# Monitoring of the hydration of Portland concrete using embedded resistivity sensors: validation with modelling

Marie-Ange Eid, Jack Atallah, Géraldine Villain, Stéphanie Bonnet, Harifidy

Ranaivomanana, Sérgio Palma Lopes, François Bignonnet

► To cite this version:

Marie-Ange Eid, Jack Atallah, Géraldine Villain, Stéphanie Bonnet, Harifidy Ranaivomanana, et al. Monitoring of the hydration of Portland concrete using embedded resistivity sensors: validation with modelling. NDE NucCon 2023 - International Conference on Non-destructive Evaluation of Concrete in Nuclear Applications, Jan 2023, Espoo, Finland. pp.237-243. hal-04303717

HAL Id: hal-04303717

https://hal.science/hal-04303717v1

Submitted on 23 Nov 2023

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>

Distributed under a Creative Commons CC BY 4.0 - Attribution - International License
# Monitoring of the hydration of Portland concrete using embedded resistivity sensors: validation with modelling

Marie-Ange Eid<fnref n="1" />,<fnref n="2" />*, Jack Atallah<fnref n="2" />, Géraldine Villain<fnref n="1" />, Stéphanie Bonnet<fnref n="2" />, Harifidy Ranaivomanana<fnref n="2" />, Sérgio Palma Lopes<fnref n="3" /> and François Bignonnet<fnref n="2" />

## ABSTRACT

Reinforced concrete structures exposed to aggressive environments, such as nuclear and offshore structures, may be subjected to several hydric and ionic transfers that can affect their service life as well as their long-term durability. This type of structures may be sometimes difficult to access for inspection, thus several Non-Destructive testing Techniques (NDT) were developed in order to monitor and to assess such concrete structures.

The work presented in this paper consisted on studying the evolution of the hydration phase of a concrete formulated with CEM I, by evaluating its resistivity over time and depth using embedded resistivity sensors connected to a resistivity meter. Resistivity profiles obtained using these embedded sensors were compared to surface resistivity measurements carried out using a Wenner device. Moreover, this experimental campaign was validated by numerical hydration modelling, showing the evolution of the general kinetic coefficient of concrete with respect to time along its hydration phase.

**Keywords:** monitoring, resistivity, hydration degree, modelling

## 1. INTRODUCTION

Endogenous and exogenous attacks to which concrete structures can be subjected represent a major concern in the evaluation of the durability of these structures and their long-term performance. Destructive testing by local sampling of cores is not recommended for some types of structures, such as nuclear plants and offshore structures. Thus, several Non-Destructive Evaluation (NDE) techniques were developed in order to carry out a specific diagnosis of structures exposed to aggressive environments [1]. The work presented below is carried out within the DEMCOM French project which pays particular attention to the durability and NDE of maritime structures, of which tidal zones may be inaccessible for inspection. One of the main causes of degradation of these structures is the corrosion of reinforcement bars due to the penetration of chloride ions from seawater. The penetration of chloride is related to the durability properties of concrete such as the chloride diffusion coefficient. This property depends on the hydration of concrete as it governs the hydrated phases, the open porosity and the composition of the poral solution [6].

In the work presented below, the evolution of the hydration phase of concrete is monitored using embedded resistivity sensors developed by Badr et. al [2], that enable to evaluate resistivity profiles over time and over the entire thickness of the structure. The electrical resistivity of a material describes its ability to resist the flow of electric current, and is highly sensitive to water and chloride contents in concrete [3-4]. The Printed Circuit Board (PCB) sensor used in this work provides a good estimation of resistivity profiles and enables to study the gradient of the degree of saturation during the drying cycles of concrete [2].

The first part of this paper presents the experimental campaign (formulation of concrete, instrumentation with the PCB resistivity sensors and conditioning of the samples). In the second part, we report and discuss the results of the monitoring of the hydration phase, which are compared

<footnote n="1">¹ Univ Gustave Eiffel, MAST-LAMES, Campus de Nantes, F-44344 Bouguenais</footnote>

<footnote n="2">² Nantes Université, Ecole Centrale Nantes, CNRS, GeM, UMR 6183, F-44600 Saint Nazaire</footnote>

<footnote n="3">³ Univ Gustave Eiffel, GERS-GEOEND, Campus de Nantes, F-44344 Bouguenais</footnote>

<footnote>*Marie-Ange Eid: +33 (0)2 40 84 59 27, marie-ange.eid@univ-eiffel.fr</footnote>
with hydration numerical modelling. This work will allow us to assess the capacity of electrical methods to follow the evolution of the hydration phase of concrete.

## 2. EXPERIMENTAL CAMPAIGN

### 2.1. Formulation of concrete

The aim of the experimental campaign is to study the behaviour of a Portland cement concrete during its hydration phase. The corresponding formulation is presented in Table 1 [5].

<table><caption>**Table 1:** Formulation of concrete</caption><thead><tr><td>Components</td><td>kg/m3</td></tr></thead><tbody><tr><td>Gravel, 4-12 mm (Boulonnais)</td><td>1041.7</td></tr><tr><td>Sand, 0-4 mm (Boulonnais)</td><td>910.3</td></tr><tr><td>CEM I 52,5 N - SR 5 CE PM-CP2 NF HTS (Lafarge)</td><td>302.5</td></tr><tr><td>Superplasticizer MasterGlenium 201 (BASF)</td><td>2.94</td></tr><tr><td>Efficient water (Eeff)</td><td>151.7</td></tr><tr><td>Water-to-binder ratio (W/B)</td><td>0.5</td></tr></tbody></table>

### 2.2. Methods and instruments

Three cylindrical specimens with a diameter of 11 cm and a height of 18 cm were cast for the studied concrete formulation (Table 1), and were instrumented with a PCB resistivity sensor which has a ladder shape and is composed of 15 electrodes distributed on both sides of the PCB. The latter is placed at the centre of the specimen along its z axis (representing the thickness of the concrete sample), between two metal grids well anchored in concrete and serving for current injection [2] (Figure 1).

During the monitoring, one instrumented specimen is connected to a commercial resistivity meter: a Syscal Junior Switch 72 (from IRIS Instruments), that manages simultaneously up to 72 electrodes and injects an alternating current of very low frequency. The measurements were made according to the Transmission mode (Trans) [2]: an electric current is injected between two metal grids, and the potential drop is measured between two consecutive electrodes on the same side of the PCB. An additional measurement is made according to the Wenner configuration (Wen) by injecting a current and measuring the potential drop on 4 electrodes on one side of the PCB without using the grids [2].

<figure><img src="image_2.png" /><figcaption>**Figure 1:** (a) PCB resistivity sensor with 15 electrodes, (b) instrumented mould before casting of concrete.</figcaption></figure>
approximately at 70 Ω.m at Tc+70 days. The increase in the apparent resistivity at young age and its near stabilization at Tc+70 days allow us to assess the setting and hydration phase of the concrete along its curing period.

The apparent resistivity values obtained using the surface Wenner device appear to be higher than those obtained with the PCB sensor. For example, at young age (Tc+6 days), the apparent resistivity starts with a value of 65 Ω.m. It does not seem to increase during the first 28 days of cure, although some large uncertainty bars may partly hide the real trend. Then it starts to increase until it stabilizes at 86 Ω.m. Let us note that the rate of increase is quite similar for both surface and embedded measurements from Tc+40 to Tc+86 days. We explain these differences in apparent resistivity magnitudes by the difference between the two measurement techniques, including the fact that surface measurements are more prone to variations in electrical contact quality than embedded measurements (therefore the larger uncertainty bars), as well as the fact that the samples and the observation times are not the same for both datasets. However, we can notice that the two types of curves are globally consistent, showing a similar trend for both embedded PCB and surface Wenner measurements. Thus, we believe that our experimental resistivity monitoring can be a good proxy for the hydration phase of concrete, yet the comparison between the two resistivity techniques remains qualitative in order to validate the response of the PCB sensors during the hydration phase. That is why, only resistivity measurements obtained with the PCB sensors will be compared to numerical modelling, which was the major aim of this paper.

## 3.2. Comparison of experimental results with numerical hydration modelling

The results obtained in the experimental campaign are compared to numerical hydration modelling, in order to validate the capacity of the electrical measurements in showing the evolution of the hydration phase of concrete. That is why, the graphs in Figure 3 show a comparison between the apparent resistivity measured experimentally and the hydration degree obtained numerically by 3 different models: VCCTL [7], Avrami's equations [14] and Bernard et al. (2003) [15]. These 3 models are widely used in literature, therefore considered as reliable models to describe the hydration degree variation in function of time.

<figure><img src="image_3.png" /><figcaption>Figure 3: (a) Evolution of the normalized hydration degree and normalized apparent resistivity over time, (b) normalized hydration degree versus normalized apparent resistivity.</figcaption></figure>

First of all, the Virtual Cement and Concrete Testing Laboratory (VCCTL) [7] is a virtual laboratory software based on the CEMHYD3D system where cement paste and concrete materials are computed in a virtual environment allowing the creation, hydration and estimation of the 3D cement material microstructure [8-12]. Whereas, Avrami's equations [13-14] are best adapted to explain nucleation and growth events established empirically. They are used as an approximation for all Portland cements; as they are expected to react at similar relative rates. These equations present a basic kinetic model that provides acceptable fits for hydrated pastes. The third model used in this work is that of Bernard et al. [15] which is a multi-phasic kinetic model that describes the variation rates of each clinker phase hydration, by kinetics laws that link the reaction rate with the
[6] El Achrafi, M. (2022). *Détermination des indicateurs de durabilité du béton en utilisant des observables d'évaluation non destructives : application aux ouvrages maritimes* (Doctoral dissertation, Nantes).

[7] Bentz, D. P., & Bentz, D. P. (2005). *CEMHYD3D: A three-dimensional cement hydration and microstructure development modelling package. Version 3.0.*

[8] Garboczi, E. J., & Berryman, J. G. (2001). Elastic moduli of a material containing composite inclusions: effective medium theory and finite element computations. *Mechanics of materials*, 33(8), 455-470.

[9] Bentz, D. P., & Garboczi, E. J. (1990). Digitised simulation model for microstructural development. *Ceram. Trans.*, **16**, 211-226.

[10] Garboczi, E. J., & Bentz, D. P. (1991). Digital simulation of the aggregate-cement paste interfacial zone in concrete. *Journal of materials Research*, **6**(1), 196-201.

[11] Jennings, H. M., & Johnson, S. K. (1986). Simulation of microstructure development during the hydration of a cement compound. *Journal of the American Ceramic Society*, **69**(11), 790-795.

[12] Watts, B. E., Tao, C., Ferraro, C. C., & Masters, F. J. (2018). Proficiency analysis of VCCTL results for heat of hydration and mortar cube strength. *Construction and Building Materials*, **161**, 606-617.

[13] Dalziel, J. A., & Gutteridge, W. A. (1986). *The influence of pulverized-fuel ash upon the hydration characteristics and certain physical properties of a Portland cement paste* (No. Tech Rept 560).

[14] Taylor, H. F. (1987). A method for predicting alkali ion concentrations in cement pore solutions. *Advances in Cement Research*, **1**(1), 5-17.

[15] Bernard, O., Ulm, F. J., & Lemarchand, E. (2003). A multiscale micromechanics-hydration model for the early-age elastic properties of cement-based materials. *Cement and concrete research*, **33**(9), 1293-1309.