Post on 19-Mar-2020
Applications and Qualities of NDE Technologies for Bridge Deck Assessment
Glenn A. Washer, Ph.D.
Department of Civil and Environmental EngineeringUniversity of Missouriwasherg@missouri.edu
ThermalStare, LLC www.thermalstare.com
Objective• Describe the applications and qualities of different NDE technologies that can be
used for bridge deck evaluations• Motivation:
– The capabilities of NDE technologies are sometimes not well understood in the highway community
• GPR has been used to detect damage or deterioration in bridge decks for 40+ yrs. – Scales such as (SHRP II Report)
» Serious, poor, fair, good » Probable delamination, probable corrosion damage, probable sound concrete» Serious, poor, fair, good
– IR depends on the weather, analysis that included subjective judgements, and the characteristics of the defects
• Depth and thickness of the defects• Unlikely it would detect all of the defects
– Time (weather) dependent behavior– Impact echo/acoustic methods
• Point by point
• Traffic control – Speed – Accuracy– Reliability (whatever that means… )
• SATO– Speed-accuracy trade-off– Its hard to be fast and good……..
• Overlay / no overlay– Thin overlay – Thick overlay
• Debonding• Delamination
– Asphalt overlay
Fulcrums for NDE Applications
• To identify the area to be repaired accurately? (size and location)• To identify the extent of repair? (%)
– How accurately do you require the answer to be?
• To prioritized a group of bridges rapidly for further evaluation?• To make a decision regarding overlay, replace, or patch?
What are the goals of the condition assessment?
Delamination in bridge deck
• Corrosion can cause delamination in bridge decks– Not all delamination is caused by corrosion– Not all corrosion results in delamination (or has yet resulted in delamination)– Not all damage in a bridge deck is in the form of a delamination
• What tools are available for detecting delamination prior to spalling?– Hammer sounding
• Subjective, requires traffic control – Acoustic methods– Infrared Thermography– Ground penetrating RADAR (?)
• There are no NDE technologies that detect defects• The data present variations that we interpret as being a defects
– Lots of things can effect the response from the NDE system– Assumptions / expert judgement / analysis are usually required to interpret
these data – Threshold values are used (on varying levels) to identify defects – Subjective decisions
How do NDE technologies work
Electrical Methods for Condition Assessment
• Half-Cell Potential– Potential for active corrosion
• Resistivity– Resistance to current flow, conductivity
– Permeability
• Galvanostatic pulse– Polarization resistance
– Related to corrosion rate
• These are survey methods– Don’t detect damage
– Point by point (traffic control)
– Need to be coupled with engineering judgement and experience
Resistivity Measurement
Effect of moisture content on resistivity measurements
GPR and IRT
• GPR– Electromagnetic wave reflected from rebar
• Amplitude and return time analyzed • Dielectric properties of the material between the surface and the rebar depth
– Moisture, chloride content, ….
• ASTM procedure
– Scan over surface, collect data
• IRT– Radiant thermal energy detected by a camera – Anomalies interpreted as defects
NDE Technologies
11
• A stress wave technique.• Uses stress waves’ propagation and reflection.• Sensitive to change in acoustic impedance. • Main output is the frequency of P-wave.
• An electromagnetic technique. • Uses EM waves’ propagation and reflection.• Sensitive to change in dielectric properties. • Main output is amplitude of reflected signals.
• A thermal technique.• Detects objects’ thermal radiation.• Sensitive to thermal properties. • Main output is the thermal radiation.
Acoustic Methods IRT GPR
• Sounding• Impact echo• Seismic response• Surface acoustic wave
– Seismic analysis of surface waves (SASW)• Modulus / delamination
• Question: what is the surface quality of the concrete? Is it tined? Is there a thin asphalt/flexible overlay? Rigid overlay?
• Advantages: Matches well with chain drag• Disadvantages: Mostly requires lane closure• Point by point (mostly)
Flavors of acoustic methods
Implementation of Acoustic Approach
Acquisition
Unit
• Temperature anomalies at the surface of the deck – Hand-held cameras used from the roadside– Vehicle mounted bolometers
• Most cost effective, greater time constant• Slower speeds for quality data
– Vehicle mounted-quantum detectors• $$$ equipment
• Ultra-Time Domain Thermography (IR-UTD)– Thermal inertia of the concrete – NOT TEMPERATURE– Time-lapsed measurement
Flavors of Infrared Thermography
Conventional IR Technologies
IR-UTD
IR –UTD Images of thermal inertia showing subsurface defects and structural features
A
B C D
E
Challenge for Conventional IRT
Flavors of GPR
Test points for GPR
2 ft
2 ft
# XX Rebar @ YY Spacing
2 ft
Bridge Deck
2 ft
2 ft
Possibly won't
be detected
Long. SteelGPR Scans
Delamination of irregular shapes
Trans. Steel
Analysis Sequence of GPR
21
Ali A. Sultan – April, 2017
IR Data reduction
• Conventional IR camera mounted on vehicle with encoder – Stitch images together
– Compare pixel to pixel w/ diagram
of ground truth
22
Effect of Threshold Setting GPR Data Bridge A2111
22% damage
43% damage
Effects of threshold setting
68
69
70
71
72
73
74
75
76
77
78
0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0 4 0 0 4 5 0
TE
MP
. F. D
EG
RE
E
PIXEL
∆T
Delaminations
Sound concrete
TP
TNTN
TN
FN
Temp. of known
sound pixel
FN
Effects of threshold setting
68
69
70
71
72
73
74
75
76
77
78
0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0 4 0 0 4 5 0
TE
MP
. F. D
EG
RE
E
PIXEL
∆T
Temp. of known
sound pixelDelaminations
Sound concrete
TP
TN
FP
TP
FPTP
1
54
3
2
TP
R
FPR0, 0
1, 10, 1
5 1234
Thermal Contrast
PositivesNegatives
th Positive th Negative
36.41
37
37.5
38
38.5
39
39.5
40
40.5
41
41.84
°C
36.41
37
37.5
38
38.5
39
39.5
40
40.5
41
41.84
°C
36.41
37
37.5
38
38.5
39
39.5
40
40.5
41
41.84
°C
36.41
37
37.5
38
38.5
39
39.5
40
40.5
41
41.84
°C
36.41
37
37.5
38
38.5
39
39.5
40
40.5
41
41.84
°C
Very low
thermal
contrast
Very high
thermal
contrast
Better than guessing line
ROC Analysis
In-Service Bridge Decks
27
• 3-spans.• 216 ft long, tapered width 39 ft to 21.5 ft.• The deck is 7” thick. • Has not been opened to traffic.
• 3-spans. • 153 ft long, width 44 ft.• The deck is 7” thick. • Minimal signs of deterioration.
A0295 A2112A2111
• 3-spans.• 175 ft long, width 44 ft.• The deck is 7” thick. • Extensive signs of deterioration.
Delamination
Ground truth • Sounding by team• Impact echo in select locations to confirm
sounding results• Boroscope used to view delams
Analysis Sequence of IE
29
Results: Kansas Bridge A0295 Curb
-26.
47
-25.
47
-24.
47
-23.
47
-22.
47
-21.
47
-20.
47
-19.
47
-18.
47
-17.
47
-16.
47
-15.
47
-14.
47
Depth-Uncorrected Amplitudes, dB
First scan, 2 ft
from the curb
-28 -27 -26 -25 -24 -23 -22 -21 -20 -19 -18 -17 -16 -150
50
100
150
200
250
300
350
Count
Reflection Amplitude, dB
Results of Actually Negative Test Points
Results of Actually Positive Test Points
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Tru
e P
ositiv
e R
ate
(T
PR
)
False Positive Rate (FPR)
ROC of GPR
Reference Line
AUC=0.475
Bridge A2111
Bridge A2112
ROC Curves • IRT and GPR results
IR = 0.80GPR = 0.68
IR = 0.85GPR = 0.78
IR-UTD Field Results
IR-UTD
Conventional IR
Deck with 1.75 in. rigid overlay - IR-UTD
35
Speed
Accuracy relative to sounding
GPRcorrosionIRT -BolometerAcoustic (Auto) Sounding
Impact echo
IR-UTD
IRT - Quantum
Speed Qualities
Impact on Traffic
GPR – corrosionIRT -Bolometer Acoustic (Auto) Sounding
Impact echo
IR-UTD
IRT - Quantum
Impact on Traffic Qualities
GPR corrosion
IRT -Bolometer Acoustic (Auto) Sounding
Impact echo
IR-UTD
IRT - Quantum
Depth of damage
Rigid Overlays
• IE• GPR corrosion• IR-UTD• Sounding• Acoustic• IRT – debonding
Asphalt Overlays
• GPR corrosion • IR-UTD
Conclusions
• Key qualities for NDE technologies– Traffic impact
• Once a lane closure is used, everything is available– Why not just sound
– Accuracy – Objective of the test
• Survey, prioritization, forecasting• Detection of delamination, correlation with sounding
– Overlays affect the quality of NDE results• Acoustic • IRT
Discussion• GPR may not detect delamination, it detects conditions that lead to
corrosion-induced delamination– Sometimes, these occur at the same locations– Results indicate that GPR reliability values were based on the likelihood of an
area with moisture and chlorides also having a delamination
• IR showed higher AUC due (in part) to fewer false calls– Weather and Depth dependent
• IE and acoustic methods match chain drag, obviously– Traffic control is the primary disadvantage
• IR-UTD technology overcomes IRT issues– Designed for High accuracy – Minimum impact on traffic
Questions?
1. Sultan, A., Washer, G., (2017) “Comparison of Two Nondestructive
Evaluation Technologies for the Condition Assessment of Bridge Decks,”
Transportation Research Record, accepted.
2. Sultan, A.A. and Washer, G.A., (2017) “Reliability Analysis of Ground-
Penetrating Radar for the Detection of Subsurface Delamination,” Journal
of Bridge Engineering, 2017. 23(2): p. 04017131.
3. Sultan, A.A. and Washer, G., (2017) “A pixel-by-pixel reliability analysis
of infrared thermography (IRT) for the detection of subsurface
delamination,” NDT & E International, 92: p. 177-186.