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 decisionmaking 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.
Result of mixture
design, material
characteristics,
construction practices,
and variability.
Source: Boere, 2009
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)
Source: ISO 13473-2, 2002
10
Effects of Texture Spectrum
Mobile
Measurement
Methods
Stationary
Measurement
Methods
ISO 13473-2, 2002
Investigating Surface Texture
•
Micro-texture
•
• Rubber pad friction
• Skid trailers
tests
•
Macro-texture
Mega-texture
• Mobile profilers
•
Unevenness
• Texture meter
• Mobile profilers
• Sand patch
• Full-scale ride
• Laser profilers
testers
12
Effects of Texture Spectrum: Micro-Texture
13
Dynamic Friction Tester (DF Tester)
•
Rotating rubber
sliders contact
pavement surface to
produce friction
profile.
•
Available for field
tests.
•
Requires water
supply.
14
British Pendulum Tester (BPT)
•
Rubber slider
mounted on
pendulum contacts
pavement surface
while raising pointer
on BPN scale.
BPN
SCALE
RUBBER
SLIDER
BPT
•
Available for lab and
field tests.
SGC
SAMPLE
JIG ASSEMBLY
15
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
Macrotexture PSD
1.E-07
y = 4E-06x-1.613
R² = 0.9537
1.E-08
1.E-09
PSD (m3)
•
1.E-10
1.E-11
1.E-12
1.E-13
1.E-14
10.00
100.00
1000.00
f (cycles/m)
10000.00
27
Amplitude & Texture Spectra
Amplitude Spectrum, Octave Bands
0.70
0.60
al (mm)
0.50
Texture Spectrum in octave bands
60
0.40
0.30
0.20
50
0.10
40
1000.0
100.0
10.0
1.0
0.1
l (mm)
30
20
0.5
1.0
2.0
4.0
8.0
16.0
32.0
0
64.0
10
128.0
Ltx (dB)
0.00
l (mm)
28
Texture Level Distribution
29
Lessons Learned
•
Need full-scale field experimentation for
validation!
•
Lab work demonstrates texture-friction
relationship to micro-texture and macrotexture 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