Hafeez Rutting Prdeiction of Asphalt Mixtures

Corresponding Author, Tel: +989121713297 Transportation Research Journal, Vol. 2, No. 1, 2012/ 25 E-mail address: [email protected]

Transportation Research Journal 1 (2012) 25-36

Rutting Prediction of Asphalt Mixtures from Asphalt Cement

Imran Hafeeza, Mumtaz Ahmad Kamalb, Mohammad Reza Ahadic*

a. Assistant Professor, Department of Civil Engineering, University of Eng. & Tech. Taxila, Pakistan. b. Professor, Department of Civil Engineering, University of Eng. & Tech. Taxila, Pakistan.

c. Assistant Professor, Transportation Research Institute, Iran university of Science and Technology, Tehran, Iran. Received: 6 June 2011 – Accepted: 16 October 2011

ABSTRACT Asphalt cement is a visco-elastic material used for cementing materials in preparation of hot mix asphalt. Its

performance in the field mainly depends on the size and proportions of aggregates of hot mix asphalt being used. The main objective of this study was to characterize asphalt cement and to investigate the influence of asphalt cement on the rutting of asphalt mixture. Two bituminous binders (PG76-22 and PG 58-16) and two aggregate gradations (coarse and fine) were selected to study their effect on the mixtures rutting behavior. A wheel tracking test and a dynamic modulus test were selected to determine the rutting potential of asphalt mixtures at different temperature levels. The study revealed that high performance grade bitumen with fine aggregate gradation may offer more resistance to rutting than low grade bitumen with coarse aggregate gradation. The master curve technique can be used to predict asphalt mixtures’ rutting performance from asphalt binders. Complex shear modulus of asphalt binder and mixtures can fairly be correlated with each other. Keywords: Hot Mix Asphalt, Performance Testing, Dynamic Modulus, Wheel Tracker Machine, Master Curves

1- Introduction Bitumen commonly known as asphalt cement

(AC) is a viscoelastic material used for binding materials in road pavements (Soleimani, 2009). Its deformation and flow measurement in the laboratory, when subjected to stress, explains the elastic and viscous behavior. Complex modulus (G*) and phase angle (δ) are considered to be the principal rheological parameters, normally measured from a device known as a Dynamic Shear Rheometer (DSR) (Huang, Shin-Che et.al 2007).A number of studies had been conducted to investigate asphalt binder rheology (Tarefder Zaman 2003 & Kanitpong, Bahia, 2005).

Asphalt concrete is a generally a mixture of bitumen and aggregates used for the construction of road pavements. An accumulation of small strain values under repeated cycles of loading is commonly known as rutting (Faheem and Bahia, 2004). Performance of asphalt mixtures in terms of linear viscoelastic behavior can be predicted using stress-strain behavior which can be defined by a dynamic or complex shear modulus test or wheel tracker machine (Loulizi, Flintsch, Al-Qadi and Mokarem, 2006). Dynamic modulus (E*) is the ratio of the absolute value of the peak to peak shear stress by the absolute value of the peak to peak shear strain under

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sinusoidal loading conditions (Anderson and Christensen, 1992). The master curve enables fundamental characterization of asphalt concrete in which the time and temperature dependencies can be fully described. Various functional forms like the sigmoidal fitting function can be used to mathematically model the response of asphalt mixes (Pellinen and Witczak, 2002).

(Colbert and Zhanping 2012) characterized the rheological properties of asphalt binders extracted from a recycled asphalt pavement (RAP) mixture and observed significant differences in dynamic shear moduli master curve performance for high percentage RAP binder blends versus virgin binders at the three aging states (Colbert and Zhanping,2012.). Nur et al. (2011). Reports based on existing literature stated that the use of reliable models can in general be considered as a valuable alternative tool for estimating the Linear viscoelastic rheological properties of bitumen. (NurIzzi, et al. (2011) recommended the significance of creep compliance on G*/sinδ in predicting the rutting behavior of asphalt mixtures. (Wasage et al, 2011) Kumar et al (2011) studied the effect of styrene butadiene styrene (SBS) polymer and crumb rubber modified asphalt binders on asphalt mixtures’ dynamic mechanical behavior using dynamic modulus, dynamic and static creep tests at varying temperatures and frequency levels. It was revealed that the mechanical response of the SBS polymer modified asphalt binders were significantly correlated with the rutting resistance of asphalt concrete mixes (Kumar et al, 2011).

The relationship between the dynamic modulus in compression |E*| of the asphalt mixer to the G*, and the complex shear modulus of the binder developed through engineering mechanics were generated by equation 1 (Charles et al, 2003);

E 2 1 µ G (1)

The effectiveness of binder’s stiffness can be used to predict the mixture’s stiffness and can be studied using a different mode of testing. Interaction of low and high performance grade bitumen with coarser and finer aggregate gradation in rut prediction would be an interesting phase. The wheel

tracking machine and dynamic modulus testing can be used to compare with the results of frequency sweep testing on asphalt binders.

2- Objectives To characterize the asphalt mixtures using a high

and a low grade asphalt binder and a coarse and a fine aggregate gradations.

To find out the possible correlation between asphalt binders and asphalt mixtures using the master curve techniques.

To develop any possible relationship between wheel tracker rutting with binder rut factor

3- Experimental program The experimental program comprises of testing

individual binders and aggregates followed by their combined mixture’s testing on two different testing protocols.

3-1-Binders PG76-22 and PG58-16 were collected from

single source. These binders were used on highways and motorways which have been carrying approximately 75% of the total road freight in Pakistan. Rolling Thin Film Aging Oven aged specimens were used in binder testing (AASHTO T 240). Sinusoidal, oscillatory stress over a range of temperatures and loading frequencies were applied to a 25 mm diameter and 2mm thin disc of asphalt binder using Dynamic Shear Rheometer (AASHTO T 240, 2004). Dynamic Shear Rheometer was applied to determine the phase angle and Complex Shear Modulus at different temperatures and frequency ranges (AASHTO, 1995).

Master curves were constructed and accordingly, shift factor and sigmoidal function were computed to check the accuracy of the data.

3-2- Asphalt mixes Four asphalt mixtures were prepared using two

binders and two aggregate gradations namely Class-A (Coarser) and Class-B (Finer) using the National Highway Authority from Pakistan. The specifications are shown in Figure 1 (National Highway Authority, 1998).

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Corresponding Author, Tel: +989121713297 Transportation Research Journal, Vol. 2, No. 1, 2012/ 28 E-mail address: [email protected]

Table 1. Stress levels at each temperature in Dynamic Modulus Test

Description Temperatures (oC)

25 40 55

Stress Level (kPa) 700, 500 300 250, 200 150 70, 50, 30

Figure 2. Sinusoidal loading pulse pattern in dynamic modulus testing (Geoffrey, Rowe and Sharrock, 2000)

Figure 3. Wheel Tracker Machine (Cooper Technology, 2006)




Transportation Research Journal, Vol. 2, No. 1, 2012 /29

Table 2. Experimental Program

Step No. Descriptions Details of activities in the experimental design

1 Materials

Asphalt Binders

PG58-16 (neat binder 60/70 pen. grade)

PG 76-22 (modified binder prepared using 60/70 pen. grade with 1.65% Elvaloy)

Asphalt Mixtures

PG76-22 +Class-A

PG76-22 +Class-B

PG58-16 +Class-A

PG58-16 +Class-B

2 Testing machine/

Procedures Frequency sweep test at Dynamic Shear Rheometer

i) Dynamic modulus testing at NU-14 (AASHTO TP 62) ii) Wheel Tracker Test (EN, 2003)

3 Testing Conditions Frequency:100 to 1Hz Temperature ; 25, 40, 55oC

Frequency: 25 to 0.1Hz Temperature ; 25, 40, 55oC 53 Passes per minute on Wheel Tracker

4 Output parameters Complex shear modulus (G*) Phase angle (δ)

Dynamic modulus (E*) Phase angle (φ)

5 Characterization Master curves development Shift factor computation, Sigmoidal parameters of best fit

Master curves development Shift factor computation, Sigmoidal parameters of best fit

6 Generating the Correlations

Comparison of G* and E* master curves on single plots and development of relationships at highest degree of determinacy. Correlation between Log G* and E*.

7 Wheel Tracker

Testing Rut development history of asphalt mixtures using wheel tracker machine.

A summary of the experimental program has been reported in Table 2 in order to understand the volume of work and the testing methodology.

4- Results and Discussions

4-1-Test results Two binders and four mixes were studied under

different times and temperature conditions. Master curves were developed to evaluate the relationship between the complex modulus and the phase angle at different frequency levels. Shift factor curves were also plotted to determine temperature sensitivity of binders and mixes. Results showed that the temperature and frequency of loading had a significant influence on the behavior of asphalt. The complex modulus decreases with an increase in test

temperature under a specific loading frequency, whereas it increases with an increase in frequency at a specified temperature. This shows that the elastic portion of viscoelastic property decreases or is reduced over a range of temperatures from 25oC to 55oC. The complex shear modulus and phase angle values of binders have been reported in Table 3. The phase angle values of the binders mostly ranged between 70o and 87o, whereas for mixes it ranged from 12o to 33o. These values of phase angles, for both asphalt binders and mixtures, confirm the results of previous research and are in accordance with their limits. Also, The phase angle of the above asphalt mixtures are three times less than the corresponding asphalt binders at any temperature and frequency level. The reduction is mainly contributed by the aggregates in the mixtures.



Table 3a. Complex shear modulus (G*) of asphalt binders

Temperature Description

PG76-22 (PMB)

PG58-16 (60-70Grade Bitumen)

G*at 0.1Hz(MPa)

Phase Angle (δ) G*at 0.1Hz

(MPa) Phase Angle (δ)

25oC A

spha

lt B

inde

rs 20.72 72.44 12.479 77.56 40oC 5.65 81.80 3.97 82.18 55oC 1.40 87.41 1.00 87.33

Table 3b. Dynamic modulus (E*) of asphalt mixtures

Temperature Description of

Mixtures

PG76-22 (PMB)

PG58-16 (60-70 Grade Bitumen)

E* at 0.1Hz (MPa)

Phase Angle (φ) E* at 0.1Hz

(MPa) Phase Angle

(φ)

25oC Class-A 3897 17.46 2811 19.46 Class-B 2978 21.09 1754 22.34

40oC Class-A 1652 23.27 956 25.56 Class-B 1245 27.96 743 30.02

55oC Class-A 1157 28.59 453 31.84 Class-B 1007 32.54 348 33.57

Figure 4. Relationship between asphalt binder and mixture’s rut factors

The elastic modulus (G*) of binder mostly range between 20 MPa and 1 MPa and that of mixtures between 400 and 4000MPa. A significant change was observed within the selected temperature range which depicts the changed behavior of asphalt mixes over the said range of temperatures in the field. Furthermore, rut depth factors for asphalt binder (G*/Sinδ) and mixture (E*/Sinφ) were computed

and compared to ascertain possible relationship. Logarithmic scale was used to cover the entire range of data set.

Figure 4 reveals that prediction of asphalt mixture’s rut factor can be made from asphalt binder rut factor with a degree of determinacy of over 0.8.

0

2000

4000

6000

8000

10000

12000

14000

0 1 10 100 1000

E*/

Sinφ

Log(G*/Sinδ)

Class-A, PG76

Class-A, PG58

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

0 1 10 100 1000

E*/

Sinφ

Log(G*/Sinδ)

Class-B, PG76

Class-B, PG58



4-2- Development of Master Curve The time and temperature super positioning

(TTS) method was adopted to develop master curves. This principle describes the same viscoelastic properties of asphalt binder and mixtures measured from different temperatures over the same period of time. Viscoelastic properties measured at 40 and 55oC were shifted to 25oC by a horizontal shift (aT) and they developed Sigmoidal fit master curves which have been shown in Figures 5 and 6 for asphalt binders and mixtures respectively. These curves actually describe the time and temperature dependent shear properties of

asphalt binders. One can observe the effect of PG grading and aggregate gradation on the viscoelastic behavior of asphalt mixtures. Asphalt mixtures with PG 76 and coarser aggregate gradation showed higher E* values at all frequency levels and PG 58 with finer gradation showed minimum values at all levels of frequency and temperature.

Also, Asphalt mixture with finer aggregate gradation and PG 76 showed relatively good results than PG58 and coarser gradation. This means that the effect of aggregate gradation can be improved by binder stiffness effects.

Figure 5. Development of master curves for asphalt binders

Figure 6. Development of master curves for asphalt mixtures

‐2

‐1

0

1

2

3

4

‐2.0 ‐1.0 0.0 1.0 2.0 3.0

Log

(G

*)

Log (Tr)

PG 58‐16

2.4

2.6

2.8

3

3.2

3.4

3.6

3.8

4

‐2.0 ‐1.0 0.0 1.0 2.0 3.0

Log

(E

*)

Log (Tr)

Class‐A, PG76

Class‐A, PG58



Master curves of asphalt binders (log G*) and mixtures (log E*) were compared on single space as presented in Figures 7 and 8. The purpose of comparing both the materials’ curve (s) was to estimate the influence of the binder’s stiffness on the mixture’s stiffness.

At low frequency the asphalt binder response becomes viscous and the slopes of the curve become steeper. One can conclude from these Figures that by using the PG 76 in asphalt mixtures the effect of aggregate gradation is not distinguished when compared to PG 58.

Figure 7. Comparison of G* and E* master curves using PG 76-22

Figure 8. Comparison of G* and E* master curves using PG58-16

yClas‐A = ‐0.033x2 ‐ 0.182x + 3.686

R² = 0.998

yPG76= ‐0.153x2 ‐ 0.746x + 1.978

R² = 0.997

yClass‐B = ‐0.011x2 ‐ 0.192x + 3.551

R² = 0.997

‐2.0

‐1.0

0.0

1.0

2.0

3.0

4.0

‐3.0 ‐2.0 ‐1.0 0.0 1.0 2.0 3.0 4.0

Log

(D

ynam

ic M

odu

lus)

Log (Tr)

Class‐A, PG 76

PG 76‐22

Class‐B, PG76

yClass‐A = ‐0.039x2 ‐ 0.194x + 3.550

R² = 0.999

yPG58 = ‐0.081x2 ‐ 0.956x + 1.286

R² = 0.997

yClass‐B = ‐0.045x2 ‐ 0.189x + 3.368

R² = 0.999

‐2.0

‐1.0

0.0

1.0

2.0

3.0

4.0

‐3.0 ‐2.0 ‐1.0 0.0 1.0 2.0 3.0 4.0

Log

(D

ynam

ic M

odu

lus)

Log (Tr)

Class‐A, PG58

PG 58‐16

Class‐B, PG58



4-3- Sigmoidal parameters of Master Curves Sigmoidal parameters best describes the shape

and the location of the master curve by mathematical modelling, using the following relationship (State Highway and Transportation Officials (TP-62) 2004).

)(log1*

TreELog

(2)

Where δ, α are known to be the fitting parameters that depend on aggregate gradation, binder contents and air void, while β, γ depend on characteristics of

asphalt binder and describes the shape of the sigmoidal functions. Sigmoidal functions (δ, α, β, & γ) for binders and mixtures were determined simultaneously and reported in Table 4 for comparison purposes. Sigmoidal functions help to characterize the master curves in terms of shape and location. Values of sigmoidal functions at different test conditions as reported by different researcher in the past have been given in Table 5 for comparison. One can observe from this Table that values of signmoidal function depend upon mix properties and testing features that mainly involve types of testing, material types and test conditions.

Table 4. Sigmoidal parameters for binders and mixtures

Parameters PG76-22 (PMB) PG58-16 (60-70Grade Bitumen)

Binder Mix. Class

A Mix. Class

B Binder

Mix. Class A

Mix. Class B

δ -2.55 2.36 2.50 -0.22 1.67 1.79

α 9.11 1.62 1.54 6.21 1.96 2.08

β -1.14 -1.58 -0.81 -1.70 -1.90 -1.73

γ 0.58 0.79 0.62 0.89 0.80 0.71

Table 5. Sigmoidal functions reported in other studies

Sr. No. References of

previous studies Sigmoidal Functions

1

Geoffrey et al., 2009

Witczak parameters computed with RHEA Software: For mix at 3.8% air voids; δ = -0.954, α = 4.613, β = -1.64, γ = -0.428, Richard parameters for dynamic modulus master curve: For mix at 3.8% air voids; δ = 0.301, α = 4.094, β = -1.513, γ = -0.395,

2 Kim and Partl., 2009 For Mastic asphalt tested under uniaxial compression test: δ = 1.350,α = 1.860, β = -2.820, γ = 0.680,

3 Amara et al., 2006 For in place hot mix asphalt cores taken from 18 sites; Average values δ = 4.2837, α = 2.1672, β = -0.6373, γ = 0.5853,



Figure 9. Typical Rut depth formation of Asphalt Mixtures at 55oC

Table 6. Summary of Rut Depth of different asphalt Mixtures tested under wheel tracker

NMAS Size (mm)

Rut depth of SMA mixtures (mm)

25oC 40oC 55oC Class-A,PG 76-22 2.23 4.16 6.59 Class-B,PG 76-22 2.57 6.39 9.12 Class-A,PG 58-16 2.62 9.41 11.02 Class-B,PG 58-16 3.31 11.12 14.15

4-4- Wheel Tracking Test

Rut development history of asphalt mixtures used at different temperature levels have been shown in Figure 9. One can observe that rut depth formation at any number of load repetitions depends mainly on mixture compositions, especially the asphalt binder grade. Asphalt mixture with finer gradation and PG 76 showed more resistance to rutting than a coarser gradation and PG 58 asphalt binder. A detailed comparison of rut development in different mixtures at different temperature levels under the wheel tracker machine have been reported in Table 6.

The above table shows that the rut depth of mixtures increases with an increase in the temperature levels. Also, one can easily compare the rut resistance of different mixtures at different temperatures. Asphalt mixture with finer aggregate gradation and PG 58 showed minimum resistance to rutting at any temperature level.

5-iConclusion This study characterizes two asphalt binders and

four mixtures based on their stiffness modulus and phase angles and determine some possible correlations between the set performance’s criteria for both. The following conclusions have been drawn from this study:

Dynamic modulus and shear complex modulus are sensitive to test temperature and frequency of loading. The elastic modulus (G*) of the binder mostly ranges between 20 to 0.01 MPa and that of mixtures between 400 and 4000 MPa in a temperature range of 25 to 55oC.

Dynamic modulus and wheel tracker testing showed that asphalt mixtures with finer gradation and PG76 resist more against rutting than PG 58 and finer aggregate gradation.

Performance of asphalt mixtures under a domain of frequency and temperatures can easily be

0

2

4

6

8

10

12

14

16

0 2000 4000 6000 8000 10000 12000

Ru

t D

epth

(m

m)

Load Cycles (N)

Class-A,PG76Class-B,PG76Class-A,PG58Class-B,PG58



predicted from that of asphalt binders using the master curve techniques.

References AASHTO T 240, (2004) "Standard Method of Test for

Effect of Heat and Air on a Moving Film of Asphalt Binder (Rolling Thin-Film Oven Test)".

Amara Loulizi, Gerardo Flintsch, and Kevin McGhee (2006) "Determination of the In-Place Hot-Mix Asphalt Layer Modulus for Rehabilitation Projects Using a Mechanistic-Empirical Procedure" FHWA/VTRC 07-CR1, Virginia Transportation Research Council, Charlottesville, Virginia.

American Association of State Highway and Transportation Officials (1995) "AASHTO Provisional Standard TP5-93: standard test method for determining the rheological properties of asphalt binder using a dynamic shear rheometer". Washington D.C.

American Association of State Highway and Transportation Officials (TP-62) (2004) "Determining Dynamic Modulus of Hot-Mix Asphalt Concrete Mixtures".

Anderson, D. A. and Christensen D.W. (1992) "Interpretation of Dynamic Mechanical Test Data for Paving Grade Asphalt Cements," Proceedings of the Association of Asphalt Paving Technologists, volume 61, pp. 67-116.

Charles, E. Dougan, Jack, E. Stephens, James Mahoney and, Gilbert Hansen, (2003) "E*-DYNAMIC MODULUS" Test Protocol – Problems and Solutions, Report Number-CT-SPR-0003084-F-03-3, University of Connecticut, USA.

Colbert B. and Zhanping, (2012) "The properties of asphalt binder blended with variable quantities of recycled Asphalt using short term and long term aging simulations", Journal of Construction and Building Materials, Vol. 26, pp. 552–557.

Cooper Technology, (2006) "Wheel Tracker Small Device", Product Catalogue, Issue 1, CRT-WTEN1& CRT-WTEN2 in conformance to E13108.

European Standard; (2002) "Bituminous mixtures-Test methods for hot mix asphalt", EN 12697-22, part-2, Wheel Tracking.

Faheem, A., and Bahia H.U. (2004) "Using Gyratory Compactor to Measure Mechanical Stability of Asphalt Mixtures", Wisconsin Highway Research Program.

Geoffry M. Rowe, Salman HakimzadheKhee, PhillilBlanenship and Kamyar C. Mahboub (2009) "Evaluation of Aspects of E* Test by using Hot-Mix Asphalt Specimens with Varying Void contents", Transportation Research Record, Journal of the Transportation Research Board, No. 2127, Transportation Research Board of the National Academies, Washington D.C, pp. 164-172.

Huang, Shin-Che and Zeng Menglan, (2007) "Characterization of aging effect on rheological properties of asphalt-filler systems", International Journal of Pavement Engineering, 8:3, pp. 213-223.

Kanitpong, K., Bahia, H., (2005) "Relating adhesion and cohesion of asphalts to the effect of moisture on laboratory performance of asphalt mixtures", T. R. R, 1901, pp. 33-43.

Kim H. AND Partl M.N., (2009) "Stiffness comparison of mastics asphalt in different tests modes", 2nd workshop on four point bending, pais (ed.), University of Minho, ISBN 978-972-8692-42-1.

Kumar S. A. and Veeraragavan A., (2011) "Dynamic mechanical characterization of asphalt concrete mixes with modified Asphalt binders", J. Materials Science and Engineering, Vol. 528, pp. 6445– 6454.

Loulizi, Flintsch, Al-Qadi and Mokarem, (2006) "Comparison between Resilient Modulus and Dynamic Modulus of Hot-Mix Asphalt as Material Properties for Flexible Pavement Design".

National Highway Authority, (1998) "Surface course", Item No. 305-I, General Specification, Pakistan.

NurIzzi Md. Yusoff, Montgomery Shaw T. and Gordon D. Airey, (2011) "Modeling the linear viscoelastic rheological properties of bituminous binders", J. Construction and Building Materials, Vol. 25, pp. 2171–2189.



Pellinen, T K and Witczak, M W., (2002) "Stress dependent master curve construction for dynamic modulus".

Soleimani A., (2009) "Use of dynamic phase angle and complex modulus for the low temperature performance grading of asphalt cements", Ph.D. Thesis, Queen’s University, Kingston, Canada, Page 7.

Tarefder, R.A., Zaman, M., Hobson, K., (2003) "A Laboratory and statistical evaluation of factors affecting rutting", International Journal of Pavement Engineering”. Vol. 4 (1), pp. 59-68.

Wasage T.L.J., Jiri Stastna and LudoZanzotto, (2011) "Rheological Analysis of multi-stress creep recovery test", in Int. J. of Pavement Eng., Vol. 12, No. 6, pp. 561-568.

Hafeez Rutting Prdeiction of Asphalt Mixtures

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