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Article

Investigation of Corrosion Product Distribution and Induced Cracking Patterns in Reinforced Concrete Using Accelerated Corrosion Testing

by
Olfa Loukil
1,
Lucas Adelaide
1,
Véronique Bouteiller
1,
Marc Quiertant
1,2,*,
Frédéric Ragueneau
3,4 and
Thierry Chaussadent
1
1
Univ. Gustave Eiffel, MAST-EMGCU, F-77447 Marne-la-Vallée, France
2
Institut de Recherche, ESTP, 28 Avenue du Président Wilson, F-94230 Cachan, France
3
Université Paris-Saclay, CentraleSupélec ENS Paris-Cachan, CNRS, Laboratoire de Mécanique Paris-Saclay (LMPS), F-91190 Gif-sur-Yvette, France
4
EPF Ecole d’ingénieurs, 55 Avenue du Président Wilson, F-94230 Cachan, France
*
Author to whom correspondence should be addressed.
Appl. Sci. 2024, 14(23), 11453; https://doi.org/10.3390/app142311453
Submission received: 21 October 2024 / Revised: 28 November 2024 / Accepted: 2 December 2024 / Published: 9 December 2024
(This article belongs to the Special Issue Advances in Reinforced Concrete Structural Health Monitoring)
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Abstract

:
The present study investigates the corrosion development and induced cracks in reinforced concrete specimens submitted to an accelerated corrosion test. The accelerated chloride-induced corrosion test was performed using an impressed current mode. Three current densities (50, 100 and 200 µA/cm2 of steel) and different exposure times were considered. The objective of the experiments is to analyse two distinct types of damage: firstly, internal damage near the steel/concrete interface, which can be observed in the distribution of corrosion products, as well as damage within the concrete cover, which manifests as cracking. Secondly, external damage, which can be observed in the form of rust spots and concrete surface cracks. The aim of this analysis is to elucidate the relationship between internal damage and external damage. The study confirmed that the corrosion products are non-uniformly distributed around and along the steel reinforcing bar. It also highlighted that the accelerated corrosion test conditions, such as current density, duration, environmental conditions and the specimen geometry, have a significant influence on the distribution of the corrosion products and their thickness around the steel reinforcement and therefore on the internal and external crack patterns. The data analysis revealed a substantial dispersion and contrast in terms of the data, which precluded the establishment of a definitive correlation between internal and external deterioration.

1. Introduction

The main cause of environmental degradation in existing reinforced concrete (RC) structures is the corrosion of carbon steel reinforcement [1,2]. This mechanism leads to a reduction of the steel reinforcement bar (rebar) cross-section [3,4], the cracking of the concrete cover [3,4] and a decrease of the bond properties between the steel and concrete [3,4]. Indeed, once the passivation layer around the reinforcement is broken down, corrosion is activated as long as the environmental conditions are favourable (in terms of oxygen, water and temperature) [5,6]. The resulting accumulation of corrosion products occupies a volume approximately two to seven times larger than that initially taken up by the steel. This leads to an increasing radial pressure at the interface between the rebar and the surrounding concrete, causing tensile stresses in the concrete along the length of the corroded rebar, which develop slowly [5,6]. If these stresses exceed the concrete tensile strength, cracks appear and spread towards the outer surface, potentially leading to spalling and delamination of the concrete cover and serious damage to the concrete cross-sections [5,6]. These cracks can become the primary paths for a quicker ingress of aggressive agents into the steel bars, which accelerates the corrosion process [5,6].
Furthermore, it is increasingly recognised that the performance of existing RC structures can be compromised by the presence of aggressive agents, such as chloride ions. In countries with a long maritime environment (coasts) and winter de-icing periods, it is obvious that the structural safety and serviceability of corroded RC structures and infrastructures can be consequently affected by the corrosion process. This process can subsequently result in a loss of serviceability of the RC structure. In the absence of appropriate maintenance measures, the structural safety of existing structures may be compromised. Consequently, at the structural scale, there is a need to identify cost-effective solutions that can maintain or even enhance the performance of existing structures, ensuring their continued safe load-bearing capacity.
Considering that surface cracks are the most visible signs of corrosion progress, their width can be considered as the most reliable indicator to assess the actual corrosion level [4,7]. Consequently, corrosion-induced cracking appears as one of the most important key parameters to predict the durability of RC structures and therefore to plan their maintenance [4,7].
Therefore, establishing a well-defined relationship between the corrosion level and the width of the corrosion-induced cracks and their crack patterns would greatly facilitate the assessment of the condition of a structure based on visual inspection. In view of all the aforementioned detrimental effects of corrosion, many researchers have devoted significant effort to developing tools, such as non-destructive evaluation techniques [8,9], as well as empirical or numerical predictive models, to assess the corrosion evolution of RC structures [10,11]. However, most of these tools have not yet been applied in the scope of application, thus preventing end users of structures from having access to an efficient maintenance policy.
As part of the efforts in this research area, many experimental tests are available in the literature to investigate corrosion-induced crack initiation and propagation in reinforced concrete [12,13,14,15,16,17,18,19,20,21,22,23,24]. These tests consider various types of RC specimens and different parameters. For example, some authors have accelerated the corrosion of RC specimens by applying regular wetting (salt water spraying) and drying cycles in an artificial climate room with controlled temperature and relative humidity [12]. In other studies [13,14,15,16], an impressed current mode was used. A constant current from a direct current source is applied to the steel in order to accelerate the chloride ion diffusion in the concrete cover during the corrosion initiation phase until the depassivation of the steel bar and thus induce significant corrosion in a short period of time during the following corrosion phase. Furthermore, the addition of chloride ions into the concrete mixture further accelerates the process [7,17,18,19,20,21,22]. These two common methods can be applied to any RC specimen.
To investigate the effects of the corrosion products on the cracking process and/or the relationship between the corrosion level and the corrosion-induced crack pattern and its widths, many researchers have paid particular attention to the possibility of linking the rebar section loss to the corrosion-induced crack pattern and its widths [21,25,26,27,28]. Nevertheless, it is more relevant to analyse and determine the thickness of the corrosion products directly rather than from the rebar section loss in order to obtain a more accurate distribution of the corrosion product thickness [29,30].
Generally, the corrosion product layer is not constant at the steel/concrete interface, and previous studies have reported that its distribution strongly and intricately affects the crack pattern [27,31,32,33,34]. It is therefore insufficient to solely consider the amount of corrosion products (rebar section loss) when studying the damage process of a corroded RC element; only a clear analysis of the distribution of corrosion products around the rebar cross-section can help to extend the current understanding of cracking mechanisms in reinforced concrete [29,30]. This is the reason why the authors have selected this approach.
It can also be noted that although some published studies have focused on the corrosion products’ thickness at the steel/concrete interface [15,35,36], very few have investigated the relationship between the actual thickness of corrosion products and the cracking [16,37].
In light of the findings of the literature review carried out in the preceding paragraphs, the aim of the present paper is to generate a steel rebar corrosion in a short time in order to analyse the relationship between the distribution of corrosion products around the rebar, the evolution of concrete cover cracking (internal cracking) and the concrete surface crack patterns (external cracking) of RC specimens. The particularity of this study also lies in some geometrical features, such as a corner rebar and a concrete strength representative of old RC structures and a ribbed steel rebar as commonly implemented in the field.
Additionally, the natural corrosion process in concrete can take place gradually over a very long period of time before visible damage in the structure is observed. For this reason, techniques such as impressed current methods are often considered by many authors to induce an artificial steel corrosion to simulate real corroded conditions in laboratory [4,6,7,13,14,15,16,17,18,19,20,21,22]. Although there are some differences between natural corrosion and artificial corrosion (for example, the anode and cathode locations are predefined or the chemical composition of corrosion products), the use of these accelerated corrosion methods is one of the most popular ways to study the behaviour of corroded structures and obtain results that come close to those obtained from natural corrosion in a short time [17,38,39,40]. Given the benefits offered by this technique, the authors decided to use it for their experimental tests.
At the present time, analysis of the surface corrosion-induced crack patterns (their orientations, widths and lengths) does not allow an assessment of the internal damage state caused by corrosion (distribution and thickness of the corrosion products and internal corrosion-induced cracking) [4,5]. The reverse is also not as straightforward to accomplish [4,5]. This is the reason why the ambition of this study is to be able to predict the internal degradation state of structural RC elements from the external crack patterns (crack lengths, crack orientations and crack widths). This would make it possible to take the appropriate repair and/or maintenance decisions at the appropriate time.

2. Experimental Program

2.1. Specimen Details

Thirty prismatic RC specimens (500 × 125 × 100 mm3) were cast with a carbon steel deformed rebar (600 mm long and 20 mm diameter). The rebar was located in the corner of the prism to obtain a 30 mm concrete cover on two faces (Figure 1), as commonly implemented in the field. Standard Portland cement (CEM I 52.5 CP2 NF, Vicat Group, L’Isle d’Abeau, France) and different sizes of Palvadeau siliceous aggregate were used for the concrete composition (Table 1). A high water to cement ratio of 0.7 was chosen to produce a concrete with high porosity that allows a quicker diffusion of chloride ions and consequently accelerates the corrosion process activation. The specimens were cast in a horizontal position, as shown in Figure 1. After casting, prisms were moist cured for 28 days before testing. Compressive strengths then were measured on nine concrete cylinders (160 mm in diameter, 320 mm length) according to NF EN 12390-3 [41] standard. The measured compressive strength and Young’s modulus are 34.5 MPa (±2.46) and 36.5 GPa (±1.58), respectively. The concrete strength of the specimens is indicative of that observed in old reinforced concrete structures that have been in place for more than fifty years (C25/30).

2.2. Accelerated Corrosion Test

The accelerated corrosion of the carbon steel rebar was performed using the impressed current mode [38,42,43]. This type of method has been reported in numerous previous studies and has proved its effectiveness and relevance [7,14,17,18,19,20,21,22]. Figure 2 presents the experimental setup. The current density between the rebar and the platinum mesh was controlled by a power supply (Agilent 6614C, Agilent Technologies, Les Ulis, France, 100 V, 0.5 A) where the positive and negative poles were, respectively, connected to the rebar and the mesh. The platinum mesh (275 mm long, 75 mm wide) was placed into a bottomless PVC tank glued (a cyanoacrylate-type mastic was applied) on the centre of the top face of the RC prisms (Figure 2). The length of rebar that is considered to be corroding is the length of the platinum mesh. Therefore, the surface area of the carbon steel rebar was equal to 172.8 cm2. For each current density, the RC prisms were connected in series. For illustrative purposes, an example is shown in Figure 2a.
Three days before starting the accelerated corrosion test, the PVC tanks were filled up with an alkaline and chloride solution composed of NaOH (1 g/L), KOH (4.65 g/L) and NaCl (30 g/L). The solution level was maintained constant by refilling the tanks daily. This allowed the prism to remain in a state of wetting, making it possible to lower the voltage needed to provide the impressed current. Chloride ions migrated from the solution to the rebar in two stages: firstly, by diffusion and secondly, by an electrical field.
Three series of impressed current densities (50, 100 and 200 µA/cm2 of surface of steel) were used to accelerate the corrosion of the rebar (Table 2). These three current densities are not chosen at random but according to the literature [7,13,14,15,16,17,18,19,20,21,22]. Indeed, the current density of 100 μA/cm2 is frequently used in the literature by many authors [7,13,14,15,16,17,18,19,20,21,22]. Some authors state that it corresponds to the highest corrosion current density recorded in existing RC structures [17,30,44]. Others say that this represents a reasonable value that enables the acceleration of the corrosion process, the achievement of a corrosion pattern similar to that obtained under natural corrosion and the prevention of excessive internal pressure within the concrete sample without altering the concrete and without compromising the reality of the corrosion products formed [4,38,39,45,46]. The other two current densities, 50 and 200 µA/cm2, were chosen in order to analyse the effect of the current density and the exposure time on the corrosion-induced damage (thickness and distribution of corrosion products and cracks) for the same total charge. For further clarification, please refer to the definition provided in the final paragraph of this section.
Total charges according to current density and duration of the test (from 3.5 to 78 days) are reported in Table 2. The purposes of these parameters were
-
To obtain external cracks with visible widths within a period that was compatible with the duration of the project (3 years);
-
To determine whether the internal (corrosion product layer distribution and concrete cracking) and external (rust stains and concrete cracking) degradation states of specimens exposed to the same total charge are similar at different current densities and accelerated corrosion exposure times.
During the accelerated corrosion test, the temperature, impressed current (constant) and voltage of each prism were recorded every two hours with a data acquisition unit.
Different durations of the corrosion tests were defined according to the impressed current density (Table 2). Each duration was associated with an impressed current density to achieve a targeted value of the total charges. To illustrate, 14, 7 and 3.5 days were associated with 50, 100 and 200 µA/cm2, respectively, to give a total charge of 168 A.h/m2. At the end of each duration, two prisms were disconnected (Table 2). The top (T) and front (F) faces of these two prisms were immediately photographed in order to keep a record of the crack pattern. Widths of external cracks were recorded after different exposure times using a crack-measuring magnifier (resolution 0.05 mm). One prism was used for non-destructive electrochemical characterizations and the other one for physical characterizations (indicated with an * in Table 2).

2.3. Electrochemical Characterizations

In order to determine the corrosion state of the rebar, non-destructive electrochemical measurements such as half-cell potential (Ecorr), linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) were carried out using a potentiostat (PARSTAT2263, Ametek®, Elancourt, France). Subsequently, the corrosion current density was calculated. Electrochemical characterizations were performed after the accelerated corrosion test, following depolarisation of the rebar.
Half-cell potential measurements (Ecorr) are correlated to a probability of corrosion [8,47]. The ASTM C876-15 standard [8,48] provides a correlation between potential values and probability of corrosion. Potential values with electronegativity exceeding −350 mV/SCE indicate a high probability of corrosion (>90%).
The corrosion current density Jcorr (µA/cm2) was calculated based on the Stern and Geary equation [49]
J c o r r     = B R p S
where B is a constant (26 mV), Rp (Ohm) is the linear polarization resistance (determined through the measurement of LPR and EIS) and S (cm2) is the polarized steel surface corresponding to the electrochemical cell design. In order to calculate this surface area, it was assumed that the corrosion will take place under the platinum mesh, which has a length of 275 mm. The steel bar was thus subjected to corrosion over a length of 275 mm, i.e., a surface area of 172.78 cm2. According to the RILEM recommendations [50], values below 0.1 µA/cm2 indicate a negligible level of corrosion. Those between 0.1 and 0.5 µA/cm2 are indicative of a weak corrosion level. From 0.5 to 1 µA/cm2, the corrosion level is moderate, and values higher than 1 µA/cm2 indicate a high level of corrosion.

2.4. Physical Characterizations

First of all, in order to understand the methodology applied, it is necessary to understand that different scales of observation have been used, namely prism (Pn), slice (Ti) and square samples (Ei).
Indeed, this methodology consists of three steps (Figure 3, Figure 4, Figure 5, Figure 6 and Figure 7) and has been developed to characterize the observed corrosion-induced damage.
(1)
On the concrete surface of the RC prisms.
The corrosion degradations (rust stains, cracks, etc.) were visually observed on the RC prisms, considering the two faces (T and F) with the 30 mm concrete cover. Photographs of the T and F faces of each prism were taken. In addition, the maximum crack width on the T and F faces of the twenty-eight prisms was measured using a crack-measuring magnifier with transparent ruler, procured from Walmart, Bentonville, AR, USA (precision of 0.05 mm).
(2)
Inside the prisms at the level of the concrete cover.
Slices 20 mm thick were drawn along the longitudinal X direction on prisms that had been marked with an asterisk (Figure 4 and Figure 5 and Table 2). Each of the slices had been assigned a designation, ranging from T1 to T25 (Figure 4 and Figure 5). The slices were sawn with dimensions of 125 × 100 × 20 mm3. Slices T2 and T3 were considered as reference samples, as they were outside the accelerated corrosion test area. The slices from T10 to T17 were inside the accelerated corrosion test area. As expected, slices T2 and T3 exhibited no sign of corrosion and thus were excluded from the subsequent analysis. The total number of slices to be studied is therefore one hundred twelve.
The two faces of slices T10 to T17 were photographed and examined in order to characterize their degradation based on the methodology developed by [51] and adapted for our study. In order to determine the angular position of the root of each visible crack in each face of the slices, a graduated circle was positioned on the photograph of each face (Figure 6a). The length of each crack was assessed using the concentric circles (one circle drawn every centimetre) (Figure 6b). The crack widths of all faces were subsequently measured using the same crack-measuring magnifier.
(3)
At the steel/concrete interface close to the rebar.
The steel/concrete interface was analysed using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) (FEI QUANTA 400-EDAX, FEI, Villebon-sur-Yvette, France. In order to reduce the time required for analysis, three slices were selected from the eleven prisms. This approach was deemed to be more appropriate than analysing eight slices per prism, given the time constraints. The selected slices were T10, T13 and T16 per prism, thus allowing for the assessment of the steel/concrete interface degradation at each end and in the middle of the accelerated corrosion test area, with the same gap between the three slices. The total number of selected slices is therefore forty-two.
Prior to analysis, the slices T10, T13 and T16 were impregnated with an epoxy resin under vacuum at room temperature and subsequently dried in an oven at 45 °C for 24 h in accordance with ASTM standard C642 [52]. Smaller square samples (Ei with dimensions 45 × 45 × 20 mm3), including the complete steel/concrete interface, were sawed at slow speed from the Ti slices. This resin application prevents damage, such as concrete cracking or debonding between concrete and steel, which may occur during the cutting process. The samples were progressively polished in four stages using 220, 9, 3 and 1 µm abrasive paper in order to minimize the surface relief. Subsequently, the samples were then carbon metallised. Finally, they were vacuum dried in a desiccator before observation to remove air from the concrete pores and prevent oxidation of the metallised surface.
SEM/EDS images provided a clear view of the boundaries between the steel rebar, the corrosion products, the transformed medium (mixed areas containing elements coming from the corrosion layer and the concrete microstructure) and the cementitious matrix. As the square sample Ei was still too large for SEM analysis, it was divided into eight observable areas (Cj) (Figure 7). This allowed for the identification of the thickness and distribution of the corrosion products around the rebar.

3. Results

In the Results section, the first subsection is devoted to the electrochemical characterizations of the prisms after the accelerated corrosion test. The following subsections present the experimental results (Figure 3, Figure 4, Figure 5, Figure 6 and Figure 7) with the aim of studying the following three key aspects:
  • The thickness and distribution of corrosion products around and along the rebar;
  • The internal cracks coming from the rebar and going into the concrete;
  • The external cracks that are visible on the surface of the prism.
This will allow a relationship to be established between the internal degradation and the external degradation.

3.1. Electrochemical Characterizations

The depolarisation of the rebar was monitored on each prism (by checking that the steel/concrete system was in equilibrium with its environment) for the purpose of ensuring the validity of the electrochemical measurements.
Following the depolarisation of the RC prisms submitted to the accelerated corrosion test, the half-cell potential (Ecorr) was measured, and the corrosion current density was calculated. Rebar depolarization was observed to occur between 49 and 77 days after the end of the accelerated corrosion test.
The results presented in Figure 8 indicate a decrease in half-cell potential with an increase in the duration of the accelerated corrosion test. Based on the probability of corrosion [48], as marked by the red dotted lines on the graphs, the rebars are likely to corrode in all the prisms regardless of the exposure time and the impressed current density. Conversely, the current density increases (from 1 to 10 µA/cm2) with the duration of the accelerated corrosion test. In accordance with the corrosion levels (negligible, moderate and high) as recommended by [50], and indicated with red dotted lines in the graphs, all the corrosion current densities are indicative of a high corrosion level. From the literature, it is established that the appearance of concrete cracking is considered to occur at corrosion current densities exceeding 1 µA/cm2 [53].
In conclusion, the presented graphs highlight that potential decreases and corrosion current density increase with total charge. Furthermore, these non-destructive electrochemical analysis results reveal corrosion and cracking in all the RC prisms, thus attaining the goal of the accelerated corrosion test. The remaining question to be addressed is whether the efficiency of the accelerated corrosion test allows for the generation of controlled cracks.

3.2. Thickness and Distribution of Corrosion Products Around the Steel Rebar

This subsection presents an analysis of the thickness and distribution of corrosion products around the steel rebar. In the measurement of the thicknesses of the corrosion products, the layer representing the transformed medium was not considered.
Contrary to expectations, the largest thickness of corrosion products was observed for the impressed current density of 50 µA/cm2 and after 14 days (Table 3). For the current density of 100 µA/cm2, the overall thickness increased with the duration of the accelerated corrosion test, with the exception of the 21st day (Table 3). The maximum thickness of corrosion products at 200 µA/cm2 impressed current density seemed to stabilize quickly (after 3.5 days of accelerated corrosion). Corrosion products may possibly increase rapidly until a threshold value and then stabilize due to the withdrawal of corrosion products along the cracks. The results do not permit showing a clear trend due to the dispersion of corrosion product thicknesses obtained around and along at the steel/concrete interface.
Regarding the location of corrosion products, it is obvious that the accumulation of the corrosion products at the steel/concrete interface is not uniform around the rebar, whether along the rebar or inside each Ci area (Table 3). As a general result, the maximum thickness of corrosion products was mainly observed in areas C8, C1, C2 and C3 since they were facing the thinnest concrete covers and the top concrete surface, where the counter-electrode is located. This resulted in the generation of an electrical field that forced chloride ions to migrate to the rebar.
Figure 9 shows the boundaries of steel rebar, corrosion products and concrete and illustrates the evolution (kinetics) of the corrosion product formation and location.
The corrosion products are barely discernible at the lowest current density (50 µA/cm2). An increase in the current density (100 µA/cm2) results in the formation of corrosion products with a thickness of approximately 250 µm (Figure 9). It can be observed that the corrosion product thickness at the highest current density (200 µA/cm2) is locally larger (exceeding 500 µm), which is in accordance with the results presented in Table 3.
During the corrosion process, corrosion products first diffuse into the voids and microcracks of the surrounding concrete. This region of the concrete is called the porous zone [35,54]. Once the porous zone has been filled with corrosion products or when corrosion product accumulation occurs at a faster rate than the diffusion process into the porous zone around the steel rebar, tensile stresses are initiated in the surrounding concrete, which subsequently induces cracking. Consequently, a higher current density reduces the timespan available for corrosion products to penetrate the porous zone, therefore leading to an acceleration of the occurrence of cracking. This phenomenon was also observed by [51,55]. In addition, Ref. [56] observed that there are areas where almost no corrosion products penetrate into the pore structure of the concrete, while other areas show clear corrosion products in the cement matrix.
Indeed, the formation of corrosion products in RC elements is a complex process that is influenced by the variation in environmental conditions (such as the diffusion of oxygen and water). This also affects the composition and properties of the resulting corrosion products [57]. This variation leads to an interaction between the various types of corrosion products, namely iron oxides and iron hydroxides [57]. As a result, the volume of corrosion products is regarded as a dynamic process [57,58]. Furthermore, the presence of chloride ions has a tendency to increase the solubility of corrosion products, which can result in the migration of these corrosion products through the cement paste (voids and micro-cracks) instead of depositing at the steel/concrete interface [5,59]. Consequently, the growth of the thickness of the corrosion products is weaker. Additionally, the prism geometrical parameters and the concrete properties affect the formation process of the corrosion products [28,30,40]. Therefore, the distribution and the thickness of the corrosion products may vary around and along the rebar.
Moreover, Ref. [57] has proposed a four-stage approach to the corrosion process of the rebar which is as follows: stage 1 is the depassivation, stage 2 is the local corrosion, stage 3 is the accelerated corrosion and stage 4 is the constant rate corrosion. This is in accordance with the observations carried out from our experimental tests.
This may explain why the distribution of corrosion products at the steel/concrete interface is observed to vary significantly regardless of the current density, even within the same Ci area.

3.3. Internal Cracks at the Steel/Concrete Interface

In order to obtain a realistic view of the degradation state of corroded structural elements, it is essential to conduct an accurate assessment of the internal crack patterns. Despite the absence of visible indications on the surface of the concrete, this degradation has a significant influence on the service life of RC structural elements.
Different internal crack patterns were observed in slices T10 to T17. Three main directions of cracks were observed: vertical (V), horizontal (H and H’) and oblique (O and O’) (Table 4). The apostrophe « ’ » represents the occurrence of a second crack. Table 4 illustrates a selection of representative internal crack patterns observed. Table 5, Table 6 and Table 7 summarise the average and standard deviation (in italics) for the 16 samples per prism based on the three impressed current densities of 50, 100, and 200 µA/cm2.
Table 5 indicates that crack H was consistently present in all the slices of the studied RC prisms, followed by the occurrence of crack V. Crack O exclusively occurred at a total charge of 336 A.h/m2 and current densities of 100 and 200 µA/cm2. Crack O’ only appeared at the highest current density (200 µA/cm2) and total charge (840 A.h/m2). Crack H’ was only observed for a total charge of 840 A.h/m2 (at the current densities of 50 and 200 µA/cm2). Cracks O, O’ and H’ only occurred when a significant total charge was achieved (336 or 840 A.h/m2).
Regarding Table 6, the maximum duration of the accelerated corrosion tests conducted for all current densities, resulted in the formation of cracks H and V reaching the surface of the concrete. The propagation of cracks through the concrete cover was more easily observable when the cover was thinner (30 mm in comparison to the 50 and 75 mm concrete covers on the other faces). The remaining cracks (H’, O and O’) never run through the entire concrete cover. This observation is in accordance with the findings reported by [7,18,20,22,25,26,33,38,56,60,61,62,63,64].
Table 7 illustrates that the crack width increased for all cracks and current densities, with the exception of crack H with current densities of 50 and 200 µA/cm2. This can be attributed to the occurrence of crack H’. Indeed, the evolution of the width of the first cracks can be explained by the posterior development of new cracks that may be formed depending on the current density and the test duration. However, the sum of the crack widths at each total charge reveals an increase with the duration of the accelerated corrosion test for all current densities used.
Additionally, the results presented in Table 4, Table 5, Table 6 and Table 7 also show (i) an increase in the orientation, length and width of internal crack patterns in conjunction with the increase of the total charge, and (ii) that for a chosen total charge, the internal crack pattern was more developed for higher values of current density. The differences in the observed crack patterns can be attributed to two factors: (i) the heterogeneity of the concrete (in terms of aggregate size and shape in proximity to the rebar, and the presence of voids) and (ii) the non-uniform distribution of the corrosion products, which exhibited varying ranges of thickness around and along the steel rebar.
Few researchers have worked on the analysis of internal crack patterns due to corrosion induced by an impressed current mode. A comparison was made between the results presented here and those published in the literature on the subject of RC prisms with a corner rebar [18,20,33,38,56,60,64]. The number of cracks described in these studies varies between one and six cracks. In all cases, the main cracks are vertical and/or horizontal. These cracks usually propagate throughout the concrete cover and become externally visible. Our findings are in accordance with those previously reported in the literature.
Very few studies have measured the width of corrosion-induced internal cracks located in close proximity to the rebar [22,25,26,63]. In these studies, experiments focused on corrosion-induced cover cracking due to centre rebars. To our knowledge, no published work to date has measured internal cracks (width and length) in samples with a rebar in the corner. However, the assessment of the corrosion-induced crack patterns for RC specimens with a corner rebar is important to evaluate the degradation state of RC structural elements, as this is the most unfavourable configuration.

3.4. External Cracks

External cracks are the key point in an investigation to identify the degradation of an RC structure suffering from corrosion. In this study, external cracks were characterized by means of visual inspections and crack widths (Figure 10 and Table 8).
From the visual observations of the RC prisms after the accelerated corrosion test, concrete deteriorations were easily observed on T and F faces, which are those closest to the steel rebar. No deterioration was observed on the other faces.
The following four types of external crack pattern induced by corrosion (Figure 10 and Table 8) were identified on the RC prisms:
-
Crack pattern 1: A single longitudinal crack formed on the front face with a maximum width range of between 0.1 and 0.7 mm. This crack pattern was observed for the three current densities. The width of the crack increased with the duration of the corrosion test;
-
Crack pattern 2: A single longitudinal crack formed on the top face with a maximum width of between 0.2 and 0.3 mm. This crack pattern was observed exclusively for a current density of 100 µA/cm2 and durations of 7, 14 and 35 days;
-
In crack patterns 3 and 4, two longitudinal cracks formed on the front face as well as on the top face (with increasing duration of the accelerated corrosion test). The difference between these patterns was the appearance of the first crack, on the front face for crack pattern 3 and on the top face for crack pattern 4. The initiation of the crack took place in the middle section of the PVC tank, and the propagation of the crack followed the rebar until the cracks reached the two extremities of the RC prism. However, a more detailed observation reveals the opposite for RC prisms P12 and P32, where the crack occurred at the extremities. It is important to mention that such crack occurrence is possible.
-
Regrettably, it was not possible to determine the precise timing at which the crack on the top face occurred (i.e., before or after the onset of the crack at the front face) due to the location of the PVC tank. Consequently, crack pattern 3 is assumed for a RC prism with two cracks when the front face crack was wider than the top face crack at the end of the corrosion test. The opposite approach was adopted in the case of crack pattern 4.
Cracks appeared for a minimum total charge of 168 A.h/m2 and were due to the propagation of the internal vertical (V) and horizontal (H) cracks. Based on Faraday’s law, one might expect that the maximum crack width increases with time and current density. However, this is not precisely what was observed, although the maximum width of the external crack as a whole increased with the total charge (Figure 11). In addition, when two cracks were observed on the RC prism, the maximum width of the top face crack was wider than that of the front face at current densities of 100 and 200 µA/cm2. Opposite observations were made at the 50 µA/cm2 current density.
The percentage of cracks occurring on face T and face F are, respectively, 28.6% and 64.3%. The percentages of patterns 1, 2, 3 and 4 are, respectively, 53.6, 14.3, 10.7 and 14.3%. A value of 7.1% represents the percentage with no cracking.

4. Discussion

4.1. Comparison of External Crack Widths from This Work and from the Literature

The external crack width is an interesting value that would be very useful for determining the service life of a RC structure.
From the results of our work, together with those of the existing literature previously considered [17,19,20], a linear band containing almost all the points is highlighted (Figure 12). It is very likely that the width of this band depends on various experimental parameters, such as the w/c ratio of the concrete, the tensile concrete strength, the addition of chloride ions to the concrete mix and other parameters. The results also clearly show that crack width increases with total charge. However, the influence of current density on the relationship between crack width and total charge is also evident. When considering experimental points (external crack widths) obtained for the same total charge in Figure 12, it can be noted that crack width can vary according to the impressed current density. Moreover, identical external crack width values could be obtained after the application of different total charges, sometimes using the same current density and sometimes not.
It must be underlined that in [20], a crack width of 0.7 mm was achieved with a total charge of 1536 A.h/m2 and a current density of 200 µA/cm2. This crack width value is smaller than that obtained by [20] (0.9 mm), with a total charge of 1344 A.h/m2 and a current density of 350 µA/cm2. Similar cases can also be observed in the present study. Such results highlight the importance of the intensity of the current density and the duration of the corrosion process in the degradation of RC prisms. It can be inferred that in order to predict the corrosion-induced internal degradation, it is crucial to consider the corrosion method and the test duration in the evolution of the crack widths.

4.2. Tentative Explanations of the Evolution of Corrosion-Induced Cracking

The preceding experimental results from both the published literature and our study show a notable dispersion and contrast in the data. This could be due to the large variety of parameters involved, such as the geometry of the prism, the geometry of the accelerated corrosion test setup, the test duration and the impressed current density.
Figure 13 provides a preliminary illustration of the potential stages of the corrosion process from internal to external.
The experimental observations indicate that the stresses generated by the corrosion products in the concrete surrounding the corner steel rebar lead mainly to the appearance of top and front face cracks. This corrosion-induced behaviour of RC prisms can be attributed to two factors: (i) the location of the steel rebar near these two faces and (ii) the location of the PVC tank, which generates a vertical water and chloride ion content gradient in the concrete cover.
Indeed, it can be stated that the most significant generating current lines are located between a part of the circumference of the steel rebar (specifically the upper-front section) and the top face of the prism. Since the rebar was located in the RC prism corner, the current lines generated around the rebar are unequally distributed. In addition, the concrete heterogeneity and the numerous phenomena occurring during the accelerated corrosion test (such as the dissolution/diffusion/precipitation of iron in the concrete pores and cracks, the oxygen content and gradients of humidity and of chloride ions), result in the generation of sloping pressures due to the corrosion products that are formed mainly in the upper-front section (between C8 and C3). These pressures therefore promote the formation of a shear crack in the concrete cover, which mainly manifests as an H crack and a V crack, as presented in Figure 13. But due to the non-uniform accumulation of the corrosion products, a delay in occurrence between these two cracks is observed. One may note that the H crack is the most common (64.3%), occurring first to due to the superior supply of oxygen to the steel surface facing to the front face [57]. This facilitates the formation process of corrosion products, which in turn leads to cracking of the concrete cover [57]. This crack evolution can then be schematically presented in Figure 13.
In light of the aforementioned findings, it can be concluded that the order of appearance of cracks is complex to predict. The unequal development and distribution of the corrosion products exert an influence on the formation of the cracks.
In the course of this present study, a total of sixty-five papers were reviewed. Of these, only four have investigated the internal degradation of RC elements, particularly in direct relation to the morphology and distribution of corrosion products [16,30,37,65]. However, it is essential to correctly determine the distribution of corrosion products in order to provide an adequate assessment of the internal and external crack patterns. As previously stated in the literature, the thickness of the corrosion layer around the steel rebar is generally determined by the depth of the corrosion damage to the steel rebar, either from the rebar section loss or from the rebar mass loss. However, the results obtained by researchers such as [34,66,67,68] indicate that the direct determination of the corrosion layer thickness through SEM/EDS analysis is a more realistic approach to reach this goal. This is why our investigation has focused on the experimental determination of the distribution of corrosion products around the steel rebar through direct observations.
In their work, refs. [22,25,26] showed that the corrosion product distribution exhibits an elliptical shape. Other studies, such as [33], have shown that the measured corrosion layers produce corrosion thickness peaks that are located opposite the concrete surface from which the chloride ions have penetrated the concrete cover. This is more closely aligned with our experimental findings.
Once cracking has initiated at the steel/concrete interface, corrosion-induced cracks propagate outwards as the steel rebar corrosion continues. Some cracks continue to propagate until they reach the surface of the concrete cover while others remain below the surface. The cracks that do not reach the surface also contribute to the internal degradation of the concrete. This deterioration can have harmful effects on the service life of the RC structures. Therefore, it is crucial to analyse the internal crack pattern. Indeed, this internal crack pattern depends on the distribution of the corrosion products at the steel/concrete interface and geometrical parameters, as previously discussed.

5. Conclusions

The work presented in this paper consisted of generating a controlled and accelerated process for steel rebar corrosion. It sought to identify and quantify a relation between internal and external degradations.
Additionally, to understand the combined effect of the current density and the corrosion exposure time on the cracking, three current densities associated with different exposure times were considered. The total charge was then used as a parameter of the analysis. The electrochemical characterizations after depolarisation made it possible to demonstrate the transition from passive to active corrosion of rebars in concrete on a macroscopic scale.
The analyses carried out showed, and in some cases confirmed, that
❖
A disparity in the thickness and the location of the corrosion products around the steel rebars was found;
❖
The number of cracks that constitutes the internal crack pattern increases with the total charge. As the internal crack patterns are conditioned by the distribution of the corrosion products, they also depend on a number of factors, including the heterogeneity of the concrete, the concrete cover, the rebar location, where the chloride ions come from, the location of the counter electrode and various mechanisms, such as the dissolution/diffusion/precipitation of iron in the concrete pores and cracks, the oxygen content and gradients of humidity and of chloride ions;
❖
The concrete surface cracks observed in our study are related to the geometry of the prisms. In accordance with the results from the literature, the external crack width tends to increase as the total charge increases. It is noted that not all internal cracks run through the concrete cover;
❖
The higher the current density, the earlier the mechanical consequences become harmful;
❖
The environmental conditions of the accelerated corrosion test and the geometry of the RC prism conditioned the distribution of corrosion products around the rebar;
❖
The development and distribution of the corrosion products is unequal and influences the order of occurrence of cracks. This process is difficult to predict.
The prospects are as follows:
❖
Feed the numerical modelling from the experimental database created with the thickness and location of corrosion products, internal cracking and external cracking;
❖
Clarify the relationship between internal and external degradations by improving the experimental protocol;
❖
Once this relation has been established for accelerated corrosion tests, it is necessary to establish this relationship for natural corrosion.

Author Contributions

Validation, L.A.; Formal analysis, L.A., V.B., M.Q., F.R. and T.C.; Investigation, O.L., L.A., V.B. and F.R.; Writing—original draft, O.L. and L.A.; Writing—review & editing, L.A., V.B. and M.Q.; Supervision, L.A., V.B., M.Q., F.R. and T.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the Université Gustave Eiffel and Andra, the French National Agency for Radioactive Waste Management (Xavier Bourbon and Laurent Trenty).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author. The data are not publicly available due to future publications.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Schematic representation of RC prisms. (a) Side view, (b) cross-section view (dimensions are in mm).
Figure 1. Schematic representation of RC prisms. (a) Side view, (b) cross-section view (dimensions are in mm).
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Figure 2. Accelerated corrosion setup: (a) RC prisms connected in series; (b) subcircuit involving a single RC prism; (c) cross-section view (T means top face and F means front face).
Figure 2. Accelerated corrosion setup: (a) RC prisms connected in series; (b) subcircuit involving a single RC prism; (c) cross-section view (T means top face and F means front face).
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Figure 3. Overview of step 1 of the methodology for physical characterizations (The orange square and blue line indicate the location of the PVC tank and the crack respectively).
Figure 3. Overview of step 1 of the methodology for physical characterizations (The orange square and blue line indicate the location of the PVC tank and the crack respectively).
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Figure 4. Schematic representation of a sample preparation for step 2.
Figure 4. Schematic representation of a sample preparation for step 2.
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Figure 5. Overview of the step 2 (prism cutting) of the methodology for physical characterizations.
Figure 5. Overview of the step 2 (prism cutting) of the methodology for physical characterizations.
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Figure 6. Overview of step 2 (analysis of the crack patterns) of the methodology for physical characterizations (the labels used were Pn-Xd-Y-Ti, where Pn refers to the RC prism name, Xd to the time of exposure (in days), Y to the impressed current (µA/cm2) and Ti to the slice name).
Figure 6. Overview of step 2 (analysis of the crack patterns) of the methodology for physical characterizations (the labels used were Pn-Xd-Y-Ti, where Pn refers to the RC prism name, Xd to the time of exposure (in days), Y to the impressed current (µA/cm2) and Ti to the slice name).
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Figure 7. Overview of the step 3 (analysis of the steel/concrete interface) of the methodology for physical characterizations (Ti refers to the slice name, Ei to the slice name and Cj to the observed area name).
Figure 7. Overview of the step 3 (analysis of the steel/concrete interface) of the methodology for physical characterizations (Ti refers to the slice name, Ei to the slice name and Cj to the observed area name).
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Figure 8. Half-cell potential (Ecorr) and corrosion current density (Jcorr) of the RC prisms versus duration of the accelerated corrosion test in the first and second columns, respectively. Data obtained using different impressed current densities: (a) 50 µA/cm2 (represented by green triangles), (b) 100 µA/cm2 (represented by blue squares), (c) 200 µA/cm2 (represented by red circles).
Figure 8. Half-cell potential (Ecorr) and corrosion current density (Jcorr) of the RC prisms versus duration of the accelerated corrosion test in the first and second columns, respectively. Data obtained using different impressed current densities: (a) 50 µA/cm2 (represented by green triangles), (b) 100 µA/cm2 (represented by blue squares), (c) 200 µA/cm2 (represented by red circles).
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Figure 9. SEM images of the steel/concrete interface showing the thickness of the corrosion products layer for a total charge equal to 168 A.h/m2. (a) 50 µA/cm2 (P23-14d), (b) 100 µA/cm2 (P31-7d) and (c) 200 µA/cm2 (P14-3.5d).
Figure 9. SEM images of the steel/concrete interface showing the thickness of the corrosion products layer for a total charge equal to 168 A.h/m2. (a) 50 µA/cm2 (P23-14d), (b) 100 µA/cm2 (P31-7d) and (c) 200 µA/cm2 (P14-3.5d).
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Figure 10. Maximum width of external cracks in RC prisms using different impressed current densities. (a) 50 µA/cm2, (b) 100 µA/cm2 and (c) 200 µA/cm2.
Figure 10. Maximum width of external cracks in RC prisms using different impressed current densities. (a) 50 µA/cm2, (b) 100 µA/cm2 and (c) 200 µA/cm2.
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Figure 11. Evolution of the maximum external crack width as a function of total charge, according to the current density.
Figure 11. Evolution of the maximum external crack width as a function of total charge, according to the current density.
Applsci 14 11453 g011
Applsci 14 11453 g012
Figure 12. Evolution of external crack widths from this work and from the literature [17,19,20].
Figure 12. Evolution of external crack widths from this work and from the literature [17,19,20].
Applsci 14 11453 g012
Applsci 14 11453 g013
Figure 13. Evolution of internal cracking leading to external crack patterns 1 and 3; (a) current phenomenon during the corrosion process; (b) occurrence of the first crack H; (c) occurrence of the second crack V.
Figure 13. Evolution of internal cracking leading to external crack patterns 1 and 3; (a) current phenomenon during the corrosion process; (b) occurrence of the first crack H; (c) occurrence of the second crack V.
Applsci 14 11453 g013
Table 1. Concrete mix composition.
Table 1. Concrete mix composition.
AggregatesCementWater
Size (mm)0/0.3150.315/10.5/11/42/44/88/1212.5/20
Composition (kg/m3)14927718017057324265473275192.5
Table 2. Overview of the samples and parameters for the accelerated corrosion test.
Table 2. Overview of the samples and parameters for the accelerated corrosion test.
RC Prism
Label		Impressed Current Density
(µA/cm2 of Steel Surface)		Duration of the Accelerated Corrosion Test (Days)Total Charge
(A.h/m2)
ReferenceP01, P02000
Series 1P21, P2250560
P23*, P245014168
P25*, P265028336
P27*, P285070840
P29, P305078936
Series 2P31*, P321007168
P05*, P0610014336
P07, P08*10021504
P09*, P1010028672
P11*, P1210035840
Series 3P13, P14*2003.5168
P15, P16*2007336
P17*, P1820017.5840
P19, P2020019.5936
Table 3. Minimum and maximum thicknesses of corrosion products at the steel/concrete interface and corresponding locations using different impressed current densities (50, 100 and 200 µA/cm2).
Table 3. Minimum and maximum thicknesses of corrosion products at the steel/concrete interface and corresponding locations using different impressed current densities (50, 100 and 200 µA/cm2).
RC Prism
Pn-Xd-Y		Minimum Thickness of Corrosion Products (µm)Location of the Minimum ThicknessMaximum Thickness of Corrosion Products (µm)Location of the Maximum Thickness
P23-14d-5050C21502C2
P25-28d-5029C5828C8
P27-70d-5023C1873C2
P31-7d-10022C2 and C6736C2
P05-14d-10036C2827C2
P08-21d-10029C8617C2
P09-28d-10082C41112C8
P11-35d100111C11584C8
P14-3.5d-20050C51287C1
P16-7d-200100C61374C8
P17-17.5d-20028C41228C3
Table 4. Examples of internal crack patterns (where Pn-Xd-TiR represents the right face of the slice Pn-Xd-Ti).
Table 4. Examples of internal crack patterns (where Pn-Xd-TiR represents the right face of the slice Pn-Xd-Ti).
Total Charge (A.h/m2)
Current density (µA/cm2)168336840
50Applsci 14 11453 i001
P23-14d-T12R		Applsci 14 11453 i002
P25-28d-T16R		Applsci 14 11453 i003
P27-70d-T14R
100Applsci 14 11453 i004
P31-7d-T11R		Applsci 14 11453 i005
P05-14d-T10R		Applsci 14 11453 i006
P11-35d-T11R
200Applsci 14 11453 i007
P14-3.5d-T11R		Applsci 14 11453 i008
P16-7d-T16R		Applsci 14 11453 i009
P17-17.5d-T13R
Table 5. Average and standard deviation of the angular positions (in degrees) of internal cracks.
Table 5. Average and standard deviation of the angular positions (in degrees) of internal cracks.
Type of Crack
RC SpecimenH’HVOO’
P23-14d-50 6.670.02
P25-28d-50 23.445.2192.817.69
P27-70d-50346.568.6015.949.22905.27
P31-7d-100 19.627.7188.135.55
P05-14d-100 22.8115.90 15216
P11-35d-100 10.635.8283.444.9112010.54
P14-3.5d-200 52.50112.6978.4422.82
P16-7d-200 19.695.1489.387.88147.1911.45
P17-17.5d-20011.255.9942.2713.3788.133.90114.6913.7415717.05
Table 6. Average and standard deviation of the lengths (mm) of internal cracks.
Table 6. Average and standard deviation of the lengths (mm) of internal cracks.
Type of Crack
RC SpecimenH’HVOO’
P23-14d-50 30-
P25-28d-50 30-194.3
P27-70d-5024.23.330-30-
P31-7d-100 14.42.3330-
P05-14d-100 30- 20.600.8
P11-35d-100 30-30-19.600.8
P14-3.5d-200 30-7.604.86
P16-7d-200 30-11.102.1613.302.94
P17-17.5d-20014.1130-30-22.701.5624.21.24
Table 7. Average and standard deviation of the widths (mm) of internal cracks.
Table 7. Average and standard deviation of the widths (mm) of internal cracks.
Type of Cracks
RC SpecimenH’HVOO’
P23-14d-50 0.090.02
P25-28d-50 0.160.030.100.04
P27-70d-500.140.040.110.030.110.04
P31-7d-100 0.080.030.080.03
P05-14d-100 0.140.07 0.100.03
P11-35d-100 0.220.060.450.080.170.06
P14-3.5d-200 0.050.040.080.02
P16-7d-200 0.190.040.090.040.110.07
P17-17.5d-2000.100.030.180.070.180.080.150.070.080.05
Table 8. Pictures of external crack patterns of RC prisms using different impressed current densities (50, 100 and 200 µA/cm2). (* asterisk indicates the prism used for physical characterizations; total charge values in bold print are those that can be found in all series).
Table 8. Pictures of external crack patterns of RC prisms using different impressed current densities (50, 100 and 200 µA/cm2). (* asterisk indicates the prism used for physical characterizations; total charge values in bold print are those that can be found in all series).
RC Specimen
Name		Top Face (T)Front Face (F)Corrosion Test Duration (Days)Impressed Current Density (µA/cm2)
P21-5d-50Applsci 14 11453 i010Applsci 14 11453 i011550
P22-5d-50Applsci 14 11453 i012Applsci 14 11453 i013
P23*-14d-50Applsci 14 11453 i014Applsci 14 11453 i0151450
P24-14d-50Applsci 14 11453 i016Applsci 14 11453 i017
P25*-28d-50Applsci 14 11453 i018Applsci 14 11453 i0192850
P26-28d-50Applsci 14 11453 i020Applsci 14 11453 i021
P27*-70d-50Applsci 14 11453 i022Applsci 14 11453 i0237050
P28-70d-50Applsci 14 11453 i024Applsci 14 11453 i025
P29-79d-50Applsci 14 11453 i026Applsci 14 11453 i0277950
P30-79d-50Applsci 14 11453 i028Applsci 14 11453 i029
P31*-7d-100Applsci 14 11453 i030Applsci 14 11453 i0317100
P32-7d-100Applsci 14 11453 i032Applsci 14 11453 i033
P05*-4d-100Applsci 14 11453 i034Applsci 14 11453 i03514100
P06-14d-100Applsci 14 11453 i036Applsci 14 11453 i037
P07-21d-100Applsci 14 11453 i038Applsci 14 11453 i03921100
P08*-21d-100Applsci 14 11453 i040Applsci 14 11453 i041
P09*-28d-100Applsci 14 11453 i042Applsci 14 11453 i04328100
P10-28d-100Applsci 14 11453 i044Applsci 14 11453 i045
P11*-35d-100Applsci 14 11453 i046Applsci 14 11453 i04735100
P12-35d-100Applsci 14 11453 i048Applsci 14 11453 i049
P13-3.5d-200Applsci 14 11453 i050Applsci 14 11453 i0513.5200
P14*-3.5d-200Applsci 14 11453 i052Applsci 14 11453 i053
P15-7d-200Applsci 14 11453 i054Applsci 14 11453 i0557200
P16*-7d-200Applsci 14 11453 i056Applsci 14 11453 i057
P17*-17.5d-200Applsci 14 11453 i058Applsci 14 11453 i05917.5200
P18-17.5d-200Applsci 14 11453 i060Applsci 14 11453 i061
P19-19.5d-200Applsci 14 11453 i062Applsci 14 11453 i06319.5200
P20-19.5d-200Applsci 14 11453 i064Applsci 14 11453 i065
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MDPI and ACS Style

Loukil, O.; Adelaide, L.; Bouteiller, V.; Quiertant, M.; Ragueneau, F.; Chaussadent, T. Investigation of Corrosion Product Distribution and Induced Cracking Patterns in Reinforced Concrete Using Accelerated Corrosion Testing. Appl. Sci. 2024, 14, 11453. https://doi.org/10.3390/app142311453

AMA Style

Loukil O, Adelaide L, Bouteiller V, Quiertant M, Ragueneau F, Chaussadent T. Investigation of Corrosion Product Distribution and Induced Cracking Patterns in Reinforced Concrete Using Accelerated Corrosion Testing. Applied Sciences. 2024; 14(23):11453. https://doi.org/10.3390/app142311453

Chicago/Turabian Style

Loukil, Olfa, Lucas Adelaide, Véronique Bouteiller, Marc Quiertant, Frédéric Ragueneau, and Thierry Chaussadent. 2024. "Investigation of Corrosion Product Distribution and Induced Cracking Patterns in Reinforced Concrete Using Accelerated Corrosion Testing" Applied Sciences 14, no. 23: 11453. https://doi.org/10.3390/app142311453

APA Style

Loukil, O., Adelaide, L., Bouteiller, V., Quiertant, M., Ragueneau, F., & Chaussadent, T. (2024). Investigation of Corrosion Product Distribution and Induced Cracking Patterns in Reinforced Concrete Using Accelerated Corrosion Testing. Applied Sciences, 14(23), 11453. https://doi.org/10.3390/app142311453

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