# Detection and evaluation of macro-cracks and micro-cracking by using automated surface wave non-contact scanners

Charles Ciccarone, Bogdan Piwakowski, Frédéric Skoczylas, Radoslaw Drelich, Jean-Marie Henault

► To cite this version:

Charles Ciccarone, Bogdan Piwakowski, Frédéric Skoczylas, Radoslaw Drelich, Jean-Marie Henault. Detection and evaluation of macro-cracks and micro-cracking by using automated surface wave non-contact scanners. Academic Journal of Civil Engineering, 2020, 38 (2), pp.72-75. 10.26168/ajce.38.2.17. hal-03594376

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# Detection and evaluation of macro-cracks and micro-cracking by using automated surface wave non-contact scanners

Charles Ciccarone, Bogdan Piwakowski, Frédéric Skoczylas, Radoslaw Drelich, Jean-Marie Henault

► To cite this version:

Charles Ciccarone, Bogdan Piwakowski, Frédéric Skoczylas, Radoslaw Drelich, Jean-Marie Henault. Detection and evaluation of macro-cracks and micro-cracking by using automated surface wave non-contact scanners. Academic Journal of Civil Engineering, 2020, 38 (2), pp.72-75. 10.26168/ajce.38.2.17. hal-03594376

HAL Id: hal-03594376

https://uphf.hal.science/hal-03594376v1

Submitted on 7 May 2024

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

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# Detection and evaluation of macro-cracks and micro-cracking by using automated surface wave non-contact scanners

Charles Ciccarone<fnref n="1" />,<fnref n="2" />,⁵, Bogdan Piwakowski<fnref n="2" />, Frederic Skoczylas<fnref n="1" />, Radosław Drelich<fnref n="3" />

Jean-Marie Henaut<fnref n="4" />

## RESUME.

The goal of the presented work is the detection and evaluation of cracks, in the VeRCoRs mock-up which constitutes the double-wall containment building of a Nuclear Power Plant in scale 1/3. The experiments are conducted in situ, on the inner wall of the VeRCoRs mock-up. The detection is performed by means of two automated scanners designed for the non-destructive non-contact control of concrete using surface waves (SW). The SW signal assures the penetration in a concrete wall between 1 to 60 cm. The scanners provide the non-contact measure which permits to avoid a modification of the concrete surface by a coupling agent and a time-consuming coupling procedure. The results, obtained during pressure test in the VeRCoRs mock-up, prove that the scanner can be successfully used in the detection of micro-cracking, of cracks location, the evaluation of their opening and of the progressive ageing of the mock-up.

**Mots-clefs:** Automated NDT, concrete, surface waves, cracks, velocity, attenuation, non-contact.

## I. INTRODUCTION

The paper presents the research conducted in the frame of the French research project "Non-Destructive Evaluation of Containment Nuclear Plant Structures" (ENDE) in the period of 2015-2020. The project aims to develop the Non-Destructive Testing techniques that can be applied to evaluate and monitor the concrete in containment enclosures. [Garnier et al.2018]. The presented experiments were carried out in the VeRCoRs containment mock-up which constitutes the double wall containment building of a nuclear power plant in scale 1/3 [Henault et al.2018].

The common feature of the method presented in this paper is the use of acoustic surface waves (SW). They propagate along the surface of the inspected material and their depth of penetration $d_p$ is frequency-dependent and is close to SW wavelength. Therefore, the concrete wall can be examined in two scales:

(1). The evaluation of concrete through the total thickness of the examined wall. This task is realized by the recently developed Low Frequency Surface Wave scanner (LFSW) which provides

<footnote n="1">¹ Univ. Lille, CNRS, Centrale Lille, UMR 9013 - LAMCube, F-59651 Lille, France</footnote>

<footnote n="2">² Univ. Lille, CNRS, Centrale Lille, UMR 8520 - IEMN, TPIA F-59651 Lille, France</footnote>

<footnote n="3">³ Faculty of Mechatronics, Kazimierz Wielki University, Bydgoszcz, Poland</footnote>

<footnote n="4">⁴ Electricite de France R&D, PRISME 6 Quai Watier, BP 49, 78401 Chatou, France</footnote>
# Detection and evaluation of macro-cracks and micro-cracking by using automated surface wave non-contact scanners

Charles Ciccarone<fnref n="1" />,<fnref n="2" />,⁵, Bogdan Piwakowski<fnref n="2" />, Frederic Skoczylas<fnref n="1" />, Radosław Drelich<fnref n="3" />

Jean-Marie Henaut<fnref n="4" />

## RESUME.

The goal of the presented work is the detection and evaluation of cracks, in the VeRCoRs mock-up which constitutes the double-wall containment building of a Nuclear Power Plant in scale 1/3. The experiments are conducted in situ, on the inner wall of the VeRCoRs mock-up. The detection is performed by means of two automated scanners designed for the non-destructive non-contact control of concrete using surface waves (SW). The SW signal assures the penetration in a concrete wall between 1 to 60 cm. The scanners provide the non-contact measure which permits to avoid a modification of the concrete surface by a coupling agent and a time-consuming coupling procedure. The results, obtained during pressure test in the VeRCoRs mock-up, prove that the scanner can be successfully used in the detection of micro-cracking, of cracks location, the evaluation of their opening and of the progressive ageing of the mock-up.

**Mots-clefs:** Automated NDT, concrete, surface waves, cracks, velocity, attenuation, non-contact.

## I. INTRODUCTION

The paper presents the research conducted in the frame of the French research project "Non-Destructive Evaluation of Containment Nuclear Plant Structures" (ENDE) in the period of 2015-2020. The project aims to develop the Non-Destructive Testing techniques that can be applied to evaluate and monitor the concrete in containment enclosures. [Garnier et al.2018]. The presented experiments were carried out in the VeRCoRs containment mock-up which constitutes the double wall containment building of a nuclear power plant in scale 1/3 [Henault et al.2018].

The common feature of the method presented in this paper is the use of acoustic surface waves (SW). They propagate along the surface of the inspected material and their depth of penetration $d_p$ is frequency-dependent and is close to SW wavelength. Therefore, the concrete wall can be examined in two scales:

(1). The evaluation of concrete through the total thickness of the examined wall. This task is realized by the recently developed Low Frequency Surface Wave scanner (LFSW) which provides

<footnote n="1">¹ Univ. Lille, CNRS, Centrale Lille, UMR 9013 - LAMCube, F-59651 Lille, France</footnote>

<footnote n="2">² Univ. Lille, CNRS, Centrale Lille, UMR 8520 - IEMN, TPIA F-59651 Lille, France</footnote>

<footnote n="3">³ Faculty of Mechatronics, Kazimierz Wielki University, Bydgoszcz, Poland</footnote>

<footnote n="4">⁴ Electricite de France R&D, PRISME 6 Quai Watier, BP 49, 78401 Chatou, France</footnote>
6cm < $d_p$ < 60cm. (Fig.1.a) [Piwakowski et al.2019].

(2). The evaluation of properties of the concrete cover that is of the layer between the rebar's and the wall surface requires $d_p < 5$cm. This objective is accomplished by the High Frequency Surface Wave scanner (HFSW) (Fig.1.b) which is the "older brother" of the (LFSW). This scanner has been in practical use for 8 years [Piwakowski & Safinowski, 2009, Abraham et al, 2012].

Both scanners allow fully non-contact measurements which avoid a modification of concrete surface by a coupling agent and a time consuming coupling procedure.

<figure><img src="image_2.png" /><figcaption>FIGURE 1. (a) The LWSF scanner during leakage test in VeRCoRs mock up. (b) The HFSW scanner during leakage test in VeRCoRs mock up.</figcaption></figure>

## II. RESULTS

### A. Imaging and tracking of cracks during the pressure test in VeRCoR

The experiments were performed automatically by using LFSW scanner in VeRCoRs during the complete cycle of the pressure test carried out in March 2019 at a zone displaying two known macro cracks at positions 39 and 107 cm in the gusset lower part (Fig.2.a). During this test, the internal pressure increases up to 4 bars (Fig.2.d), and then decreases. The crack position is detected by the specially introduced $\alpha_{local}(x)$ which express the local SW attenuation and is defined as the modulus of the transfer function between SW signals recorded at neighboring points.

<figure><img src="image_3.png" /><figcaption>FIGURE 2. (a) Inspected concrete wall with positions of known cracks: in red: cracks seen at the surface, black: unknown further discovered); (b); $\alpha_{local}(x,t)$ as a function of profile position and of time for increasing pressure (c) Symbolic plot of the internal pressure (see Fig.2.d). (d) Internal pressure during the test; (e) $\alpha_{local}(x=39 \ cm, t)$ as a function of time; (f) $\alpha_{local}(x=39 \ cm)$ as a function of pressure; (g) correlation between $\alpha_{local}(x=39 \ cm)$ and crack opening determined by Fiber Optics measurements.</figcaption></figure>
6cm < $d_p$ < 60cm. (Fig.1.a) [Piwakowski et al.2019].

(2). The evaluation of properties of the concrete cover that is of the layer between the rebar's and the wall surface requires $d_p < 5$cm. This objective is accomplished by the High Frequency Surface Wave scanner (HFSW) (Fig.1.b) which is the "older brother" of the (LFSW). This scanner has been in practical use for 8 years [Piwakowski & Safinowski, 2009, Abraham et al, 2012].

Both scanners allow fully non-contact measurements which avoid a modification of concrete surface by a coupling agent and a time consuming coupling procedure.

<figure><img src="image_2.png" /><figcaption>FIGURE 1. (a) The LWSF scanner during leakage test in VeRCoRs mock up. (b) The HFSW scanner during leakage test in VeRCoRs mock up.</figcaption></figure>

## II. RESULTS

### A. Imaging and tracking of cracks during the pressure test in VeRCoR

The experiments were performed automatically by using LFSW scanner in VeRCoRs during the complete cycle of the pressure test carried out in March 2019 at a zone displaying two known macro cracks at positions 39 and 107 cm in the gusset lower part (Fig.2.a). During this test, the internal pressure increases up to 4 bars (Fig.2.d), and then decreases. The crack position is detected by the specially introduced $\alpha_{local}(x)$ which express the local SW attenuation and is defined as the modulus of the transfer function between SW signals recorded at neighboring points.

<figure><img src="image_3.png" /><figcaption>FIGURE 2. (a) Inspected concrete wall with positions of known cracks: in red: cracks seen at the surface, black: unknown further discovered); (b); $\alpha_{local}(x,t)$ as a function of profile position and of time for increasing pressure (c) Symbolic plot of the internal pressure (see Fig.2.d). (d) Internal pressure during the test; (e) $\alpha_{local}(x=39 \ cm, t)$ as a function of time; (f) $\alpha_{local}(x=39 \ cm)$ as a function of pressure; (g) correlation between $\alpha_{local}(x=39 \ cm)$ and crack opening determined by Fiber Optics measurements.</figcaption></figure>
An example of $\alpha_{local}(x,t)$ obtained during pressure increase is shown in Fig.2.b. It can be seen that maxima's of $\alpha_{local}(x, t)$ observed at positions 39 and 106 cm correlates well with the position of cracks. This shows that this parameter can be used to detect the crack position. Additionally, the previously unknown crack was found at 130 cm (its presence was confirmed optically). During the construction of the VeRCoRs, fiber optic (FO) cables were embedded in concrete which enabled the monitoring of the evolution of crack opening, expressed in micrometers [Henault et al.2012]. It can be seen that for the crack at position 39 cm the $\alpha_{local}$ and internal pressure correlate well ((Figs 2. d,e,f)). The correlation of $\alpha_{local}$ with FO (Fig.5.f) is quite good as well, thus showing that the value of $\alpha_{local}$ parameter is proportional to the crack opening.

## B. Evaluation of the global crack activity during the pressure test in VeRCoR in the cracked zone

The signal recorded by LFSW scanner can be also used in order to determine the global velocity $V_{sw}$ of the SW wave. The term *global* indicates that the estimated $V_{sw}$ characterizes the total width of the inspected zone (here 1.5 m). Figure 3.a shows the velocity decrease is also very well correlated with the FO parameter during one pressure test thus showing that the $V_{sw}$ is also directly related with the cracks opening. These measurements were conducted in the same zone during 3 pressure tests in 2017, 2018 and 2019. Figure 3.b shows the obtained limit velocities $V_{swmax}$ (pressure = 0 and $V_{swmin}$ (pressure = 4000hPa). It is clearly seen that both values decrease with time. This could be explained by the coupled effects of concrete drying and cracks opening and/or micro-cracking increase each year. Finally, the $V_{swmin}$ and $V_{swmin}$ observed as a function of time could be used as a concrete aging indicator.

<figure><img src="image_4.png" /><figcaption>FIGURE 3. (a) FO as a function of $V_{sw}$; (b) $V_{swmax}$ and $V_{swmin}$ obtained during the successive leakage tests in the years 2017, 2018, 2019.</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>FIGURE 4. (a) Global SW velocity in a crack free zone during the leakage test in VeRCoRs in March 2017 as a function of increasing pressure; (b) same for SW attenuation</figcaption></figure>

## C. Evaluation of stress and micro-cracking during the pressure test in VeRCoRs macro-crack free zone

The measurements were performed by using the HFSW scanner (thus in concrete skin) in VeRCoRs, in March 2017, in a macro-crack-free zone. The acquisition was carried out for 12 hours
An example of $\alpha_{local}(x,t)$ obtained during pressure increase is shown in Fig.2.b. It can be seen that maxima's of $\alpha_{local}(x, t)$ observed at positions 39 and 106 cm correlates well with the position of cracks. This shows that this parameter can be used to detect the crack position. Additionally, the previously unknown crack was found at 130 cm (its presence was confirmed optically). During the construction of the VeRCoRs, fiber optic (FO) cables were embedded in concrete which enabled the monitoring of the evolution of crack opening, expressed in micrometers [Henault et al.2012]. It can be seen that for the crack at position 39 cm the $\alpha_{local}$ and internal pressure correlate well ((Figs 2. d,e,f)). The correlation of $\alpha_{local}$ with FO (Fig.5.f) is quite good as well, thus showing that the value of $\alpha_{local}$ parameter is proportional to the crack opening.

## B. Evaluation of the global crack activity during the pressure test in VeRCoR in the cracked zone

The signal recorded by LFSW scanner can be also used in order to determine the global velocity $V_{sw}$ of the SW wave. The term *global* indicates that the estimated $V_{sw}$ characterizes the total width of the inspected zone (here 1.5 m). Figure 3.a shows the velocity decrease is also very well correlated with the FO parameter during one pressure test thus showing that the $V_{sw}$ is also directly related with the cracks opening. These measurements were conducted in the same zone during 3 pressure tests in 2017, 2018 and 2019. Figure 3.b shows the obtained limit velocities $V_{swmax}$ (pressure = 0 and $V_{swmin}$ (pressure = 4000hPa). It is clearly seen that both values decrease with time. This could be explained by the coupled effects of concrete drying and cracks opening and/or micro-cracking increase each year. Finally, the $V_{swmin}$ and $V_{swmin}$ observed as a function of time could be used as a concrete aging indicator.

<figure><img src="image_4.png" /><figcaption>FIGURE 3. (a) FO as a function of $V_{sw}$; (b) $V_{swmax}$ and $V_{swmin}$ obtained during the successive leakage tests in the years 2017, 2018, 2019.</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>FIGURE 4. (a) Global SW velocity in a crack free zone during the leakage test in VeRCoRs in March 2017 as a function of increasing pressure; (b) same for SW attenuation</figcaption></figure>

## C. Evaluation of stress and micro-cracking during the pressure test in VeRCoRs macro-crack free zone

The measurements were performed by using the HFSW scanner (thus in concrete skin) in VeRCoRs, in March 2017, in a macro-crack-free zone. The acquisition was carried out for 12 hours
with an interval of 1h during the first cycle of pressure increase. As obtained before for the cracked zone, $V_{sw}$ decreases with the pressure (Fig.4.a), and global attenuation $\alpha_c$ increases (Fig.4.b) thus confirming that both quantities $V_{sw}$ and $\alpha_c$ can be used to monitor the stress in concrete and /or the related micro cracking. Note that $\alpha_c$ is found to be much more sensitive: its variation is close to 500% but velocity variation is of 1.3% only.

### III. CONCLUSION

The obtained results prove the utility of the two automated SW scanners for the monitoring the concrete.

- They permit to detect the cracks, follow the micro-cracking, and finally monitor the internal stress. They can cover the thickness of inspected wall at depth ranging from 1 to 60 cm.

- They give coherent results with embedded techniques like fiber optics and thus enable to follow qualitatively the cracks evolution during the monitoring of structures not equipped with fiber optics (if the SW penetration exceeds the crack depth).

- They display the ability to detect very small crack openings of a few micrometers. It makes it possible to use this approach in nuclear industry as well in other civil engineering applications where crack openings are greater (order of 100 micrometers).

- The non-contact operation potentially enables the automatic scanning of greater surfaces just like containment walls, bridges, beams etc. They can operate automatically; without operator's presence so are well adapted for the NDT monitoring.

- Both scanners constituent prototypes which can be easily implemented to industrial use.

### REFERENCES

O. Abraham, B. Piwakowski, G. Villain, O. Durand "Non-contact, automated surface wave measurements for the mechanical characterization of concrete", Construction and Building Materials, Volume 37, December 2012, pp 904-915.

V. Garnier, B. Piwakowski, J.M. Henault, J. Verdier, J.P. Balayssac, N. Ranaivamonana, J.F. Chaix, S. Rakotonarivo, G. Villain, O. Abraham, X. Derobert, C. Payan, Sbartai, J. Saliba, E. Larose, H. Hafid, R. Drelich, Ch. Ciccarone, "Non Destructive Evaluation of the durability and damages of concrete in nuclear power plants", 12th European Conference on Non-Destructive Testing Goteborg Sweden, June 2018.

J. M. Henault, M. Quiertant, S. Delepine-Lesoille, J. Salin, G. Moreau, F. Taillade, K. Benzart "Quantitative strain measurement and crack detection in RC structures", Construction and Building Materials 37 (2012), pp 916-923.

B. Piwakowski, R. Drelich, Ch. Ciccarone, L. Ji, "Non-destructive non-contact concrete evaluation by sound and ultrasound using an automated surface wave scanner", International Congress on Ultrasonic ICU2019, Bruges 2019B.

Piwakowski, P. Safinowski, "Non-destructive non-contact air-coupled concrete evaluation by an ultrasound automated device", 7-th Intern. Symposium on Non Destructive Testing in Civil Engineering, NDTCE09, Nantes 2009 pp 603-608.
with an interval of 1h during the first cycle of pressure increase. As obtained before for the cracked zone, $V_{sw}$ decreases with the pressure (Fig.4.a), and global attenuation $\alpha_c$ increases (Fig.4.b) thus confirming that both quantities $V_{sw}$ and $\alpha_c$ can be used to monitor the stress in concrete and /or the related micro cracking. Note that $\alpha_c$ is found to be much more sensitive: its variation is close to 500% but velocity variation is of 1.3% only.

### III. CONCLUSION

The obtained results prove the utility of the two automated SW scanners for the monitoring the concrete.

- They permit to detect the cracks, follow the micro-cracking, and finally monitor the internal stress. They can cover the thickness of inspected wall at depth ranging from 1 to 60 cm.

- They give coherent results with embedded techniques like fiber optics and thus enable to follow qualitatively the cracks evolution during the monitoring of structures not equipped with fiber optics (if the SW penetration exceeds the crack depth).

- They display the ability to detect very small crack openings of a few micrometers. It makes it possible to use this approach in nuclear industry as well in other civil engineering applications where crack openings are greater (order of 100 micrometers).

- The non-contact operation potentially enables the automatic scanning of greater surfaces just like containment walls, bridges, beams etc. They can operate automatically; without operator's presence so are well adapted for the NDT monitoring.

- Both scanners constituent prototypes which can be easily implemented to industrial use.

### REFERENCES

O. Abraham, B. Piwakowski, G. Villain, O. Durand "Non-contact, automated surface wave measurements for the mechanical characterization of concrete", Construction and Building Materials, Volume 37, December 2012, pp 904-915.

V. Garnier, B. Piwakowski, J.M. Henault, J. Verdier, J.P. Balayssac, N. Ranaivamonana, J.F. Chaix, S. Rakotonarivo, G. Villain, O. Abraham, X. Derobert, C. Payan, Sbartai, J. Saliba, E. Larose, H. Hafid, R. Drelich, Ch. Ciccarone, "Non Destructive Evaluation of the durability and damages of concrete in nuclear power plants", 12th European Conference on Non-Destructive Testing Goteborg Sweden, June 2018.

J. M. Henault, M. Quiertant, S. Delepine-Lesoille, J. Salin, G. Moreau, F. Taillade, K. Benzart "Quantitative strain measurement and crack detection in RC structures", Construction and Building Materials 37 (2012), pp 916-923.

B. Piwakowski, R. Drelich, Ch. Ciccarone, L. Ji, "Non-destructive non-contact concrete evaluation by sound and ultrasound using an automated surface wave scanner", International Congress on Ultrasonic ICU2019, Bruges 2019B.

Piwakowski, P. Safinowski, "Non-destructive non-contact air-coupled concrete evaluation by an ultrasound automated device", 7-th Intern. Symposium on Non Destructive Testing in Civil Engineering, NDTCE09, Nantes 2009 pp 603-608.