From the extensive literature review conducted in this chapter, it is concluded that existing experimental studies are insufficient to allow a thorough understanding on the mechanisms of skid resistance and tire/road noise on porous pavements. The lack of appropriate numerical models discourages the optimization of porous pavement functional performance. Porous pavement design, therefore, fails to directly consider the frictional and acoustical performances simultaneously. To address this problem, the following research needs are identified.
To develop numerical simulation models of skid resistance and tire/road noise for porous pavements, with proper representations of the porous layer properties.
To analyze the phenomena of skid resistance improvement and tire/road noise reduction on porous pavements and to quantify the effects of major factors affecting porous pavement frictional and acoustical performances.
To optimize the functional performances of porous pavements according to the numerical results and to improve the porous mixture design process to include the consideration of functional performances.
The primary objective of this study is to develop and apply numerical models to analyze the skid resistance and tire/road noise on porous pavements. The numerical simulations are cost- and time-saving and are easy to be implemented. They can serve as a complementary research approach to experimental studies. This study should enhance the understanding in the mechanisms of skid resistance and tire/road noise on porous pavements and provide a clear picture on the influencing factors. When integrated with existing design practices, the findings in this study should be able to predict the functional performance of finished porous pavements and could be used to optimize the mixture design. Furthermore, the models and analyses could also be
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used in the maintenance management of porous pavements to help in deciding the maintenance strategies.
The present study will focus on the simulations of lock-wheel trailer skidding test and close-proximity noise measurement. These two tests are the most popularly used methods to date and the test conditions are clearly defined in the specifications.
Only the simple situation of straight traveling of vehicles at a constant speed is considered, since it is the standard test scenario and also the most common traveling condition on roads. Moreover, to simplify the problem and focus on pavement properties, only smooth tires with no tread patterns are adopted in the current simulation models. This is also because smooth tire experiences the most adverse skid resistance on wet pavements and generates a noise level with no much difference from that of a treaded tire on porous pavements. Based on the scope of this work, the following tasks are identified to be carried out in the remaining chapters.
To develop a numerical methodology to replicate the drainage capacity of porous pavements using the finite element method, and apply this approach in the skid resistance modeling of porous pavements. The resulted overall FE model should be able to simulate the ASTM E274 lock-wheel trailer test on porous pavements and should be validated against experimental data.
To develop an analytical framework to compare the frictional performance of porous and non-porous pavements under the same condition. This framework is then used to explain the mechanisms of skid resistance improvement on porous pavements and analyze the effects of major factors (such as porosity, porous layer thickness, rainfall intensity and vehicle speed) that can affect skid resistance on a porous pavement.
To develop a numerical model simulating the close-proximity tire/road noise measurement according to ISO 11819-2 specification. The model should cover the major noise generation, amplification and reduction mechanisms, such as the
89 tire vibration, horn effect and pavement acoustic absorption. It may involve both the finite element method and the boundary element method. The model needs to be calibrated and validated against the experimental measurements as well.
To apply the tire/road noise model to compare the noise levels on porous and non-porous pavements, and explain the mechanisms. The developed model is then used to analyzed the effects of major factors affecting porous pavement acoustical performance. These factors include porosity, porous layer thickness, surface texture and vehicle speed.
To integrate skid resistance and tire/road noise performances into porous pavement design. The developed models serve as a tool to predict the frictional and acoustical performances of the finished porous pavement in the design phase and the extensive analysis results are used to optimize the mixture design. The identification of key variables and design criteria is an essential challenge in this task, as well as the valuation of safety and comfort benefits.
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Table 2.1: Major mechanisms in tire/road noise generation and amplification
Generation mechanisms
Structure-borne mechanisms
Impact-induced vibration
Tread impact Texture impact Running deflection Friction/adhesion-
induced vibration
Stick-slip Stick-snap Air-borne mechanisms
Air pumping Air turbulence
Amplification mechanisms
Tire-pavement configuration Horn effect
Tire carcass Cavity resonance
Tread patterns
Helmholtz resonance Pipe resonance
Table 2.2: Effects of major influencing factors on tire/road noise variation (Sandberg and Ejsmont, 2002)
Influencing factor Noise level variation (dB)
Vehicle speed (30-130 km/h) 25
Road surface (conventional) 9
Road surface (including extremes) 17
Truck tire type (same width) 10
Car tire type (same width) 8
Car tire type (including width influence) 10
Studs in tire 8
Wheel load and tire inflation (±25%) 5
Road condition (wet/dry) 5
Temperature (0-40°C) 4
Torque on wheel (0-3 m/s2 acceleration) 3
91 Table 2.3: Coefficients in the linear equation describing the speed-dependency of
tire/road noise
Source A B Method Remarks
Anonymous (1971)
24.1 30.5
CB
Truck, rib
9.3 41.6 Truck, Lug
Steven and Pauls (1990)
26.2 32.9
CPX
Porous 0/5
27.3 33.5 Porous 0/8
23.4 37.3 ISO surface
24.4 36.9 SMA 0/5
24.6 37.2 Surface dressing
21.9 39.9 PCC pavement
27.9 35.5 AC 0/11
27.1 36.7 Asphalt 0/11
Ivannikov et al.
(1998)
7.1 37.6
CB
ISO surface
11.8 36.3 SMA
10.7 36.8 porous
Steven et al.
(2000)
30.6 34.9
CPX
AC 0/16 with chippings on surface
33.5 33.0 SMA 0/4
34.2 32.6 SMA 0/6
30.4 34.9 SMA 0/8
27.8 37.0 Surface dressing 5/8
39.5 29.2 Porous 6/16
37.1 29.0 Porous 4/8+11/16
34.4 29.2 Porous 2/4+11/16
38.9 30.9 Gussasphalt 0/11+2/5+5/8
20.3 42.0 PCC transversely brushed
32.7 34.2 PCC with epoxy-durop 3/4
24.3 37.8 PCC burlap drag
27.6 36.9 PCC exposed aggregate
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Table 2.4: Potential influences of pavement properties on tire/road noise (Sandberg and Ejsmont, 2002)
Parameter Degree of influence
Macrotexture Very high
Megatexture High
Microtexture Low to moderate
Unevenness Minor
Porosity Very high
Porous layer thickness High
Adhesion Low to moderate
Friction Low to moderate
Stiffness Uncertain
Table 2.5: Noise reduction on porous pavements in selected countries
Country Noise reduction [dB(A)]
Denmark 3 to 5
The Netherland more than 3 to 5 United Kingdom 5 to 6
France more than 5
United States 3 to 6
Sweden 7 to 12
Switzerland 7 to 9
China 3 to 6
Japan 4 to 6
93 Figure 2.1: General iterative procedure for elasto-hydrodynamic lubrication
Figure 2.2: Three-zone model for sliding tire on wet pavement (Moore, 1966)
Stress-Strain Relationship Modified Film
Thickness Distribution
Hydrodynamic Pressure Generation
Elastic Displacements
Reynolds' Equation
Reynolds' Equation Assumed Film
Thickness Distribution
Convergence?
No
Finish Yes
Start
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Figure 2.3: British pendulum tester
Figure 2.4: Dynamic friction tester
Figure 2.5: Accelerated polishing machine
95 Figure 2.6: Lock-wheel skid resistance trailer
Figure 2.7: Griptester
Figure 2.8: Side force and yaw angle Side Force
Tire Plane Direction of Travel
Yaw Angle
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Figure 2.9: Mu-meter
Figure 2.10: Sideway-force coefficient routine investigation machine (SCRIM)
Figure 2.11: Pavement microtexture and macrotexture (Flintsch et al., 2003) microtexture λ < 0.5 mm
0-0.2 mm (amplitude)
macrotexture
0.5 mm < λ < 0.5 mm
0.2-3.0 mm (amplitude)
97 Figure 2.12: Skid numbers of different texture characteristics (Sabey, 1966)
Figure 2.13: Effects of vehicle speed and water film thickness on skid number (Benedetto, 2002)
Figure 2.14: Friction coefficient at different slip ratios (Hall et al., 2009)
Vehicle Speed (km/h)
Note: t refers to water film thickness t = 1.5 mm t = 1 mm t = 0.5 mm t = 0.1 mm t = 0 mm Dry pavement surface
0
20 40 60 80 100 120 140
10 20 30 40 50 60 70 80
Skid Number
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Figure 2.15: Illustrative relationship of tire/road noise and power unit noise with vehicle speed (Rasmussen et al. 2007)
(a) (b)
Figure 2.16: Texture impact and resulted tire vibration (not to scale) (Dare, 2012)
70 75 80 85 90
20 40 60 80 100
Speed (km/h)
Sound Pressure Level [dB(A)] Total noise
Power unit noise Tire/road noise
99 Figure 2.17: Test site configuration in SPB measurement (ISO, 1997a)
Figure 2.18: CPX trailer (Bakker et al., 2012)
100
Figure 2.19: Microphone positions in CPX measurement (ISO, 2013)
(a) CPX reference tire P1
(b) CPX Reference tire H1
Figure 2.20: CPX reference tires and tread patterns (Bakker et al., 2012)
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(a) Single probe (b) Dual probe
Figure 2.21: Configuration of OBSI measurement (Rasmussen et al., 2011)
(a) Outer drum (b) Inner drum
Figure 2.22: Illustration of the two types of drum facilities used in laboratory Drum
Pavement surface Tire
Tire
102
Figure 2.23: Illustrations of the speed dependency of tire/road noise
Figure 2.24: Pavement texture direction
Figure 2.25: Noise level variations of different surface types with pavement age (Bendtsen, 1998)
(a) Positive texture (b) Negative texture
66 70 74 78 82 86 90
20 40 60 80 100 120
Speed (km/h)
Sound Pressure Level [dB(A)]
1 2 3 4 5 6
1. Cars 2. Light trucks 3. Busses 4. Trucks with 2 axles 5. Trucks with 3 axles 6. Heavy trucks, more than 3 axles
Porous asphalt (18-22%) Porous asphalt (>22%) Porous asphalt (>22%) Dense asphalt concrete Open graded asphalt concrete
Sound Pressure Level [dB(A)]
Pavement Age
103 Figure 2.26: Measured sound levels on different types of pavement surfaces
(der Graaff et al., 2005)
Figure 2.27: Acoustic absorption spectra of porous layers with different thicknesses (Losa and Leandri, 2012)
t = 40 mm t = 60 mm t = 100 mm
t = 80 mm S: steer axle
D: drive axle T: trailer axle
PAC: porous asphalt concrete DAC: dense asphalt concrete SMA: stone mastic asphalt DSK: Dünne schicht im Kalteinbau
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Figure 2.28: O'Boy and Dowling's model (2009)
Figure 2.29: Examples of low-order modes in the WFEM model developed by Kropp et al. (2012)
p: applied load per unit area w: normal displacement x, y: plane coordinate t: time
h: thickness R0: radius of tire E: Young's modulus ν: Poisson's ratio D: bending stiffness T: in-plane tension (a) Complete viscoelastic cylindrical model or the tyre belt
(b) A thin bending plate with finite width and in-plane tension Outer layer, r0
Multiple layer, r0 Annular bands Inner layer
Springs representing sidewalls and dampers Air pressure
Wheel hub fixed to ground Excitation force