ELSEVIER

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Constru.ction cued Building Materials. Vol. II, No. I. pp. 15-22. 1997 <C 1997 Elsevier Science Ltd. All rights reserved

Printed in Great Britain 0950-0618/97 SJ7.()(}rO.OO

PI!: S095~618(97)00002-0

Development of performance-based bitumen specifications for the Gulf countries

Hamad I. AI-Abdul Wahhab', Ibrahim M. Asi", Ibrahim A. AI-Dubabet and Mohammad Farhat Ali!

• Department of Civil Engineering, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia tAwazel Company, Riyadh, Saudi Arabia I Department of Chemistry, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia

Received 9 April 1996; revised 3 January 1997; accepted 5 February 1997

The rheological behaviour of bitumen has a great influence on the behaviour of bitumen mixtures. Bitumen plays a significant role in a pavement's ability to withstand thermal and fatigue cracking and contributes to permanent deformation behaviour. The current binder specifications, as applied in the Gulf countries including Saudi Arabia, Kuwait, Bahrain. Qatar, United Arab Emirates and Oman, are based primarily on either penetration or viscosity testing which does not properly account for pavement performance. This research was undertaken to provide a performance-based binder specification forthe Gulf countries, based on the findings of the Strategic Highway Research Programme (SHRP) carried out in the United States, considering the prevailing environmental and traffic conditions and type of locally produced bitumen. Results indicated that locally produced 60nO penetration grade bitumen satisfies the environmental condition of less than 30% of the Gulf countries' area. Air blowing of bitumen is required to satisfy the performance requirement of another 25% of Gulf countries area, while polymer modification is necessary to satisfy the performance requirements for the other parts of the Gulf countries which include eastern parts of Saudi Arabia, Kuwait, Bahrain, Qatar, United Arab Emirates and Oman. © 1997 Elsevier Science Ltd.

Keywords: bitumen; performance-based specifications; SHRP

Introduction measured by either penetration test or viscosity test. Unfortunately, these measures do not relate well to pavement behaviour and performance2

. Fatani et al. 3, in a

study on permanent deformation in the Kingdom of Saudi Arabia, have concluded that bitumen is responsible for a major part of the Kingdom of Saudi Arabia's pavement rutting, and that the current bitumen specifications have failed to produce mixtures that can sustain the harsh environment of the region.

The bituminous constituents of petroleum are usually dark brown to black, sticky, and semi-solid to solid. They are obtained from various refining processes such as the residuum from vacuum distillation, or as the material precipitated by liquid propane-liquid butane mixtures during the de-asphalting stage of petroleum refining. Most bitumens consist of straight distillation residue. The behaviour and properties of bitumens are dependent on their constituents. Most petroleum scientists support the model that describes bitumen as a relatively homogenous and randomly distributed collection of molecules differing in polarity and molecular size, rather than the traditional model which represents bitumen as a colloidal dispersion of asphaltenes in maltenes 1

.

The rheological behaviour of bitumen has a great influence on the behaviour of bitumen mixture. Bitumen ,Iays a significant role in a pavement's ability to withstand .hermal and fatigue cracking, and contributes to permanent deformation behaviour. The current binder specifications, as applied in the Arabian Gulf countries (Saudi Arabia, Kuwait, Bahrain, Qatar, United Arab Emirates and Oman), are based primarily on the consistency of bitumen as

15

Studies on both physical and chemical aspects of bitu­men have recently been receiving greater attention; one of the major researches is the Strategic Highway Research Programme (SHRP). The principal goal of the SHRP bitumen research programme was to develop performance­based specifications for bitumen and bitumen mixture. The bitumen specifications will allow the engineer to select the bitumen on the basis of the performance level required of the pavement under the present and predicted traffic and environmental conditions. The SHRP bitumen programme and its experimental designs have further established that pavement performance is definitely affected by the physio­chemical properties of the bitumen. However, these require­ments must be based on the climatic regime prevailing at the specific location where bitumen will be used.

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16 Bitumen specifications for the Gulf countries: H. I. AI-Abdul et al.

In an effort to establish a sound bitumen specification, which is based on prevalent environmental conditions in the Gulf countries, traffic loading and native bitumens, King Abdulaziz City for Science and Technology has funded a project entitled "Adaptation of SHRP Performance Based Asphalt Specifications to the Gulf Countries" for a period of 30 months. The project is undertaken with the following broad objectives:

I. To determine suitable temperature zoning for the Gulf countries (GC).

2. To study the chemical and physical characterization of Arab bitumen (GC-bitumen).

3. To evaluate the suitability of the presently used regional bitumen on the basis of the SHRP performance-based specifications.

4. To study ways to improve bitumen to meet the proposed specifications.

This paper describes the findings of the study as related to results of the physical and performance-based testing of Arab bitumens, temperature zoning and the suitability of currently used bitumen for the Gulf region.

Design

In order to achieve the stated objectives, the work is being carried out in six tasks and it extends for 30 months. A schematic flow chart for the project design is shown in Figure 1. Details of some of the planned tasks are as follows:

1. Temperature data collection and temperature zoning. Metrology and Environmental Protection Agencies, Directorate of Climatology and other similar agencies in the Gulf countries were approached to provide the research team with the available historical annual environmental data covering the Gulf countries (GC). These data were analysed and used to build a temperature data base and to develop suitable tempera­ture zoning for the Gc.

2. Bitumen samples collection. Bitumen samples were col­lected from all bitumen-producing refineries in the Gulf which included Ras Tanura and lliyadh (Saudi Arabia), AI-Ahmadi (Kuwait), and BAPCO (Bahrain), and an additional sample was collected from Awazel private company which modifies bitumen produced by lliyadh refinerY using air-blowing process.

Task)

Uterature

Review

T"'k2 Procurement of

Equipment &r. Materials

Task 3

Temperature Data CoUectJoll &. ZouJ.ne

Task 4

BitUnll'h Samples

Colledion

T",k5 BltwlIen Testinl::

a. Consistency b. Perfonnance c:. Olemisfry Task 6

Bitwllen Modification

No

Figure 1 Schematic flow chart of the project design

Bitumen specifications for the Gulf countries: H. I. AI-Abdul et al. 17

3. Bitumen testing. Collected bitumen samples were sub­jected to comprehensive testing to determine their phy­sical and chemical properties. The testing included:

(a) Consistency testing: viscosity at 25°C (ASTM D 3570), 60°C (AASHTO T-202-S0) and 135°C (AASH­TO T-201-S0), penetration at 25°C and 4°C (AASHTO T-49-S0), softening point (AASHTO T-53-SJ) and ductility (AASHTO T-51-S1). The testing was carried out on fresh bitumen and a rolling thin-film-oven (RTFO) residue (AASHTO T-240-7S). (b) Performance-based testing, which was performed on original bitumen, RTFO residue and pressure-aging vessel (PAV) residue4• Tests included flash point, rotational viscosity, dynamic shear, mass loss after RTFO, flexural creep stiffness and direct tension failure strain3

.

(c) Chemistry: chemical composition of the collected samples was determined using Corbett's method, ion­exchange chromatography and high-pressure gel per­meation chromatography.

4. Bitumen modification. Bitumen, which has a perfor­mance grade that does not satisfy the binder specification as determined by temperature zoning in step I, will be modified to improve its qUality. Modified bitumen will be subjected to the same set of tests as in step 3. The potential output of this step is a modified bitumen that will satisfy the performance requirements of the Gulf countries.

Five representative bitumen samples were collected, according to statistical sampling plan, at a rate of one sample every two weeks. In addition, one sample from Awazel Company was included in the testing programme since it is the only source within the Kingdom of Saudi Arabia that produces a 40150 penetration grade bitumen.

Results and discussion

Temperature zoning

Metrology and Environmental Protection Agencies in the Gulf countries were approached through the Gulf Coopera­tion Council (GCC) to provide the research team with the available environmental data that has been collected up to the present time. Forty-four weather stations across the Gulf countries were included and data covering up to 26-year period were collected. Table 1 presents a list of weather stations in the Gulf countries with minimum air temperature and average maximum air temperature over seven consecutive days.

Temperature is known to be one of the most important factors that influence bitumen-mixture design and perfor­mance. Extensive research studies on temperature distribu­tion in bitumen pavements have been carried out in many different climatic areas of the world. These studies were

...,..Ieither manifestations of temperature variation3,,S-13 or

attempts to incorporate temperature effect in pavement analysis and design 14-17 Strategic Highway Research Programme (SHRP), for example, used the average

Table 1 Mini~um and seven-day maximum air temperature for the different used weather stations

Country Station location Minimum Average seven-day temp., oC maximum temp., °C

Saudi Arabia Jeddah 8.2 43.6 Saudi Arabia Makkah 10.2 45.9 Saudi Arabia Taif -1.2 37.6 Saudi Arabia AI-Baha 0.6 37.5 Saudi Arabia Sulayyil 0.6 46.2 Saudi Arabia Bisha -0.8 41.1 Saudi Arabia Abba 0.0 32.5 Saudi Arabia Khamis Mushayt - 3.1 34.0 Saudi Arabia Najran - 0.5 41.0 Saudi Arabia Sharurah 0.8 44.5 Saudi Arabia Jizan 14.0 41.4 Saudi Arabia 1\rraif -8.0 43.4 Saudi Arabia Alar -5.6 46.9 Saudi Arabia Gurail -8.0 45.3 Saudi Arabia AI-Jauf -7.0 44.7 Saudi Arabia Ra/ha -6.6 48.3 Saudi Arabia Qaisomab -4.1 48.8 Saudi Arabia Tabuk -5.0 43.8 Saudi Arabia Hail -9.4 42.3 Saudi Arabia Ai-Wajh 5.0 39.4 Saudi Arabia Qassim -4.0 46.1 Saudi Arabia Dhahran 1.6 46.3 Saudi Arabia Riyadh -0.5 47.3 Saudi Arabia Yanbu 6.5 44.4 Saudi Arabia Madinah 1.0 46.1 Saudi Arabia AI-Hasa -2.3 47.6 Saudi Arabia AI-Dawadmi 5.7 34.1

U.A.E .• Abu Dhabi 5.4 47.6 Int. Airport

U.A.E. Ai Aln 0.6 48.5 U.A.E. Bu Hasa 4.0 49.0 U.A.E. Dibba 8.0 48.6 V.A.E. Dubai Int. Airport 7.4 47 .3 V.A.E. Kalba 8.4 49.6 V.A.E. R.AL Khaimab 4.4 48.2

In!. Airport U.A.E. Sharjah lot. Airport 2.5 49.2

Kuwait Kuwait Airport -1.6 49.9

Oman Seeb Airport 10.0 49.2 Oman Khasab 8.4 49.0 Oman Buraimi 2.6 50.8 Oman Sur 7.0 49.8 Oman Salalah 10.0 47.2 Oman Thumrait 1.6 46.0

Qatar Doha Airport 3.8 49.0

. • United Arab Emirates

maximum consecutive seven-day pavement temperature and minimum pavement temperature in the application of the new SHRP performance-based specificationsl4. In the Gulf region, Fatani et al.' , AI-Abdul Wahhab and Balghunaim5 , Bissada· and Potocki7 have carried out different research to quantify temperature regimes in local pavements. It was observed that the single most important factor that affects pavement temperature was air tempera­ture which is directly affected by cloud cover and solar radiation and that the minimum pavement temperature is always recorded on the surface of the pavements which matches the lowest air temperature. The average maximum pavement design temperature over a consecutive seven-day

18 Bitumen specifications for the Gulf countries: H. I. AI-Abdul et al.

Figure 2 Recommended temperature zoning for bitumen specification for the Gulf region

period is measured at a depth of 20 mm in the pavement, as recommended by the FHWA LTPP study!4. Regression relationships were developed to correlate air temperature to the 20 mm-depth pavement temperature with high accu­racy. Contour maps for both the minimum temperature and! or the average maximum consecutive seven-day pavement (at 20 mm depth) temperature were developed. Based on those contour maps and considering slow transient loads, four bitumen performance grades (PG) are recommended: PG 76-10, PG 70-10, PG 64-10 and PG 58-10, as shown in Figure 2. For example, a binder with a performance grade PG 76-10 designates a bitumen that will satisfy perfor­mance requirements for a temperature zone that has an average maximum consecutive seven-day temperature less than 76°C and a minimum pavement temperature greater than -IO'C. Bitumen used in any of these zones must meet the performance requirements for these temperature extremes, namely. maximum consecutive seven-day tem­perature and minimum pavement temperature.

Bitumen testing

Collected bitumen samples were subjected to comprehen-) ,ive testing to determine their physical and chemical

properties. The measured physical properties were utilized to grade the bitumen samples according to penetration (AASHTO M20) and AASHTO-AC (asphalt cement) and AR (asphalt residue) bitumen grading (AASHTO M226),

and to calculate relevant temperature susceptibility indices such as: penetration index (PI), penetration viscosity number (PVN) and viscosity temperature susceptibility (VTS). Results are shown in Table 2. The following observations can be stated for bitumen produced in the Gulf:

• Bahrain Refinery (BH) samples met the 40150 penetra­tion grade, two Ras Tanura Refinery (RT) samples met the 60170 penetration grade, while the rest of the samples did not meet any penetration grade.

• Softening point of all samples ranged from 49-5 I .5'C except the Awazel Company (AZ) sample which had a softening point of 54.8' C.

• Samples are graded as AC-40 according to the AASHTO-AC grading method, except three RY samples which had a grade of AC-20 and the AZ sample which could not be defined.

• Samples are graded as AR-8000 according to the AASHTO-AR grading method, except one Ras Tanura Refinery (RT) sample, two RY samples and three BH samples, which had a grade of AR-4000.

• Samples have a penetration index (PI) ranging from -0.44 to -1.53. The RT samples have the lowest temperature susceptibility while the BH samples have the highest temperature susceptibility.

• The penetration viscosity number (PVN) of all samples ranged from -0.36 to -0.83.

Bitumen specifications for the Gulf countries: H. I. AI-Abdul et al. 19

Table 2 Summary of grading and physical testing results

Country Sample Softening Penetration@ Penetration Penetration Viscosity Bitumen grade Bitume~ grade Bitumen perfor-of origin ID point, OC 25°C index viscosity

number AASHTO M20 PI PYN

RTl 50.25 60 0.72 0.75 n Saudi Arabia RTI 50.75 63 - 0.44 -0.42 RTI 50.00 56 - 0.95 -0.56 RT4 50.75 51 - 0.98 -0.66 RT5 50.75 56 - 0.73 -0.70 RYI 49.25 54 -1.20 -0.83 RY2 49.75 57 -0.98 -0.70 RY3 49.75 50 -1.28 -0.74 RY4 50.00 54 -1.01 - 0.50 RY5 51.25 51 -0.86 -0.48 AZI 54.75 38 -0.68 -0.83

Bahrain BHI 50.00 45 - 1.41 - 0.79 BH2 49.50 47 -1.45 - 0.74 BH3 49.00 48 - 1.53 -0.82 BH4 49.75 50 - 1.25 -0.78 BH5 50.00 48 - 1.27 -0.83

Kuwait KWI 50.25 53 - 1.01 -0.51 KW2 51.00 51 - 0.93 -0.42 KW3 51.50 54 -0.63 -0.48 KW4 50.00 56 - 0.93 -0.44 KW5 50.50 55 - 0.86 -0.36

• The viscosity temperature susceptibility (VTS) ranged from 3.37-3.71.

The rheological performance-based properties of these samples were determined using the Dynamic Shear Rheometer (DSR)4 to measure the complex shear modulus and phase angle, the Bending Beam Rheometer (BBR)4 to measure the flexural creep stiffness and creeping slope, the rolling thin-film-oven test (RTFOT) to simulate the short­term aging, and the pressure-aging vessel (PAy)4 to simulate the long-term aging. The evaluation process starts by determining the temperature at which the viscous component of overall binder stiffness, G' I sin 8, is more than 1.00 kPa, where G' and 8 are the overall shear modulus and the phase angle of the bitumen, respectively. The conformation of the high-temperature evaluation is performed by testing the RTFOT-aged sample (RTFOT residue) of bitumen using the DSR. The G' I sin 8 value of the RTFOT-aged bitumen sample must be greater than 2.20 kPa.

Then, the intennediate temperature evaluation was performed. This involved the determination of the tem­perature at which the parameter 0- x sin 6 is more than 5000 kPa, by testing a bitumen sample of the PAY-aged bitumen (PAY residue) using the DSR. The low-tempera­ture evaluation was accomplished by testing an aged bitumen sample (PAY residue) using the BBR. It involved the determination of the temperature at which the creep stiffness, S, that describes whether the binder will behave

-' more like an elastic solid or a viscous fluid, is less than 300 MPa and the m-value, which is the rate at which the binder stiffness changes with creep load, is greater than 0.300.

temperature (AASHTO-AC (AASHTO-AR mance grade (SHRP susceptibility classification) classification} classification)

VTS AASHTO M226 AASHTO M226

3.65 AC-40 AR-4000 PO 64-22 3.50 AC-40 AR-8000 PO 64-22 3.52 AC-40 AR-8000 PO 64-28 3.55 AC-40 AR·8000 PO 64-28 3.56 AC-40 AR-8000 PO 64-28 3.56 AC-20 AR-4000 PO 64-22 3.53 AC-20 AR-8000 PO 64-22 3.53 AC-40 AR-8000 PO 64-22 3.37 AC-20 AR-4000 PO 64-22 3.37 AC-40 AR·8000 PO 64-22 3.71 Not defined AR-16000 PO 70-22

3.54 AC-40 AR-8000 PO 64-22 3.49 AC-40 AR-8000 PO 64-22 3.53 AC-40 AR·4000 PO 64-22 3.54 AC-40 AR-4000 PO 64-22 3.54 AC-40 AR-4000 PO 64-22

3.43 AC-40 AR-8000 PO 64-22 3.39 AC-40 AR-8000 PO 64-22 3.50 AC-40 AR-8000 PO 64-22 3.45 AC-40 AR-8000 PO 64-22 3.42 AC-40 AR-8000 PO 64-22

Based on the performance testing of the locally produced bitumen and on the SHRP-recommended perfor­mance grading system, the grade of the bitumen is selected, as shown in Table 34 The performance grades of the tested samples are shown in Table 2.

Results indicate that Arabian bitumens, as produced by local refmeries, are variable when penetration grading (AASHTO M20) is used. For example, bitumen produced by Ras Tanura Refinery has penetration ranging from 51-60. Similar variability exists with the other two classifica­tion systems, namely AC and AR grading (AASHTO M226), but to a lesser extent. On the other hand, the traditional grading system does not relate to the tempera­ture ranges in which a certain bitumen will be used. In a comprehensive study of permanent deformation in Saudi Arabia, in which two of the authors were members, Fatani ef al. 3 have reported that bitumen has a significant contribution to rutting on the Saudi roads. Table 4 indicates that the recovered bitumen from rutted pavement sections is significantly softer than the bitumen from non-rutted pavement sections. In this table, the road pavement sections were selected to cover the Kingdom of Saudi Arabia's temperature zones.

The new bitumen specifications have consistently given the same grade for all neat bitumens produced locally, i.e. 64-10. This indicates that locally produced bitumens can perform satisfactorily in areas where the average maximum consecutive seven-day temperature is less than 64°C and minimum pavement temperature is greater than - 10°C. However, from temperature zoning map (Figure 2), this is less than 30% of the Gulf countries ' area. The remaining bulk area of the Gulf countries will require PO 70-10 for the central and

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Table 3 Perfonnance-graded bitumen specification

Perfonnance grade PG 64- PG70-

10 16 22 28 34 40 10 16 22 28

Average seven-day maximum pavement <64 <70 design temperature, °C Minimum pavement design temperature, °C > - 10 > -16 > - 22 > -28 > - 34 > -40 > - 10 > -16 > :-22 >-28

Original binder flash point temp., T-48: 230

Minimum °C Viscosity. ASTM 0 4402:

Maximum, 3 Pa-s, 135 Test temp., °C

Dynamic shear, TP5: G- I sin 6, minimum, 1.00 kPa 64 70 Test temp. @ 10 cad/s, °C

RoIling thin-film oven (T240) or thin-film oven residue (1'179) Mass loss, maximum, percentage 1.00 Dynamic shear, TPS:

G· I sin 6, minimum. 2.20 kPa 64 70 Test temp.@ 10 cad/s, °C

Pressure-aging vessel (PAV) residue (PPI) PAY-aging temperature, °C 100 100(IlO) Dynamic shear, TPS:

G· x sin 6, maximum. 5000 kPa 31 28 25 22 19 16 34 31 28 25 Test temp. @ 10 rad/s, cC

Physical hardening Report Creep stiffness, TPI:

S, maximum, 300 MPa m~value, minimum, 0.300 0 - 6 -12 -18 -24 -30 0 -6 - 12 - 18 Test temp. @ 60 s, cC

Direct tension, TP3: Failure strain, minimum. 1.0% 0 -6 -12 -18 -24 -30 0 -6 -12 -18 Test temp. @ 1.0 mm1min, cC

PO 76-

34 40 10 16

> -34 > - 40 >-10 > - 16

22 19 37 34

-24 - 30 0 -6

-24 -30 0 -6

22 28

<76

> -22 > -28

76

76

100(110)

31 28

-12 -18

- 12 - 18

34

> -34

25

-24

-24

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" '" Cl' .... g. <D

G'l ~ '"" " Q c:

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Bitumen specifications for the Gulf countries: H. I. AI-Abdul et al. 21

Table 4 Physical properties of recovered bitumen from rolled and non-rutted sections in the Kingdom of Saudi Arabia)

Road name Study section Absolute viscosity Kinematic viscosity Softening point, °c @ 60"C. P @ 135"C. cSt

Ahu-Hadriyah Expressway, Section A Non-rutted 64795 1843 66.2 Abu-Hadriyah Expressway, Section A Rutted 20765 1258 62.1 Ahu-Hadriyah Expressway, Section B Non-rutted 48228 1559 67.6 Abu-Hadriyah Expressway, Section B Rutted 42365 1646 64.1 Riyadh-Qassim Expressway, Section 2 Non-rutted 66252 1264 65.3 Riyadh-Qassim Expressway, Section 2 Rutted 20601 930 60.5 Riyadh-Qassim Expressway, Section 3 Non-rutted 206568 2344 14.2 Riyadh-Qassim Expressway, Section 3 Rutted 33826 1352 63.2 lammom-Zima Road Non-rutted 93732 2128 10 Jammom-Zima Road Rutted 65862 1920 68.6 Jeddah-Makkah Expressway Non-rutted 114691 2218 12.2 Jeddah-Makkah Expressway Rutted 43668 1420 64.6 Makkah-Taif Expressway Non-rutted 11351 893 58.8 Makkah-Taif Expressway Rutted 7552 769 54.1

Statistical analysis of the asphalt process Variable Mean

Non-rutted Absolute viscosity. P 88861.88 Kinematic viscosity. cSt 1782.75 Softening point. °C 67.9

northwestern parts of the Kingdom of Saudi Arabia. The performance requirements of this temperature zone can be met using air-blown asphalt similar to that of Awazel. The eastern part of the Kingdom of Saudi Arabia and Gulf counlries will require polymer­modified bitumen (PG 76-10) to meet the perfonnance requirement.

Conclusions

I. Bitumens. as produced by Gulf refineries, are variable. 2. Penetration and viscosity are not sound bases for local

bitumen specifications. 3. Temperature zoning. a prerequisite for perfonnance­

based specification for the Gulf countries, was devel­oped. Temperature zones range from PG 58-10 to PG 76-10.

4. Locally produced bitumen needs modification to suit the different Gulf temperature zones.

Acknowledgements

The authors would like to thank King Abdulaziz City for Science and Technology (KACS1) for providing support to this research and to the King Fahd University of Petroleum and Minerals for providing the laboratory space and facilities.

References

Petersen, J. C., Robertson. R. E., Branthaver, J. F., Harnsberger, P. M., Duvall, J. J., Kim, S. S., Anderson, D. A., Christiansen. D. W. and Bahia, H. U., Binder characterization and evaluation. Report No. SHRP-A-367. Strategic Highway Research Program, National Research Council. Washington. D.C .• 1994, Vol. L

P-value Significant @ 0.1

Rutted 33519.86 0.056 Yes

1327.86 0.078 Yes 62.46 0.04 Yes

2 Bahia, H. U. and Anderson, D. A., The new rheological properties of asphalt binders: why are they required and how they compare to conventional properties. In Physical Properties of Aspha.lt Cement Bindus, ASTM STP 1241. ed. 1. C. Harden, American Society for Testing and Materials, Philadelphia, 1994.

3 Fatani, M. N., Al-Abdul Wahhab, H. 1. Balghunaim, F. A., Bubshait, A., Al-Dubabe. I. and Noureldln, A. S., Evaluation of pennanent deformation of asphalt concrete pavement in Saudi Arabia. Final Report, National Research Project, King Abdulaziz City for Science and Technology, Riyadh, Saudi Arabia. 1992.

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(

22 Bitumen specifications for the Gulf countries: H. I. AI-Abdul et al.

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15 Venkataraman, T. S. and Venkatasubramanian. V .• Temperature studies on bituminous pavements in tropics. Auslr. Rd. Res.. 1977, 7(1 ). 32-37.

16 Dickinson, E. J., A method of calculating temperature gradients in asphalt concrete pavement structures based on climatic data. AuslT.

Rd. Res .• 1978.8(4). 16-34. 17 Thompson, M. R., Dempsey, B. J" Hill, H. and Vogel, J .•

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