absorption

over entire damage process. The peak load, which is used in the calculation of fracturetoughness, was similar in concept to the IDT strength as it also is just a single reading off the

experiment, as seen in Figure 5. Reasonably, IDT strength correlated better with fracturetoughness, as seen in Figure 7b.



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Zofka, Braham 11

0 200 400 600 8000

2

4

6

8


IDTTensileStren

gth[MPa]


R2=0.1187

0 0.2 0.6 0.9 1.20

2

4

6

8

SCB Fracture Toughness [MPa*m0.5

]

IDTTensileStren

gth[MPa]


R2=0.4103

(a) (b)

FIGURE 7 Correlation between IDT tensile strength and a) fracture energy from DC(T),

b) SCB fracture toughness, for low temperature group.

Based on the Analysis of Variance (ANOVA) and multiple comparisons, it was found

that on average IDT tensile strength results at the intermediate temperatures are statistically

different from the low temperature results. However, there was no statistical difference betweenthe results from the high temperature group and either intermediate or low group results. The

graphical summary of this comparison is shown in Figure 8.

High Temp. Intermed. Temp. Low temp.0

1

2

3

4

5

6

7

8

IDTTensileStrength[MPa]

MN 75 2

MN 75 4

MnRoad Cell 03

MnRoad Cell 19MnRoad Cell 33

MnRoad Cell 34

MnRoad Cell 35

FIGURE 8 IDT tensile strength results.



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One of the tools used currently in pavement evaluation is TCMODEL [7, 8]. TCMODELrequires creep compliance and coefficients of thermal contraction to determine the critical

cracking temperature, Tcr. As a part of the low temperature cracking study [1], the University of

Wisconsin Madison measured the coefficients of thermal contraction for the ten pavement

sections using the dilatometric method [6]. Thermal stress curves and the creep complianceallowed the determination of Tcr. The Tcr calculated from TCMODEL was compared with a low

PG grade limit of the binders that were originally used in the construction of the sections, as seenin Figure 9. A relatively weak trend could be observed between these two parameters, but T cr was

consistently lower than the low binder grade. This relationship implied that the PG grading

system and TCMODEL are correlated, but due to the aging process in the field, the field

materials became brittle and gave lower Tcr values. In addition, the IDT measurements, bothcreep compliance and strength that provide data for Tcr calculations, were not able to fully

distinguish between materials.

40

35

30

25

20

15

10

5

0

Calculate

dCriticalCrackingTemp.TCR

[oC]

MnROAD 35

MN 75 4

MnROAD 34

MN 75 2MnROAD 33

MnROAD 03

MnROAD 19

PG... 40PG... 34

PG... 28

PG... 22

FIGURE 9 Comparison of low PG grade and critical cracking temperature calculated

from TCMODEL.

Comparison of Low Temperature Laboratory and Field Results

In order to ensure that field data and laboratory results were compared at similar conditions, thelaboratory fracture energy, fracture toughness, and indirect tensile strength values were

interpolated to the LTPP low-pavement temperature. Low-pavement temperature values were

obtained at 50% reliability level from LTPPBIND software [14] using the weather stations in theclosest vicinity to considered test sites. The station and low-pavement temperatures are presented

in Table 2.



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TABLE 2 LTPP low-pavement temperatures.

Site StationLTPP low-pavement

temperature [C]

MN75 Collegeville, MN -24.4

MnROAD Buffalo, MN -23.8

US20 6 Freeport, IL -19.7

IL I74 Urbana, IL -16.4

The comparisons between laboratory parameters and field performance data are shown inthe semi-log plots of Figure 10. Field performance was measured as the length of cracking in feet

per 500 feet of pavement section. Several points were observed:

IDT tensile strength and SCB fracture toughness correlated in a similar manner withfield cracking data. This confirmed the earlier observation that these laboratory

parameters provide similar information on the material response.

SCB fracture energy shows the best correlation with the field data for these tenpavement sections.

Visually, all four parameters exhibit similar trend: the lower the parameter value, themore cracking occurs in the pavement.

Correlation for DC(T) fracture energy seems to be weak primary due to one potentialoutlier point without which the R

2increases to 0.22.



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1 10 100 1000 100000

1

2

3

4

5

6

7

8

Transverse cracking [ft/500ft]

IDTTensileStrength[MPa] R

2=0.41

1 10 100 1000 100000

200

400

600

800

1000

1200


DC(T)FractureE

nergy[J/m2] R

2=0.19

1 10 100 1000 100000

0.2

0.4

0.6

0.8

1

1.2


SCBFractureToughness[M

Pa*m0.5]

R2=0.41

1 10 100 1000 100000

100

200

300

400

500

600

700


SCBFractureEnergy[J

/m2]

R2=0.56

FIGURE 10 Comparison of laboratory parameters and field performance data.

Another method for comparing the data is presented in Table 3. Spearman's rankcorrelation coefficient was determined by calculating Pearson correlation coefficient on the

ranked data. In this way, two tests can be compared not in terms of the absolute values but in

terms of how closely they rank the data. From Table 3, it can be concluded that fracture tests, in

general, rank better the data than IDT strength test. Also, the SCB fracture energy has thehighest rank correlation with field data.

TABLE 3 Spearman's rank correlation coefficient.

DC(T) Fracture

Energy

[J/m2]

SCB Fracture

Toughness

[MPa*m^0.5]

SCB Fracture

Energy

[J/m2]

IDT Tensile

strength

[MPa]

-0.527 -0.588 -0.855 -0.393

SUMMARY AND CONCLUSIONSIn this study, low temperature properties of asphalt mixtures were evaluated in the laboratory

conditions using three experimental configurations. The comparison of the experimental resultsshowed good correlation between two fracture tests, the SCB and DC(T), especially at lower and

intermediate test temperatures. It is believed that the discrepancy between these two tests is



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Zofka, Braham 15

caused primary by different specimen geometry and loading rates applied during the tests. Also,

it was observed that correlation between fracture energy from either of the fracture tests and theIDT strength results was poor since both parameters measure conceptually different phenomena.

Fracture energy measured material ability to resist cracking over entire test duration whereas

IDT strength gave only a point measure at the peak load. Further analysis of the IDT results also

showed that the IDT strength results obtained at high test temperatures are not statisticallydifferent from the values measured at the intermediate or lowest temperatures.

The results from experimental evaluation were compared with the quantity of crackingobserved in the pavement. SCB fracture energy showed the best correlation with the field data

for a considered dataset and it also had the highest rank correlation coefficient. IDT strength and

SCB fracture toughness exhibited similar correlation with field data, while the DC(T) fracture

energy produced the weakest correlation due to an outlier point.The data presented in this study showed that laboratory fracture experiments, either SCB

or DC(T), are best suited for qualitative cracking performance predictions at low temperatures.

More detailed predictions can be made with advanced analytical and/or numerical models whichconsider not only material properties and whole pavement structure but also environmental and

loading conditions throughout entire service life of the pavement [15]. By combiningenvironmental and traffic loads, advanced models can explain abnormal behavior of otherwisesuperior materials, such as PG 58-40 mixture that is presented in Figure10. That material from

MnROAD Cell 35, showed significant amount of cracking that can be explained only by

combining thermal and traffic loading [1].It is recommended to perform similar studies that compare laboratory fracture parameters

with field performance data using different mixture types and different test sections at various

climate conditions. This study only looked at a small geographic area in the north-central United

States. Collected data should be also used for further verification and validation recentlydeveloped advanced thermal cracking models.

ACKNOWLEDGEMENTThe work in this paper was sponsored by Federal Highway Administration National Pooled Fund

Study 776. This support is gratefully acknowledged. The results and opinions presented are

those of the authors and do not necessarily reflect those of the sponsoring agencies. The authorsalso acknowledge Dr. Mihai Marasteanu of the University of Minnesota and Dr. William Buttlar

of the University of Illinois for providing the resources and equipment to run these tests, and

providing the leadership for the authors during testing and analysis.

REFERENCES

1. Marasteanu M., et al.,Investigation of Low Temperature Cracking in Asphalt Pavements,National Pooled Fund Study 776 report, 2007.

2. Clyne T. R., Worel B. J., Marasteanu M.,Low Temperature Cracking Performance at

MnROAD. Minnesota Department of Transportation, report, 2006.3. Worel B. J., Andersen T., Mulvaney R.,MnROAD 1999 Superpave Construction Report

(Cell 33-35). Minnesota Department of Transportation, report, 2003.

4. Li X., Zofka A., Li X., Marasteanu M., Clyne T. R.,Investigation of the Low-Temperature

Fracture Properties of Three MnROAD Asphalt Mixtures. Minnesota Department of

Transportation, report, 2006.



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Zofka, Braham 16

5. American Association of State Highway and Transportation Officials (AASHTO) Standard

T 322-03.Determining the Creep Compliance and Strength of Hot-Mix Asphalt (HMA)

Using the Indirect Tensile Test Device. Standard Specifications for Transportation Materials

and Methods of Sampling and Testing, 25th Edition, 2005.

6. Bahia H.U. Anderson D.A., Glass Transition Behavior and Physical Hardening of Asphalt

Binders, Proceedings of the Association of Asphalt Paving Technologists, Vol. 62, pp. 93-129, 1993

7. Mechanistic Empirical pavement Design Guide (MEPDG), version 1.003, built 5/24/20078. Hallin J. P. et al.,Development of the 2002 guide for the design of new and rehabilitated

pavement structures: Phase II, Report for National Cooperative Highway Research

Program, Transportation Research Board, National Research Council, 2004

9. Chong K.P., Kuruppu M.D.,New Specimen for Fracture Toughness Determination for Rock

and Other Materials, International Journal of Fracture, Vol. 26, R59-R62, 1984

10. Molenaar J. M. M., Molenaar A.A.A., Fracture Toughness of Asphalt in the Semi-Circular

Bend Test, Proceedings of the 2nd Eurasphalt and Eurobitume Congress, Barcelona, Spain,2000

11.

ASTM D 7313-07, Test Method for Determining Fracture Energy of Asphalt-AggregateMixtures Using the Disk-Shaped Compact Tension Geometry, 200712. Braham A. F., Buttlar W. G., Marasteanu M.,Effect of Binder Type, Aggregate, and Mixture

Composition on Fracture Energy of Hot-Mix Asphalt in Cold Climates, Journal of the

Transportation Research Board, Vol. 2001, pp. 102-109, 200713. Wagoner M.P., Buttlar W.G., Blankenship P.,Investigation of the Fracture Resistance of

Hot-Mix Asphalt Concrete Using a Disk-shaped Compact Tension Test, Journal of the

Transportation Research Board, Vol. 1929, pp. 183-192, 2005.

14. LTPPBIND, ver. 3.1 Beta, Sept. 15, 2005, developed for Federal Highway Administration15. Dave E. V., Braham A. F., Buttlar W. G., Paulino G. H., Integration of Laboratory Testing,

Field Performance Data, and Numerical Simulations for the Study of Low-Temperature

Cracking, Proceedings of Sixth RILEM (Runion Internationale des Laboratoires et Expertsdes Matriaux) International Conference on Cracking in Pavements, Chicago, pp: 369-378,

June 16-18, 2008.

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