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New Technologies for NDT of Concrete Pavement Structures. John S. Popovics Department of Civil & Environmental Engineering. CEAT Seminar Series September 8, 2005. Outline. Motivation & background Current NDE techniques/applications New Research Directions (UIUC). Motivation. - PowerPoint PPT Presentation
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1
New Technologies for New Technologies for NDT of Concrete NDT of Concrete
Pavement StructuresPavement StructuresJohn S. PopovicsJohn S. Popovics
Department of Civil & Environmental Engineering
CEAT Seminar SeriesCEAT Seminar SeriesSeptember 8, 2005September 8, 2005
2
Outline
• Motivation & background
• Current NDE techniques/applications
• New Research Directions (UIUC)
3
Motivation
• US infrastructure is deteriorating: 2005 ASCE Report card for American infrastructure gave an overall grade of “D+” – estimated $1.3 trillion investment needed for improvements
• Increased use of performance-based specificationsrequire accurate in-place estimates of newpavement thickness and strength
A need for structural/pavement NDE
4
Current NDE Techniques
Concrete structures and pavements
Impact-echo, GPR (RADAR), thermography
sounding/tapping, UPV and velocity tomography, electro-chemical techniques, radiography, modal analysis, acoustic emission, impulse-response, etc.
5
Impact-Echo (ASTM C1383)
Propagating P-wavesgenerated by impact event. Multiply-reflectedwaves are detected bysurface sensor.
Reflected waves setup a resonancecondition having acharacteristic frequency
Analogous to a bell’s tone
FFT
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Impact-echo AnalysisThe resonant
frequency (at thepeak) is related to
distance to reflector (d or d*) and
wave velocity (VL):
f = VL/(2 d)
Thus,
d = VL/(2 f)
Reflection from slab bottom
Reflection from delamination
is a correction factorfor the shape of the element. = 0.96 for slabs
7
GPR (ASTM D4748)
Wave pulses are reflectedat interfaces having
a difference in electrical properties (r )
Reflected pulses (timeand amplitude) are
monitored in thetime domain signal
antennaair: r = 1
concrete: r = 6 to 11
soil: r = 2 to 10
(water: r = 80; metal r = infinite)
(ground penetrating RADAR)
8
Infra-red ThermographyMonitoring heat flow by surface temperature
Sub-surface defects disrupt heat flow. If defect near near surface, surface temperature is affected.
Temp 2
Temp 1
Air-filled voidwhere T2 < T1
heat flow(conduction)
Heat flow must be established, but direction of flow does not matter
Driven by thermal gradient
warmer zonecooler zone
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24
25
Heat flux sensorSurface
thermocouple
Surface
thermocouple
24
25
Heat flux sensorSurface
thermocouple
Surface
thermocouple
25 °C
24 °C
Flaw #5 Flaw #6 Flaw #8
25 mm
1 2 3 4
5 6 7 8
114 mm 127 mm 127 mm 127 mm 114 mm
25 mm
25 mm
25 mm
25 mm
25 mm
38 mm
38 mm
38 mm
38 mm
51 mm
25 mm 25 mm 25 mm
concrete
bonded FRP sheet
disbonds
Thermograph(disbonds are
hot spots)
Thermography Results: FRP Bond
10
New Research Directions (UIUC)
• New pavement Q/A assurance work
Accurate thickness and in situ strengthestimation for new concrete pavements
• Contact-less (air-coupled) pavement inspection using stress waves
Seismic time domain approach Surface waves
11
In-situ Pavement ThicknessMotivation:
* Accurate (5mm) and non-destructive thickness estimates needed for new pavement QC and pay factor application
* Best available method (standard impact-echo) does notprovide needed accuracy
Approaches:Frequency domainTime domain
sensors
x1
h
x2
pavement
wave source
Develop seismic approach Improve impact-echo
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Impact
h
ax
P-wave
S-waveθp
θs
(1-a)x
θpθs
P-wave
S-wave
Receiver
Seismic Approach for Slab Thickness
SPps C
hxa
C
haxt
2222 ))1(()(
s
p
Sin
Sin
Vs
Vp
Arrivals of mode-converted reflections (P-S and PP-SS) of short durationpulses used to back-compute wave velocity and slab thickness
P-S arrival time
13
Accelerometers
bb-gun Impactor
Impact positions
Impact sensor
200 250 300 350 400 450 500 550 600 650 700 750 8000.05
0
0.05
Direct P-wavetps
tppss
Time - microseconds
Surface wave
Field Testing Set-up
Field testing setupcomprised of sensedBB-gun and multipleaccelerometer set
Arrivals of mode-converted wavesdetermined in eachsignal; velocityand thicknessthen computed
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Impact-Echo
1980s in NIST and Cornell Effective in determining
thickness of slabs and depth of flaws in plate structures
Does not work on beams & columns
2
0.96 for plate
PCD
f
Targets for improvement
15
222
2222
22
22
2
22
)2(
4
)2tan(
)2tan(0
2222
22
222
22
2
22
4
)2(
)2tan(
)2tan(0
Solutions: dispersion curve
Symmetric modes Anti-symmetric modes
Lamb Wave Basis for Impact-Echo
S1-Cg=0
S1-k=0
A1-k=0
Guided waves in free plates
Resonance conditionsrepresented at zero wave number orzero group velocitylocations
Impact-echo?
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0.942
0.946
0.950
0.954
0.958
0.15 0.16 0.17 0.18 0.19 0.2 0.21 0.22 0.23 0.24 0.25 0.26
Poisson's ratio
S1 Mode ZGV
FEM resonance
β
0 500 1000 1500 2000
Time (microseconds)
Am
plit
ud
e
Experimental
FEM
0 5000 10000 15000 20000Frequency (Hz)
Am
plitu
de
Experimental
FEM
Verification
FEM (ABAQUS) model verified by experiment
Analytical (Lamb) model verified by FEM
Impact-echo frequency
Impact echo frequencyis S1 ZGV
= 0.96
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In-situ Strength EstimationMotivation:
* Accurate and non-destructive in situ concrete strength estimation needed for new pavement QC and pay factors
* Best available methods (rebound hammer, UPV, maturity) do not provide needed accuracy, reliability, or applicability
Approach:
Wave source
Surface waves
d
SensorsUse surface waves: one-sided method
Measure surface wave velocityand transmission (attenuation)and correlate to in situ strength
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Testing Set-upUltrasonic wave source
(200 kHz)
Wave sensors(accelerometers)
Field testing set-up
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Surface Wave Measurements
-1.5
-1
-0.5
0
0.5
1
1.5
0.00E+00 2.00E-05 4.00E-05 6.00E-05 8.00E-05 1.00E-04
Acceleration signals
t
A
Surface wave transmission: amplitude ratio for far sensor/near sensor
Surface wave velocity: arrival time of far sensor- near sensor
far sensor
near sensor
20
In the frequency domain, we can represent wave signal sent by i and received by j (Vij) as
V12=A1d12S2, V13=A1d12d23S3, V43=A4d43S3 and V42=A4d43d32S2,
where Ai and Si are the sending and receiving response functions, dij is the transmission between points i and j.
We aim to isolate and measure d23
Self-calibrating Wave Transmission
1 2 3 4
surface waves
V12 V43
V13 V42d23 = “T”
21
Correlation to Concrete Strength
2220
2260
2300
2340
2380
2420
2460
3000 4000 5000 6000 7000
compressive strength, psi
wav
e ve
loci
ty, m
/s
0.46
0.48
0.5
0.52
0.54
0.56
0.58
0.6
0.62
0.64
3000 4000 5000 6000 7000
compressive strength, psiT
ran
smis
sio
n @
hig
h f
req
uen
cies
On-going work: correlation to flexural strength
22
Contact-less (air-coupled) inspection
• NDT imaging techniques provide a direct approach for assessment
• Stress-wave based NDT methods are usually less efficient due to coupling problem
• Here we aim to develop effective non-contact NDT techniques for pavements
23
Wave Source
Blind zone
Air-coupled Sensing Challenge: Large acoustic impedance mismatch
between air and concrete
Use leaky R-waves?
24
Air-Coupled SASW
0 5 10 15 20 250.7
0.8
0.9
1
frequency (kHz)
Co
he
ren
ce
SASW Test ( Impactor: Medium Ball), window=400s
0 5 10 15 20 252000
2100
2200
2300
2400
2500
frequency (kHz)
Ve
loci
ty(m
/s)
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.52000
2100
2200
2300
2400
2500
Wavelength(m)
Ve
loci
ty(m
/s)
SASW provides surface wave velocity profiles with depth (layered system) SASW test performed on floor slab (thickness 200mm) Signals show good coherence through 22kHz Rayleigh wave velocity is about 2300m/s
25
Air-Coupled MASW Multichannel analysis of surface waves (MASW)
Compared to SASW, MASW can determine phase velocities precisely using whole waveform data
Avoids spatial aliasing Distinguish fundamental mode from higher modes and body waves
Time(s)
dist
ance
(cm
)
Image of response (Mic)
0 0.5 1 1.5 2 2.5 3 3.5
x 10-3
50
100
150
200
250
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
Multi-source setup
Multi-sensor setup
26
Air-Coupled MASW
Phase velocity (m/s)
Fre
quen
cy (
Hz)
Vidale EB12 run1c (Mic)
1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
x 104
MASW 2D spectrum image Test performed on a concrete slab with thickness 200mm, CR=2300m/s
Nils Ryden provided the MASW analysis program
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Imaging surface-opening cracks
Wave propagationdirection
Scanningdirection
surface crack
Wave propagationdirection
Scanningdirection
surface crack
Top layer concrete thickness 180-210mm Concrete R wave velocity VR=2300m/s Microphone height h = 66cm Shadow zone size: 15cm
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Imaging surface-opening cracks
0 20 40 60 80 100 120 140 160
40
60
80
100
120
140
160
180
0 100 2000
0.5
1
Hanningwindow
2ix
1 2 1
2 3 2
/
/
R A A
R A A
0 1 1
1 1 1
2 2 2
/
/
/
m
m
m
R A A
R R R
R R R
energy
ratio
normalization
1 1.5 2 2.5 3 3.5 4-1
0
1
1 1.5 2 2.5 3 3.5 4-1
0
1
1 1.5 2 2.5 3 3.5 4-1
0
1
2 2.5 3 3.5-1
0
1
2 2.5 3 3.5-1
0
1
2 2.5 3 3.5-1
0
1
1
2
3
A
A
A
Raw signals Windowed signals
0 100 2000
0.5
1
Hanningwindow
2ix
1 2 1
2 3 2
/
/
R A A
R A A
0 1 1
1 1 1
2 2 2
/
/
/
m
m
m
R A A
R R R
R R R
energy
ratio
normalization
1 1.5 2 2.5 3 3.5 4-1
0
1
1 1.5 2 2.5 3 3.5 4-1
0
1
1 1.5 2 2.5 3 3.5 4-1
0
1
2 2.5 3 3.5-1
0
1
2 2.5 3 3.5-1
0
1
2 2.5 3 3.5-1
0
1
1
2
3
A
A
A
Raw signals Windowed signals
1-D Y scan
1-D X scan 2-D scan
Energy Ratio
0 20 40 60 80 100 120 140
50
100
150
200
250
0 20 40 60 80 100 120 140
40
60
80
100
120
140
160
180
29
Air-Coupled Impact-Echo
Air-coupled sensor Tested in ambient noise condition wit
hout any sound insulation Good agreement with the contact imp
act-echo test result The PCB microphone can determine t
hickness of shallow delaminations
Musical microphone: frequency response 20Hz-20kHz
PCB measurement microphone: 4Hz-80kHz
30
Air-Coupled Impact-Echo – Delamination Delamination at depth 60mm Flexual mode at 2.68kHz
strong and easy to detect Impact-echo mode 33.2kHz for delaminati
ons Gives delamination depth 58mm 33.2kHz can be detected by the PCB micropho
ne
5 10 15 20 25 30 35 40 45 50 55
0
5
10
15
20
25
30
35
40
45
50
x(cm)
y(cm
)
3000 4000 5000 6000 7000 8000 9000
Frequency (Hz)
0 1 2 3 4 5 6 7 8 9
x 10-3
-0.08
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
0 5 10 15 20 25 30 35 400
1
2
3
4
5
6slab1_p8_b1w_R0C0_2.dat df=0.24414
f=33.2kHz
Frequency (kHz)
f=2.68kHz
31
Summary Non-destructive test methods are needed for concrete pavements.
Many existing NDT methods exist for concrete pavements
New research efforts focus on improving the capability of NDT for pavements, for example for in-place pavement thickness estimation
Surface wave measurements can be carried out on concrete. The self-compensating scheme allows measurement of surface wave signal transmission. Results show correlation to in-place strength.
Contact-free methods have potential for rapid and effective NDT for pavements
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