a practice-driven approach to the development of the ...€¦ · 15th asia-pacific conference for...

A practice-driven approach to the development of the ultrasonic pulse echo technique applied to concrete structural assessment

15th Asia-Pacific Conference for Non-Destructive Testing (APCNDT2017)Singapore, November 14, 2017

D. Corbett, F. Gattiker, S. Vonk, A. Taffe, L. Raj*Proceq SA, Proceq Asia Pte Ltd., HTW Berlin

© Proceq 2017 1

1

Overview

Large-scale scanning

Research on cover depth

Tendon duct analysis


© Proceq 2017 Practice-driven approach for the development of ultrasonic pulse echo for concrete structural assessment 2

2

3

4 Conclusions4

1

Overview






2

3

44 Conclusions


One major drawback of pulse echo testing is the total effort required for large-scale scanning

• Large-scale project

(shopping mall)

• Repeated scanning of

column & beam structures


The task was to detect grouting defects in couplers that could weaken the structure

Horizontal scanning with Pundit 200PE single-channel pulse echo instrument

Horizontal test

of coupler

assembly

Vertical

direction of

each coupler

test


Pulse echo works well to detect voids, but requires numerous measurements

Typical vertical scan

• Voids in the coupler section

• At depth: 10 cm

• Length: 30 cm

• 32 individual measurements

460

scans

32 measurements

per scan× 13’800 individual

measurements=


There is a clear need to improve scanning speed and reduce total effort.

The effort involved in collecting data for one section on-site is considerable

84

columns

4 scans

per column× + 40

beams

3 scans

per beam× 460

scans=

Single-channel transducer 8-channel array transducer


A practical solution to improve scanning speed is to switch to an array

Image built up in small increments

on the display device

B-scan presented in real time directly

on the display device

Single-channel transducer 8-channel array transducer


Switching to an array reduces the scanning effort by a factor of 15

64 measurements → 2 minutes 37 seconds

13’800 individual measurements per section

4 measurements → approx. 10 seconds

920 individual measurements per section

1

Overview




Conclusions


2

3

4 Conclusions4


Research on pulse echo showed discrepancies in measured cover depth above reinforcing steel

• Pulse velocity calibrated against known

back wall depth

• Individual rebars and a hollow pipe are

clearly visible

• Discrepancies of cover depth of about

10% were noted

• Research carried out at University of Applied

Sciences Rapperswil in Switzerland

• Pulse echo could be used to determine concrete

cover in fiber-reinforced concrete

Proceq Pundit 250 Array with multichannel technology,

real-time B-scan with image stabilizer


Dedicated test blocks to investigate detection capabilities of latest array transducers

• Ongoing investigations /

research project

• University of Applied

Sciences in Berlin

30 × 20 × 150 cm | Ø 16 mm reinforcing bars at increasing cover depth (5 zones)


Image-stitched panorama B-scan of test block reveals cover discrepancies

Scan with Pundit 250 Array

transducer (8 channels)

• 21 cm wide scan,

18 cm overlap (stitching)

• Data analysis with

Proceq PL-Link software

Zone 1 2 3 4 5

Actual cover [cm] 1.2 3.0 5.0 7.0 9.0

Detected cover [cm] 4.0 4.4 6.8 8.7 9.5


Resolution at shallow depths improved significantly by reducing pulse velocity


Depth estimation depended on pulse velocity, but reasons are unclear

• Unclear whether / why:

Pulse velocity varies

throughout test block

Pulse velocity lower

near the surface

• Root cause currently

being investigated0

4

8

12

16

20

RB1 (1.2 cm) RB2 (3.0 cm) RB3 (5.0 cm) RB4 (7.0 cm) RB5 (9.0 cm) Back wall (20 cm)

Dep

th e

stim

atio

n [c

m]

Depth estimation depending on pulse velocity c [m/s]

2200

2400

2600

2700

1

Overview






2

3

4 Conclusions4


Routine destructive maintenance revealed grouting defects in tendon ducts

Brent Cross Flyover

(London)


Can grouting duct failures be analyzed using pulse echo technology?

Duct with

known void

Healthy

duct

Tendon ducts located

with GPR and openings


Comparison of B-scans shows that pulse echo can detect the presence of voids

Data collected with

Proceq Pundit 250 Array

DUCTDUCT

BACK WALLBACK WALL

Very strong echo Weak echo

with secondary echo

Duct with known void Healthy duct


A post-processed C-scan comparison obviously differentiates healthy and unhealthy ducts

C-scan generated from B-

scans across the duct

• Raw data export

• External software

Duct with known void Healthy duct

B-s

cans

On-board C-scan feature would

accelerate on-site analysis

1

Overview






2

3

4 Conclusions4


Technological progress

Contribution to NDT inspections

Key drivers of improvement

Taking a look at challenging applications drives us to constantly improve pulse echo technology

• Real-time on-board B-scan imaging

• C-scanning functionality desirable

• Detects grouting defects

• Complementary to GPR, Eddy Current

• Speed of on-site testing

• Ease of data interpretation

• Calibration accuracy

• Position/stitching accuracyProceq Pundit 250 Array / Pundit Live Array Pro

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