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.