Vol-7, Special Issue3-April, 2016, pp1946-1950 http://www.bipublication.com
Research Article
Investigation of perpetual pavement using finite element modelling
Monireh Zokaei1 and Mansour Fakhri2
1 Department of Civil engineering,
Khajeh Nasiroldin Toosi University–Tehran, Iran. 2
Khajeh Nasiroldin Toosi University –Tehran, Iran.
ABSTRACT
With considering numerous failures which exist in flexible pavements, a huge amount of money is spending on treatment and reconstructing pavements. Many researches have been performed to with improving pavement quality, increased the performance and pavements life. One type of long lasting pavements is perpetual pavement. In this research ABAQUS software is used to simulate pavement. . Materials are modelled as visco-elastic type and loading wheel is assumed to be moving. After gaining results, the effects of different parameters on pavements function is assessed. Modelling movements of loading wheel is very effective in viscoelastic condition, increase more accuracy of the finite-element model.
Key words:- perpetual pavement, ABAQUS, empirical mechanistic system.
1. INTRODUCTION
Pavement engineers have been producing long-lasting asphalt pavements since the 1960s. Research has shown that well-constructed and well-designed flexible pavements can perform for extended periods of time. Various countries of the world, especially America are going to construct perpetual pavements to reduce destructions as much as possible regarding to high rate of destructions and short life of pavements. Full-depth pavements are constructed by placing asphalt layers on modified or unmodified soil or subgrade material. In recent years, pavement engineers have begun to adopt a methodology of designing pavements to resist bottom-up fatigue cracking and deep structural rutting, the two most devastating pavement distresses, and through this change in thinking the idea of Perpetual Pavements or long-lasting pavements has evolved. The approach to the design of long-life or Perpetual Pavements requires a different strategy than that which has
normally been applied to pavement design in the past. Empirical pavement design must rely on relationships between observations of pavement performance, a scale that represents traffic, some gross indicator of material quality such as a structural coefficient, and the thickness of the layers.
surface cracking. The basic concept of a Perpetual Pavement is illustrated in Figure 1. While the importance of proper design for a long-lasting pavement must be recognized, one must also understand that design life is a function of the design requirements, material characteristics, construction practices, layer thicknesses, maintenance activities, and the failure criterion. A perpetual pavement road is smooth, safe and the cost is very low compared with ordinary pavement, and the life is high and it is not needed to waste traffic time for extensive crossroad and linear reconstruction or repair. Effective service life of Pavement structure is increased, concept of perpetual pavement increases more lifecycle of asphalt; accordingly, the structural capacity is high too. As shown in fig.2 every upper, middle and lower layer must have the following features. If pavement is withstanding against expected heavier loads, tensions, strains and displacements are trivial, thus the structure remains sound, thus it is called perpetual pavement. Cross- sections more than 200mm or 8 inch may have to rut and in cross-sections higher than 8 inches only the upper layer is rutted Consequently, only the upper layer needs to be repaired in several years interval to solve the problem.
According to researches, finite horizontal strains at the bottom of lower layer of asphalt are helpful for rut control. Increased thickness of pavement structure reduce possible bottom up fatigue rut lower thickness of the mixed pavement material. Perpetual pavement needs more focus on details and requirements of construction to be constructed with desirable quality from lower layer to upper layer. A perpetual pavement must be executable in view of engineering and economic. Preliminary engineering process needs effective pavement design by selecting quality material, rut elimination, fewer recurrent pavement process, maintenance, and applicability of the desirable pavement. Also, effective design, low repair and maintenance cost and high lifecycle are very important in view of economy.
2. MODELLING BY USING FINITE- ELEMENT SOFTWARE
In this research, ABAQUS software is
implemented for analysing and simulation of perpetual pavement. ABAQUS is very capable software of finite element. It is using linear analysis as well as non-linear analysis for simple
and complex problems respectively.
This model illustrated in Figure 3.
3. PARAMETRIC STUDY OF THE FINIT-ELEMENT VISCOELASTIC MODEL
Fig.4 shows changed longitudinal tensile strain for different traffic speeds. Strain rates are 67.3 and 70 for 35 mph and 25mph speed. Tensile strain is increases to 83 when the speed is decreased. Hence, effect of traffic velocity is high and must be used for analysis.
Majority of executed project papers have shown that elastic analysis is used for many pavements. Linear elastic module is compared with viscoelastic module to compare their relative functions. Following figure shows the rate of linear tensile strain in 40.8 and 70km/h velocity for both modules. As shown in fig.10, viscoelastic module is highly concise for pavement anticipation; also, its function is better than that of the elastic modules. We conclude that behaviour of asphalt material is not explained well unless time and temperature are entered to the system.
4. RESULTS
• Obtained results of the model for linear tensile stain are compatible with measured results of project U.S.30. Furthermore, tension and strain are conformable.
• Modelling movements of loading wheel is very effective in viscoelastic condition, increase more accuracy of the finite-element model.
• The studied the effect of traffic velocity and realized that it is very effective. Advantage of studied impact of traffic velocity on max tensile strain helps us to define minimum velocity on the concerning path. 70km/h is recommended to be the least velocity because it is compatible with fatigue tolerance, which is equal to 70 micro strain, then fatigue rut is not occurred for higher velocities.
• By comparing elastic and viscoelastic conditions concluded that linear elastic model
does not resist effectively against high traffic speeds at the high temperature according to the anticipations, actual parameters cannot be obtained by this model; it is not a conservative policy for effective design, consequently, pavement is demolished soon but a viscoelastic model is the best choice for effective asphalt pavement analysis.
5. REFERENCES
1. ABAQUS user’s manual version 6.9. Simulia, Providence, RI. 2009.
2. Newcomb, Dave, and Larry Scofield, "Quiet Pavements Raise the Roof in Europe," Hot Mix Asphalt Technology, National Asphalt Pavement Association, 2003.
3. Liao, Y., Sargand, S. M., Khoury, I. S., and Harrigal, A. In-Depth Investigation th of Premature Distresses of Four Ohio SHRP Test Road Sections,” 86 TRB Annual Meeting
(CD-ROM), Board, National Research
Council, Washington, D. C.2007.
4. Transportation Research Perpetual
Bituminous Pavements. Transportation Research Circular 503, Transportation Research Board, National Research Council, December 2001.
5. Liao, Y. Viscoelastic FE modeling of asphalt pavements and its applications to U.S. 30 perpetual pavement. Ph.D. Dissertation, Civil Engineering Department, Ohio University, Athens, OH. 2007.
6. Abraham, H. Asphalts and Allied Substances: Their Occurrence, Modes of Production, Uses in the Arts and Methods of Testing, Third Edition. D. Van Nostrand Co., Inc. New York, NY. 1929.
7. Elseifi, M. A.; Al-Qadi, I. L.; Yoo, P. J. Viscoelastic Modeling and Field Validation of Flexible Pavements,؛ ASCE Journal of Engineering Mechanics, Vol. 132 No. 2, pp 172-178. 2006.
Validation of Perpetual Pavement Response to Vehicular Loading. Paper submitted to Transportation Research Board Annual
Meeting. Transportation Research Board. Washington, DC. 2008.
Fig.(1). Simplified Flowchart of Perpetual Pavement Design
}
100to 150 mm
surface
intermediate
HMA base
pavement foundation Max Tensile Strain
High quality HMA or OGFC 40 to 75 mm
High Modulus Rut Resistant Material 100 to 175 mm
Flexible Fatigue Resistant Material 75 to 100 mm Zone
of High Compression
Fig. (3). Meshed model of finite elements
Fig.(4). Tensile strain change due to different traffic velocity
