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Abstract
1. Introduction
2. Methodology
3.Results and Discussion
4.Conclusions
5.References |
| Accelerated Aging of Embedded Electrical Resistivity Sensor for Monitoring Concrete Structures |
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Sam Ang Keo1, Jean-Paul Balayssac2, Géraldine Villain3, Yannick Fargier4, Béatrice Yven5
1 Cerema, Research team ENDSUM, 23 Amiral Chauvin Avenue, 49130 Les Ponts-de-Cé, France, sam-ang.keo@cerema.fr / keo_samang@yahoo.com
2 LMDC, UPS-INSA Toulouse, 135 Avenue de Rangueil, 31077 Toulouse Cedex 4, France, balayssa@insa-toulouse.fr
3 MAST - LAMES, Université Gustave Eiffel, Campus de Nantes, 44344 Bouguenais, France, geraldine.villain@univ-eiffel.fr
4 GERS - RRO, Université Gustave Eiffel, Campus de Lyon, 25 avenue François Mitterrand, 69675 Bron Cedex, France, yannick.fargier@ifsttar.fr
5 ANDRA, 1 Rue Jean Monnet, 92290 Châtenay-Malabry, France, beatrice.yven@andra.fr |
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Abstract
The paper presents a study on accelerated aging of electrical resistivity sensors implemented for monitoring the water content of concrete structures built in the Callovo-Oxfordian clay formation at a depth of more than 500 m. The objective is to test the response of the sensors in the case that the interstitial solution of the argillite penetrates into the concrete pores or because the carbonation reaches a sufficient depth to reach the first electrodes of the sensor. Two experimental campaigns with cylindrical specimens (11 cm diameter and 22 cm height) were carried out: one for the tests in contact with the argillite solution (over a period of 80 days of immersion), and the another for accelerated carbonation tests up to 165 days. The results of measurements in transmission and Wenner configurations were interpreted. The tests for the sensors in contact with the interstitial solution of the argillite enables to verify the good resistance of the sensors in a neutral pH environment compared to the basis medium of the concrete. The accelerated carbonation tests reveal a high sensitivity to carbonation for the transmission configuration, and the good resistance of the sensors. This study confirms the good function of the sensors implemented for structural health monitoring (SHM). The sensors can be also used for monitoring other types of concrete structu. |
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| Introduction |
Electrical resistivity is one of the durability indicators of concrete. It is sensitive to constituents of the concrete and in particular its water content. With the aim of characterizing and monitoring the water content in the concrete (C37/45) of the ANDRA structures, two electrical resistivity multi-electrode sensors (ladder-shaped and ring-shaped) in the form of printed circuit board (PCB) were designed and produced [1]. These two multi-electrode sensors are embedded in the concrete and make it possible to obtain an electrical resistivity profile as a function of depth and to monitor its evolution over time. The “ladder-shaped” sensors, allowing centimeter measurements, have been validated based on tests on cylindrical specimens having a diameter of 11 cm and a height of 22 cm [2], [3]. Moreover, the temperature effect on the measurements with the sensor was also already studied [4]. The study on the accelerated aging of the "ladder-shaped" sensors, presented in this article, aims to test the response of the sensors in case the interstitial solution of the argillite penetrates into the porosity of the concrete or when the carbonation would reach a depth corresponding to the first electrodes of the sensor. For this purpose, two experimental campaigns with specimens were carried out: one for the tests in contact with the argillite solution and the other for accelerated carbonation tests.
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| Materials and Methods |
| Five cylindrical specimens of concrete (11 cm diameter and 22 cm height) were prepared with cement type I (CEM I 52,5N). The studied concrete has water/cement/sand (0/4mm)/gravel (4/12mm) mixing ratio of 1:1.7:4.32:4.78 (by mass). |
| Sensor and principle of measurements |
| the ladder-shaped PCB sensor is presented in Figure 1. There are 19 electrodes in total, regularly placed at 2 cm on both sides, allowing to obtain many measurements (at every 1 cm) along the sensor. The electrical resistivity is measured by using the following principle: |
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| Figure 1. Electrical resistivity multi-electrode sensor in form of "ladder-shaped" printed circuit board, (a) Photo of the sensor, (b) schema of the sensor |
| In our study, the calculation of the values of the geometrical factor (G) are done with modelling in COMSOL multi-physics, as shown in Figure 2 |
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| Figure 2. Model in COMSOL for calculating the geometrical factor, (a) Model with grids and sensor embedded in the cylindrical sample, (b) Electrical current in case of transmission configuration |
Figure 2 (a) shows the model representing the sensor embedded in a cylindrical concrete sample with two grids at both extremities. Figure 2(b) shows electrical current lines (red lines) between both grids in the sample in case the calculation of G for the measurements in transmission configuration. It is worthy to remind that the sensor was used to measure electrical resistivity in many different configurations in the previous study [1], but only two configurations (transmission and wenner) are discussed in the present study.
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| Experimental tests in contact with interstitial solution of argillite |
| The composition of the interstitial solution of the Callovo-Oxfordian argillite provided by Andra, already used in several other studies on argillite [5]–[7] is given in Table 1. |
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Table 1. Concentration of the interstitial solution of the argillite [8]
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| Three specimens having the age of 18 months (marked 2, 4 and 5), each instrumented with a ladder-shaped sensor, were partially immersed in the solutions (as shown in Figure 3). A measurement of the electrical resistivity was carried out at different times. These specimens had been stored in a room at a temperature of 20 °C and a relative humidity (RH) of 65% before these tests in argillite solution (and had also been conditioned, after casting, for 1 month in a wet cure). The pH of the solution was also measured at each measurement of the electrical resistivity. |
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| Figure 3. Experimental set-up of the tests with interstitial solution of argillite |
| Tests with accelerated carbonation |
| In order to test the response of the sensors in the case of concrete carbonation, two specimens were placed under accelerated carbonation condition in an enclosure containing 50 % CO2 (as shown in Figure 4). The specimens were covered with aluminum foil on their side face and one end, while the other end was exposed to the CO2 penetration. The relative humidity in the enclosure is regulated to 65 %. The specimens had been kept for two months at this relative humidity before placing them in the chamber. |
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| Figure 4. Specimens placed in the carbonation chamber for the tests with accelerated carbonation |
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| Results and Discussions |
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Results from the tests with interstitial solution of argillite
Figure 5 presents the results, obtained on specimen 4 over a period of 80 days of immersion, in the transmission configuration and wenner configuration.
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| Figure 5. Evolution of the resistivity profile as a function of time for the tests with argillite solution |
| The upper surface of the specimen corresponds to the depth z = 0 cm in Figure 3. It is worthwhile to remind that the first 9 centimeters of the tested specimen are not submerged. |
We first notice a resistivity gradient between the non-submerged upper part, which is more resistive, and the submerged lower part. It is particularly visible for the measurement in the Wenner configuration. In transmission, it is difficult to differentiate the resistivity curves at the different times, including that for the latest (80 days). On the other hand, for the measurement in Wenner configuration, we note that the measurements carried out at five days don't not make it possible to detect the rise of the front of the argillite solution, whereas the resistivity significantly increases at 80 days including in the submerged part. This increase can be explained by a partial rehydration of the cement paste. It was also observed on specimen 5 at approximately the same amplitudes. Monitoring of the pH showed an increase from 7.3 to 7.9 over the first three weeks of the tests, then become stable. These tests lead to conclude the ability of the sensors to withstand an environment different from that imposed by the interstitial solution of the concrete having a pH equal to 13. The contact of the sensor with the argillite solution seems not alter its operation, at least over the observation period of this study.
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Results from the tests with accelerated carbonation
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Figure 6 presents the results obtained from the test on a specimen in transmission and wenner configurations. The depth z is measured from the surface
exposed to CO2 penetration (the top).
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| Figure 6. Resistivity as a function of depth and time in specimen exposed to accelerated carbonation |
| First of all, there is a significant difference between the profile measured under reference condition and that measured after 41 days of exposure in the carbonation chamber. In Wenner configuration, the resistivity increases throughout the depth which could be attributed to drying. On the other hand, in transmission, this gradient is not observed, and only from 92 days that the resistivity evolves but initially without significant variation as function of the depth. Between 92 and 165 days, the resistivity in transmission significantly increases inside the specimen. This increase is also greater between 8 and 12 cm depth in the Wenner configuration. |
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| Conclusions |
| This study on accelerated aging makes it possible to conclude the capability of the developed sensors to withstand an environment which is different from that imposed by the interstitial solution of the concrete (with a pH approximately equal to 13). The tests of the sensors in contact with the interstitial solution of argillite allow to verify the good behavior of the sensors over 80 days in an environment at neutral pH compared to the basic medium of the concrete and a better sensitivity of the measurements in Wenner configuration. This behavior was confirmed by the productivity of the measurements on different specimens. The accelerated carbonation tests revealed a high sensitivity of the measurements in transmission and good resistance of the sensors over 165 days. In perspective, additional longer-term tests should be carried out to confirm the observed behaviors. |
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Acknowledgement :
The authors would like to acknowledge ANDRA (French National Radioactive Waste Management Agency) for the financial support.
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| References |
| 1 - J. Badr, ‘Conception et validation d’un capteur noyé de résistivité électrique en vue du suivi des profils de teneur en eau dans les bétons’, PhD thesis (in French), Université Toulouse 3 Paul Sabatier, Toulouse, France, 2019. |
| 2 - J. Badr et al., ‘Design and validation of a multi-electrode embedded sensor to monitor resistivity profiles over depth in concrete’, Constr. Build. Mater., vol. 223, pp. 310–321, Oct. 2019, doi: 10.1016/j.conbuildmat.2019.06.226. |
| 3 - Y. F. J. Badr F. Deby, G. Villain, S. Palma-Lopes, S. Delepine-Lesoille, J. P. Balayssac, L. M. Cottineau, ‘Design and implementation of embedded sensors based on electrical resistivity to determine water content profiles in thick concrete structures’, presented at the 9th European Workshop on Structural Health Monitoring, Manchester, United Kingdom, 2018. |
| 4 - J. Badr et al., ‘Temperature Effect on Electrical Resistivity Measurement Using an Embedded Sensor to Estimate Concrete Water Content’, Appl. Sci., vol. 12, no. 19, p. 9420, Sep. 2022, doi: 10.3390/app12199420. |
| 5 - D. Jougnot, ‘Étude géophysique des phénomènes de transfert dans les argilites du Callovo-Oxfordien partiellement saturées en eau: application à l’EDZ du site de Bure’, PhD thesis (in French), Université de Savoie, Bourget du Lac, 2012. |
| 6 - F. Bazer-Bachi et al., ‘Characterization of iodide retention on Callovo-Oxfordian argillites and its influence on iodide migration’, Phys. Chem. Earth Parts ABC, vol. 31, no. 10–14, pp. 517–522, Jan. 2006, doi: 10.1016/j.pce.2006.04.015. |
| 7 - F. Bazer-Bachi et al., ‘Characterization of sulphate sorption on Callovo-Oxfordian argillites by batch, column and through-diffusion experiments’, Phys. Chem. Earth Parts ABC, vol. 32, no. 8–14, pp. 552–558, Jan. 2007, doi: 10.1016/j.pce.2006.01.010. |
| 8 - Jacquot E., ‘Composition des eaux interstitielles des argilites du Callovo-Oxfordien non perturbées: état de la modélisation’, ANDRA Rep. NT ASTR 02-041, 2002. |
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