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

HAL
open science

# A new protocol to evaluate the behaviour and durability of marine structures

Marinelle El-Khoury, Emmanuel Rozière, Frédéric Grondin, Mathias Marcel, Rachid Cortas, Fadi Hage Chehade

► To cite this version:

Marinelle El-Khoury, Emmanuel Rozière, Frédéric Grondin, Mathias Marcel, Rachid Cortas, et al. A new protocol to evaluate the behaviour and durability of marine structures. Ocean Engineering, 2024, 302, pp.117579. 10.1016/j.oceaneng.2024.117579. hal-04934703

HAL Id: hal-04934703

https://nantes-universite.hal.science/hal-04934703v1

Submitted on 19 May 2025

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_2.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_3.png" /></figure>

Research paper

# A new protocol to evaluate the behaviour and durability of marine structures

Marinelle El-Khoury<sup>a</sup>, Emmanuel Rozière<sup>a, *</sup>, Frédéric Grondin<sup>a</sup>, Mathias Marcel<sup>a</sup>, Rachid Cortas<sup>b</sup>, Fadi Hage Chehade<sup>c</sup>

<figure><img src="image_4.png" /></figure>

## ARTICLE INFO

### Keywords:

- Creep

- Seawater

- Chemo-mechanical

- Cement

- Procedure

## ABSTRACT

Sustained mechanical and environmental loadings on offshore structures result in creep phenomena. Creep and relaxation significantly affects the development of strains and stresses, thus they influence the durability of structures. Creep originates from the behaviour of the phases within the cement matrix. Seawater modifies the phases composition of cement matrix because of the variety of ions and their possible interactions with cement hydration products. This, in turn, affects the mechanical behaviour of structures, including creep. For durability and safety purposes, the design of offshore structures should consider the possible coupling between cement hydration, seawater exposure, and creep. Therefore, there was a need to develop a new protocol to evaluate the behaviour and durability of marine structures. As part of this new protocol, a new rig has been developed to evaluate the creep of cement-based materials immersed in seawater. The obtained results show that the short-term creep of structures in seawater is faster than in tap water. In the long term, even though multiple phases are microscopically formed due to seawater attack, the positive and negative effects of these phases formation and dissolution lead to almost similar creep development in seawater. This protocol can be used to assess the chemo-mechanical durability of multiple structural materials in order to develop low carbon materials. Additionally, it could improve the design of offshore structures by estimating the maximum permissible load based on the rigidity of structures and their chemical degradation level.

## 1. Introduction

Countries with coastal areas are more and more interested in marine renewable energy. The development of offshore structures requires an optimization of the construction cost, the durability, and the sustainability of materials and structures. The use of concrete is relatively common in these types of structures as it is a reliable and cost-effective option for large-scale offshore structures (Fernández and Pardob, 2013). Offshore structures are exposed to chemical reactions as well as mechanical loadings for long periods. Concrete undergoes chemical and physical degradations in seawater (Mehta, 1991). Creep refers to the time-dependent behaviour of cement-based materials under sustained loadings. It can be explained by two different physical mechanisms with different kinetics: in the short term, there is micro-diffusion of water between capillary pores, and in the long term, there is sliding of C–S–H; involving mechanisms such as shear sliding and micro cracking (Ulm,

F.-J. Acker, 1998; Ulm et al., 1999). Therefore, creep is of high influence on the long-term performance and safety of structures. Creep is likely to generate some damage (Bazant, 2001; Betten, 2005), and creep-damage coupling has been previously reported (Omar et al., 2009; Pijau-dier-Cabot et al., 2004). The delayed strains influence the development and evolution of mechanical stresses in such key structures, subsequently influencing their durability. Consequently, the creep phenomenon cannot be overlooked when assessing the long-term durability of these structures.

The creep of cement-based materials originates from the behaviour of phases formed in cement paste as a result of cement hydration and environmental actions. Seawater represents a combination of multiple ions (carbonates, chloride, sulfate, magnesium, sodium, etc.). The interaction between cement hydration products and these ions can modify the cement phases, and therefore the creep phenomenon in seawater is affected. Seawater is significantly different from sulfate

<footnote><sup>a</sup> Nantes Université, Ecole Centrale de Nantes, CNRS, GeM, UMR 6183, F-44000, Nantes, France</footnote>

<footnote><sup>b</sup> Centre de Recherches Scientifiques en Ingénierie (CRSI), Université Libanaise, Beyrouth, Lebanon</footnote>

<footnote><sup>c</sup> Centre de Modélisation, Ecole Doctorale des Sciences et Technologie, Université Libanaise, Lebanon</footnote>

<footnote>* Corresponding author.
E-mail address: emmanuel.roziere@ec-nantes.fr (E. Rozière).</footnote>
attacks at equivalent sulfate concentrations (Santhanam et al., 2006). Several research studies indicate that the service life is often compromised as a result of elevated aggressiveness within this particular environment (De Medeiros-Junior et al., 2015; Fernández and Pardob, 2013). Numerous works have focused on the study of cement-based materials exposed to external sulfate attack (Ragoug et al., 2019; Schmidt et al., 2009) and chloride diffusion (Wang et al., 2023; Zhang et al., 2013). However, few studies considered the combined effect of sulfate and chloride ions on materials behaviour (Sun et al., 2021; Wang et al., 2021). The cations present in the exposure solutions are considered as an important parameter that can affect the chemical reactions; Al-Amoudi et al. (1995) showed the influence of sodium and magnesium solutions on mortar and concrete samples. Due to the chemical reactions complexity, it is necessary to combine all the anions and cations present in seawater (De Weerdt et al., 2014, 2023; Santhanam et al., 2006) in order to assess the behaviour of cementitious materials in seawater solutions. For example, this can be performed using in situ tests in natural seawater sites (De Weerdt et al., 2014; Georges et al., 2021; Touil et al., 2022) or using laboratory reconstituted seawater (El-Khoury et al., 2022; Islam et al., 2010). The combined effects of ions and their reaction with hydration products actually induce a competition between the formation of protective layers, and damage due to leaching and expansion caused by ettringite formation (El-Khoury et al., 2022; Guil-lon, 2004). An example of protection is highlighted in studies focusing on the self-healing capacity of cementitious materials in saline solutions (Khan et al., 2021, 2022; Maes et al., 2016). Therefore, in this study, all the ions present in the seawater are considered.

The chemo-mechanical assessment of cementitious materials aims at investigating the coupling between chemical changes induced by environmental actions (air, underground water, seawater, tap water, etc.) and mechanical properties of cement-based materials (strength, stiffness, shrinkage, creep, etc.). This field of study has received major attention in recent years due to the increasing demand for sustainable and durable construction materials.

The literature has tackled the chemo-mechanical coupling between mechanical loadings and chemical degradations through various approaches. These include combining creep and leaching phenomena (Bernard et al., 2003a; Bes, 2019; Lacarrière et al., 2006; Torrenti et al., 2008), associating chloride diffusion with the time-dependent behaviour of concrete structures (Wang et al., 2023), and simulating the impact of coupled axial loading and sulfate attack on the time-dependent mechanical behaviour of concrete (Yin et al., 2017). The term “leaching” is used for concrete to refer to the dissolution and decalcification of hydration products during the percolation of acid and/or poorly mineralized water (Gauthier, 2020). It implies an increase in porosity and a modification of the microstructure of concrete, which in turn influences its mechanical behaviour. In the experimental device proposed by Torrenti and Nguyen (Nguyen et al., 2007; Torrenti et al., 2008), plain cylindrical samples were tested but samples were not fully immersed in the solution. In this work, a part of the sample was immersed in exposure solutions using test tubes. The parts outside of the containers were covered with silicone resin and a plastic film that prevents parasitic diffusion in the test tubes or possible drying. Plain cylindrical specimens were also tested by Bes (2019). In this work, a central reservation was provided to insert the LVDT sensors (Linear Variable Differential Transformer). The specimens were placed in stainless steel containers filled with exposure solutions. The size of the steel trays was defined so that the specimen was not fully immersed in the solution to avoid penetration of the solution into the specimen reservation. Although previous developments and results, there is still a need for a testing procedure of plain and hollow cylindrical samples fully immersed in solution to allow a chemo-mechanical assessment of the durability of structural materials.

There is currently no experimental data or testing techniques to investigate the effects of combined seawater attack and creep of cement-based materials. A new protocol and test rig have been designed and

implemented in this study. This original approach allows assessing the behaviour and durability of multiple cement-based materials, and testing other types of structural materials. Contrary to what has been previously developed (Bes, 2019; Nguyen et al., 2007; Torrenti et al., 2008), the present device presents the originality of testing hollow and solid cylindrical samples fully immersed in liquid solutions and subjected to the phenomena induced by long-term loading, i.e. creep, with a possible circulation of different fluid solutions around and inside the sample. Thus, this device ensures the implementation and the experimental assessment of the chemo-mechanical coupling.

The primary objective of the novel rig was to facilitate the monitoring of mechanical deformations resulting from applied loads, while subjecting the specimens to chemically aggressive solutions. Mortar samples were immersed in seawater and tap water solutions. In order to investigate the impact of cement type on seawater attack, this study examined two distinct types of cement: Ordinary Portland Cement (OPC) and another seawater resistant type of Portland Cement (SR). First, the main challenges and novelty of this research are highlighted. Then, the detailed experimental program is given concerning the materials, the exposure conditions, and the testing procedures used. A detailed description of the new implemented device is presented. The experimental characterization includes the assessment of macroscopic properties and microstructural analyses. Finally, the results are analysed and discussed.

## 2. Materials and methods

In this section, materials and mixtures used are first defined and the composition and preparation of exposure solution are explained. The chemo-mechanical evaluation was carried out using the novel rig. The experimental protocol is defined in Fig. 1 and detailed in this section. In order to analyse the results of the creep-seawater test, the studied materials were characterized at both macroscopic and microstructural scales. The microscopic characterization was held at the scale of cement pastes using X-Ray diffraction test and thermogravimetric analysis. Mechanical evaluation was performed at the mortar scale to determine the compressive strength and the Young's modulus.

### 2.1. Materials and mixtures preparation

The use of mortar instead of concrete allows decreasing the representative volume of tested material thus accelerating the testing process (Boudache et al., 2021; Massaad et al., 2016) by reducing the characteristic time of diffusion, and it allows taking into account the phenomena occurring at the paste-aggregates interface. The mortar specimens were made with two cement types: an Ordinary Portland Cement (OPC) "CEM I 52.5 N" and another cement "CEM I 52.5 N PM" ("SR" in the results) considered as resistant to seawater attack according to the French standard NF P 15-317. Both cement types are commercial products and the SR-cement has been used in marine construction. To accelerate the degradation process, a water-to-cement (w/c) ratio of 0.6 was adopted. It was higher than the recommendations of NF EN 206 standard (NF EN 206-1, 2014) for seawater exposure, in order to accelerate the diffusion process. Two criteria were employed beforehand to assess the resistance of cement to seawater. The first criterion is based on Sadran's index (Rilem, 1970) retained in French standard NF P 15-317. If cement composition has a Sadran's index ($SI=\frac{C_3A}{0.27C_3S}$) lower than 23.5 it can be labeled as "seawater resistant" and therefore used in marine constructions. The second criterion evaluates the $C_3A$ content: for seawater-resistant cement, $C_3A$ content should be lower than 8% (ASTM C150, 2002). To prevent leaching and reactions caused by the calcium carbonate present in limestone aggregates, siliceous sand (0-2 mm) was used in the study (Justnes, 2003; Lee et al., 2008). The sand had a density of 2.61, a fineness modulus of 2.6, and a water absorption coefficient of 0.44%. Preliminary tests were conducted to estimate the paste volume and achieve a workable mortar, taking into
<figure><img src="image_5.png" /><figcaption>Fig. 1. Flow chart summarizing the experimental protocol.</figcaption></figure>

consideration the shape of the sand particles and the particle size distribution. The mortar mixture was composed of 500 kg/m³ of cement, 307 kg/m³ of water, and 1305 kg/m³ of sand. The cement mineralogical composition and properties are summarized in Table 1.

Plain cylindrical cement paste samples of 25 mm diameter were made with a w/c ratio of 0.5. This ratio was chosen in order to obtain a workable and stable paste with the same cements as the mortars. A lower w/c ratio was adopted in this case for stability and homogeneity purposes. These samples were used in microscopic characterization.

Hollow and solid cylindrical mortar specimens of 160 mm height and 70 mm outer diameter were cast. An inner diameter of 30 mm was adopted for the hollow specimens, which implies a mortar thickness of 20 mm (Fig. 2). By using hollow cylindrical specimens, both internally and externally exposed to the aggressive solutions, the diffusion of ions is accelerated, leading to an intensified seawater attack. After the mortar and paste mixtures were prepared, the specimens were stored for 24 h in their molds at 20 °C and 90% relative humidity. Then the samples were demolded and a layer of waterproof epoxy resin was applied to both circular ends of the specimen. At the age of 48 h, a second layer of epoxy resin was applied. The purpose of this resin layer is to ensure two-dimensional ionic diffusion. At the age of 3 days, the samples were immersed in exposure solutions (denoted “SW”) and others in tap water (denoted “Ref”).

## 2.2. Exposure solutions

Multiple ions are present in seawater such as magnesium, sulfate, chloride, sodium, etc. This variety of ions makes seawater a complex environment. Data on salinity, temperature, alkalinity, and pH for multiple oceans can be accessed through the Global Ocean Data Analysis Project (Feely et al., 2009). The Reference-Composition Salinity is 35.165 g/kg (Millero et al., 2008). In this study, the seawater solution was reformulated in the laboratory, by dissolving multiple salts in demineralized water (El-Khoury et al., 2022; Rozière, 2012). For acceleration purposes, the laboratory-reconstituted seawater had a salinity of 70 g/L. It represents twice the normalized reference one. This convenient method allowed avoiding the trouble of transporting samples to seawater sites and exclude the problem of determining the seawater composition and salinity and its evolution with weather and

<table><caption>**Table 1**

Cement properties and composition.</caption><thead><tr><th colspan="3">Cement composition</th></tr><tr><th></th><th>CEMI 52.5 N (OPC)</th><th>CEMI 52.5 N PM (SR)</th></tr></thead><tbody><tr><td>C<sub>2</sub>S</td><td>16 %</td><td>18 %</td></tr><tr><td>C<sub>3</sub>S</td><td>60 %</td><td>58 %</td></tr><tr><td>C<sub>3</sub>A</td><td>8 %</td><td>7 %</td></tr><tr><td>C<sub>4</sub>AF</td><td>11 %</td><td>11 %</td></tr><tr><td>Gypsum</td><td>4 %</td><td>5 %</td></tr><tr><td>Other constituents</td><td>2 %</td><td>2 %</td></tr><tr><th colspan="3">Cement properties</th></tr><tr><td>Density (10<sup>3</sup> kg/m<sup>3</sup>)</td><td>3.16</td><td>3.18</td></tr><tr><td>Blaine fineness (m<sup>2</sup>/kg)</td><td>400</td><td>430</td></tr><tr><td>Sadran's index (SI ≤ 23.5)</td><td>23.9</td><td>22.4</td></tr></tbody></table>

<figure><img src="image_6.png" /><figcaption>Fig. 2. Geometry and dimensions (mm) of solid and hollow mortar samples.</figcaption></figure>

time. The seawater salinity and composition thus remained constant all over the testing period. The pH was not controlled as the seawater is known to be a buffer solution where the pH is maintained even with limited addition of acids and bases (Lide, 2004; Rozière, 2012). To distinguish the impact of hydration from seawater exposure, control samples were immersed in tap water. Both the samples and the solutions were stored in a temperature-controlled room at 20 °C.

## 2.3. Design of a new creep-seawater testing device

The goal of our study is to evaluate simultaneously and in real-time the deformations and degradations due to compression creep and chemical attack. Therefore, the exposure to an aqueous environment (seawater, solution rich in sulfate ions, chlorides, etc.) is necessary. This leads to the use of a solution tank and a mechanical press. Linear Variable Differential Transformer (LVDT) sensors were used to track the deformations in real-time. The originality of this device also lies in the possibility of using non-waterproof sensors.

Associated with a press and a set of LVDT sensors, this device allows:

* The immersion of samples in aggressive solutions,

* The generation and the monitoring of the mechanical load,

* The measurement of vertical displacements.

The dimensions of the frame were calculated and chosen so that the frame does not show excessive deformations under the effect of the mechanical load. To ensure the performance of the testing device a test phase was performed on a steel sample.

Fig. 3 represents a 2D section (section A-A) and Fig. 4 is a 3D perspective of the implemented device.

Due to the use of aggressive ions dissolved in solutions, the material forming the device must be resistant to the attack of the selected aggressive environments. To ensure that the frame will not deform significantly over time and during the loading of the structures, the frame was tested using steel samples.

This device includes a container where the liquid solution and the sample are placed. It offers the possibility and the originality to test the hollow cylinders with:

* The solution only inside the hollow sample,

* The solution only on the outside of the hollow sample,
<figure><img src="image_7.png" /><figcaption>Fig. 3. Section A-A of the implemented device.</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>Fig. 4. 3D perspective of the implemented device.</figcaption></figure>

* Solution present at the same time inside and outside the hollow cylinder (two different solutions can be used).

The lower plate is 20 mm thick and made of stainless steel. It is perforated in its center and its end to ensure the circulation of the solution inside the hollow sample. On the rectangular bottom plate, three rods placed at 120° are welded to place the supports of the LVDT displacement sensors.

## 2.4. Mechanical evaluation

Compressive strength and creep compliance were determined on both control and seawater-exposed samples. For the compressive strength, three plain cylindrical samples were carefully cut at both ends and thoroughly ground to achieve a flat loading surface. As a result of this process, each sample attained a total height of 140 mm (to comply with the ASTM recommendation, i.e. of height-to-diameter ratio of 2). The rate of the compression load application was 0.5 MPa/s until failure,

and compressive strength was determined for 3 samples exposed to seawater and 3 sample exposed to tap water, then the average value was considered.

The primary creep was assessed by applying a compressive sustained load equal to 30% of the compressive strength at the age of loading (Tsitova et al., 2023; Zhang et al., 2023). For the creep test, the hollow mortar samples were fully immersed in tap water (Ref) and in seawater (SW) and loaded. It is noteworthy that all samples were immersed in solution at the age of 3 days. Therefore, if the creep test starts at the age of 28 days (Lo28d), this means that the sample was first exposed to the solution for 25 days then loaded while immersed in the solution at the age of 28 days.

To combine creep and seawater attack several tests were performed using a newly implemented device (see section 2) on samples of hollow mortar based on OPC-cement and SR-cement, at different loading ages and different exposure solutions (Fig. 5). For each test, a control sample immersed in tap water was provided.

## 2.5. Microstructural characterization

Cement paste samples were divided into three parts. Then the surface and the central part were tested using thermogravimetric and X ray diffraction analyses, to distinguish the phases formation at the surface (0–2 mm) and the center of the sample as presented in Fig. 6.

Thermogravimetric (TGA) analysis was carried out using a Netzsch SRA449 F3 apparatus. The test was performed on cement paste crushed to powders and heated at a constant rate of 10 °C/min from $T_i = 20$ to $T_f = 900$ °C in a dry nitrogen atmosphere. Using the derivative thermogravimetric curves, brucite, calcium hydroxide (CH) and calcium carbonate (aragonite, vaterite and calcite) were identified, respectively, at the peaks 390–400 °C, 460–510 °C (Divet et al., 2005) and 600–800 °C (Drouet, 2010).

The X-ray diffraction (XRD) scan was performed using a Malvern Aeris XRD, between 7° and 70° at 30 kV and a 0.38 mm slit. XRD analysis examined cement paste crushed to powders and sieved at 80 µm, using a Cu Kα source ($\lambda$1 = 1.5405980 Å and $\lambda$2 = 1.5444260 Å).

## 2.6. Evaluation after creep test

At the end of the creep test, the static Young's modulus and the water porosity were evaluated.

The static Young's modulus was determined under compression by three loading and unloading cycles of the sample at a maximum load of 30% of its initial strength at the start of the creep test.

The total porosity was determined through vacuum saturation

<figure><img src="image_9.png" /><figcaption>Fig. 5. Summary of the experimental program adopted to combine creep and seawater attack.</figcaption></figure>
Microscopic characterization

<figure><img src="image_10.png" /><figcaption>Fig. 6. Microscopic evaluation.</figcaption></figure>

method in accordance with the French standard NF P18-459. The porosity is defined as the ratio between the void volume and the total volume of the tested sample. Hydrostatic weighing of water saturated samples allowed measuring the volume of specimens thus the porosity accessible to water. At the end of the creep test, porosity measurements were performed on the samples immersed in seawater (noted "SW") and on the corresponding control samples immersed in tap water (noted "Ref").

3. Results and discussion

3.1. Phases changes identification

The cement paste samples were characterized using TGA and XRD. The comprehensive description of the phases evolutions with time till 145 days were presented in El-Khoury et al. (2022). TGA data analysis allows quantifying phase formations. The CH content, brucite content and CaCO₃ content found at the sample surface are shown in Fig. 7 for both cement types and exposure solutions. The graph presented in Fig. 7 gathers the tests results performed at the following ages: 24 h, 28 days, 145 days, 6 months, 1 year, and 2 years.

Ettringite and Friedel's salt cannot be easily identified using TGA. Therefore, XRD tests were carried out on the surface of the paste samples after 2 years of exposure. Results are presented for OPC and SR types cements respectively in Fig. 8. The reference PDF codes of the identified phases are given in Table .2.

Brucite was only detected in the seawater samples (SW) using TGA and XRD peak (located at 2θ = 37.966°) (Figs. 7 and 8). The brucite peak was not observed in the control samples (Ref).

The CH content in SW-immersed samples was lower than in the reference samples (Ref), confirming the assumption that CH is consumed at the sample surface during the seawater attack (El-khoury et al., 2023), which was observed for both tested cement types OPC and SR (Fig. 7). This result is consistent with the formation of brucite and calcium

<figure><img src="image_11.png" /><figcaption>Fig. 7. Quantification of portlandite (CH), brucite Mg(OH)₂, and calcium carbonate (CaCO₃) contents at the samples surface from TGA.</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>Fig. 8. XRD results for OPC-cement pastes and SR-cement pastes performed at the age of two years (Ar: Aragonite, Bru: Brucite, Cal: calcite, CH: Portlandite, Ett: Ettringite, Fr: Friedel's salt, Gyp: Gypsum, Vat: vaterite).</figcaption></figure>

<caption>Table 2</caption>

Reference PDF codes of the different phases identified using PDF-4 minerals database (ICDD⁻¹).

<table><thead><tr><td>Phases</td><td>PDF Code</td></tr></thead><tbody><tr><td>Ettringite</td><td>04-013-3691</td></tr><tr><td>Portlandite</td><td>00-044-1481</td></tr><tr><td>Brucite</td><td>04-013-9511</td></tr><tr><td>Vaterite</td><td>00-067-0200</td></tr><tr><td>Friedel's salt</td><td>01-078-1219</td></tr><tr><td>Aragonite</td><td>01-075-9986</td></tr><tr><td>Calcite</td><td>00-005-0586</td></tr><tr><td>Gypsum</td><td>04-009-3817</td></tr></tbody></table>

carbonate on the surface of the attacked specimens (De Weerdt et al., 2014). The continuous consumption of CH could indicate that it is leached and involved in the formation of new phases. For example, chlorides may be incorporated into calcium chloroaluminate hydrates like Friedel's salts (De Weerdt et al., 2014) as detected using XRD peaks (Fig. 8), and the sulfate presence can lead to gypsum and ettringite formation. The precipitation of calcium carbonate (CaCO₃) phases also causes the consumption of CH. Chloride ingress profiles were detected in marine constructions (De Medeiros-Junior et al., 2015; De Weerdt et al., 2014, 2023).

Precipitation of Mg(OH)₂ near the surface is frequently observed in magnesium-rich environments (Brown and Doerr, 2000), as the result of the base exchange reaction. The evolution of the formed brucite content does not directly correlate with the amount of CH consumed, but the observed trend correspond to higher brucite content for lower CH content, which is consistent with base exchange reaction. Brucite can also be found mixed with M-S-H formed from C-S-H by ion exchange of Ca by Mg (De Weerdt and Justnes, 2015).

Calcium carbonate (CaCO₃) was detected in DTG and XRD results as aragonite, vaterite and calcite phases. Aragonite and vaterite formed on the exposed samples surface can be associated with higher CaCO₃ contents observed in TGA on the surface of samples exposed to seawater (Fig. 7). Aragonite and vaterite have been associated with C-S-H carbonation (Slegers and Rouxhet, 1976). Seawater would actually favor the formation of aragonite among the possible polymorphs of calcium carbonate (De Weerdt and Justnes, 2015). Calcite peak was detected in both control and exposed samples. The calcite peak was sharper in the SR-cement than in the OPC-cement. This appears to be consistent with the TGA results (Fig. 7). Carbonation is actually limited in the outermost part of the cement-based materials exposed to seawater: De Weerdt et al. (2016) observed the presence of CaCO₃ in the 0–1 mm section of

<footnote>a International Centre for Diffraction Data.</footnote>
concrete samples exposed to seawater for sixteen years (De Weerdt et al., 2016). Vaterite and aragonite were not observed in the center of the exposed samples confirming that CaCO₃ precipitates from the sample surface. The CaCO₃ content of the specimens exposed to seawater continuously increased near the surface. The control and SW samples made with SR-cement had higher CaCO₃ content. This suggests that the SR-cement samples could have benefited more from the protective effect of CaCO₃ through pore clogging and reduced diffusion of aggressive ions. The evolution of the amount of CaCO₃ formed does not directly correlate with the decrease of CH content. CaCO₃ can also be formed from C–S–H decalcification (Kaddah et al., 2022; Kangni-Foli et al., 2021).

The gypsum peak expected at (2θ = 11.438° and 2θ = 20.731°) could not be observed. The ettringite peak appeared in both sets of samples, although this does not necessarily suggest that its development was promoted in seawater. Sulfate attack typically triggers expansion through crystallization pressures. In this study, the sulfate attack had thus less influence than the penetration of the chlorides of the seawater. Moreover, it can be assumed that this reaction was delayed by the presence of chloride ions. The high chloride concentration in seawater induces Friedel's salt formation from AFm, which is therefore less available to form ettringite.

The findings regarding these phase changes align with previous research outcomes. (De Weerdt et al., 2014). The experimental data also show that sulfate attack and the formation sulfate-rich phases had a minor part in the degradation mechanism, compared to previous studies where significant expansion and strength loss (Florea and Brouwers, 2012; Guo et al., 2020; Santhanam et al., 2006) of Portland cement based materials exposed to seawater attack were reported.

## 3.2. Mechanical evaluation

Fig. 9 presents the creep test results performed on hollow OPC-based mortar specimens loaded at 3 days, 28 days, and 1 year and hollow SR-cement-based mortars loaded at 1 year. The curves are initialized at loading time. The creep compliance represents the creep strain per unit stress without the instantaneous elastic part of the curve.

The samples immersed in a 70 g/L saline solution generally showed more creep than those immersed in tap water, with differences depending on loading age. This highlights the complex effects that the diffusion of ions from seawater can induce especially in the first days of the degradation. The difference between the creep curves of the reference and SW mortar is more clearly visible at the loading ages of 3 and 28 days. However, when loading at the age of 1 year the strain difference between the control and SW specimens was much lower, which could highlight the positive effect of the phases formed near the surface. Additionally, we can observe that SR-based mortars had lower creep

than OPC-based mortars in both exposure solutions. This highlights the seawater resistant character of SR cement used.

To allow a deeper analysis of the creep behaviour, the curves can be divided into two parts, namely: a short-term deformation, presented as Stage A (Part A of Fig. 9) that increases logarithmically (between 0 and 3 days of loading), and a long-term part with a lower creep rate, presented as Stage B (Part B of Fig. 9). This behaviour is presented in Fig. 10, by resetting the curves in Fig. 9- Part B at the age of 3 days after loading. The equations for the trend curves are also presented. The difference between reference samples and SW samples creep compliance was relatively low for the loading ages of 3 and 28 days.

The positive effects of seawater attack (hydration progression, formation of protective layers, diffusion of chlorides attenuating the sulfate attack, clogging of pores near the surface with calcium and magnesium based products) and loading (pore closure) seem to compensate for the negative effects of seawater attack (phase dissolution) and loading (damage, micro cracking).

This competition between positive and negative effects is not limited to seawater but it can also be found in natural water where leaching and precipitation coexist. Whereas pure water is aggressive and mainly promotes leaching (Kamali et al., 2008), seawater also contains multiple ions, which promotes the formation of new solid phases. This effect can be illustrated by the 3-day and 1-year creep tests where the order is reversed, as the long-term creep of control samples loaded at 1 year was higher than the samples immersed in seawater (Fig. 10).

The short-term behaviour (Fig. 9-Part A) can be interpreted by correlating the creep compliance recorded before stabilization (after 3 days of loading) with the sample Young's modulus measured at the same age without creep (Fig. 10). It is noteworthy to mention here that the correlation is observed with the Young's modulus measured without creep because when the specimen is loaded, its Young's modulus (damaged or modified) cannot be measured without stopping the creep test.

The short-term creep compliance of the samples immersed in seawater was actually higher than the control samples for all loading ages. Comparing the types of cement, the creep of SR-resistant cement-based specimens was lower than those made with OPC. These results suggest that the first phase of creep deformation was mainly influenced by the initial stiffness, and the type of cement used influenced the chemo-mechanical tests (El-Khoury et al., 2022).

Fig. 12 shows the correlation between creep compliance and Young's modulus determined without creep at several ages. A good correlation could be established between Young's modulus and creep deformation. The slope evolutions show a stronger increase (for a given modulus of undamaged specimens) for the specimens immersed in seawater than those immersed in tap water, when loading at a relatively early age.

<figure><img src="image_13.png" /><figcaption>Fig. 9. Creep compliance of mortars immersed in seawater.</figcaption></figure>

<figure><img src="image_14.png" /><figcaption>Fig. 10. Behaviour (stage B) of OPC and SR hollow mortar samples loaded at ages of 3 days, 28 days and 1 year.</figcaption></figure>
These results highlight the apparent correlation between Young's modulus and creep. The correlation also suggests that creep could be partly driven by hydration and seawater attack: hydration continues during chemo-mechanical loading. The macroscopic behaviour of a structure is actually influenced by hydration and the chemical evolution of hydration products (El-khoury et al., 2023).

Fig. 13 gives a comparison between Young's modulus measured on the samples after creep and on samples without creep test. The results show that the combined creep-seawater attack reduced the stiffness of the specimens. A higher Young's modulus was actually found for the control specimens after creep, except for the 3-day loading, where the modulus remained almost the same. The difference in stiffness between the control and SW specimens increased with the loading age.

Despite its decrease, the stiffness of the mortar specimens loaded at one year and made with SR-cement was higher than the SW-specimens made with OPC-cement. This is consistent with the “seawater resistant” character of SR-cement evaluated using Sadran’s index (El-Khoury et al., 2022).

### 3.3. Discussion

The combined effects of seawater exposure and creep on the behaviour and durability of cement-based materials had not been previously explored. The main purpose of this new protocol was to study the interactions between hydration, seawater attack and creep at both macroscopic and microscopic scales. The new test rig implemented in this study allows the measurement of mechanical deformations caused by applied loads, while subjecting the specimens to chemically aggressive solutions. Laboratory recomposed seawater was used, with all the ions present in natural seawater. Due to the seawater ions reaction with the cement phases, the reactant and products phases were characterized using TGA and XRD analysis. Phases changes identification, presented in Figs. 7 and 8, show the formation of different phases between the surface layer and the central layer of the sample. The results highlight the consumption of portlandite and CSH and the formation of Friedel's salt, different polymorphs of calcium carbonate CaCO₃, and brucite. These experimental findings indicate a strong zonation for seawater exposed concretes similarly to previous results highlighted in (De Weerdt et al., 2014, 2016, 2023). This zonation highlights the importance of taking into consideration all the ions present in seawater because multiple simultaneous reactions take place and each ion has the capacity to diffuse and react differently with the cement phases.

The creep-seawater coupling test on different hollow mortar samples show that the creep compliance decreased with loading age (Figs. 8–10). These findings seems to be in line with the commonly-reported results showing that the creep response decreases with the increase of the age at loading (Grasley and Leung, 2011; Li et al., 2016; Østergaard et al., 2001; Wyrzykowski et al., 2019). An older specimen would exhibit a reduced creep rate due to the diminished hydration rate of cement particles in later stages (Li et al., 2016). The Young's modulus increases with time and this phenomenon is linked to the hydration process (El-khoury et al., 2023), therefore the creep compliance decreases. The results summarized in Fig. 11, indicating the value of Young's modulus determined after 3 days of loading, agree with the previously discussed results. The creep compliance was actually lower for a higher Young's modulus. In addition, the effect of the exposure solution can be highlighted: the samples in reference solutions recorded a lower creep before stabilization associated to a higher Young's modulus than samples in seawater. This correlation can explain results obtained in Figs. 9 and 10.

Indeed, seawater attack combined with cement hydration reactions can lead to contradictory effects as a gain or a loss of mechanical properties (El-Khoury et al., 2022). The phases formation during the seawater attack and cement hydration affects the mechanical behaviour of the structure especially the creep phenomenon. The service life is often undermined by the aggressiveness of marine environment (De Medeiros-Junior et al., 2015; Fernández and Pardob, 2013). The

<figure><img src="image_15.png" /><figcaption>Fig. 11. Correlation between the creep compliance recorded before stabilization (after 3 days of loading) and the Young's modulus of the structure measured at the same age without creep.</figcaption></figure>

<figure><img src="image_16.png" /><figcaption>Fig. 12. Correlation between creep compliance evolution and Young's modulus evolution determined without creep.</figcaption></figure>

<figure><img src="image_17.png" /><figcaption>Fig. 13. Comparison between Young's modulus measured on the samples after creep and without creep.</figcaption></figure>

volumes of distinct phases within a microstructure play a crucial role, primarily influencing the elastic properties and strength in a significant way. Elastic properties can be estimated based on volume fractions using composite models (El-khoury et al., 2023; Grasley and Leung, 2011; Rhardane et al., 2020). This aligns with the widely observed
phenomenon that the evolution (hardening) of elastic and strength properties after the percolation of solids is predominantly governed by the solidification of load-bearing components induced by hydration (Bernard et al., 2003b; Boumiz et al., 1996; Pichler et al., 2013; Wyrzykowski et al., 2019). It is widely accepted that the C–S–H gel primarily contributes to the creep phenomenon in cementitious materials (Li et al., 2016; Nguyen et al., 2013; Rhardane et al., 2021; Youssef Namnoum et al., 2019). Ettringite, calcium hydroxide and hydrated $C_3S$ have a relatively low creep rate on a porosity basis (Nguyen et al., 2013). Some secondary cement phases, such as gypsum and calcium carbonate, show a creeping behaviour that is comparable to that of C–S–H (Nguyen et al., 2013). In this study, a chemical competition was created in the cement paste due to seawater attack-hydration coupling. On the one hand, CH and CSH were be consumed due to seawater attack. In addition, brucite, ettringite and calcium carbonate were formed due to seawater attack. On the other hand, CH and CSH were formed due to cement hydration. These phases changes affect particularly the mortar creep at early age, but the long term global creep of the structure presents a negligible difference between the creep in tap water and seawater. The cement types used in this study had a relatively low Sadran's Index, and consequently they were not sensitive to the effect of sulfate ions present in seawater. A previous study showed that all measured expansions remained relatively low (El-Khoury et al., 2022). Other types of cement could be studied using the proposed protocol. Creep results will vary depending on the phases formed during seawater attack. Another limitation to this study is time. Indeed, seawater attack is slow and requires many years to perform. To avoid this problem we have used acceleration techniques such as increased seawater salinity and w/c ratio. The reference seawater salinity could be used using the newly implemented test rig and longer test durations could be considered.

Finally, the output of this study introduces a novel chemo-mechanical experimental protocol. Notably, it offers adaptability by being applicable to various materials such as steel, composite structures, and low-carbon concrete mixtures. Moreover, the newly developed test rig has the capability to accommodate different fluids within and outside the hollow sample. This setup enables exploration of the interaction between both fluids and the tested material. However, a limitation of this study is that the test rig was specifically designed for mortar samples. As a result, efforts are underway to manufacture a new test rig with larger solution volume and dimensions to accommodate bigger specimens.

## 4. Conclusion

This article focuses on the implementation of a new protocol and test rig for the investigation of creep - seawater attack - hydration couplings in structural materials. The analysis of the chemo-mechanical phenomena induced by the simultaneous mechanical loading and seawater exposure was based on the development of an innovative monitoring strategy including a new creep-seawater test rig and the monitoring of materials evolution at both macroscopic and microscopic scales.

The obtained results show that:

* The chemical analyses showed significant changes at the microstructural scale, concerning all the main Portland cement hydration products. Portlandite was consumed from the surface to produce Brucite and Calcite. The formation of other calcium carbonate polymorph (Vaterite) can be attributed to the decalcification of C–S–H. The incorporation of chlorides into calcium chloroaluminate hydrates (Friedel’s salt) was observed in the whole specimen.

* The evolution of creep compliance was relatively high during the first three days after loading, with higher magnitudes for specimens in seawater. The main differences between seawater-exposed specimens and control specimens could be observed at the loading ages of 3 and 28 days. These results confirmed the creep - seawater attack - hydration coupling. A correlation was actually found between the

magnitude of creep compliance recorded after 3 days of loading and the Young's modulus measured at the same age without creep.

* The evolutions of creep compliance after 3 days of loading were much closer. The creep of specimens in seawater loaded after 1 year was even lower than control specimens. This could be due to positive effects of seawater exposure (hydration enhancement, diffusion of chlorides attenuating the sulfate attack, clogging of pores near the surface with calcium carbonates and magnesium based products) and mechanical loading (pore closure), which partly compensated for the negative effects of seawater attack (phase dissolution) and loading (damage, micro cracking).

* A correlation was also observed between Young's modulus and creep evolutions, which suggests that creep could be partly driven by hydration and seawater attack, as hydration continues during chemo-mechanical loading. The macroscopic behaviour was influenced by cement hydration and the chemical evolution of hydration products.

In summary, this study presents a pioneering chemo-mechanical experimental protocol. However, it is essential to acknowledge the limitation that the current test rig was tailored for mortar samples. To address this, ongoing efforts are focused on developing a new test rig with higher dimensions, for testing materials with higher representative elementary volume. In addition, the experimental results depend on the composition of studied materials and more precisely the phases in the cement matrix for the case of cement-based materials. Additionally, the analysis of the micro-mechanisms associated with the degradation is possible experimentally after unloading, but the monitoring of its evolution during the creep-seawater test remains a challenge. Therefore, a multi-scale numerical model is under development to monitor the real-time microstructure evolution. It will be representative of the material taking into account cement hydration through the actual phases composition of the cement matrix and its evolution combined with chemical attack and creep.

It is noteworthy to mention that the newly proposed protocol presents significant adaptability, allowing its application across a range of structural materials, including steel, composite structures, and low-carbon concrete mixtures. The innovative test rig introduced in this research facilitates the investigation of material-fluids interactions by accommodating different fluids, both internally and externally in the case of hollow specimens. Therefore, the developed protocol participates in the risk analysis of seawater attack combined with mechanical loading, in order to optimize material choices in marine environments. It responds to the great global trend to develop marine renewable energies structures. Furthermore, the chemo-mechanical coupling can be used to design more sustainable structures and to estimate the maximum permissible load and strains based on the chemo-mechanical behaviour of tested structural materials.

## CRediT authorship contribution statement

**Marinelle El-Khoury:** Writing – original draft, Visualization, Methodology, Investigation, Formal analysis. **Emmanuel Rozière:** Writing – review & editing, Resources, Conceptualization. **Frédéric Grondin:** Supervision, Resources, Project administration, Funding acquisition, Conceptualization. **Mathias Marcel:** Visualization, Conceptualization. **Rachid Cortas:** Supervision, Resources, Funding acquisition. **Fadi Hage Chehade:** Supervision, Resources, Funding acquisition.

## Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
## Data availability

Data will be made available on request.

## Acknowledgements

The funding from the Lebanese University, Ecole Centrale of Nantes, and the Carnot Marine Engineering Research for Sustainable, Safe and Smart Seas Institute (Carnot MERS) is gratefully acknowledged.

## References

Al-Amoudi, O.S.B., Maslehuddin, M., Abdul-al, Y.A.B., 1995. Role of chloride ions on expansion and strength reduction in plain and blended cements in sulfate environments. Construct. Build. Mater. 9, 25-33.

ASTM C150, 2002. 04a, Standard Specification for Portland Cement.

Bazant, Z.P., 2001. Creep of concrete. In: Encyclopedia of Materials: Science and Technology. Elsevier, pp. 1791-1800.

Bernard, O., Ulm, F.J., Germaine, J.T., 2003a. Volume and deviator creep of calcium-leached cement-based materials. Cement Concr. Res. 33, 1127-1136. https://doi.org/10.1016/S0008-8846(03)00021-8.

Bernard, O., Ulm, F.J., Lemarchand, E., 2003b. A multiscale micromechanics-hydration model for the early-age elastic properties of cement-based materials. Cement Concr. Res. 33, 1293-1309. https://doi.org/10.1016/S0008-8846(03)00039-5.

Bes, T., 2019. Etude du comportement des bétons Bas-PH sous sollicitations chimiques. Université Toulouse 3 - Paul Sabatier.

Betten, J., 2005. Creep Mechanics, second ed. Springer Berlin Heidelberg.

Boudache, S., Rozière, E., Loukili, A., Izoret, L., 2021. Towards common specifications for low- and high-expansion cement-based materials exposed to external sulphate attacks. Construct. Build. Mater. 294, 123586 https://doi.org/10.1016/j.conbuildmat.2021.123586.

Boumiz, A., Vernet, C., Cohen Tenoudji, F., 1996. Mechanical properties of cement pastes and mortars at early ages. Adv. Cement Base Mater. 3, 94-106. https://doi.org/10.1016/S1065-7355(96)90042-5.

Brown, P.W., Doerr, A., 2000. Chemical changes in concrete due to the ingress of aggressive species. Cement Concr. Res. 30, 411-418. https://doi.org/10.1016/S0008-8846(99)00266-5.

De Medeiros-Junior, R.A., De Lima, M.G., De Brito, P.C., De Medeiros, M.H.F., 2015. Chloride penetration into concrete in an offshore platform-analysis of exposure conditions. Ocean Eng. 103, 78-87. https://doi.org/10.1016/j.oceaneng.2015.04.079.

De Weerdt, K., Bernard, E., Kunther, W., Pedersen, M.T., Lothenbach, B., 2023. Phase changes in cementitious materials exposed to saline solutions. Cement Concr. Res. 165, 107071 https://doi.org/10.1016/j.cemconres.2022.107071.

De Weerdt, K., Justnes, H., 2015. The effect of sea water on the phase assemblage of hydrated cement paste. Cem. Concr. Compos. 55, 215-222. https://doi.org/10.1016/j.cemconcomp.2014.09.006.

De Weerdt, K., Justnes, H., Geiker, M.R., 2014. Changes in the phase assemblage of concrete exposed to sea water. Cem. Concr. Compos. 47, 53-63. https://doi.org/10.1016/j.cemconcomp.2013.09.015.

De Weerdt, K., Orsáková, D., Müller, A.C.A., Larsen, C.K., Pedersen, B., Geiker, M.R., 2016. Towards the understanding of chloride profiles in marine exposed concrete, impact of leaching and moisture content. Construct. Build. Mater. 120, 418-431. https://doi.org/10.1016/j.conbuildmat.2016.05.069.

Divet, L., Arnaud, S., Dérobert, X., 2005. Présentation des techniques de diagnostic de l'état d'un béton soumis à un incendie, Techniques et méthodes des Laboratoires des ponts et chaussées. Institut Français des Sciences et Techniques des Réseaux, de l'Aménagement et des Transports.

Drouet, E., 2010. Impact de la température sur la modélisation des matériaux cimentaires : prise en compte des transferts hydriques. ENS Cachan.

El-khoury, M., Grondin, F., Hilloulin, B., Rozière, E., Cortas, R., Chehade, F.H., 2023. Creep analysis of cementitious materials in seawater using a poro-chemo-mechanical model. Mar. Struct. 90 https://doi.org/10.1016/j.marstruc.2023.103431.

El-Khoury, M., Rozière, E., Grondin, F., Cortas, R., Hage Chehade, F., 2022. Experimental evaluation of the effect of cement type and seawater salinity on concrete offshore structures. Construct. Build. Mater. 322, 126471 https://doi.org/10.1016/j.conbuildmat.2022.126471.

Feely, R.A., Doney, S.C., Cooley, S.R., 2009. Ocean acidification - present conditions in a high-CO2 World. Oceanography 22, 21-40. https://doi.org/10.1017/cbo9781139198776.020.

Fernández, R.P., Pardob, M.L., 2013. Offshore concrete structures. Ocean Eng. 58, 304-316. https://doi.org/10.1016/j.oceaneng.2012.11.007.

Florea, M.V.A., Brouwers, H.J.H., 2012. Chloride binding related to hydration products: Part I: ordinary Portland Cement. Cement Concr. Res. 42, 282-290. https://doi.org/10.1016/j.cemconres.2011.09.016.

Gauthier, A., 2020. Approche expérimentale et modélisation de la lixiviation des ouvrages de traitement d'eau potable en béton exposés à des eaux agressives. Ecole Centrale de Nantes.

Georges, M., Bourguiba, A., Chateigner, D., Sebaibi, N., Boutouil, M., 2021. The study of long-term durability and bio-colonization of concrete in marine environment. Environ. Sustain. Indic. 10, 100120 https://doi.org/10.1016/j.indic.2021.100120.

Grasley, Z.C., Leung, C.K., 2011. Desiccation shrinkage of cementitious materials as an aging, poroviscoelastic response. Cement Concr. Res. 41, 77-89. https://doi.org/10.1016/j.cemconres.2010.09.008.

Guillon, E., 2004. Durabilité des matériaux cimentaires: modélisation de l'influence des équilibres physico-chimiques sur la microstructure et les propriétés mécaniques résiduelles. Ecole Normale Supérieure de Cachan.

Guo, M., Hu, B., Xing, F., Zhou, X., Sun, M., Sui, L., Zhou, Y., 2020. Characterization of the mechanical properties of eco-friendly cement made with untreated sea sand and seawater based on statistical analysis. Construct. Build. Mater. 234, 117339 https://doi.org/10.1016/j.conbuildmat.2019.117339.

Islam, M.S., Mondal, B.C., Islam, M.M., 2010. Effect of sea salts on structural concrete in a tidal environment. Aust. J. Struct. Eng. 10, 237-252. https://doi.org/10.1080/13287982010.11465048.

Justnes, H., 2003. Thaumasite formed by sulfate attack on mortar with limestone filler. Cem. Concr. Compos. 25, 955-959. https://doi.org/10.1016/S0958-9465(03)00120-3.

Kaddah, F., Ranaivomanana, H., Amiri, O., Rozière, E., 2022. Accelerated carbonation of recycled concrete aggregates: investigation on the microstructure and transport properties at cement paste and mortar scales. J. CO2 Util. 57, 1-11. https://doi.org/10.1016/j.jcou.2022.101885.

Kamali, S., Moranville, M., Leclercq, S., 2008. Material and environmental parameter effects on the leaching of cement pastes: Experiments and modelling. Cement Concr. Res. 38, 575-585. https://doi.org/10.1016/j.cemconres.2007.10.009.

Kangni-Foli, E., Poyet, S., Le Bescop, P., Charpentier, T., Bernachy-Barbé, F., Dauzères, A., L'Hôpital, E., d'Espinose de Lacaillerie, J.B., 2021. Carbonation of model cement pastes: the mineralogical origin of microstructural changes and shrinkage. Cement Concr. Res. 144 https://doi.org/10.1016/j.cemconres.2021.106446.

Khan, M.B.E., Shen, L., Dias-da-Costa, D., 2021. Self-healing behaviour of bio-concrete in submerged and tidal marine environments. Construct. Build. Mater. 277, 122332 https://doi.org/10.1016/j.conbuildmat.2021.122332.

Khan, M.B.E., Shen, L., Dias-Da-Costa, D., 2022. Characterisation of autogenous healing in cracked mortars under marine water exposure. Mag. Concr. Res. 74, 91-106. https://doi.org/10.1680/jmacr.20.00162.

Lacarrière, L., Sellier, A., Bourbon, X., 2006. Concrete mechanical behaviour and calcium leaching weak coupling. Rev. Eur. Génie Civ. 10, 1147-1175. https://doi.org/10.1080/17747120.2006.969209.

Lee, S.T., Hooton, R.D., Jung, H.S., Park, D.H., Choi, C.S., 2008. Effect of limestone filler on the deterioration of mortars and pastes exposed to sulfate solutions at ambient temperature. Cement Concr. Res. 38, 68-76. https://doi.org/10.1016/j.cemconres.2007.08.003.

Li, X., Rahman, S., Grasley, Z.C., 2016. Computationally implemented modeling of creep of composite materials caused by phase dissolution. Comput. Mater. Sci. 125, 61-71. https://doi.org/10.1016/j.commatsci.2016.08.030.

Lide, D.R., 2004. CRC handbook of chemistry and physics. In: 84th Edition, Occupational and Environmental Medicine. CRC Press. https://doi.org/10.1136/oem.53.7.504.

Maes, M., Snoeck, D., De Belie, N., 2016. Chloride penetration in cracked mortar and the influence of autogenous crack healing. Construct. Build. Mater. 115, 114-124. https://doi.org/10.1016/j.conbuildmat.2016.03.180.

Massaad, G., Rozière, E., Loukili, A., Izoret, L., 2016. Advanced testing and performance specifications for the cementitious materials under external sulfate attacks. Construct. Build. Mater. 127, 918-931. https://doi.org/10.1016/j.conbuildmat.2016.09.133.

Mehta, K., 1991. Concrete in the Marine Environment, first ed. https://doi.org/10.4324/9780203498255 London.

Millero, F.J., Feistel, R., Wright, D.G., McDougall, T.J., 2008. The composition of standard seawater and the definition of the reference-composition salinity scale. Deep. Res. Part I Oceanogr. Res. Pap. 55, 50-72. https://doi.org/10.1016/j.dsr.2007.001.

NF EN 206-1, 2014. Béton - Spécification, performance, production et confirmité - Complément national à la norme NF EN 206. AFNOR.

Nguyen, D.T., Alizadeh, R., Beaudoin, J.J., Raki, L., 2013. Microindentation creep of secondary hydrated cement phases and C-S-H. Mater. Struct. Constr. 46, 1519-1525. https://doi.org/10.1617/s11527-012-9993-0.

Nguyen, V.H., Nedjar, B., Torrenti, J.M., 2007. Chemo-mechanical coupling behaviour of leached concrete. Part II: modelling. Nucl. Eng. Des. 237, 2090-2097. https://doi.org/10.1016/j.nucengdes.2007.02.012.

Omar, M., Loukili, A., Pijaudier-cabot, G., Pape, Y. Le, 2009. Creep-Damage Coupled Effects : Experimental Investigation on Bending Beams with Various Sizes 1561. https://doi.org/10.1061/(ASCE)0899-1561 (2009)21:2(65).

Østergaard, L., Lange, D.A., Altoubat, S.A., Stang, H., 2001. Tensile basic creep of early-age concrete under constant load. Cement Concr. Res. 31, 1895-1899.

Pichler, B., Hellmich, C., Eberhardsteiner, J., Wasserbauer, J., Termkhajornkit, P., Barbarulo, R., Chanvillard, G., 2013. Effect of gel-space ratio and microstructure on strength of hydrating cementitious materials: an engineering micromechanics approach. Cement Concr. Res. 45, 55-68. https://doi.org/10.1016/j.cemconres.2012.10.019.

Pijaudier-Cabot, G., Haidar, K., Loukili, A., Omar, M., 2004. Degradations and instabilities in geomaterials. In: International Centre for Mechanical Sciences Book Series (CISM, vol. 461. https://doi.org/10.1061/(ASCE)0899-1561 (2009)21:2(65).

Ragoug, R., Metalssi, O.O., Barberon, F., Torrenti, J.M., Roussel, N., Divet, L., d'Espinose de Lacaillerie, J.B., 2019. Durability of cement pastes exposed to external sulfate attack and leaching: physical and chemical aspects. Cement Concr. Res. 116, 134-145. https://doi.org/10.1016/j.cemconres.2018.11.006.

Rhardane, A., Alam, S.Y., Grondin, F., 2020. Microscopically informed upscale approach of modelling damage in mortar by considering matrix-to-grain interface and grain
micro-fracture characteristics. Theor. Appl. Fract. Mech. 109, 102725 https://doi.org/10.1016/j.tafmec.2020.102725.

Rhardane, A., Yasir, S., Frédéric, A., 2021. The role of surface micro-cracks in cementitious materials responsible for the Pickett effect. Mech. Time-Dependent Mater. 719-740. https://doi.org/10.1007/s11043-021-09509-w.

Rilem, 1970. Rapport sur les résultats d'une enquête internationale de la RILEM sur les essais et recherches relatifs au comportement des ciments dans les ouvrages à la mer. Mater. Construcción 3.

Rozière, E., 2012. Etude de la durabilité des matériaux cimentaires en milieu marin – study on the durability of cement-based materials in marine environment, Internal report of FUI MAREVA project. In: French. Nantes.

Santhanam, M., Cohen, M., Olek, J., 2006. Differentiating seawater and groundwater sulfate attack in Portland cement mortars. Cement Concr. Res. 36, 2132–2137. https://doi.org/10.1016/j.cemconres.2006.09.011.

Schmidt, T., Lothenbach, B., Romer, M., Neuenschwander, J., Scrivener, K., 2009. Physical and microstructural aspects of sulfate attack on ordinary and limestone blended Portland cements. Cement Concr. Res. 39, 1111–1121. https://doi.org/10.1016/j.cemconres.2009.08.005.

Slegers, P.A., Rouxhet, P.G., 1976. Carbonation of the hydration products of tricalcium silicate. Cement Concr. Res. 6, 381–388. https://doi.org/10.1016/0008-8846(76)90101-0.

Sun, H., Jiang, C., Cao, K., Yu, D., Liu, W., Zhang, X., Xing, F., Zhao, D., 2021. Monitoring of steel corrosion and cracking in cement paste exposed to combined sulfate-chloride attack with X-ray microtomography. Construct. Build. Mater. 302, 124345 https://doi.org/10.1016/j.conbuildmat.2021.124345.

Torrenti, J.M., Nguyen, V.H., Colina, H., Le Maou, F., Benboudjema, F., Deleruyelle, F., 2008. Coupling between leaching and creep of concrete. Cement Concr. Res. 38, 816–821. https://doi.org/10.1016/j.cemconres.2008.01.012.

Touil, B., Ghomari, F., Khelidj, A., Bonnet, S., Amiri, O., 2022. Durability assessment of the oldest concrete structure in the Mediterranean coastline: the Ghazaouet harbour. Mar. Struct. 81, 1–19. https://doi.org/10.1016/j.marstruc.2021.103121.

Tsitova, A., Bernachy-Barbe, F., Bary, B., Hild, F., 2023. Experimental and numerical analyses of the interaction of creep with mesoscale damage in cementitious materials. Mech. Mater. 184, 104715 https://doi.org/10.1016/j.mechmat.2023.104715.

Ulm, F.-J., Acker, P., 1998. Le point sur le flageu et la recouvrance des bétons. Bull. liaison des Ponts Chaussée ume spé, 73-82.

Ulm, F.-J., Le Maou, F., Boulay, C., 1999. Creep and shrinkage coupling: new review of some evidence. Rev. Fr. Genie Civ. 3, 21–37.

Wang, J.L., Yang, L.F., Huang, J.H., Yu, B., 2023. Service life prediction model for marine concrete structures considering structural shape and time-dependent behaviour. Ocean Eng. 285 https://doi.org/10.1016/j.oceaneng.2023.115276.

Wang, P., Mo, R., Li, S., Xu, J., Jin, Z., Zhao, T., Wang, D., 2021. A chemo-damage-transport model for chloride ions diffusion in cement-based materials: combined effects of sulfate attack and temperature. Construct. Build. Mater. 288, 123121 https://doi.org/10.1016/j.conbuildmat.2021.123121.

Wyrzykowski, M., Scrivener, K., Lura, P., 2019. Basic creep of cement paste at early age - the role of cement hydration. Cement Concr. Res. 116, 191–201. https://doi.org/10.1016/j.cemconres.2018.11.013.

Yin, G.J., Zuo, X.B., Tang, Y.J., Ayinde, O., Wang, J.L., 2017. Numerical simulation on time-dependent mechanical behaviour of concrete under coupled axial loading and sulfate attack. Ocean Eng. 142, 115–124. https://doi.org/10.1016/j.oceaneng.2017.07.016.

Youssef Namnoum, C., Hilloulin, B., Grondin, F., Loukili, A., 2019. Modelling of creep effect on a healed crack in cementitious materials. In: Pijaudier, G., Cabot, P.G., C, L. B. (Eds.), 10th International Conference on Fracture Mechanics of Concrete and Concrete Structures - FraMCoS-X, pp. 1–7. https://doi.org/10.21012/fc10.235563.

Zhang, M., Chen, J., Lv, Y., Wang, D., Ye, J., 2013. Study on the expansion of concrete under attack of sulfate and sulfate - chloride ions. Construct. Build. Mater. 39, 26–32. https://doi.org/10.1016/j.conbuildmat.2012.05.003.

Zhang, S., Hamed, E., Song, C., 2023. A numerical and experimental meso-mechanical approach for the prediction of creep of concrete. Comput. Struct. 286, 107109 https://doi.org/10.1016/j.compstruc.2023.107109.