EFFECTS OF DUAL VERSUS SUPER SINGLE TRUCK TIRE ON FLEXIBLE PAVEMENT PERFORMANCE; A MECHANISTICAPPROACH Ahmad M. Abu Abdo Department of Civil and Infrastructure Engineering, American University of Ras Al Khaimah, Ras Al Khaimah, United Arab Emirates E-Mail: ahmed.abuabdo@aurak.ac.ae ABSTRACT With the widely observed premature failures of flexible pavements, attentions have been directed to changes on heavy vehicles loads, axles configurations, and tire types and pressure as a cause for such phenomenon. Super single (wide-base) tires were introduced in early 1980s as a replacement to traditional dual tires, and considered beneficial to the transportation industries. However, this type of tires proved to cause more damage to flexible pavements. Recently, new generation of super single tires were developed with a promise that the damage issue was addressed. Many studies were conducted but were in disagreements in their findings. Thus, this study was conducted. 3D Move Analysis software was used to conduct analytical evaluation and compare both tire configurations by utilizing an existing project and actual materials test data. Results showed that when compared to dual tires, super single tire induced less normal stresses in the analyzed flexible pavement by 28% in the z direction, 45% in the y direction, and 47% in the x direction. Therefore and as per the results of the analysis, super single tires would inflect less percentage of bottom up cracking in the asphalt concrete layer and less permanent deformation in all pavement layers. Keywords: flexible pavement, pavement performance, dual truck tires, super single tire, mechanistic approach, 3D move analysis. INTRODUCTION Flexible pavements are deteriorating in an alarming rate, even though new design methods and materials specifications are being developed and adopted. It is believed that it is due to the changes in heavy vehicle loads, axle configurations, and tire pressure and type [1]. In early 1980s, super single (wide-base) truck tires were developed to replace conventional dual tires and used throughout Canada and Europe [2], it was developed to reduce running costs with potential savings on the long run. Earlier studies showed that first generation of super single tires caused more distresses (permanent deformation and surface cracks) to flexible pavements when compared to conventional dual tires [3-5]. Recently, new generation of super single tires was introduced with a promise that it would perform better economically and minimize inflected damages to pavements, Al-Qadi et al. [1] investigated the new generation of super single tires using Finite Element Analysis (FEA) and suggested that damage caused by the new super single tires would be similar or relatively more damaging than conventional dual-tires. Greene et al. [6] conducted a study on pavement damage potential of three different super single tires in comparison of a conventional dual tire. They concluded that super single tire performed as well as the dual tire, however it created more permanent deformation and bottom-up cracks than dual tires. A study by Xue and Weaver [7] showed that two out of three different types of super single tires have the same effects on pavement as dual tires. Grellet et al. [8] found that the use of super single tires led to a 14 to 30% increase of the tensile strains at the bottom of the surface layer. However, at a shallow depth close to the tire edge, there was a 20% reduction of the tensile strains. A recent study [9] argued that the super single tires caused greater permanent deformation than dual tires due to the load distribution. On the other hand, Pries et al. [10] utilized a mechanistic approach and field measurements to evaluate the effects of super single tires on flexible pavement. They concluded that dual and super single tire configurations caused the same horizontal strain at the bottom of the asphalt layer, and reported that the field measured stresses in the base and subgrade were the same for dual and super single tire configurations, which would result in the same permanent deformation. Wang and Roque [11] argued based on their findings that the new generation super single tire produced approximately the same damage as dual tires. A recent study by Grelletet al. [12] found that the damage caused by single super tires may cause less damage in the upper part of asphalt concrete layer and more damage in fatigue cracking and rutting of other unbound layers. However, they declared that their study was conducted under ideal conditions and cannot be generalized. SCOPE The main purpose of this study was to investigate the effect of two truck tires configurations; the dual tires and super single tire axle configuration, on flexible pavements and to evaluate the distresses caused by both using 3D Move Analysis Software. 3D MOVE ANALYSIS SOFTWARE 3D Move Analysis Software (Figure-1) was developed by the Asphalt Research Consortium (ARC), which is a group of five organizations; Western Research Institute (WRI), Texas A&M University (TAMU), University of Wisconsin-Madison (UWM), University of Nevada-Reno (UNR), Advanced Asphalt Technologies 4136
(AAT). The software is available at http://www.arc.unr.edu/index.html [13]. Figure-1. 3D Move Analysis software main screen. 3D Move utilizes a continuum-based finite-layer method to determine the pavement response under different loading conditions. Major pavement response factors such as the moving traffic-induced 3D contact stress distributions (normal and shear), vehicle velocity, and viscoelastic material properties for pavement layers can be included in the analysis. This method uses the Fourier transform technique and deals with every layer as a continuum. Therefore, complex vehicle loadings such as multiple loads and non-uniform tire pavement contact stress distributions can be incorporated in the analysis. Furthermore, 3D Move software has the ability to analyze any tire imprint, including those generated by super single tires [14-16]. Huhtala and Pihlajamaki[17] and Al-Qadi and Wang [18] suggested that the finite-layer method was better when it came to computationally efficiency than the moving load models. This is because flexible pavements are horizontally layered and pavement responses are needed at selected locations.3d Move software applies this approach in the analysis. Furthermore, 3D Move software utilizes viscoelastic materials properties in its analysis, making it an ideal method to model asphalt concrete (AC) layer s response and to simulate pavement response as a function of vehicle velocity. Furthermore, 3D Move software allows users to utilize the frequency sweep test data ( E* and G* test data) of asphalt binder and mixes in the analysis [13]. In a recent study, results illustrated that the mechanistic approach, via 3D Move software, was a better tool to determine the performance of asphalt pavement than commonly used methods, since it captured the effect of changes in materials properties and their response to different loading conditions and temperatures on flexible pavement performance [19]. METHODOLOGY To achieve the goal of this study an existing project data was used as inputs. The project was the extension of Emirates Road to Ras Al Khaimah, UAE and is currently under construction. Actual asphalt mix (HMA) dynamic elastic modulus E* and asphalt binder dynamic shear modulus G* tests data [20] were used in the analysis. To compare the effects of dual tires versus super single tire on the flexible pavement, two axle (built-in) cases were used as described in the software[21]: Case 3: This is a dual tire tandem axle load represented by four elliptical contact areas. The contact pressure is assumed to be uniform over contact area with a magnitude of 862 kpa. The half axle load is 90 kn (22.5 kn/tire). Case 8: This is a super single tire tandem axle load represented by two elliptical contact areas. The contact pressure is assumed to be non-uniform over the contact area. The half axle load is 90.0 kn (45.0 kn/tire). All Cases details and pavement structure are illustrated in Figure2 and 3, respectively. a) Case 3: Dual tire tandem axle b) Case 8: Super single tire tandem axle Figure-2. Axle configuration details (After 3D move analysis). DISCUSSION OF RESULTS Upon running the analytical models (3D Move Analysis Software) for both tire configurations, the dynamic analysis results showed that the normal stresses in all directions induced by super single tire on the analyzed flexible pavement were less than stresses caused by the dual tires. Table-1 illustrates the summary of the normal and shear stresses for both tire configurations. The differences in the normal stresses in the x, y, and z directions were -47%, -45%, and -28%, respectively when comparing super single tire to dual tires. Thus, the distresses caused by super single tire should be less than 4137
dual tires. On the other hand, the shear stress in x-y direction inflected by the super single tire was higher by 161%, but equal in the other directions. Figure-4 illustrates the normal stress in z, y, and x by super single tire is less than dual tires. Furthermore, the duration of the induced stresses in the pavement is less for directions vs. loading time for dual tires and super single tires, it can be clearly observed that normal stresses caused the super single tire. b) Case 8: Super single tire tandem axle a) Case 3: Dual tire tandem axle Figure-3. Pavement structure and response points. Table-1. Pavement stresses due to dual tires and super single tire loadings. Stress Dual tires Super single tire % Difference Normal Stress X-X(kPa) 1437.5 763.72-47% Normal Stress Y-Y (kpa) 1148.4 633.66-45% Normal Stress Z-Z (kpa) 952.39 686.76-28% Shear Stress XY (kpa) -84.825-221.23 161% Shear Stress XZ (kpa) -1.88E-07-1.88E-07 0% Shear Stress YZ (kpa) -1.88E-07-1.88E-07 0% 1.20E+03 Normal Stress (z direction), kpa 1.00E+03 8.00E+02 6.00E+02 4.00E+02 2.00E+02 5.00E 02 1.00E 01 1.50E 01 2.00E 01 2.50E 01 3.00E 01 3.50E 01 2.00E+02 Time, sec Dual Tires Super Single Tire a) Normal stress in Z direction 4138
2.00E+03 Normal Stress (x direction), kpa 1.50E+03 1.00E+03 5.00E+02 5.00E 02 1.00E 01 1.50E 01 2.00E 01 2.50E 01 3.00E 01 3.50E 01 5.00E+02 1.00E+03 Time, sec Dual Tires Super Single Tire b) Normal stress in X direction 1.40E+03 Normal Stress (y direction), kpa 1.20E+03 1.00E+03 8.00E+02 6.00E+02 4.00E+02 2.00E+02 2.00E+02 5.00E 02 1.00E 01 1.50E 01 2.00E 01 2.50E 01 3.00E 01 3.50E 01 4.00E+02 Time, sec Dual Tires Super Single Tire c) Normal stress in Y direction Figure-4. Normal vertical stress due to tire loading. As for the predicted pavement stresses, Figure- 5shows predicted AC Bottom Up Cracking (%) of the analyzed pavement. It was found that super single tire would cause less cracks than dual tires, mainly due to lower stresses. It is interesting to observe that none of the tire configurations results met the design limitations. As 60 for permanent deformation for all layers, it was found that the super tire caused less permanent deformation than dual tires in all layers. None of the tire configuration met the design limits for the AC layer. However, where the dual tires failed, the super tire passed in all other pavement layers, as shown in Figure-6. 50 AC Bottom UP Cracking (%) 40 30 20 10 0 Single Super Tire Dual Tires Acceptable Limit Figure-5. Bottom up cracking in asphalt layer due to tire loading. 4139
Permanent Deformation (mm) 40 35 30 25 20 15 10 5 0 AC Layer Base Layer Subbase Layer Subgrade Layer Single Super Tire Dual Tires Acceptable Limit Figure-6. Bottom up cracking in asphalt layer due to tire loading. SUMMARY AND CONCLUSIONS Based on this study results and when comparing the effects of super single tire to conventional dual tires on flexible pavement via 3D Move Analysis Software, the following observations and conclusions can be made: Normal stresses resulted when loading a flexible pavement using super single tire were less by 28% in the z direction, 45% in the y direction, and 47% in the x direction. Super single tires induced higher shear stress on the x- y plane than dual tires. However, both tire configurations caused the same shear stresses on other planes. Duration of stresses in the pavement caused by super single tires was shorter than by dual tires. Dual tires would cause higher percentage of Bottom Up Cracking of AC layer than super single tires. Similarly, dual tires would cause higher permanent deformation in all layers of the flexible pavement structure. Both tire configurations would inflect damage that exceed the design limits set by 3D Move Analysis Software. Unlike dual tires, permanent deformations resulting from super single tire in the base, subbase, and subgrade layers did not surpass the design limits. Thus, it speculated that by modifying the AC layer properties and/or thickness, the design would not fail. ACKNOWLEDGEMENT The author would like to extend his gratitude to the American University of Ras Al Khaimah, UAE for the provided support. REFERENCES [1] Al-Qadi IL, Yoo PJ, Elseifi MA, and Janajreh I. 2005. Effects of Tire Configurations on Pavement Damage. Journal of the Association of Asphalt Paving Technologists. 74(2005) 921-962. [2] COST. 2001. Effects of Wide Single Tyres and dual Tyres. Final Report of the Action (Version 29), European Cooperation in the field of Scientific and Technical Research. [3] Bonaquist R. 1992. An Assessment of the Increased Damage Potential of Wide Bases Single Tires. Proceeding of the 7th International Conference on Asphalt Pavements, Nottingham, UK. pp. 1-16. [4] Sebaaly PE. 1992. Pavement Damage as Related to Tires, Pressures, Axle Loads, and Configurations. Vehicle, Tire, Pavement Interface, ASTM STP 1164, American Society for Testing and Materials, Philadelphia. pp. 54-68. [5] Abu Abdo AM. 2004. Super Single vs. Dual Tires. 44th Idaho Asphalt Conference, Idaho, USA. [6] Greene J, Toros U, Kim S, Byron T, and Choubane B. 2009. Impact of Wide-Base Single Tires on Pavement Damage. Research Report FL/DOT/SMO/09-528, State Materials Office, Florida, USA. [7] Xue W and Weaver E. 2011. Pavement Shear Strain Response to Dual and Wide-Base Tires. Transportation Research Record: Journal of the Transportation Research Board. 2225:155-164, DOI: 10.3141/2225-17. [8] Grellet D, Doré G, and Bilodeau JP. 2012. Comparative Study on the Impact of Wide Base Tires and Dual Tires on the Strains Occurring within Flexible Pavements Asphalt Concrete Surface Course. Canadian Journal of Civil Engineering. 39:526-535, DOI: 10.1139/L2012-031. 4140
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