New technologies for ndt of concrete pavement structures
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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.

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New technologies for ndt of concrete pavement structures

New Technologies for NDT of Concrete Pavement Structures

John S. Popovics

Department of Civil & Environmental Engineering

CEAT Seminar SeriesSeptember 8, 2005


Outline

Outline

  • Motivation & background

  • Current NDE techniques/applications

  • New Research Directions (UIUC)


Motivation

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 specifications

  • require accurate in-place estimates of new

  • pavement thickness and strength

A need for structural/pavement NDE


New technologies for ndt of concrete pavement structures

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.


New technologies for ndt of concrete pavement structures

Impact-Echo (ASTM C1383)

Propagating P-waves

generated by impact

event. Multiply-reflected

waves are detected by

surface sensor.

Reflected waves set

up a resonance

condition having a

characteristic frequency

FFT

Analogous to a bell’s tone


New technologies for ndt of concrete pavement structures

Impact-echo Analysis

The resonant

frequency (at the

peak) 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

  • is a correction factor

    for the shape of the element.

     = 0.96 for slabs

Reflection from delamination


New technologies for ndt of concrete pavement structures

GPR (ASTM D4748)

(groundpenetratingRADAR)

Wave pulses are reflected

at interfaces having

a difference in

electrical properties (r)

antenna

air: r = 1

concrete: r = 6 to 11

Reflected pulses (time

and amplitude) are

monitored in the

time domain signal

soil: r = 2 to 10

(water: r = 80; metal r = infinite)


New technologies for ndt of concrete pavement structures

Infra-red Thermography

Monitoring heat flow by surface temperature

Sub-surface defects disrupt heat flow. If defect near near surface,

surface temperature is affected.

Temp 2

warmer zone

cooler zone

Air-filled void

where T2 < T1

heat flow

(conduction)

Temp 1

Driven by thermal gradient

Heat flow must be established, but direction of flow does not matter


New technologies for ndt of concrete pavement structures

25.5°C

25.5°C

23.2°C

23.2°C

114 mm

127 mm

127 mm

127 mm

114 mm

25 mm

38 mm

25 mm

1

2

3

4

Surface

Surface

38 mm

thermocouple

thermocouple

51 mm

38 mm

25

25

°

25

C

25 mm

7

8

5

6

Flaw #5

Flaw #8

Flaw #6

38 mm

°

24

24

24

C

25 mm

25 mm

25 mm

25 mm

25 mm

25 mm

Surface

Surface

Heat flux sensor

Heat flux sensor

thermocouple

thermocouple

Thermography Results: FRP Bond

concrete

bonded FRP sheet

disbonds

Thermograph

(disbonds are

hot spots)


New technologies for ndt of concrete pavement structures

New Research Directions (UIUC)

  • New pavement Q/A assurance work

  • Accurate thickness and in situ strength

  • estimation for new concrete pavements

  • Contact-less (air-coupled) pavement

  • inspection using stress waves

Seismic time domain approach

Surface waves


New technologies for ndt of concrete pavement structures

x1

x2

wave source

sensors

h

pavement

In-situ Pavement Thickness

Motivation:

* Accurate (5mm)and non-destructive thickness estimates

needed for new pavement QC and pay factor application

* Best available method (standard impact-echo) does not

provide needed accuracy

Approaches:

Time domain

Frequency domain

Improve impact-echo

Develop seismic approach


New technologies for ndt of concrete pavement structures

Impact

Receiver

(1-a)x

ax

P-wave

P-wave

h

S-wave

θs

θs

θp

S-wave

θp

Seismic Approach for Slab Thickness

Arrivals ofmode-converted reflections(P-S and PP-SS) of short duration

pulses used to back-compute wave velocity and slab thickness

P-S arrival time


New technologies for ndt of concrete pavement structures

bb-gun Impactor

Accelerometers

Impact sensor

Impact positions

tppss

tps

Direct P-wave

Surface wave

Time - microseconds

Field Testing Set-up

Field testing setup

comprised of sensed

BB-gun and multiple

accelerometer set

Arrivals of mode-

converted waves

determined in each

signal; velocity

and thickness

then computed


New technologies for ndt of concrete pavement structures

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

Targets for improvement


New technologies for ndt of concrete pavement structures

Lamb Wave Basis for Impact-Echo

S1-Cg=0

S1-k=0

A1-k=0

Guided waves in free plates

Anti-symmetric modes

Symmetric modes

Solutions: dispersion curve

Resonance conditions

represented at

zero wave number or

zero group velocity

locations

Impact-echo?


New technologies for ndt of concrete pavement structures

Verification

Impact-echo frequency

FEM (ABAQUS)

model verified

by experiment

Analytical (Lamb)

model verified

by FEM

b = 0.96

Impact echo frequency

is S1 ZGV


New technologies for ndt of concrete pavement structures

In-situ Strength Estimation

Motivation:

* Accurate and non-destructivein 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:

Use surface waves: one-sided method

Sensors

Wave source

d

Measure surface wave velocity

and transmission (attenuation)

and correlate to in situ strength

Surface waves


New technologies for ndt of concrete pavement structures

Testing Set-up

Ultrasonic wave source

(200 kHz)

Field testing set-up

Wave sensors

(accelerometers)


New technologies for ndt of concrete pavement structures

Surface Wave Measurements

Acceleration signals

far sensor

near sensor

DA

Dt

Surface wave velocity: arrival time of far sensor- near sensor

Surface wave transmission: amplitude ratio for far sensor/near sensor


New technologies for ndt of concrete pavement structures

V13 V42

“T”

d23 =

V12 V43

Self-calibrating Wave Transmission

  • 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

1

2

3

4

surface waves


New technologies for ndt of concrete pavement structures

Correlation to Concrete Strength

On-going work: correlation to flexural strength


New technologies for ndt of concrete pavement structures

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


New technologies for ndt of concrete pavement structures

Wave Source

Blind zone

Air-coupled Sensing

  • Challenge: Large acoustic impedance mismatch between air and concrete

Use leaky R-waves?


New technologies for ndt of concrete pavement structures

Air-Coupled SASW

  • 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


Air coupled masw

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

Multi-source setup

Multi-sensor setup


Air coupled masw1

Air-Coupled MASW

MASW 2D spectrum image

Test performed on a concrete slab with thickness 200mm, CR=2300m/s

Nils Ryden provided the MASW analysis program


Imaging surface opening cracks

Imaging surface-opening cracks

  • Top layer concrete thickness 180-210mm

  • Concrete R wave velocity VR=2300m/s

  • Microphone height h = 66cm

  • Shadow zone size: 15cm


Imaging surface opening cracks1

2-D scan

1-D X scan

1-D Y scan

Imaging surface-opening cracks

Energy Ratio


Air coupled impact echo

Air-Coupled Impact-Echo

Musical microphone: frequency response 20Hz-20kHz

  • Air-coupled sensor

    • Tested in ambient noise condition without any sound insulation

    • Good agreement with the contact impact-echo test result

    • The PCB microphone can determine thickness of shallow delaminations

PCB measurement microphone: 4Hz-80kHz


Air coupled impact echo delamination

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 delaminations

    • Gives delamination depth 58mm

    • 33.2kHz can be detected by the PCB microphone


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

Summary


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