# Analysis of a chalky earthen masonry unit from the Champagne region (France): Is it relevant to stabilize mortar with hydraulic lime ?

Guillaume Polidori, Erwan Hamard, Adrien Aras-Gaudry, Céline Rousse, Fabien Beaumont, Sébastien Murer, Mohammed Lachi, Christophe Bliard, Fabien Bogard

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## To cite this version:

Guillaume Polidori, Erwan Hamard, Adrien Aras-Gaudry, Céline Rousse, Fabien Beaumont, et al. Analysis of a chalky earthen masonry unit from the Champagne region (France): Is it relevant to stabilize mortar with hydraulic lime?. Developments in the Built Environment, 2025, 24, pp.100756. 10.1016/j.dibe.2025.100756. hal-05264329

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Submitted on 12 Nov 2025

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# Analysis of a chalky earthen masonry unit from the champagne region (France): Is it relevant to stabilize mortar with hydraulic lime?

Guillaume Polidori<sup>a</sup>, Erwan Hamard<sup>b</sup>, Adrien Aras-Gaudry<sup>a,c</sup>, Céline Rousse<sup>a</sup>, Fabien Beaumont<sup>a</sup>, Sébastien Murer<sup>a,*</sup>,<sup>id</sup> Mohammed Lachi<sup>a</sup>, Christophe Bliard<sup>d</sup>, Fabien Bogard<sup>a</sup>

## ARTICLE INFO

### Keywords:

Adobe masonry

Mortar hydraulic lime stabilization

Compressive strength

Thermal performance

Environmental impact

## ABSTRACT

This study examines the mechanical and thermal performance of adobe masonry units built with highly chalky soils from the Champagne region (France), focusing on the effect of hydraulic lime content (0, 5, and 14 wt%) in mortar joints. Adobe and mortar samples were fabricated from 19th-century adobe barn soil and tested for their physical and structural properties. Results show that adding hydraulic lime improves wall performance by 37.3 %. However, this gain remains modest in absolute terms, and all mortars exceeded the 0.3 MPa minimum required for structural adobe walls. Lime also slightly reduces thermal conductivity, enhancing insulation. Digital image correlation revealed that lime delays crack formation and modifies failure patterns. Yet, a simplified life cycle analysis showed that 14 wt% lime increases global warming potential (GWP) by 479 %. The results suggest that for low-rise adobe structures, unstabilized mortar may offer a more sustainable alternative.

## 1. Introduction

Raw earth serves as a fundamental vernacular architectural typology, with its inception dating back to approximately 10,000 BC (Belarbi et al., 2022; Hamard et al., 2022). Characterized by its abundance and environmental sustainability, it presents a cost-effective construction alternative widely available globally (Sánchez Calvillo et al., 2024; Greco and Lourenço, 2021). Current estimates suggest that around 8–10 % of the global population, and 20–25 % in developing countries, reside in earthen structures (Marsh and Kulshreshtha, 2022). To enhance the relatively low mechanical and water resistance of earth-based materials, various additives also called stabilizers, including mineral and biopolymer types (Bailly et al., 2024; Ouedraogo et al., 2019; Kafodya et al., 2019), are typically incorporated into soil mixtures. It is worth noting that the term “stabilization” is widely used in the literature, implicitly suggesting that earth without additional binder would lack structural stability, which is incorrect because construction earthen materials naturally contain clay-based binders. A more appropriate terminology would be “earth treatment”, which avoids this misleading

connotation.

Natural Hydraulic Lime (NHL) has been selected as additional binder in this study, for mortar joints only. NHL has been used for mortar production since antiquity (Bell, 1996; Holmes and Rowan, 2021; Paracha et al., 2020; Carreira et al., 2021). In recent years, it has emerged as a material of significant interest for both restoration projects and sustainable construction (Shang et al., 2024; Kang et al., 2019). When compared to cement-based mortars, NHL exhibits superior compatibility with traditional building materials, improved performance relative to aerial lime mortars, and lower environmental impact have been extensively documented in the literature (Apostolopoulou et al., 2021; Zhang et al., 2018; Barr et al., 2015; Cho et al., 2017). Natural Hydraulic Lime (NHL) is derived directly from naturally occurring raw materials, whereas Hydraulic Lime (HL) is produced by blending Calcium Lime (CL) with pozzolanic additives, primarily composed of reactive silica (SiO₂) and alumina (Al₂O₃). Both NHL and HL are capable of yielding hydraulic lime mortars and hydraulic lime renders/plasters that typically exhibit 28-day compressive strengths exceeding those of hydrated (air) limes (>2 MPa) (Smith et al., 2005). Hydrated lime, Ca(OH)₂—also

<footnote><sup>a</sup> Université de Reims Champagne-Ardenne, ITheMM, Reims, F-51100, France</footnote>

<footnote><sup>b</sup> Université Gustave Eiffel, MAST-GPEM, Bouguenais, F-44340, France</footnote>

<footnote><sup>c</sup> Université de Reims Champagne-Ardenne, GEGENA, Reims, F-51100, France</footnote>

<footnote><sup>d</sup> Université de Reims Champagne-Ardenne, ICMR, UMR 7312 CNRS, Reims, F-51100, France</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: sebastien.murer@univ-reims.fr (S. Murer).</footnote>
known as calcium hydroxide or portlandite—is obtained through the calcination of calcareous rock, producing calcium oxide (quicklime). In the presence of water, quicklime undergoes a hydration process, known as slaking, to form hydrated lime.

From a chemical viewpoint, lime engages in pozzolanic reactions that significantly improve the mechanical and hydraulic properties of the soil (Deep, 2021; Islam et al., 2019). The hydration of lime elevates Ca²⁺ and OH⁻ ion concentrations, promoting particle flocculation and affecting soil plasticity. Increased pH facilitates the dissolution of silica and alumina, leading to the formation of calcium silicate or aluminate hydrates that enhance the mechanical performance of earthen materials (Bell, 1996; Cuisinier et al., 2009).

Concerning stabilized earthen materials, the absence of a standardized optimal lime content is attributed to the diverse elemental compositions of soils. Research conducted by Ávila et al. (2022) on various rammed earth specimens, with NHL contents ranging from 0 to 18 wt%, demonstrated that a lime ratio of 12 wt% resulted in the maximal compressive strength. Similarly, Millogo et al. (2008) reported that clayey adobe bricks achieved peak compressive strength also at 12 wt% hydrated lime, whereas Nasla et al. (2021) identified a maximum compressive strength at a lower lime content of 7 wt%. Notably, the latter two studies indicated a decline in mechanical performance beyond the optimal lime content, whereas the former study found no significant variation in strength beyond 12 wt% and up to 18 wt%.

Furthermore, Fabbri et al. (2021) previously questioned the appropriateness of examining the feasibility of utilizing raw earth bricks based solely on the performance data from adobes obtained through testing campaigns. They posited that such data fail to adequately represent the behavior of masonry, thus advocating for investigations that encompass the performance of adobes when assembled in masonry configurations.

This study investigates the optimal lime-to-earth ratio in the context of adobe as a structural typology, particularly within adobe/mortar joint masonry units. The unique aspect of this research is attributed to the distinctive soil characteristics from which the adobes are fabricated, specifically highly chalky soils (Kerry et al., 2009) located in the Champagne region of France (Linoir et al., 2016). A prior comparative analysis conducted by Polidori et al. (2025a) on the vernacular earthen construction heritage of this area examined various adobe types with CaCO₃ % content ranging from 0 to 85 %. Notably, a significant negative correlation (Pearson coefficient r = -0.87) was established between peak compressive strength and CaCO₃ content. In the current investigation, the decision was made to utilize soil with a high calcite concentration (84.9 %) and minimal metallic elements (Polidori et al., 2025a), which exhibited the lowest peak stress. This selection aims to provide robust evidence regarding the effects of mortar lime stabilization on the mechanical properties of adobe-based structures.

The majority of scientific literature addressing adobe masonry predominantly concentrates on the mechanical properties of unstabilized adobes (Piattoni et al., 2011; Silveira et al., 2012). A smaller number of studies examine adobes that have been stabilized with cement or lime (Millogo et al., 2008; Bharath et al., 2014; Dao et al., 2018; Zhang and Han, 2021; Sarkar et al., 2012). However, the body of work pertaining to wall assemblies, particularly those incorporating stabilized mortars, appears to be limited. Notably, only a single investigation has been identified that evaluates mortars with varying lime content combined with fired clay bricks within a masonry assembly (Kaushik et al., 2007). To our knowledge, there exists a distinct absence of scientific research focusing specifically on wall assemblies constructed from unstabilized adobes and stabilized mortars, all of these elements being sourced from identical soils.

This raises the inquiry: could the integration of unstabilized adobe and stabilized mortar facilitate a convergence between the compressive strength thresholds of adobes and natural mortars, given the exclusion of gravel in mortar compositions, thereby enhancing overall cohesiveness in the assembly?

The second motivation for this study is grounded in the principles of

sustainable construction, which are increasingly oriented towards carbon-neutral methodologies and recyclable materials. The use of mineral binders for stabilization can potentially limit the recyclability of earthen materials (Hamard et al., 2016). Even considering that hydraulic lime content is only added for the joints, relevant inquiries must assess the advantages of stabilization against the environmental drawbacks posed by introducing a mineral binder that may contradict eco-friendly practices. This investigation will provide a partial exploration of this issue by concentrating solely on mechanical and thermal properties, excluding factors such as water resistance.

Lastly, our study is informed by the broader context of vernacular earthen architecture, particularly within France and the Champagne-Ardenne region. Despite the existence of raw earth housing throughout various regions of France, a comprehensive inventory of this vernacular heritage remains absent, making Champagne-Ardenne one of the last unexamined territories regarding earthen heritage (Aras-Gaudry et al., 2023). In addressing this knowledge gap, the present paper aims at examining wall units constructed from historic adobes bonded with mortars of varying lime content.

In brief, the novelty of this paper in comparison with the existing literature can be considered threefold. First, it addresses soils with the distinctive characteristic of being highly chalky. Second, it focuses on the comparison of masonry units, specifically their joints, which are structurally regarded as zones of weakness, and examines whether mortar joints remain untreated or are treated with the mineral binder NHL. Finally, the environmental cost of this treatment is evaluated against the corresponding gains in mechanical and thermal performance.

## 2. Materials and methods

In this section, the timeline of the whole experimental procedure is presented, as well as the details of the different experimental methods used.

### 2.1. Timeline of the experimental procedure

Fig. 1 delineates the distinct phases involved in the construction of the wall units, which are systematically outlined as follows.

<figure><img src="image_4.png" /><figcaption>Fig. 1. Timeline of the experimental procedure.</figcaption></figure>
## 1. Location of the source adobe sampling area

Raw earth was utilized in the construction of the wall units, with the adobe and mortar samples sourced from the deconstruction of a 19th-century adobe barn, rather than direct soil extraction. The village from which the raw earth is derived is situated at the base of the Île-de-France cuesta and at the onset of the Chalky Champagne plain in France, characterized by an Upper Cretaceous chalk substratum. The predominant soil types in this area are calcosols and rendosols, which are classified as soils developed from limestone, typically exhibiting clayey characteristics and a high carbonate content (Linoir et al., 2016; Polidori et al., 2024).

## 2. Recovery of old adobes

Approximately one hundred adobes, exhibiting varying degrees of preservation, were recovered during the demolition of the barn. A significant number of the original adobe vertices appeared to be compromised, likely due to the demolition process (removal of mortar joints), transport (mechanical shocks), and natural aging (erosion). Consequently, the decision was made to forgo the use of these salvaged adobes in favor of reconstituting them from the native soil from which they originated.

## 3. Crushing

The old adobes were initially crushed with a hammer into coarse pieces (between 5 and 10 cm) to facilitate the wetting and mixing processes.

## 4. Wetting and mixing

To ensure good plasticity and enhance workability, a 26 % water mass ratio has been added to the crushed adobes. This water content aligns with the value of 25 % reported in the literature for optimal plasticity (Monghassem et al., 2021; Hejazi et al., 2024).

## 5. Molding

For all compression tests carried out on base materials (adobe and mortars), specific 3D-printed prismatic molds of dimensions 10x10 × 10 cm³ were used. In the absence of recommendations as reminded by Morel et al. (2007), these dimensions were selected based on limitations of the compressive strength testing machine and inspired from French standard NF EN 12390-3 (AFNOR, 2019) on cubic, hardened concrete specimens. Regarding the wall units, wooden molds of either 22 x 10 x 7 or 10.5 x 10 × 7 cm³ were employed, in agreement with guidelines of French standard XP P13-901:2022 (AFNOR, 2022).

## 6. Drying

Before testing, samples were stored for over a month in a room at 22 °C and 55 % RH relative humidity to reach a homogeneous, low moisture content.

## 7. Wall shaping

The wall components are assembled with careful consideration of vertical alignment and uniform joint thickness. To optimize the adhesion between the adobe and the mortar, all surfaces that will be in contact with the mortar are pre-moistened using a brush to enhance cohesive interaction during the assembly process.

## 2.2. Wall unit constitution

Masonry, characterized as a composite material, necessitates a

comprehensive evaluation of its mechanical performance through experimental testing of both its constituent components and the integrated material (Sánchez et al., 2022). Among various existing bonding patterns, the "stretcher bond" has been selected for analysis, recognized as the predominant block masonry bond (Vilane and Hann, 2022; Confédération de la construction en, 2020). This specific arrangement is illustrated in Fig. 2(a).

The wall unit is constructed with upper and lower layers composed of two identical adobes measuring (70 x 100 × 220 mm³), while the central layer consists of two shorter adobes with dimensions of (70 x 100 × 105 mm³), as represented in Fig. 2. These blocks are interconnected by mortar joints with a thickness of 10 mm, constructed following standard guidelines, which stipulate a maximum grain size of less than 2/3 of the joint thickness and the application of mortar onto moistened bricks to enhance the cohesion of the brick-mortar interface (Confédération de la construction en, 2020). In this instance, all mortar particles exceeding 5 mm in size were removed through sieving. The stabilized mortar material was obtained by mixing this soil with a commercially available NHL 3.5 hydraulic lime (PRB, Les Achards, France), whose main constituents are calcium dihydroxide, silicate and carbonate (FICHE DE DONNEES DE SECURITE, 2015). The safety data sheet supplied by the lime manufacturer reports that particle sizes below 5 µm represent 20-30 %. The final mortar mixture exhibits hydraulic lime content in proportions of 0, 5 and 14 % of the total weight (referred to as 0, 5 and 14 wt% throughout). The mortar application was continuous both vertically and horizontally on bricks that had been cured for 28 days, then the wall unit was cured for an additional 28 days. Furthermore, the selected dimensions of the wall unit for the compression analysis yield a height-to-width slenderness ratio of 2.3, ensuring requisite stability during the conducted tests.

## 2.3. Morphology and elemental composition

The morphological characteristics and chemical composition of the samples were analyzed utilizing a tabletop microscope (Hitachi TM3030Plus) in conjunction with an Energy-Dispersive X-ray Spectrometer (EDXS) (SwiftES3000). The X-ray spectra were collected at an energy level of 15 kV and for an acquisition duration of 300 s. In preparation for scanning electron microscopy (SEM) observations, the specimens underwent a conductive coating of Au-Pd via sputter coater to mitigate charging effects. For EDXS analysis, soil samples were processed into compressed pellets. Each experimental procedure was replicated a minimum of three times to ensure the reliability of the results.

Granulometric analysis was performed on three samples selected randomly to further elucidate the composition of the adobe. The particle size distributions were assessed using nine sieves with mesh sizes ranging from 10 mm to 25 µm, arranged in descending order. This procedure was conducted thrice per sample to guarantee reproducibility. For particle sizes less than 25 µm (associated with the finest sieve), laser diffraction techniques in pure water solution were applied utilizing a Malvern Mastersizer 2000 particle size analyzer (Malvern Instruments Ltd, Worcestershire, UK). The laser diffraction method was favored over traditional sedimentation because of its expedited processing time and lesser sensitivity to sample preparation variations. The correlation between mass-based sieving and volume-based diffraction methods was established by maintaining consistent absolute densities across the corresponding samples. In the case of chalky soils, this approach delineates an upper threshold for clay content (defined as particles smaller than 2 µm), recognizing that fine particles may also incorporate small quantities of coccoliths and limestone fragments.

Porosity was determined from the ratio of apparent to absolute (skeletal) densities, with the latter measured using the pycnometer method (Bourdot et al., 2017).
<figure><img src="image_5.png" /><figcaption>Fig. 2. (a) Diagram of the wall unit studied; (b) Dimensions of the wall unit components.</figcaption></figure>

## 2.4. Mechanical analysis

The architectural design framework does not intentionally incorporate tensile stresses within earth materials; consequently, compression is the primary mechanical parameter examined in this study. Compression tests were conducted utilizing an Instron 9565 (Élancourt, France) testing apparatus equipped with a 50 kN load cell. These experiments occurred under controlled indoor ambient conditions, specifically at a temperature of 23 °C and a relative humidity of 50 %. The compression rate was calibrated to 8 mm/min in accordance with NF XP P 13–901 specifications (AFNOR, 2022), facilitating specimen failure within a time frame of 1–2 min. To ascertain statistical reliability, the analysis of compressive strength typically involves averaging results from five cubic specimens for qualifying adobe and three distinct mortar compositions: 0, 5, and 14 wt% lime (Abhilash et al., 2022). Additionally, three experimental tests were performed for each wall/mortar composition within the wall assemblies.

## 2.5. Failure analysis

Throughout compression tests, crack initiation and propagation in the wall units were monitored using a digital image correlation (DIC) system composed of a Zeiss Aramis SRX 3D camera and the Zeiss Inspect 2023 software (Oberkochen, Germany). The deformations are calculated from the differentiation of the determined displacement field (10⁻⁴ % accuracy).

## 2.6. Thermal analysis

The thermal performance of adobes, mortar samples, and wall assemblies was assessed by measuring their thermal conductivity. This evaluation employed an ISOMET 2114 analyzer (Applied Precision, Ltd., Bratislava, Slovakia), which implements heat flux pulses at the material surface. A total of five specimens per sample were analyzed, ensuring a comprehensive assessment of their thermal conductivity properties and facilitating a robust comparison among the various materials tested.

<figure><img src="image_6.png" /><figcaption>Fig. 3. SEM micrographs of the different elements: (a) soil; (b) lime; (c) mortar 14 wt% (x2500).</figcaption></figure>

# 3. Results and discussion

## 3.1. Morphology, elemental mapping and soil characteristics

Fig. 3(a) illustrates the microstructural characteristics of the soil from which reconstituted samples were derived, under ×2500 magnification. Given that the mortar was lime-stabilized in two out of the three wall cases investigated, the morphological features of the hydraulic lime used are depicted in Fig. 3(b). Morphology of the mortar treated with 14 wt% of lime is also presented in Fig. 3(c).

A significant presence of calcite micrograins, indicative of chalky soils and subsoils, is illustrated in Fig. 3(a). The presence of coccoliths is also noted, corroborating previous research (Polidori et al., 2025b). Additionally, it is observed that the clay-sized fraction is comprised of crystalline calcite particles ranging in size from 2 to 5 µm, aligning with documented findings in chalky soils. We observe no significant differences between these morphologies, other than perhaps a reduction in grain sizes once the stabilized mortar mix has been achieved.

The elemental compositions of soil, lime, and stabilized mortar 14 wt %, obtained by EDX spectroscopy, are summarized in Table 1, revealing notable similarities concerning the analyzed elements. Notably, the analysis excludes consideration of carbon atoms present in the form of carbonates. In this regard, XRD patterns could have provided further information regarding the phases formed following the addition of hydraulic lime. The International Mineralogical Association classifies lime as a mineral with the chemical formula CaO (Back et al., 2018). For this study, a commercial hydraulic lime, Ca(OH)₂, was used. The presence of

<table><caption>**Table 1**
Main elemental composition of soil, lime, and stabilized mortar (Atomic%).</caption><thead><tr><th></th><th>0</th><th>Ca</th><th>Si</th><th>Al</th><th>Fe</th><th>K</th><th>Mg</th><th>Si/<br>Ca</th></tr></thead><tbody><tr><td>Soil</td><td>76.3</td><td>19.3</td><td>2.7</td><td>1.0</td><td>0.2</td><td>0.2</td><td>0.2</td><td>0.1</td></tr><tr><td>Hydraulic lime</td><td>73.0</td><td>21.9</td><td>3.9</td><td>0.4</td><td>0.1</td><td>0.1</td><td>0.5</td><td>0.2</td></tr><tr><td>Stabilized mortar 14<br>wt%</td><td>78.2</td><td>17.7</td><td>2.5</td><td>1.1</td><td>0.2</td><td>0.1</td><td>0.2</td><td>0.1</td></tr></tbody></table>
silicon (Si), aluminum (Al), and magnesium (Mg) is characteristic of this type of lime and confirms that hydraulic limes contain fired clays. Furthermore, calcium (Ca) is established as the predominant mineral element within the investigated soil, which is characteristic of the geological plateau associated with the Champagne-Ardenne chalky region of France. In their analysis, Polidori et al. (2025a) quantified the CaCO₃ content at 84.9 %. It is noteworthy that the atomic percentages of metallic elements within the soil are relatively low, suggesting a limited presence of metallic oxides. This is significant, as the beneficial effects of metallic oxides on the load-bearing capacity of earthen structures have been documented by Walter et al. (2022) in tropical soils. Moreover, Polidori et al. (2025a) demonstrated a robust positive correlation (Pearson coefficient r = 0.76) between peak compressive strength and the atomic percentages of accumulated metallic elements (Al, Fe, Mg) in chalky soils.

The physical properties of the wall components are presented in Table 2. The lime utilized for mortar stabilization is a commercially available NHL 3.5 hydraulic lime, exhibiting an apparent density of 760 kg m⁻³. It is evident that both the apparent and dry densities of unstabilized mortar are comparable to those of adobe, showing deviations of -2.2 % and -2.8 %, respectively. This indicates that modifying the soil granulometry to create mortar specimens exerts minimal influence on these physical parameters. An increase in the lime content results in a reduction of dry density, exhibiting a decrease of -9.7 % at 14 wt% lime, attributable to enhanced porosity, which reaches 44.5 % at this lime concentration. These observations suggest a corresponding decrease in thermal conductivity, thereby enhancing thermal insulation as the lime content in the mortar joints increases.

## 3.2. pH and particle size distribution

In the field of soil analysis, the pH value emerges as a critical parameter influencing various material properties. Specifically, positive correlations have been established between pH levels and the compressive strength of tropical earthen mortars (Walter et al., 2025). As illustrated in Fig. 4, the pH levels of mortars exhibit variations with lime content, which spans from 0 to 20 wt%. The pH of pure lime was recorded at 12.6, while the soil constituting the adobes under investigation is classified as calcareous alkaline, exhibiting a pH value of 8.5. Fig. 4 distinctly demonstrates an upward trend in pH associated with increasing lime content, characterized by the presence of two successive plateaus in the pH profile. The phenomenon of plateau within the pH curve relative to the addition of lime has been corroborated by Millogo et al. (2008) and Dao et al. (2018), who observed similar behavior in a siliceous soil from Burkina Faso, specifically within a lime concentration range of 4 wt% to 12 wt%. These authors attribute the presence of a plateau with increasing mineral binder content to the solubilization of silica in the basic medium. Although existing guidelines caution against exceeding a 10 % threshold for the incorporation of hydraulic binders (AFNOR, 2022), this study intentionally includes investigations at two lime levels corresponding to each plateau: 5 wt% and 14 wt%, the latter exceeding the recommended threshold. These selected concentrations will facilitate a thorough examination of the potential influence of pH on the mechanical properties of chalky soils.

The particle size distributions for the adobe soil and the

<table><caption>**Table 2**
Main physical characteristics of the wall components.</caption><thead><tr><th></th><th>Adobe</th><th>Mortar 0 wt %</th><th>Mortar 5 wt %</th><th>Mortar 14 wt %</th></tr></thead><tbody><tr><td>ρ<sub>app</sub> (kg/m<sup>3</sup>)</td><td>1664</td><td>1627</td><td>1502</td><td>1465</td></tr><tr><td>Moisture content (%)</td><td>1.3</td><td>2.0</td><td>1.4</td><td>1.7</td></tr><tr><td>ρ<sub>dry</sub> (kg/m<sup>3</sup>)</td><td>1640</td><td>1594</td><td>1481</td><td>1440</td></tr><tr><td>Porosity (%)</td><td>25.8</td><td>27.4</td><td>41.1</td><td>44.5</td></tr></tbody></table>

<figure><img src="image_7.png" /><figcaption>**Fig. 4.** pH vs. lime content (wt%).</figcaption></figure>

corresponding unstabilized mortar are illustrated in Fig. 5. The observed curves demonstrate a notable shift, attributable to the elimination of larger particles (greater than 5 mm) during the mortar preparation. The soil utilized in this study is characterized by a substantial presence of gravels and stones (size >2 mm), along with coarse sand (0.2–2 mm), which is typical of limestone soils found in the Chalky Champagne plateau. A previous investigation (Polidori et al., 2025a) utilized laser granulometry to ascertain that the clay content of this soil is 14.2 %. This information highlights the specific material properties that influence the mortar’s characteristics.

## 3.3. Mechanical behavior of samples considered separately

Masonry is classified as a composite material, with its structural resistance being influenced by both the adobe units and the mechanical properties of the mortar utilized for bonding. The mortar joints are recognized as the most vulnerable aspect of this composite system due to the pressure exerted by the adobe, which induces dilation in the mortar joint bed and subsequently leads to a concentration of mechanical stress (Sánchez et al., 2022). To evaluate the mechanical properties of the wall components, cubic specimens with dimensions of 10 cm × 10 cm × 10 cm were fabricated and subjected to compression testing. The resultant values for peak stress, peak strain, and tangent Young’s modulus are

<figure><img src="image_8.png" /><figcaption>**Fig. 5.** Particle size distribution of adobe and unstabilized mortar.</figcaption></figure>
detailed in Table 3.

The peak compressive strength of mortar exhibits a positive correlation with lime content, escalating from 0.75 to 1.03 MPa, yet it remains inferior to the peak stress observed in adobe. This augmentation in peak compressive strength in relation to mineral stabilization is extensively documented in the existing literature (Bailly et al., 2024). Nonetheless, the aim of achieving homogeneity in the mechanical behavior of the wall unit components has not been entirely accomplished. The relative disparity in compressive strength thresholds between adobe and mortar diminishes with the addition of lime, ultimately reducing to 21.3 % at a lime content of 14 wt%. In earthen materials, Young's modulus is often considered difficult to calculate based on compressive tests, since its determination requires measurement of the local strain with high precision (Moevus et al., 2012).

Furthermore, an analysis of mortar ductility, defined as the material's capacity to deform without incurring fracture, is pertinent, as it elucidates its plastic behavior before failure. To facilitate this analysis, the three stress-strain curves corresponding to varying lime contents ranging from 0 to 14 wt% are illustrated in Fig. 6. A normalized representation emerges as particularly advantageous for comparative assessments of ductility across different materials, as it uniformly scales the curves along both axes, consistent with findings reported by Imanzadeh et al. (2020). In this normalized approach, the y-axis represents the dimensionless compressive stress, denoted as $\sigma/f_c$, where $f_c$ represents the maximum compressive strength, while the x-axis represents the dimensionless strain, $\varepsilon/\varepsilon_u$, with $\varepsilon_u$ corresponding to the strain associated with $f_c$. The ductility index, designated as i', in the post-peak region correlates with the normalized strain at which normalized stress declines to 85 % of its peak value. A condition of $i' = 1$ is indicative of brittle failure, wherein the material exhibits a steady hardening followed by abrupt fracture upon achieving peak strength.

The incorporation of lime in mortars enhances their compressive strength; however, it entails a considerable reduction in ductility, as previously reported by Abdi et al. (2021). The ductility index of unstabilized mortar is measured at 1.38, while the introduction of 5 wt% and 14 wt% lime results in reductions of this index to 1.22 and 1.14, corresponding to decreases of 11.6 % and 17.4 %, respectively. This observation indicates a progressive increase in the brittleness of the mortars with higher lime content, despite an accompanying rise in peak compressive stress. Additionally, an inverse relationship is noted between lime content and peak strain values; specifically, as the lime content increases, the peak stress is attained at progressively lower strain values, which correlates with marked increases in Young's modulus.

Furthermore, ductility can also be assessed through an alternative metric known as the deformability index (Vilane and Hann, 2022), defined as $I_D = \varepsilon_{ct}/\varepsilon_{cu}$, where $\varepsilon_{ct}$ and $\varepsilon_{cu}$ represent the peak strains of stabilized and unstabilized mortars, respectively. An analysis of the peak strain values presented in Table 3 reveals a decline in the deformability index, with $I_D$ recorded at 0.68 for 5 wt% lime and 0.57 for 14 wt% lime. Consequently, it is apparent that increasing lime content results in reduced axial deformation of the mortar under compressive loading conditions.

<table><caption>**Table 3**

Mechanical characteristics of samples (Mean – SD).</caption><thead><tr><th></th><th>Adobe</th><th>Mortar<br>0 wt% lime</th><th>Mortar<br>5 wt% lime</th><th>Mortar<br>14 wt% lime</th></tr></thead><tbody><tr><td>Peak stress, f<sub>c</sub> (MPa)</td><td>1.31 (0.03)</td><td>0.75 (0.18)</td><td>0.84 (0.14)</td><td>1.03 (0.04)</td></tr><tr><td>Peak strain, ε<sub>u</sub> (%)</td><td>2.29 (0.45)</td><td>2.82 (0.63)</td><td>1.92 (0.57)</td><td>1.62 (0.52)</td></tr><tr><td>Young's modulus, E<br>(MPa)</td><td>80.1 (19.7)</td><td>37.9 (13.4)</td><td>59.5 (7.6)</td><td>91.0 (22.0)</td></tr></tbody></table>

<figure><img src="image_9.png" /><figcaption>**Fig. 6.** Dimensionless stress-strain curves for mortars with varying lime content.</figcaption></figure>

### 3.4. Mechanical behavior of wall units

Fig. 7 illustrates the stress-strain curves for the three investigated wall assemblies, which contain mortar joints incorporated with 0, 5, and 14 wt% lime, respectively. A notable finding is that the peak compressive stress for each wall assembly consistently remains below the compressive strength of both adobe and pure mortar. The initial objective of this investigation was to enhance the cohesiveness of the assembly by decreasing the disparity between the peak stress values of the adobe and mortar components. As depicted in Fig. 7, an increase in lime content correlates positively with the compressive strength of the mortar.

The mechanical characteristics of the wall assemblies are intrinsically linked to those of their constituent materials; as the compressive strength of the mortar increases, the overall strength of the wall assembly similarly increases. It is found that the peak stress of the wall assembly remains inferior to that of its components. The slenderness ratio of the adobe and mortar samples, namely 1, is different from that of the wall unit (2.3) may lead to a possible overestimation of their respective peak compressive strengths. Keeping this limitation in mind, this observation is particularly intriguing, as the wall assembly does not manifest intermediary compressive behavior. Such conditions arise when there is a significant gap between the peak stresses of adobe and mortar, as documented by Kaushik et al. (2007). In this investigation, the observed gap does not exceed 0.6 MPa across the analyzed range of lime content. Furthermore, analogous conclusions have been reported regarding the compressive strength of individual specimens, which have been noted to be 65 %–80 % higher than the strengths measured in doublets and triplets (Bei and Papayianni, 2003).

The corresponding values of peak compressive stress are summarized in Table 4.

To investigate the correlation between the mechanical properties of wall structures and those of their constituent materials, various empirical equations can be employed to approximate the maximum compressive strength of composite earthen wall elements integrated with mortar joints. This estimation is contingent upon the independent mechanical characteristics of both adobe and mortar. Comprehensive reviews of the equations utilized for assessing masonry strength are detailed by Sajanthan et al. (2019) and Costigan et al. (2015).

Two different empirical relations were selected: Equation (1) from European Standard EUROCODE 6 (AFNOR, 2013), and Equation (2) from the French Guidelines for Building with Raw Earth (Confédération
<figure><img src="image_10.png" /><figcaption>Fig. 7. Stress-strain curves of wall assemblies, unstabilized adobe and mortar with 0 (a), 5 (b) and 14 wt% (c) lime content.</figcaption></figure>

de la construction en, 2020). These are the most commonly used standards and recommendations in France, although a broad range of relations may be found in the literature, with significant variations in the estimated mean compressive strength of the wall assembly, as pointed out by Sajjanthan et al. (2019). These relationships are derived from specific formulations of bricks and mortars and therefore do not exhibit the general applicability and universality provided by Eurocode 6. It should however be reminded that these estimates are not meant to be used in the frame of treated soils and are presented for comparison purposes only. Both are relevant for joint thicknesses between 10 and 15 mm, in a moderately exposed atmosphere. These equations are defined as follows:

$$ \sigma_{cw} = 0.55 \sigma_{ca}^{0.7} \sigma_{cm}^{0.3} \qquad (1) $$

$$ \sigma_{cw} = 0.8 \sigma_{ca}^{0.8} \sigma_{cm}^{0.2} / 1.5 \qquad (2) $$

Where $\sigma_{cw}$, $\sigma_{ca}$, and $\sigma_{cm}$ are the mean compressive strengths of the wall assembly, adobe unit, and mortar, respectively.

The estimates presented in Table 4 closely align with the experimental data obtained from compression tests, with the maximum relative deviation not surpassing 22 % (mean deviation 12 %). The experimental findings indicate that the peak stress attained by the wall assembly is significantly lower than that of the individual adobe and mortar components. It is important to note that adobe-based wall masonry typically relies on the assumption of a uniform load distribution within the material, which considers a maximum compression resistance of 0.3 MPa (Confédération de la construction en, 2020). In this context, even a wall constructed from unstabilized mortar adheres to this mechanical criterion.

Other types of masonry have been investigated using lime in mortar, although not on raw earth bricks. For instance, although not based on raw, unfired earthen materials, Kaushik et al. (2007) concluded that, in the case of masonry components with comparable strength and stiffness, the resulting masonry stress-strain curve may be lower than those of (fired clay) bricks and mortar. D'Amato et al. (D'Amato et al., 2023) showed that for weak units-strong mortar masonry prisms, the compressive behavior only depends on the (tuff) brick units. Ravula and Subramaniam (2019) submitted triplets specimen consisting of three fired clay bricks and two mortar bed joints to shear tests and observed crack branching into the mortar bed, followed by propagation along the mortar-brick interface.

### 3.5. Failure modes

Fig. 8 presents different stages of cracking on selected wallette configurations. Given the similarities between their mechanical behaviors, only those with unstabilized mortar joints and joints containing 14 wt% of lime are depicted.

In all examined instances, crack initiation occurs along a vertical trajectory primarily due to the horizontal tensile stress induced by Poisson's effect. It is noteworthy that these cracks are not entirely vertical; rather, the frictional forces present at the interface with the pressure plate contribute to their deflection. Furthermore, the propagation behavior of cracks remains largely consistent irrespective of variations in lime content within the mortar.

To provide more quantitative information about cracking modes, failure was monitored using digital image correlation over the window presented in Fig. 9 on the different wall units, namely that with unstabilized mortar joints (Fig. 10) and joints containing 14 wt% of lime.

<caption>**Table 4**</caption>

Experimental mean compressive strength of the wall with varying lime content vs. empirical predictions.

<table><thead><tr><th>Wall with</th><th>Experimental<br>Present study</th><th>Empirical (1) BS EN<br>1996-1-1, 2012</th><th>Empirical (2)<br>Guide des Bonnes<br>Pratiques, 2020</th></tr></thead><tbody><tr><td>Mortar<br>joint<br>0 wt%<br>lime</td><td><strong>0.51</strong> (0.04)</td><td><strong>0.61</strong></td><td><strong>0.62</strong></td></tr><tr><td>Mortar<br>joint<br>5 wt%<br>lime</td><td><strong>0.57</strong> (0.07)</td><td><strong>0.63</strong></td><td><strong>0.64</strong></td></tr><tr><td>Mortar<br>joint<br>14 wt%<br>lime</td><td><strong>0.70</strong> (0.16)</td><td><strong>0.67</strong></td><td><strong>0.67</strong></td></tr></tbody></table>
<figure><img src="image_11.png" /><figcaption>Fig. 9. Location of the DIC monitoring window (greyscale) on the wall unit (green).</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>Fig. 10. Location of the DIC monitoring window (greyscale) on the wall unit (green).</figcaption></figure>

(Fig. 11) are depicted. Only the major strain $ε_1$ is analyzed, as it is the primary cause for crack opening in this type of material and makes it easier to follow cracking paths.

In the case of unstabilized mortar, cracks initiate in the central joint at 23.1 % of the peak force (Fig. 10(a)), before deviating along the mortar bed (25.7 % peak). More cracks initiate through the adobe and along the second vertical interface of the central joint (Fig. 10(b)) at 50.4 % peak force. In contrast, for stabilized joints, crack initiation occurs at 53.8 % peak along both the vertical interfaces of the central joint (Fig. 11(a)). At 69.2 % peak, crack coalescence is observed within the adobe (Fig. 11(b)). Given these findings, it can reasonably be said that lime stabilization significantly delays the occurrence of cracks during the loading path.

Collectively, these findings substantiate the classification of adobe masonry as a quasi-brittle material, primarily attributable to its

relatively low tensile strength and its softening behavior following the peak tensile strength, as reported by Fages et al. (2022).

## 3.6. Thermal analysis

The impact of utilizing joints composed of lime-stabilized mortar on the thermal performance of wall units warrants thorough assessment. Accordingly, the thermal conductivities of both adobes and joints will be measured independently, with a particular emphasis on determining the equivalent conductivity of the wall assembly. It can be seen as the conductivity of a homogeneous material equivalent to the considered composite wall. These parameters are critical for calculating the thermal resistance of the wall, given that the widths of the joint and adobes are uniform at 70 mm. The equivalent conductivity is derived from the mortar/adobe cell configuration illustrated in Fig. 12, facilitating a comprehensive understanding of the thermal dynamics involved.

Given the selected dimensions for the cell (see Fig. 2), the equivalent conductivity may be expressed as:

$$ \lambda_w = \frac{\lambda_a S_a + \lambda_m S_m}{S_a + S_m} = 0.836[\lambda_a + 0.195 \lambda_m] \quad (3) $$

The thermal resistance of the wall is defined by $R_w = e/\lambda_w$, where e stands for the thickness of the masonry. The values of thermal conductivity and resistance as a function of lime content are summarized in Table 5.

The thermal conductivity of mortar exhibits a downward trend as lime content increases, with measured values ranging from 0.568 W/(mK) for unstabilized mortar to 0.392 W/(mK) for a lime concentration of 14 wt%. This reduction in thermal conductivity may be attributed to the role played by lime, which prevents shrinkage and consequently increases porosity. Indeed, air can be considered an insulating medium, with a thermal conductivity value of $\lambda = 0.026$ W/(mK), as noted by Bamogo et al. (2022).
<figure><img src="image_13.png" /><figcaption>Fig. 10. Color-coded major strain ε₁ at 23.1 % (a), 50.4 % (b) and 100 % (c) of peak compressive stress on a wallette with unstabilized mortar joints (from DIC).</figcaption></figure>

<figure><img src="image_14.png" /><figcaption>Fig. 11. Color-coded major strain ε₁ at 53.8 % (a) and 69.2 % (b) of peak compressive stress on a wallette with mortar joints stabilized with 14 wt% of lime (from DIC).</figcaption></figure>

<figure><img src="image_15.png" /><figcaption>Fig. 12. Definition of a mortar joint/adobe cell: (S<sub>a</sub>, λ<sub>a</sub>) and (S<sub>m</sub>, λ<sub>m</sub>) refer to the surface areas and thermal conductivities of the adobe (green) and mortar joint (red), respectively.</figcaption></figure>

<table><caption>**Table 5**

Influence of lime stabilization on the thermal conductivity of mortar.</caption><thead><tr><th>Adobe</th><th>Mortar</th><th colspan="3">Wall</th></tr><tr><th>λ<sub>a</sub> (W/(mK))</th><th>Lime wt%</th><th>λ<sub>m</sub> (W/(mK))</th><th>λ<sub>w</sub> (W/(mK))</th><th>R<sub>w</sub>/e (mK/W)</th></tr></thead><tbody><tr><td rowspan="3">0.720 (0.020)<sup>a</sup></td><td>0</td><td>0.568 (0.034)</td><td>0.695</td><td>1.440</td></tr><tr><td>5</td><td>0.417 (0.025)</td><td>0.670</td><td>1.493</td></tr><tr><td>14</td><td>0.392 (0.006)</td><td>0.666</td><td>1.502</td></tr></tbody></table>

### 3.7. Synthesis on the benefits of mortar stabilization with lime

To evaluate the significance of incorporating lime stabilization in the mortar utilized for wall assembly joints, three critical parameters are analyzed: thermal performance enhancement, mechanical performance improvement, and a simplified estimate of the relative variation in

global warming potential (GWP). The decision-making process involves a trade-off among these factors, reflecting a balance between the associated benefits and environmental costs, not to mention the economic cost of lime addition.

Considering the apparent densities of the various constituents—namely, adobe, lime, and mortar—alongside the dimensions of masonry elements, specifically the joints of adobe and mortar, the application of hydraulic lime stabilization at concentrations of 5 wt% and 14 wt% results in the incorporation of 0.39 wt% and 1.07 wt% lime at the wall unit scale, respectively. Although these relative concentrations may seem minimal, they translate into substantial quantities of lime at the overall masonry level, thereby raising concerns regarding the environmental implications of such use.

To substantiate these claims, the GWP of hydraulic lime is reported to range between 740 and 898 kgCO₂eq/tonne (Maïni and Thautam, 2013; European Lime Association (EuLA and) B, 2024), while the GWP of the soil used to produce adobe and mortar is estimated at 2 kgCO₂eq/tonne (Maïni and Thautam, 2013). Consequently, the GWP associated with a mortar joint/adobe cell can be computed based on the lime content in the mortar, coupled with the environmental impact defined as the relative GWP variation in comparison to the unstabilized scenario. The comprehensive results of this analysis are presented in Table 6.

It can be seen that the use of stabilized mortar results in a significant increase in the GWP of the wall, reaching +479 % for mortar joints stabilized with 14 wt% of lime.

Regarding the benefits of stabilization, the thermal gain brought by the addition of lime on the thermal resistance of the wall may be defined as:

$$G_{Ti} (\%) = 100 \frac{R_{wi} - R_{w0}}{R_{w0}} = 100 \left[ \frac{\lambda_{w0}}{\lambda_{wl}} - 1 \right] \quad (4)$$

Where index *i* denotes the lime content of the mortar, expressed in wt%.

For illustration purposes, let us consider a 40 cm-thick wall comprising mortar joints stabilized with 14 %wt lime. Using the values of thermal conductivity in Table 5 and to achieve equal thermal resistance, the thickness of a wall with unstabilized mortar joints would have to be 41.2 cm. It should be noted that this calculation does not consider exterior insulation or interior finishes, which will attenuate the value of

<table><caption>**Table 6**

Environmental harm relative to lime content of the mortar joint in the wall assembly.</caption><thead><tr><th>Lime content (wt%)</th><th>GWP (kgCO<sub>2</sub>eq/tonne)</th><th>GWP variation (%)</th></tr></thead><tbody><tr><td>0</td><td>2</td><td>-</td></tr><tr><td>5</td><td>5.49</td><td>+175</td></tr><tr><td>14</td><td>11.59</td><td>+479</td></tr></tbody></table>

<footnote>a From Polidori et al. (2025).</footnote>
the global thermal gain even more.

On the other hand, the mechanical gain may be defined as:

$$G_{Mi}(\%) = 100 \frac{f_{ci} - f_{c0}}{f_{c0}} \qquad (5)$$

Where $f_{ci}$ denotes the peak compressive stress of the wall with stabilized mortar, and $f_{c0}$ that of the wall with unstabilized mortar.

Fig. 13 presents both the thermal and mechanical gains for unstabilized and stabilized mortars at the wall unit scale, as well as the corresponding environmental harm. The relative mechanical gain is found to reach 37.3 % for joints with 14 %wt lime. However, the absolute difference in compressive strength is only 0.2 MPa, ranging from 0.51 to 0.70 MPa, which lies at the lower end of standard XP P13–901:2022 (AFNOR, 2022).

The addition of a significant amount of lime may be irrelevant, since 0.51 MPa seems to be sufficient for the one or two storey dwellings that represent the majority of uses of earth bricks, as reminded by Ouedraogo et al. (2020). In addition, a widely accepted guideline for the structural design of adobe masonry walls is to assume a uniform load distribution within the material, leading to a maximum allowable stress of 0.3 MPa (Confédération de la construction en, 2020). This mechanical requirement is satisfied even when the mortar is used in its unstabilized form.

Evaluating lime stabilization in earthen construction must extend beyond mere considerations of global warming potential (GWP), compressive strength, and thermal resistance. In this study, we have deliberately confined our analysis to these critical parameters to assess the implications of lime addition in mortar within the framework of sustainable construction. It is acknowledged that lime stabilization may be warranted in particular scenarios, including inadequate soil quality, insufficient aggregate availability, or exposure to extreme climatic conditions, such as flooding and monsoonal precipitation (Van Damme and Houben, 2020). The findings presented align with the conclusions drawn by Van Damme and Houben (Van Damme and Houben, 2018), which indicates that using Portland cement for stabilization purposes is generally neither technically nor environmentally preferable. Thus, while our study focuses on specific metrics, a broader context regarding certain construction challenges can exist where lime stabilization is relevant and necessary.

In summary, this study clearly illustrates the environmental burden of incorporating hydraulic lime, which outweighs the mechanical and thermal benefits, irrespective of the lime content in the mortar. In detail, we observed no thermal benefit, only moderate mechanical enhancement, and a substantial environmental cost. Furthermore, from a

<figure><img src="image_16.png" /><figcaption>Fig. 13. Thermal, mechanical gain and GWP variation at the wall assembly scale vs. mortar lime content (unstabilized mortar used as baseline for the calculation of incidence).</figcaption></figure>

sustainability viewpoint, lime-stabilized mortar compromises recyclability, in contrast to untreated earth-based materials.

## 4. Conclusion

When the mortar used to seal adobes is taken from the same soil as the latter, the exclusion of pebbles and gravel results in weaker mechanical performance than that of adobes. It may therefore be tempting to mechanically reinforce the mortar by stabilizing it with mineral binders such as lime, to mechanically homogenize the walls thus formed. The question is whether the advantages of stabilization outweigh the disadvantages, particularly from an environmental point of view.

Several conclusions can be drawn from this study. The first is general and tends to show that limiting ourselves to a single study of the compression thresholds reached by adobes to qualify the load-bearing capacity of raw earth construction is certainly necessary but perhaps not sufficient. Indeed, the mechanical properties of heterogeneous structures such as wall assemblies made of adobe and stabilized or unstabilized mortar joints are significantly different from those of individual components. For example, the peak compressive stress of adobe alone reaches 1.31 MPa, while that of the wallette ranges from 0.51 to 0.70 MPa, for unstabilized and stabilized mortar joints with 14 wt%, respectively.

Secondly, from a mechanical viewpoint, lime stabilization of mortar increases the peak compressive stress of the wall unit by 37.2 %, corresponding to a relatively low 0.19 MPa increase which remains globally insignificant. Besides, lime also affects the compressive stress at crack onset, which shifts from 23.1 to 53.8 % of the peak and can be considered beneficial. This observation is most likely due to the lower ductility of stabilized mortar with increasing lime content.

Regarding the thermal properties, the gain observed in conductivity and deducted thermal resistance per unit thickness at the wall unit scale is modest, proving that adding lime does not influence the thermal characteristics of the assembly.

Finally, from an environmental perspective, the balance is far bleaker, with GWP increasing drastically by up to 479 % for 14 wt% of lime in the mortar composition.

The starting premise of this article was to assess the relevance of stabilizing mortar with hydraulic lime: it can be concluded that it brings no thermal advantage, moderate mechanical improvement, and high environmental cost. Besides, such stabilized mortar prevents recyclability, contrary to fully earth-based materials.

Future works on this topic should focus on confirming the observed trend, which shows that mortar is the restricting factor and that the predictive models of masonry wall behavior are inadequate, as far as Chalky Champagne soils are concerned. The masonry response also depends on the hierarchy between blocks and mortar, and future studies on the current topic should examine the influence of the arrangement between bricks and mortar joints. Moreover, from a mechanical viewpoint, both tensile and shear tests should be performed on the wall assembly in view of their key influence on the failure mechanisms. Finally, from an environmental viewpoint, improving the performance of a masonry wall through treatment of the mortar should rely on natural products with reduced carbon footprint.

### CRediT authorship contribution statement

Guillaume Polidori: Writing – review & editing, Writing – original draft, Supervision, Conceptualization. Erwan Hamard: Writing – review & editing, Conceptualization. Adrien Aras-Gaudry: Resources, Investigation. Céline Rousse: Visualization, Investigation. Fabien Beaumont: Validation, Investigation. Sébastien Murer: Writing – review & editing, Visualization, Investigation, Formal analysis. Mohamed Lachi: Validation, Investigation. Christophe Bliard: Validation, Investigation. Fabien Bogard: Visualization, Data curation.
# 5. Declaration of generative AI and AI-assisted technologies in the writing process

During the preparation of this work the authors used ChatGPT 40 (OpenAI, https://chat.openai.com, accessed September 2, 2025) for language improvement purposes only. After using this service, the authors reviewed and edited the content as needed and take full responsibility for the content of the published article.

## 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.

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