Evaluation of Mechanical Properties of Alternative ...

Evaluation of Mechanical Properties of Alternative Pavement Designs for the State of Qatar Husam Sadek1*, Eyad Masad2, Okan Sirin3, Khaled Hassan4, Hussain AlKhalid5 1

Department of Civil & Architectural Engineering, College of Engineering, Qatar University, Doha, Qatar, P.O.Box 2713, [email protected]; Centre for Engineering Sustainability, School of Engineering, University of Liverpool, Liverpool, UK, Brodie Tower, L69 3GQ, [email protected] 2 Mechanical Engineering Program, Texas A&M University at Qatar, Doha, Qatar, PO Box 23874, 253 Texas A&M Engineering Building, Education City, [email protected] 3 Department of Civil & Architectural Engineering, College of Engineering, Qatar University, Doha, Qatar, PO Box 2713, Civil Engineering Department, [email protected] 4 Regional Manager – Middle East, Transport Research Laboratory, UK, QSTP – B, [email protected] 5 Centre for Engineering Sustainability, School of Engineering, University of Liverpool, Liverpool, UK, Brodie Tower, L69 3GQ, [email protected] *Corresponding author: +97466040174; +97444034172

Abstract The review of the current pavement designs and development of new designs for the State of Qatar are needed because of the tremendous economic growth and the significant increase in traffic loading. The use of the conventional Marshall Design method might not be the best approach to design mixtures that can withstand the increase in traffic loading. In order to assess the long-term performance of different pavement designs, six site trials were constructed in the south of Qatar. The objective of the trial sections were to demonstrate changes that could be made to the current design standards and the influence of these changes on material properties and performance. This paper presents part of a study for monitoring the performance of the trial sections. The dynamic modulus and the FWD tests were conducted to evaluate the influence of mix design, binder type and aggregate source on the performance of the trial sections. The results showed that variation in temperature between summer and winter times in Qatar reduced the stiffness of mixtures by around 80%. In addition, sections with polymer-modified binder had the lowest temperature susceptibility. The authors will continue to monitor the performance of these sections using mechanical and field tests in order to develop guidelines for mixture designs in the State of Qatar.

Keywords: FWD; Dynamic Modulus; Perpetual Pavement; Mechanistic-Empirical Pavement Design; Master Curve; Qatar

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1. INTRODUCTION The Public Works Authority (Ashghal) in the State of Qatar has developed several programs and initiated projects to enhance the specifications and designs of asphalt pavements. One of these programs is the “Road Pavement Technology” project with TRL (the UK Transport Research Laboratory) which involved reviewing pavement designs and performance besides developing new pavement designs for the State of Qatar. For this purpose, site trials were constructed in Qatar to investigate changes to the design method and the use of materials not currently permitted in the QCS. The trials consisted of six different asphalt mixtures constructed in 2010 by TRL under a contract with Ashghal on a route used by heavy truck traffic. The structural designs follow the perpetual pavement concept. This paper presents part of a study for monitoring the performance of the road and its sections with the purpose of developing guidelines and specification for asphalt pavements in Qatar. The dynamic modulus (|E*|) and the Falling Weight Deflectometer (FWD) tests were conducted to evaluate the influence of a number of parameters, including mix design and binder and aggregate type on the performance of each trial section. The performance of different asphalt mixtures, after two years in service, was compared and the results were used to make recommendations for updating the materials and design of asphalt pavements. In addition, the results were used to determine some of the input parameters for Mechanistic-Empirical analysis of asphalt pavements in Qatar. 2. OBJECTIVES OF THE STUDY The main objective of this paper is to present the first stage of a study for monitoring the performance of the road and its trial sections. This paper involves the following:  Conducting FWD tests at low and high air temperature to obtain the moduli of each layer by using Elmod6 software for all sections.  Conducting the dynamic modulus (|E*|) test using the Asphalt Mixture Performance Tester (AMPT) on specimens extracted from base layer of each section to develop dynamic modulus master curves for the trial sections. 3. GENERAL INFORMATION ABOUT THE SITE TRIALS Six different asphalt concrete sections, about 150 m length each, were constructed in 2010 as a part of an access road to a sand processing plant in the south of Qatar. The location shown in Fig. 1 was selected due to its high traffic loading on the trial sections.

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Fig. 1. Site location in Qatar (TRL client report, phase D, 2010) 3.1. Trial section design and site layout All trial sections were designed and constructed as perpetual pavements as shown in Fig. 2. The sections were designed to compare type of binder, type of aggregate and type of mix design against different surface distresses and deteriorations under the same traffic conditions.

Fig. 2. Typical cross-section of trial sections. Table 1 shows the layers and properties of each trial section. The aggregate used in the surface course for all trial sections was imported Gabbro. Crushed stone was the granular material used in the sub-base layer in all sections with a modulus of 450 MPa. In addition, Qatar generally has high strength natural soils consisting of weathered limestone or sand. Sometimes a rock layer was encountered right up to the sub-base surface (Sadek et al. 2012). In the site of the trial sections, the subgrade elastic modulus of 200 MPa was estimated. Table 1. Location, layers, materials and properties of perpetual designs of trial sections. Section Surface/Wearing Course Upper Base + Lower Base 3

# 1 2 3A 3B 4* 5 6

Mix Design Marshall/PRD1 Marshall/PRD Marshall/PRD Marshall/QCS2 Marshall/QCS Marshall/PRD Marshall/PRD

Binder Pen 40-50 Pen 60-70 Pen 60-70 Pen 60-70 Pen 60-70 PMB3 PMB

Aggregate Mix Design Binder Aggregate Gabbro Marshall/PRD Pen 40-50 Gabbro Gabbro Marshall/PRD Pen 60-70 Gabbro Gabbro Marshall/PRD Pen 60-70 Limestone Gabbro Marshall/PRD Pen 60-70 Limestone Gabbro Marshall/QCS Pen 60-70 Gabbro Gabbro QCS Shell Thiopave Gabbro Gabbro Marshall/PRD PMB Gabbro

* Section 4 is the control section. 1 Percentage Refusal Density Design Method (BS EN 12697-32:2003). 2 Qatar Construction Specifications. 3 Polymer-Modified Bitumen/Binder (SBS modifier).

3.2. Traffic data From the opening of the trial road in 2010, about 1800 trucks are passing the trial road daily in each direction and 50% of them are fully loaded with washed and unwashed sand. Based on the traffic data, the 20 years ESALs was calculated to be 115 millions. This traffic loading is very high and more than double the maximum traffic class T6 (50 million) provided in Qatar Highway Design Manual (QHDM). 4. SAMPLING AND TESTING SCHEME In order to monitor the performance of the trial sections, many field and laboratory tests were conducted on these sections. The field work started in January 2012 with collecting pavement condition data by the Automatic Road Analyzer (ARAN - ROADWARE GRP Company) vehicle. Then, 10 cores, 150 mm diameter and 320 mm high, were extracted from one direction of each trial section for laboratory testing in addition to two trial pits extracted from sections 2 and 5 as shown in Fig. 3.

Fig. 3. Cores layout and location. The FWD test was conducted to evaluate pavement structural condition by getting the deflections of each layer and backcalculating the modulus of each layer; asphalt concrete thick layer, base layer and sub-base layer, using Elmod6 software. FWD was conducted in February and August 2012 to monitor the performance in low and high temperatures. For laboratory testing, a total of twelve cores, two replicates from each section, were subjected to the dynamic modulus |E*| test using the IPC Global Asphalt Mixture Performance Tester (AMPT).

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5. RESULTS AND DISCUSSIONS 5.1. FWD results The FWD test was conducted twice on the trial road. For the first test, the average air temperature was about 23°C while the average surface temperature was about 25°C. However, in the second test, the average air temperature was 46°C while the average surface temperature was about 63°C. Fig. 4 shows a comparison between the Elmod6 modulus results for each layer per trial section. As would be expected, the results illustrated that the moduli of the thick asphalt concrete layer and sub-base layer at low temperature are much higher than those at high temperature. The subgrade layer is not exposed directly to the weather change, so the difference between both moduli results was relatively small. In addition, it can be noticed that the difference is decreasing with depth because the effect of change in temperature decreases. In general, it can be stated that the asphalt concrete layer, with PMB, in sections 5 and 6 had the lowest temperature susceptibility, but section 2 had the highest temperature susceptibility. Furthermore, the moduli for the asphalt concrete layers of sections in the summer time were very close to each other (≈ 2000 MPa) in contrast to the winter case. This indicates how the increase in temperature in Qatar decreases the stiffness of asphalt concrete layers regardless of the properties of each section. Generally, the stiffness of the asphalt mixtures decreased by around 80% due to the high air temperature in Qatar as shown in Fig. 4.

Fig. 4. Comparison between moduli of each layer in low and high air temperatures.

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5.2. Dynamic modulus test results The dynamic modulus (|E*|) is a key test within the simple performance test (SPT) suite. It was developed under NCHRP Project 9-19 and applied in the Superpave mix design procedure (Zhu et al. 2011, Yan-zhu et al. 2012). The |E*| test is a non-destructive test that was used to measure the dynamic modulus and phase angle for each section. Master curves were developed from the test data using a sigmoidal fitting function proposed by Pellinen et al. (2002). The sigmoidal function can be described as follows. Log (| E* |)   

 1 e

(1)

   (log  )

where, δ is the minimum modulus value; α, β and γ are the regression coefficients for the fitting function; and ξ is the reduced frequency. The dynamic modulus data of the master curve are used as the design stiffness parameter for all three input levels of the Mechanistic-Empirical Pavement Design Guide (ME PDG) (Masad et al. 2011). In addition, master curve and shift parameters shown in Table 2 and Fig. 5 are used for viscoelastic analysis of materials and the basic data for viscoelastic mechanical analysis of pavement structures (Zhu et al. 2011). In the |E*| test, a repeated load, with zero confinement, was applied at 4.4, 21.1, 37.8 and 54°C with loading frequencies of 25, 10, 5, 1, 0.5 and 0.1Hz (AASHTO Designation: TP 79-11). In this paper, 21.1°C was taken as the reference temperature. A total of twelve specimens collected from base layer were cored and prepared to standard size of 100 mm diameter and 150 mm in height. Fig. 5 shows the dynamic modulus master curve, log loading frequency versus |E*| and log shift factor α(T) versus temperature for the mixture in trial section 1.

Fig. 5. Dynamic modulus master curve; |E*| versus loading frequency (left); shift log α(T) versus temperature (right) for section 1. 6

Table 2. Master curve and shift parameters. Section δ α β 2.8673 3.8635 -1.63406 1 2.7077 3.9330 -1.80664 2 3.1681 3.2661 -1.66311 3B 0.1092 6.5814 -2.32379 4 3.6125 3.0056 -1.59428 5 3.2771 3.3186 -1.53360 6

γ 0.4901 0.4377 0.4143 0.3628 0.5522 0.4217

a 0.0009 0.001 0.0009 0.0011 0.0008 0.0009

b -0.1659 -0.1681 -0.1639 -0.1772 -0.1567 -0.1639

c 3.062 3.0864 3.0283 3.2084 2.9393 3.0437

Fig. 6 shows the effect of loading frequency on the dynamic stiffness modulus of samples obtained from trial sections taking the |E*| at reference temperature of 21°C. Section 1, Marshall/PRD with Pen 40-50, has the highest dynamic modulus value, which indicates that it is the stiffest section. However, section 3B, Marshall/PRD with Pen 60-70 and limestone aggregate, had the lowest stiffness value; it is around half of that of Section 1. The effect of test temperature on dynamic modulus values of trial sections at loading frequency of 25 Hz, |E*|, can also be seen in Fig. 6. This figure shows that all trial sections attained almost the same |E*| value at the maximum temperature of 54°C. In addition, it was noticed that section 1, again, is the stiffest section and section 3B had the lowest stiffness value. The dynamic stiffness modulus of section 3B was around half of that of Section 1. The effect of using different asphalt binders, aggregates, mix design and base layers is discussed in the following sections.

Fig. 6. Plot of loading frequency versus |E*| for all trial sections at 21°C (left); Plot of temperature versus |E*| for all trial sections at 25 Hz (right). 5.2.1. Effect of asphalt binder To study the effect of using different asphalt binders, master curves of trial sections 1, 2 and 6 were compared as shown in Fig. 7. that the results clearly show the effect of using different binders on the mixture stiffness. The figure shows that section 1, Marshall/PRD with Pen 40-50, has the highest dynamic modulus compared to sections 2 and 6 at low reduced time (high frequency) and temperature. In contrast, the stiffness of section 1 became lower than sections 2 and 6 at high reduced time and temperature. This concluded that stiff unmodified asphalt binders, such as Pen 40-50, make thick asphalt concrete layers stiffer at low reduced time (high frequency) than those of Pen 60-70 or polymer-modified binders. However, it is the lowest in stiffness at high reduced time which reduces its resistance to permanent deformation. Thus, polymer-modified binders are performing better at high reduced time than unmodified binders.

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Fig. 7. Dynamic modulus master curves for sections 1, 2 and 6. 5.2.2. Effect of aggregate type To study the effect of using different aggregates, master curves of trial sections 2, with Gabbro, and 3B, with limestone, were compared as shown in Fig. 8. Section 2 had higher dynamic modulus than that of section 3B at low-to-intermediate reduced times (intermediateto-high frequencies) and temperatures. This result demonstrates that using Gabbro increases the stiffness of the mixture for most of the range of reduced time used in this study.

Fig. 8. Dynamic modulus master curves for sections 2 and 3B. 5.2.3. Effect of mix design The effect of using different design mixes was studied by comparing master curves of sections 2 (Marshall/PRD), and 4 (Marshall/QCS) as shown in Fig. 9. Both sections performed the same at low-to-intermediate reduced times while section 2 has a slightly higher dynamic modulus value at very high reduced time or temperature. It can be stated that the Marshall/PRD and Marshall/QCS design mixes did not have much effect on the stiffness of both sections.

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Fig. 9. Dynamic modulus master curves for sections 2 and 4. 6. CONCLUSIONS In order to evaluate the long-term performance of trial sections, laboratory and field tests were conducted. The following are the conclusions based on the results obtained during the first phase of this study:    

Variation between summer and winter temperatures in Qatar reduced the stiffness of asphalt concrete layers by about 80%. In addition, at high temperature, all sections had almost the same modulus value measured using FWD of 2,000 MPa. Sections 5 and 6, with PMB, were the lowest in temperature susceptibility. Section 1, Marshall/PRD with Pen 40-50 and Gabbro, was the stiffest compared to all other sections, while section 3B, Marshall/PRD with Pen 60-70 and limestone in the base layer, was the least stiff. The use of Gabbro aggregates increased the stiffness of the mixture and improved its performance more than that of limestone at low-to-intermediate reduced times and temperatures but only marginally.

More laboratory and field tests will be conducted in the near future to evaluate the fracture and fatigue resistance in addition to some field testing. Results will help to make recommendations for updating the materials and design of asphalt pavements and determining more of the input parameters for Mechanistic-Empirical analysis of asphalt pavements in Qatar. 7. ACKNOWLEDGEMENTS The authors would like to acknowledge the financial support provided by Qatar National Research Fund (QNRF) through the National Priority Research Program project 08310-2-110. This project was awarded jointly to Texas A&M at Qatar and Qatar University. Support of Fugro Peninsular company in field testing is duly acknowledged. 8. REFERENCES AASHTO Designation: TP 79-11

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Masad, E., Kassem, E., Little, D. Characterization of Asphalt Pavement Materials in the State of Qatar: A Case Study. International Journal of Road Materials and Pavement Design (2011), vol. 12, no. 4, 739-765. M-E PDG, 2009. Version 1.1. Applied Research Associates, Inc. Pellinen, T.K., Witczak, M.W., Bonaquist, R.F. Asphalt Mix Master Curve Construction Using Sigmoidal Fitting Function with Non-liner Least Squares Optimization. 15th ASCE Engineering Mechanics Conference, Columbia University, New York, 2002. Qatar Highway Design Manual (QHDM). 1997, The State of Qatar. Sadek, H., Masad, E., Sirin, O., Al-Khalid, H., Little, D., 2012. The Implementation of Mechnistic-Empirical Pavement Design Method to Evaluate Asphalt Pavement Design in Qatar. 5th Eurasphalt & Eurobitume Congress, Istanbul, 13-15th June 2012. TRL Client Project Report 282, Phase D, 2010 Yan-zhu, P., Duan-yi, W. Experimental Study on Dynamic Modulus Master Curve on ATPB Mixture. Applied Mechanics and Materials Vols. 117-119 (2012) 1556-1560. Zhu, H., Sun, L., Yang, J., Chen, Z., Gu, W. Developing Master Curves and Predicting Dynamic Modulus of Polymer-Modified Asphalt Mixtures. Journal of Materials in Civil Engineering (2011), vol. 23, no. 2, 131–137.

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