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Timothy D. Miller
Fugro Consultants, Inc.
Austin, TX
1
Presentation Overview
• Pavement Surface Texture
• Specifications
• Measurement Methods
• Surface Texture & Friction
• Next Steps
2
Why Surface Texture?
• Surface texture affects the user!
• Safety
• Vehicle fuel economy
• Noise
• Surface conditions influence decision-
making processes and asset management
strategies of state highway agencies.
3
Big Questions
• How is texture related to friction?
• What are desired test specifications and methods?
• What analysis techniques are available?
• What data is most critical for state agencies?
4
Pavement Surface Texture
• Defined by four primary ranges.
Source: Boere, 2009
Result of mixture
design, material
characteristics,
construction practices,
and variability.
Effects of Surface Texture
• Rolling resistance
• Friction
• Tire wear
• Noise
• Vibration
Source: ISO 13473-2, 2002
Specifications
• AASHTO, ASTM, ISO standards for
friction and texture measurement
methods and devices.
• Several indices have been developed,
though a unified standard has not
appeared.
Ratings and Indices
• Roughness and Unevenness • International Roughness Index (IRI)
• Friction Indices • International Friction Index (IFI)
• Friction Number (FN)
• Texture • Mean Profile Depth (MPD)
• Mean Texture Depth (MTD)
• Other rating systems
8
Key Processing Method
• Use laser profiling techniques and theories to analyze surface texture.
• Treat surface profiles as signals, analyze with Discrete Fourier Transform methods to determine frequency spectral content.
• Investigate asperity distribution, relate spectral attributes to user impacts and pavement distresses.
Current Texture Metrics
• Mean profile depth (MPD)
• Mean texture depth (MTD)
10
Source: ISO 13473-2, 2002
Effects of Texture Spectrum
11
Stationary
Measurement
Methods
Mobile
Measurement
Methods
ISO 13473-2, 2002
Investigating Surface Texture
• Micro-texture
• Rubber pad friction
tests
• Macro-texture
• Texture meter
• Sand patch
• Laser profilers
• Mega-texture
• Skid trailers
• Mobile profilers
• Unevenness
• Mobile profilers
• Full-scale ride
testers
12
Effects of Texture Spectrum: Micro-Texture
13
• Rotating rubber sliders contact pavement surface to produce friction profile.
• Available for field tests.
• Requires water supply.
Dynamic Friction Tester (DF Tester)
14
British Pendulum Tester (BPT)
• Rubber slider
mounted on
pendulum contacts
pavement surface
while raising pointer
on BPN scale.
• Available for lab and
field tests.
15
JIG ASSEMBLY
SGC
SAMPLE
BPT
RUBBER
SLIDER
BPN
SCALE
Effects of Texture Spectrum: Macro-Texture
16
Circular Track Meter (CTM)
• Laser traces circle,
which is divided into 8
segments for analysis.
• When combined with
the DF Tester, the CTM
can be used to
calculate IFI values.
17
Sand Patch Test
• Basic, widely used
test to estimate
pavement mean
texture depth (MTD).
• Spread circle of sand
on pavement,
measure circle
diameter, calculate
MTD.
18
Stationary Linear Profiler (SLP)
• Assembly developed
by UW-Madison for
FHWA’s ARC program.
• Evaluate in-service
pavements, HMA cores
and SGC lab samples.
• Obtain profiles for TSA
evaluation.
19
Effects of Texture Spectrum: Mega-Texture
20
Mobile Profiling Equipment
• Automated data
collection vehicle
(ARAN)
• Laser profiler in
front, imaging
cameras in back
• GPS and GPR
integration 21
Skid Testing
• States contracting network-level skid projects to inform asset management strategies.
• Requires two people, tow vehicle, skid trailer, data processing.
22
Effects of Texture Spectrum: Unevenness
23
How do we link all this together?
• Texture spectral analysis
Pavement “Fingerprinting”
• A person’s fingerprint distinguishes them from billions of other people.
• Texture spectral analysis (TSA) techniques allow for unique identification of pavement surface characteristics.
25
Pavement “Fingerprinting”: TSA
• Utilize a stationary linear profiler (SLP).
• Analyze profile using Discrete Fourier
Transform to produce the power spectral
density (PSD).
• Two types of spectra derived from the PSD:
• Amplitude Spectrum
• Texture Level Spectrum
26
Power Spectral Density
• Describes frequency content of
pavement signal
27
y = 4E-06x-1.613 R² = 0.9537
1.E-14
1.E-13
1.E-12
1.E-11
1.E-10
1.E-09
1.E-08
1.E-07
10.00 100.00 1000.00 10000.00
PS
D (
m3)
f (cycles/m)
Macrotexture PSD
Amplitude & Texture Spectra
28
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.11.010.0100.01000.0
al (
mm
) l (mm)
Amplitude Spectrum, Octave Bands
0
10
20
30
40
50
60
12
8.0
64
.0
32
.0
16
.0
8.0
4.0
2.0
1.0
0.5
Ltx
(d
B)
l (mm)
Texture Spectrum in octave bands
Texture Level Distribution
29
Lessons Learned
• Need full-scale field experimentation for validation!
• Lab work demonstrates texture-friction relationship to micro-texture and macro-texture at low end of spectrum.
• Questions remain at high end of spectrum with mega-texture and unevenness.
30
Next Steps
• Expand data collection efforts to other
states and regions.
• Validate findings at existing test tracks.
• Develop pooled-fund proposal among state
agencies.
31
Acknowledgements
• Asphalt Research Consortium,
Federal Highway Administration
• Modified Asphalt Research Center,
University of Wisconsin – Madison
• Fugro Consultants, Inc.
32
Thanks for listening!
Questions?
Comments?
Other Feedback?
33