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Evaluation of NDTE Technologies for Airport Pavement Maintenance
and Acceptance Activities
Imad L. Al-QadiJohn S. Popovics
Wei XieSara Alzate
University of Illinois at Urbana-Champaign
Outline
• Project Scope and Objectives
• NDTE State-of-art report: Promising NDTE technologies to assess existing and new airport pavements
• Future Work
Objectives
• To determine the effectiveness and practicality of new and existing NDTE technologies for maintenance, evaluation, quality control and acceptance of flexible airport pavements
• To evaluate and recommend appropriate NDTE technologies to the FAA based on field evaluation results
Scope of workReview and summarizeexisting and new NDTE
technologies
Identify promising NDTE technology
(technical and practical suitability)
Identify current NDTE needs for airport pavements
and facilities
Field testing andanalysis of promising
NDTE technology
State-of-the-artreport
Finalreport
New research
NDTE State-of-the-art Report• Existing NDTE methods are summarized in a
draft report, for FAA review and comment• Each method is presented in a chapter:
– 1) Impact-echo – 2) Surface waves – 3) Sonic/ultrasonic – 4) Nuclear radiometry – 5) Infrared thermography – 6) GPR – 7) Laser profiling – 8) Digital imaging
NDTE State-of-the-art Report
• Each chapter discusses the following:– Theory– Equipment– Benefits and applications– Limitations – Recent developments
Nuclear Density Gauge
• The radiation intensity of gamma rays that passes through a medium, or is scattered back from a medium, is used to measure density.
• Nuclear density gauges are compact and provide direct and rapid measurements
Application of Nuclear Density Gauge
• Measuring in-situ HMA, concrete and solid densities
• Suitable for both thin and thick layers; better for thick layers.
Limitations of Nuclear Density Gauge
• Need for calibration
• Affected by lift thickness and variability of supporting layer
• Difficulties in identifying levels of segregation
• High initial cost, certification requirement, periodic inspection, and difficulties in shipping and transport and disposal.
Impact Echo
Resonant frequency interpreted for thickness information
Application of Impact-echo
• Measuring concrete slab thickness
• Identifying location and depth of delamination defects in concrete
Limitations of Impact-echo
• Local, point contact measurement
• Not effective for HMA pavements
• Only effective for top layer in pavement system
• Difficulties in locating small defects
Surface Waves (Spectral/Multiple Analysis of Surface Waves
(SASW/ MASW)
Measure dispersion of surface waves in layered media
Application of surface waves
• Estimate pavement layer properties (thickness and modulus)
Portable Seismic Pavement Analyzer (PSPA) for SASW
Estimated
stiffness
profile
Interpretation of MASW
Time(s)
dist
ance
(cm
)
0 0.5 1 1.5 2 2.5 3 3.5
x 10-3
50
100
150
200
250P
hase
vel
ocity
(m/s
)
Frequency (kHz)2 4 6 8 10 12 14 16 18 20
1000
2000
3000
4000
5000
6000
Impact-echo mode
Stacked multiple signal data MASW mapping of signal data
Lamb wave curve best fit to data to give layered structure
Limitations of surface wave• Local, point contact measurement
• Data inversion is complicated (MASW approach has sounder technical basis than SASW)
• Not reliable for accurate thickness measurements of a specific layer
Sonic/ Ultrasonic
http://www.cflhd.gov/agm/engApplications/Pavements/413SpecAnalySurfWaveandUltrSonicSurfWaveMethods.htm
1 105
2 105
3 105
4 105
5 105
6 105
7 105
0.04
0.03
0.02
0.01
0
0.01
0.02
0.03
0.04
Near sensorFar sensor
Time (s)
Am
plitu
de
ΔtΔt
Measure velocity of various wave modes propagating in pavementand relate to mechanical properties
Application of sonic/ ultrasonic• Estimate mechanical properties of
pavement (Modulus, strength, damage level, etc.)
• Locate voids/ interfaces
Limitations of sonic/ ultrasonic
• Local, point contact measurement
• Estimation of absolute values of modulus and strength of concrete is not accurate
Digital Imaging Technology• Automated digital imaging system consists of
image acquisition and distress image processing
After Huang et al. 2006
Equipment and Data Collection• DMI is used to control the acquisition of
digital image• Distress detection, isolation, classification,
segmentation, and compress• Fast wavelet transform for the wavelet-based
distress detection, isolation, and evaluationVideoVideo
Application of Video Imaging• Segregation measurement:
– Identify texture variation related to HMA segregation– Use GLCM technique to identify segregation
• Crack Detection/ Surface Distress– Individual crack information can be vectorizing– WiseCrax is used to automatically detect cracks,
classify and generate crack map– Recent development uses processing algorithm for
high-speed, real-time inspection of pavement cracking
Limitations of Imaging Technique
• Video image can only detect surface distress
• There is environmental requirement during data collection
• The system is vulnerable to vehicle vibration
• Video image can measure gradation segregation level; but not temperature segregation
Laser Technique• Pavement surface information can be determined by the
movement of reflected beam spot on the detector• It can supply rapid, continuous, and high accurate
measurement
Laser Beam
Pavement Surface
Lens
Detector
Laser Beam
Pavement Surface
Lens
Detector
Laser Beam
Pavement Surface
Lens
Detector
Equipment and Data Collection
Line scan and area scan laser systems (Xu et al. 2006)
Two types of laser camera are available to digitally image pavement surface: area scan and line scan
Friction and Roughness Measurements
Texture Classification Relative Wavelength
Microtexture λ<0.5 mm
Macrotexture 0.5mm < λ < 50mm
Megatexture 50mm < λ < 500mm
Roughness 0.5m < λ < 50m
• For friction use high-pass filter with 50mm wavelength cutoff
• For roughness use low-pass filter with 0.5m wavelength cutoff
Applications• Detect segregation:
– texture ratio of segregated to non-segregated area to measure segregation level
• Rutting measurements:– Automatic, rapid and continuous
• Crack measurements:– Valley detection of candidate cracks– Validation algorithm– Characterize crack types and pattern– 3D laser imaging has been introduced
Limitations• It provides pavement surface condition
only• Difficult to distinguish between texture
and crack • Transversal cracks are likely to be
detected, while longitudinal cracks are easily missed
• Narrow and shallow cracks may be filtered out during data processing
Infrared Thermography• Infrared thermography is standardized by ASTM
D4788. It includes passive and active methods• Subsurface changes in pavements generate surface
temperature variations
Equipment and Data Collection
Infrared sensors bar
Applications• QC/QA
• Segregation measurement
• Crack and defect measurement detection
Defect
Limitations
• It is applied for near-surface surveys
• It cannot distinguish between gradation and temperature segregation
• For existing pavements, it depends on solar energy
Ground Penetrating Radar• Ground Penetrating Radar (GPR) is a
special kind of RADAR• Purpose of using GPR:
– Detect targets buried in a dielectric medium
– Estimate their depths• GPR applications: geophysics,
archeology, law enforcement, evaluation of civil structures (buildings, bridges, pavements)
Principle of GPR
Layer 1
Layer 2
Control Unit
Transceiver
Antenna DMI
GPR Antennae• Ground-coupled antenna: in contact with ground
surface• Air-coupled antenna: 1 to 2 ft above surface
Ground Coupled Antenna Horn Antennae
Typical GPR Response (scan)
HMA
Base
Subgrade
t1
t2
A1
A2
-80
00
-60
00
-40
00
-20
00 0
20
00
40
00
60
00
80
00
10
00
0
12
00
0
02
46
81
01
21
41
6
Tim
e (n
s)
Amplitude
HM
AB
aseS
ub
grad
e
A0
GPR Data Collection
HMA
Base
Subgrade
HMA
Base
Subgrade
Layer Thickness Estimation
2
12
1
2
0
12
1
2
0
1,,
1
1
p
nn
i p
ii
p
p
nn
i p
ii
p
n-rnr
A
A
A
Aγ
A
A
A
A
A
Aγ
A
A
εε
Thickness of i th layer:HMA
Base
Subgrade
t1, d1
t2, d2
A0
A1
A2
r,1
r,2
r,3
1,,
1,,
irir
iriri
ir
ii
ctd
,2
2
1,
op
opr AA
AAε
New Pavements (QC/QA )Classic GPR thickness estimation gives accurate results:
0
50
100
150
200
250
300
350
400
450
500
40 42.5 45 47.5 50 52.5 55 57.5 60Distance (m)
De
pth
(m
m)
HMA Base
HMA Design Base Design
GPR Accuracy: New Pavements
Dielectric Constant Using CMP
Common midpoint (CMP) technique (or common-depth point, CDP) is used as follows:
T/RT R
x
t1
t2
P
HMAr1
h
: EM velocity in the layer 2
21
22
2
21
22
222
1
22
2
x
ttc
tt
xcv
xhvt
hvt
r
r
)(
)/(
Modified CMP Technique Modified common midpoint technique:
h1
T/R
x0
t1
t2
P
PCCr1
h0
airr0=1
x1
T R
i
t
Snell’s law of refraction:
Using the figure:
(1)
(2)
(3)
(4)
Modified CMP Technique Modified common midpoint algorithm:1. Measure the reflection times t1 and t2
2. Calculate the transmission angle t using:
3. Find the angle i by solving numerically
4. Solve for r1 using:
5. Compute HMA thickness using t1 and r1
2
t
i1 θsin
θsin
r
111 2 rcth Modified CMP Setup
-6000
-4000
-2000
0
2000
4000
6000
8000
10000
12000
0 5 10 15
Time (ns)
Am
pli
tud
e
Surface Reflection
OGDL/Base Reflection
WS/BM-25.0 Reflection
BM-25.0/OGDL Reflection
Base/Subgrade Reflection
Depth Resolution Enhancement
Measured Signal from:
Thin layer interfaces not visible because of
reflection overlap
Synthesized Signal
-8000
-6000
-4000
-2000
0
2000
4000
6000
8000
10000
12000
0 5 10 15
Time (ns)
Am
pli
tud
e
Reflection Overlap
Surface Reflection HMA/Base
Reflection
Base/Subgrade Reflection
Base
OGDL
WS
BM-25.0
Measured vs. Simulated Signal
Layer Thickness Estimation by Iteration
Raw GPR Data
Layer Interface Detection
Dielectric Properties Estimation
Layer Thicknesses
Preprocessing
Detection Results
0
2
4
6
8
10
12
14
16
20 30 40 50 60
Distance (m)
Tim
e D
elay
(n
s)
Detected Layer Interfaces
WS
BM-25.0
OGDL
Base
Copper plates
GPR Data Analysis Software
Channel 1
Channel 2
Channel 1
Channel 2
Density Measurement with GPR• According to volumetric mixture theory, HMA dielectric
constant depends on aggregate, binder and air volumes
abeavoid (%)
Note: calibration coefficients (a and b) are determined from field cores.
• A drop in dielectric value may indicate a density change
• 2GHz antenna is preferred• It has potential….it requires more investigation
Defects Detection with GPR• Segregation: locations of course-graded and
dense-graded mixes has been reported
• Stripping: additional reflections appear between surface and layer interface
• Moisture content: relationship between dielectric constant and moisture content
bDCmoisture (%)
Ground-Coupled Data, CRCP, VA. Smart Road
Locating Reinforcement (CRCP)
Copper Plate under Slab
Transversal Reinforcement
Concrete
Asphalt OGDL Longitudinal Reinforcement
GPR Application on Composite Pavement
100 ft Joint Spacing
Rebar
Interface of HMA and PCC
Surface
8 in
Overlay
Measure overlay thickness and detect overlaid joints:
3 ft 3 ft
ISAC
Limitations of GPR Technique• Air-coupled antenna has limited penetration
depth • GPR survey requires dry pavement condition• Errors may result from dielectric constant
estimates from surface reflection • Cores may be needed to determine
calibration coefficients • Strong reflection may mask weak signals• Accuracy of GPR results depends on
adopted data analysis technique
Future Work
• During this project year, we aim to
– Identify current NDTE needs for airport flexible pavements
– Identify promising NDTE technology, and carry out new research efforts to meet those needs