# Selection of pultruded composite materials for new, low-carbon emission, lightweight railways tracks, with a focus on mechanics, economics and sustainability

Léo Sudriès, I. Diboune, Aubin Cloos, O. de Almeida, J. Serra, Wiyao Azoti, Bruno Castanié

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## To cite this version:

Léo Sudriès, I. Diboune, Aubin Cloos, O. de Almeida, J. Serra, et al.. Selection of pultruded composite materials for new, low-carbon emission, lightweight railways tracks, with a focus on mechanics, economics and sustainability. Materials & Design, 2026, 261, pp.115401. 10.1016/j.matdes.2025.115401. hal-05462297

HAL Id: hal-05462297

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Submitted on 19 Jan 2026

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# Selection of pultruded composite materials for new, low-carbon emission, lightweight railways tracks, with a focus on mechanics, economics and sustainability

L. Sudriès, I. Diboune, A. Cloos, O. De Almeida ID, J. Serra ID, W. Azoti, B. Castanié* ID

Institut Clément Ader (ICA), Université de Toulouse, CNRS UMR 5312, ISAE-SUPAERO, INSA, IMT Mines Albi, 3 Rue Caroline Aigle, 31400 Toulouse, France

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## ARTICLE INFO

**Keywords:**

Eco-design

Rail track

Decarbonization

Pultruded composite

GWP

## ABSTRACT

In the context of decarbonizing transport, the selection of materials for lightweight pultruded composite railway tracks adapted for light trains has been achieved. The candidates are made of thermoplastic PA6 and of acrylic-based resin, as well as thermoset epoxy resin with carbon, glass, basalt and flax fibres. A comparison of the economic cost and carbon emissions of each configuration is presented. 175 tensile, compression and off-axis tests were performed. The elastic properties and sizing allowances are provided. An initial estimate of the ecological cost of materials combinations was assessed using a cradle-to-gate approach on raw materials with the Global Warming Potential (GWP) criterion only. The mechanical properties of composites made of acrylic resin are affected by the nature of the fibres due to poor impregnation and the presence of porosity. Compared to acrylic resin, PA6 resin achieves higher strength values. This suggests that the pultrusion process for PA6 resin is less challenging, as it minimizes the occurrence of porosity. As expected, better properties were obtained with carbon fibres, albeit at a significantly higher ecological cost. Configurations involving basalt fibres offer the best ecological cost/performance ratio. Therefore, basalt fibres open up new possibilities for designing and sizing the next generation of composite railways.

## 1. Introduction

In the context of the ongoing challenge of reducing carbon emissions, adopting sustainable transport methods seems to be the way forward. In France, for example, 30 % of national CO₂ emissions in 2021 came from internal transport. Of this figure, 94.9 % came from road transport, with 53 % coming from cars and 27 % from heavy goods vehicles carrying passengers and freight [1]. Between 1990 and 2021, the volume of freight transported by truck increased by 15.1 %. Consequently, the ADEME "INFRALight" project is studying a new local transport system that uses light trains for local services and light, lowcarbon infrastructure (see Fig. 1(a) and reference [2]). This system requires lightweight rail tracks to be designed; for instance, composite materials could be used. Reducing the weight of rail tracks would make them easier to install and maintain, and the infrastructure could be functionalized by embedding sensors. Furthermore, economic and ecological costs must be considered as central factors in the design of this new composite product. According to Chanes de Souza et al. [3], composite materials can be used for two main elements: railway infrastructure (e.g., sleepers, rail

clips, rail bolts and rail tie plates) and railcars (e.g., train structures, toilet modules and vestibule panels). Classical railway infrastructure can be schematized as shown in Fig. 1(b) below. A subgrade is prepared directly on the ground. Sub-ballast and ballast made of stones are then filled in to absorb vibrations and keep the tracks in position. Then, sleepers are added and affixed to the rails.

Thompson et al. [4] have performed a life cycle cost and economic comparison between traditional concrete and wood sleepers, and new short and long fibre composite materials. Their results show that composite sleepers made using recycled short fibres can be produced at a cost comparable to concrete sleepers. The mechanical and structural properties of sleepers made of glass fibres and a recycled plastic matrix are investigated in the work of Khalil [5]. Equivalent or better mechanical properties compared to traditional sleepers are achieved. A review by Arafat and Imam [6] on the suitability of recycled materials for composite sleepers confirms the mechanical resistance of composite material sleepers. To reduce the weight of railcars, many composite materials have been investigated as a substitute for steel, such as areca and sisal plants, and carbon-reinforced hybrid epoxy composites [7], as

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: bruno.castanie@insa-toulouse.fr (B. Castanié).</footnote>
<figure><img src="image_5.png" /><figcaption>Fig. 1. (a) INFRAlight Concept and (b) traditional ballasted rail track [3].</figcaption></figure>

well as glass fibre-reinforced polymers (GFRP) panels [8]. Zinno et al. [9] studied composite sandwich structures for the roof of a railway vehicle. Similarly, the design of a carbon fibre sandwich panel for the floor of high-speed train sets was investigated. Ultimately, it was demonstrated that this design was 35.7 % lighter than the metallic structures usually used in the rail industry [10]. Mistry et al. [11] designed a train axle. Switching from a conventional steel part to a composite axle achieved a weight reduction of 75 %. The axle's mechanical strength was assessed using structural analysis of the axle with finite elements. Ultimately, a generic design methodology for similar composite parts was developed [12]. Recently, an innovative, lightweight rural train (Draisy) and system were designed to reuse the 9,000 km of 'fine service' lines in France with a minimum of investment in infrastructure [13]. This research is related to this type of solution, providing a low-cost, low-carbon emission alternative for railway tracks. These examples demonstrate that, as in the aerospace sector [14], composites can be used in rail transportation as a viable alternative to conventional designs.

The few examples presented above illustrate the use of composite materials in the railway sector. With regard to the railway track, much research is being conducted into the design of composite sleepers. However, at the authors' best knowledge there is no research specifically on composite train rail track with a focus on mechanical performance and ecological/economical cost ratio. Developing such an innovation using a composite made of thermoplastic resin and natural fibres could drastically reduce CO₂ emissions throughout the product's entire life cycle, from conception and installation to dismantling and recycling. Nevertheless, the design of innovative composite structures depends on the shape of the products, the materials used, and the manufacturing method [15]. Recent studies demonstrate how manufacturing and post-treatment processes influence the performance and design of composite

products. Yaka et al. show how drilling affects the mechanical properties of basalt fiber-reinforced composites (BFRCs) used in the aerospace, marine, and automotive industries [16]. Al-Nadhari et al. investigated the influence of glass/Kevlar hybridization on the tensile and shear properties of 3D woven composites to improve the design of composite structures [17].

Among the numerous composite manufacturing processes, pultrusion seems the most suitable a priori because of the shape of the rails, and because it enables continuous manufacturing of constant geometries at low cost for large-scale production [18]. This method can be used for straight or curved structures, as illustrated in Fig. 2 [19]. This process has already been investigated for the design of new sleeper reinforcement using GFRP [20]. Thanks to its symmetrical and linear geometry, pultrusion therefore represent a particularly suitable option for railways fabrication.

Designing composite structures such as railway tracks requires knowledge of the elastic properties and strength of the materials used [21]. Despite the large number of papers in the literature related to pultrusion technology and pultruded composite rods, especially in the construction sector and for some applications in aeronautics, there is a lack of data and comparisons devoted to recyclable composite materials with low carbon emissions. To address this gap, the present study investigates the mechanical properties of pultruded composites manufactured using low-environmental-impact resins combined with synthetic and natural fibres. The aim of this work is to develop a comprehensive material data sheet providing stiffness moduli and strength values to support the design of new composite railway components. Reactive matrices allowing in-situ polymerization within the pultrusion die were chosen, since the initial low viscosity of these systems facilitates fibre impregnation during this process. The acrylic-based resin obtained from the Elium® reactive system developed by Arkema was selected due to its recyclability. Once polymerized, this acrylic resin can replace commonly used epoxy resins in highly loaded applications, as it exhibits a glass transition temperature of about 105 °C, a rigid elastic behavior and is recyclable [22]. This resin has been studied and applied in offshore renewable energy applications [23] and marine applications, among others [24]. The second matrix used is polyamide 6, a low-cost thermoplastic resin matrix commonly used in mass production applications [25]. In the present study, the PA6 matrix was obtained via in-situ polymerization of ε-caprolactam [26], which also allows in-situ polymerization within the pultrusion die. Synthetic fibres such as carbon, glass and basalt, as well as natural flax fibres, were embedded in the selected matrices for reinforcement. For comparison purposes with the two low-carbon-footprint resins, a final configuration based on a thermoset epoxy resin reinforced with basalt fibres was also investigated in the transverse direction. Despite the lack of viable recycling solutions for epoxy resins, this configuration allows the use of solvolysis [27] or pyrolysis [28] for reusing basalt fibres at the end of composite life.

The paper is organized as follows: section 2 presents the material configurations and methods while section 3 is devoted to the experimental results and a discussion. Section 4 concludes the paper.

<figure><img src="image_6.png" /><figcaption>Fig. 2. Pultrusion process manufacturing a) Straight pultrusion b) Curved pultrusion [17].</figcaption></figure>
## 2. Materials and methods

### 2.1. Materials a priori selection

The first matrix considered in this study is the Elium® resin obtained by radical polymerization of methyl methacrylate (MMA). The Elium® system contains approximately 80 % MMA and 20 % acrylic oligomers, which can undergo free-radical polymerization with the addition of peroxide initiators. After polymerization, the Elium system leads to a material close to poly methyl methacrylate (PMMA). In the present study, the C195E grade, specifically designed for pultrusion processing, was used. This grade contains a low content of multifunctional acrylic monomer that induces the formation of crosslinks. Their addition in low proportion stabilizes pultrusion processing without compromising the solubility of this infusible thermoplastic matrix in chloroform [29].

Polyamide 6 (PA6) obtained by anionic ring-opening polymerization (AROP) of ε-caprolactam was also selected in this study, as the AROP reaction allows obtaining an actual thermoplastic polymer, which facilitates the end-of-life recycling of composite parts. The AROP reaction is well adapted to the pultrusion process, since it is thermally activated and initiated thanks to the combination of a catalyst and an activator [26]. One configuration with an epoxy matrix in conjunction with basalt fibres was selected to enable comparison of the effect of resins on mechanical properties. Three other fibres were studied: carbon fibre, which was used as a reference despite its high cost; glass fibre, which is the most common and least expensive; and flax fibre, which is a natural fibre.

The properties of each material can be summarized for resins and fibres, respectively, in Tables 1 and 2, according to the manufacturer's data sheets, which are available in the supplementary materials. Prior to sample production, the project's industrial partners verified the number of threads and the fibre linear mass.

Unidirectional samples were prepared by pultruding different combinations of fibres and matrices at speeds ranging from 0.3 to 0.5 m/min. This study analyses seven configurations, which are detailed in Table 3. The samples were delivered as rectangular rods with a width of 100 mm and a thickness of 2–3 mm, depending on the manufacturer (see Fig. 3). Specimens were then cut from the rods using a 4 mm saw.

### 2.2. Fibre fraction and void content determination

The composite's fibre volume ratio and void content are determined using the triple weighing method. It requires the knowledge of the following material properties and processing parameters available in Table 1 and Table 2: the fibre density $ρ_f$, the matrix density $ρ_m$, the fibre linear mass $μ$ and the number of threads in the pultruded composite $n_f$. For each configuration, four composite's samples of 1 x 1 cm² taken from pultruded coupons are weighed in air ($m_c^{air}$) and water ($m_c^{water}$). The true density of the composite ($ρ_c$) can then be calculated using water density ($ρ_{water}$) with Eq. (1).

$$ρ_c = ρ_{water} \frac{m_c^{air}}{m_c^{air} - m_c^{water}} \quad (1)$$

The third weighing gives the mass of a pultruded composite ($m_c$) of known length ($l_c$) and enables to calculate the total fibres mass in the composite ($m_f$) and the fibre weight ratio ($W_f$), using Eqs. (2) and (3).

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

Elium®, PA6 and Epoxy resins properties after polymerization.</caption><thead><tr><th>Resins</th><th>Resin references</th><th>ρ<sub>m</sub> [g/cm<sup>3</sup>]</th><th>E<sub>m</sub> [GPa]</th><th>σ<sub>m</sub> [MPa]</th></tr></thead><tbody><tr><td>Elium®</td><td>C195 E</td><td>1.13</td><td>3.2</td><td>66</td></tr><tr><td>PA6</td><td>From caprolactame</td><td>1.14</td><td>3.3</td><td>79</td></tr><tr><td>Epoxy</td><td>LITESTONE 3400E/3102H</td><td>1.2</td><td>2.7</td><td>65</td></tr></tbody></table>

$$m_f = l_c \cdot μ \quad (2)$$

$$W_f = \frac{m_f}{m_c} \quad (3)$$

The fibre volume ratio ($V_f$) can then be calculated with Eq. (4):

$$V_f = W_f \frac{ρ_c}{ρ_f} \quad (4)$$

Void content ($V_v$) is calculated from the theoretical density of the composite ($ρ_c^{theo}$) assuming the sample free from porosity (Eqs. (5) and (6)).

$$ρ_c^{theo} = \frac{1}{\frac{1 - W_f}{ρ_r} + \frac{W_f}{ρ_f}} \quad (5)$$

$$V_v = \frac{ρ_c^{theo} - ρ_c}{ρ_c^{theo}} \quad (6)$$

As shown in Table 4, although pultrusion is the most technically and economically suitable process for manufacturing composite rails owing to their considerable length and constant cross-section, the low pressure inherent to this process makes it difficult to limit void formation below 2 vol%. In particular, configurations based on the acrylic resin system exhibit significantly higher porosity levels than those manufactured with PA6 or epoxy matrices.

This increased void content can be considered intrinsic to the acrylic system when processed by pultrusion. Methyl methacrylate (MMA) is a highly volatile monomer, with a saturation temperature of 103.1 °C [30], which is lower than the processing temperature used for manufacturing the acrylic plates (approximately 110 °C). In addition, the acrylic system undergoes substantial chemical shrinkage during polymerization. Considering the density increase from MMA (0.94 g/cm³ [31]) to PMMA (1.21 g/cm³ [32]), polymerization induces a volumetric shrinkage of nearly 20 % even when assuming a MMA mass ratio of 80 %, thereby promoting pore nucleation and growth in a process where material compaction remains limited.

As a result, the porosity levels measured in pultruded acrylic-based samples are consistent with the combined effects of monomer volatility, chemical shrinkage, and the low-pressure nature of the pultrusion process. These porosity levels are explicitly accounted for in the rail sizing methodology, and the resulting mechanical properties are therefore considered conservative.

The micrograph of the C2 sample (Acrylic/glass) cross-section shown in Fig. 4 confirms the presence of a high density of pores with significantly larger sizes than those observed in the PA6/glass composite. In the reinforced PA6 material, porosity remains relatively homogeneous over the entire cross-section, except for a few large pores located in the sample core. By contrast, the C2 sample exhibits distinct porous bands extending through the material thickness, suggesting the presence of preferential weak planes in the pultruded composite, potentially oriented along the XZ or XY directions. The origin of this pore alignment is not straightforward to identify, but it may be related to the accommodation of polymerization shrinkage within the material. A delayed polymerization of the core relative to the skins, which solidifies first during the pultrusion process, could promote the formation and alignment of pores along specific planes.
<caption>**Table 2**</caption>

Carbon, Glass, Basalt and Flax fibres properties according to Manufacturers with $ρ_m$ the matrix density, $ρ_f$ the fibre density, $E_m$ the matrix tensile strength, $E_f$ the fibre tensile modulus, $σ_m$ the fibre tensile strength, $n_f$ the number of threads in the pultruded composite and $μ$ the fibre linear mass.

<table><caption>**Table 3**</caption><thead><tr><th>Fibres</th><th>Fibres references</th><th>ρ<sub>f</sub> [g/cm<sup>3</sup>]</th><th>n<sub>f</sub></th><th>μ [Tex]</th><th>E<sub>f</sub> [GPa]</th><th>σ<sub>f</sub> [MPa]</th></tr></thead><tbody><tr><td>Carbon fibres</td><td>SIGRAFIL® C T50-4.0/240</td><td>1.8</td><td>110</td><td>3300</td><td>240</td><td>4000</td></tr><tr><td>Glass fibres</td><td>PULSTRAND® 4100</td><td>2.6</td><td>74</td><td>4800</td><td>75</td><td>2100</td></tr><tr><td>Glass fibres</td><td>JM STARROV® 086</td><td>2.6</td><td>60</td><td>2400</td><td>75</td><td>2100</td></tr><tr><td>Basalt fibres</td><td>BASALTEX® 2400tex</td><td>2.67</td><td>216</td><td>2400</td><td>85</td><td>2900</td></tr><tr><td>Flax fibres</td><td>LINCORE® 2400tex</td><td>1.45</td><td>110</td><td>2400</td><td>60</td><td>800</td></tr></tbody></table>

Pultruded rods configurations.

<table><thead><tr><th>Configurations</th><th>Resin</th><th>Resin references</th><th>Fibres</th><th>Fibre references</th><th>Thickness</th><th>Pultrusion speed</th></tr></thead><tbody><tr><td>C-1</td><td>Elium®</td><td>C195 E</td><td>Carbon</td><td>SIGRAFIL® C T50-4.0/240</td><td>3 mm</td><td>0.3 m/min</td></tr><tr><td>C-2</td><td>Elium®</td><td>C195 E</td><td>Glass</td><td>PULSTRAND® 4100</td><td>2 mm</td><td>0.3 m/min</td></tr><tr><td>C-3</td><td>Elium®</td><td>C195 E</td><td>Basalt</td><td>BASALTEX® 2400tex</td><td>3 mm</td><td>0.3 m/min</td></tr><tr><td>C-4</td><td>Elium®</td><td>C195 E</td><td>Flax</td><td>LINCORE® 2400tex</td><td>3 mm</td><td>0.3 m/min</td></tr><tr><td>C-5</td><td>PA6</td><td>☒-caprolactame</td><td>Glass</td><td>JM STARROV® 086</td><td>2 mm</td><td>0.5 m/min</td></tr><tr><td>C-6</td><td>PA6</td><td>☒-caprolactame</td><td>Carbon</td><td>SIGRAFIL® C T50 4.0/240</td><td>2 mm</td><td>0.5 m/min</td></tr><tr><td>C-7</td><td>Epoxy</td><td>LITESTONE 3400E/3102H</td><td>Basalt</td><td>BASALTEX® 2400tex</td><td>3 mm</td><td>0.3 m/min</td></tr></tbody></table>

<figure><img src="image_7.png" /><figcaption>**Fig. 3.** Rectangular rods from manufacturers a) Acrylic/Flax b) PA6/glass c) Acrylic/carbon.</figcaption></figure>

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

Fibre fraction and void fraction for each configuration determined using tripled weighting method.

<table><thead><tr><th>Configurations</th><th>Resin</th><th>Fibres</th><th>Fibre fraction V<sub>f</sub> [%]</th><th>Void V<sub>v</sub> [%]</th></tr></thead><tbody><tr><td>C-1</td><td>Acrylic</td><td>Carbon</td><td>68.8</td><td>3.3 ± 0.05</td></tr><tr><td>C-2</td><td>Acrylic</td><td>Glass</td><td>69.0</td><td>3.6 ± 0.32</td></tr><tr><td>C-3</td><td>Acrylic</td><td>Basalt</td><td>66.5</td><td>4.2 ± 0.47</td></tr><tr><td>C-4</td><td>Acrylic</td><td>Flax</td><td>61.7</td><td>7.0 ± 0.02</td></tr><tr><td>C-5</td><td>PA6</td><td>Glass</td><td>62.1</td><td>3.8 ± 0.08</td></tr><tr><td>C-6</td><td>PA6</td><td>Carbon</td><td>69.8</td><td>1.8 ± 0.22</td></tr><tr><td>C-7</td><td>Epoxy</td><td>Basalt</td><td>65.1</td><td>2.4 ± 0.17</td></tr></tbody></table>

In addition, the micrographs suggest that the actual porosity level of the C2 sample may be higher than the value measured using the triple weighing method. This discrepancy is likely associated with the presence of open porosity, which is not accurately captured by density-based measurements. During immersion in water, open pores may become filled, leading to an overestimation of the apparent density and, consequently, to an underestimation of the true porosity content. Although the triple weighing method may therefore introduce some uncertainty

related to fibre volume fraction variations or open porosity, it was retained in this study because it can be consistently applied to all material configurations investigated, ensuring a meaningful comparison between composite systems.

## 2.3. Expected tensile moduli and tensile strengths

To compare the experimentally obtained properties with the ex-
<figure><img src="image_8.png" /><figcaption>Fig. 4. Micrographic analysis of the cross-section of pultruded material a) Acrylic/Glass b) PA6/Glass. Fibers are along the X-axis.</figcaption></figure>

pected mechanical properties of each configuration, the Young's modulus and strength in the longitudinal and transverse directions are calculated theoretically using the mixture law [33]:

$$V_f + V_m + V_v = 1 \qquad (7)$$

$$E_{\text{longitudinal}} = E_m \cdot V_m + E_f \cdot V_f \qquad (8)$$

$$\sigma_{\text{longitudinal}} = \sigma_m \cdot V_m + \sigma_f \cdot V_f \qquad (9)$$

$$E_{\text{transversal}} = \frac{E_f \cdot E_m}{V_f \cdot E_m + V_m \cdot E_f} \qquad (10)$$

$$\sigma_{\text{transversal}} = \sigma_m \cdot (1 - V_v) \qquad (11)$$

With the fibre volume fraction $V_f$, the matrix volume $V_m$, the void volume $V_v$, the matrix Young modulus $E_m$ and the fibre Young modulus $E_f$. It should be noted that the strength of the specimen depends on its failure scenario and can lead to significant differences with the theoretical values especially for $\sigma_t$. The results are provided Table 5.

## 2.4. Economical and ecological impact

In order to design a low-carbon, affordable solution for railway tracks, it would be interesting to conduct a life cycle cost and economic comparison between traditional materials, such as steel, and composite

materials that have been selected in advance. Life cycle assessment (LCA) enables the potential environmental impact of a product to be determined throughout its life cycle [34]. This analysis can focus on the partial life of a product, from extraction to the factory gate ('cradle-to-gate'), or on the full life of the product, from extraction to use and disposal ('cradle-to-grave') [35]. LCAs produce many indicators, such as acidification potential, eutrophication potential and stratospheric ozone depletion [36]. However, results may vary depending on factors such as the country of production, the energy source used, or the mode of transport employed to deliver the material [37]. Due to the complexity of the LCA approach and the lack of knowledge regarding the recycling methods for the finished product, a cradle-to-gate approach has been chosen for this study. Therefore, only the Global Warming Potential (GWP) criterion will be presented to provide a comparison of equivalent CO₂ emissions for the seven material configurations. Several sources from the literature are presented for each material (Table 6). For each material, all data from the same source is averaged. Then, an average value is calculated using data from different sources to provide an estimate of the carbon cost emission of each configuration.

In terms of economic costs, the price of each raw material depends heavily on the market and the country of production. Therefore, an estimate cost was made (see Table 6) by comparing prices from several industrial manufacturers in the European market in 2025. The aim is to obtain a representative estimate. Regarding acrylic resin, Arkema states

<caption>**Table 5**</caption>

Theoretical tensile modulus and tensile strength for each configuration. $E_1$ is the longitudinal tensile modulus, $\sigma_1$ the longitudinal tensile strength, $E_t$ the transversal tensile modulus and $\sigma_t$ the transversal tensile strength.

<table><thead><tr><th>Configurations</th><th>Resin</th><th>Fibres</th><th>Theoretical E<sub>1</sub> [GPa]</th><th>Theoretical σ<sub>1</sub> [MPa]</th><th>Theoretical E<sub>t</sub> [GPa]</th><th>Theoretical σ<sub>t</sub> [MPa]</th></tr></thead><tbody><tr><td>C-1</td><td>Acrylic</td><td>Carbon</td><td>165.0</td><td>2,750</td><td>11.0</td><td>64</td></tr><tr><td>C-2</td><td>Acrylic</td><td>Glass</td><td>52.6</td><td>1,450</td><td>10.5</td><td>64</td></tr><tr><td>C-3</td><td>Acrylic</td><td>Basalt</td><td>57.5</td><td>1,950</td><td>10.0</td><td>63</td></tr><tr><td>C-4</td><td>Acrylic</td><td>Flax</td><td>38.0</td><td>515</td><td>9.2</td><td>61</td></tr><tr><td>C-5</td><td>PA6</td><td>Glass</td><td>47.7</td><td>1,330</td><td>8.9</td><td>76</td></tr><tr><td>C-6</td><td>PA6</td><td>Carbon</td><td>168.5</td><td>2,800</td><td>11.2</td><td>78</td></tr><tr><td>C-7</td><td>Epoxy</td><td>Basalt</td><td>56.2</td><td>1,900</td><td>7.8</td><td>63</td></tr></tbody></table>
<caption>**Table 6**</caption>

Estimate global warming potential in cradle-to-gate analysis and estimate cost for all material (¹ This data is taken from a report produced by EcovaMed at Arkema's request and, at the authors' best knowledge, has not been verified in the literature).

<table><thead><tr><th>Materials</th><th>GWP [kg CO<sub>2</sub>eq/kg]</th><th>References</th><th>Average [kg CO<sub>2</sub>eq/kg]</th><th>Estimate price [€/kg]</th></tr></thead><tbody><tr><td rowspan="2">Steel</td><td>2.00</td><td>[38]</td><td rowspan="2">2.2</td><td rowspan="2">0.8</td></tr><tr><td>2.30</td><td>[39]</td></tr><tr><td rowspan="3">Epoxy resin</td><td>2.00 – 10.15</td><td>[37]</td><td rowspan="3">6.8</td><td rowspan="3">10.0</td></tr><tr><td>6.73 – 8.60</td><td>[40]</td></tr><tr><td>6.70</td><td>[41]</td></tr><tr><td>Elium® resin</td><td>4.30</td><td>[42]<sup>1</sup></td><td>4.3</td><td>10.0</td></tr><tr><td rowspan="3">PA6 resin (from caprolactame)</td><td>3.30 – 5.50</td><td>From Europe [43]</td><td rowspan="3">8.8</td><td rowspan="3">5.0</td></tr><tr><td>11.00 – 20.00</td><td>From China [43]</td></tr><tr><td>6.00 – 7.00</td><td>[44]</td></tr><tr><td rowspan="4">Carbon fibres</td><td>26.40 – 49.10</td><td>[40]</td><td rowspan="4">34.0</td><td rowspan="4">20.0</td></tr><tr><td>24.50</td><td>[45]</td></tr><tr><td>38.90</td><td>[46]</td></tr><tr><td>0.24 – 3.73</td><td>[37]</td></tr><tr><td rowspan="2">Glass fibres</td><td>1.98</td><td>[46]</td><td rowspan="2">1.9</td><td rowspan="2">1.5</td></tr><tr><td>1.70</td><td>[47]</td></tr><tr><td rowspan="2">Basalt fibres</td><td>0.40</td><td>[47]</td><td rowspan="2">0.5</td><td rowspan="2">4.0</td></tr><tr><td>0.15 – 1.00</td><td>[40]</td></tr><tr><td rowspan="2">Flax fibres</td><td>1.40</td><td>[48]</td><td rowspan="2">0.9</td><td rowspan="2">4.0</td></tr><tr><td>0.35</td><td>[49]</td></tr></tbody></table>

that its price is comparable to that of thermoset epoxy resins currently on the market [50].

Fig. 5 (a) presents the results more clearly. Basalt fibres have the lowest GWP. This fibre is considered a natural material because it is simply made from rocks, which are abundant on Earth [47].

Furthermore, despite the heating necessary to melt the rocks, the manufacturing method is less energy-consuming than that used for glass and carbon fibres. Despite their natural origin, the necessary treatment for flax fibres seems to be detrimental. Carbon fibres exhibit the highest GWP and costs. Nevertheless, these fibres are used in aviation because their contribution to GWP during manufacturing is negligible compared to the carbon emissions produced by an aircraft over its lifetime [14]. Petrol-based resins are still the most widely available with sufficient mechanical properties; however, this analysis shows that their GWP is significant and even higher than that of fibres.

To enable comparison with conventional steel railway tracks, calculations were made based on the fibre-to-resin ratio of each configuration listed in Table 4, and the results are presented in Fig. 5 (b) in terms of linear meters of rail. The actual design of the composite rail tracks cannot be disclosed until the patent is published. However, this comparative study considers a mass of 15 kg/m for the composite solution, compared to a mass of 50 kg/m for a conventional steel rail. This mass corresponds to the initial sizing and design calculations for the composite rail in the project.

According to these results, all configurations without carbon fibres appear to be more advantageous than the conventional steel solution. Solutions incorporating basalt fibres appear to be the most promising option for achieving CO₂ emission reduction targets. From an economic point of view, solution C5 (PA6/glass) appears to be equivalent to the steel solution. Once the mechanical characteristics have been obtained, the carbon cost/performance ratio will be presented and discussed in Section 3.

## 2.5. Mechanical testing methods

The properties of pultruded composites that were investigated are the orthotropic modulus: Eᵢ, Eᵣ = Eᵤ, Gᵢt = Gᵤz, Gᵣt, Poisson's ratios: νᵢt = νᵤz, νᵣt, and mechanical strength: σᵢ₁, σᵣ₁, σᵤ₁, σᵣ₄, τᵢt = τᵤz and τᵣt. Tensile and

<figure><img src="image_9.png" /><figcaption>**Fig. 5.** (a) Estimate GWP and economic cost per 1 kg for each single material used (b) GWP and economic cost of raw materials for 1 m of rail.</figcaption></figure>
compression tests are performed to determine these properties. The dimensions of the specimens are defined by the NF EN ISO 527-4 standard [51] for tensile tests. For the compression test, ASTM 3410 [52] serves as a basis, but must be adapted for the transverse compression $\sigma_x^t$ due to the manufacturing process of the rod (see Fig. 3) with a width of only 100 mm. Due to the same geometric constraints, the angle of the fibres for determining shear properties is 10°, according to the Composite Material Handbook CMH-17 [53]. This configuration is preferable to a 45° angle, which cannot be manufactured for this study. While this configuration enables the characterization of intralaminar shear, this approach has limitations that must be considered. At such a small off-axis angle, the mechanical response is largely dominated by the fibers. Stiffness and strength are mainly governed by their longitudinal properties [53,54]. Additionally, the measured shear deformation component remains relatively low, reducing the sensitivity of the measurement to shear and increasing the influence of experimental noise [55]. Consequently, the obtained shear properties require careful interpretation to account for edge effects and stress heterogeneity in the sample.

Shear stress and shear modulus are calculated using Eqs. (12) and (13) where $c = \cos(\Theta)$, $s = \sin(\Theta)$ and $\Theta$ is the fibre angle. Other variables are $\varepsilon_x$ the strain, $\sigma_x$ the stress, $E_t$ the longitudinal Young modulus, $E_t$ the transversal Young modulus and $\nu_{lt}$ the Poisson's ratio.

$$ \tau_{lt} = -s.c.\sigma_x \quad (12) $$

$$ G_{lt} = \left[ \frac{\varepsilon_x}{c^2 \cdot s^2 \cdot \sigma_x} - \frac{c^2}{s^2 \cdot E_t} + \frac{2 \cdot \nu_{lt}}{E_t} - \frac{s^2}{c^2 \cdot E_t} \right]^{-1} \quad (13) $$

According to the standards, aluminum or glass fibre tabs, each 1.5 mm thick, are added to each sample. Araldite® 2015 is used as an adhesive for acrylic and epoxy resin, and Araldite® 2021 is used for PA6 resin. Tensile and compression tests are performed using INSTRON 8862 tensile testing equipment with a capacity of 100 kN at a crosshead speed of 1 mm/min. Table 7 summarizes the test configurations, identifying the type of loading, fibre orientation and mechanical properties for each.

Digital Image Correlation (DIC) was used in stereo-correlation mode for the displacement measurement. This allowed the positioning of the specimens and the alignment of the jaws to be checked. The aim of using DIC was also to validate the uniaxial plane character of the tests performed, based on the authors' past experience with complex natural materials [56]. The speckles were created using spray paint cans (Fig. 1 (a). in supplementary materials). VIC-3D software from Correlation Solutions® was used to process the data (Fig. 1(b). in supplementary materials).

### 3. Experimental results and discussion

The experimental results are presented in four distinct sections. The first section details the results of transverse tensile and compression tests on different composites containing the same resin, in order to assess the influence of the fibres on Young's modulus and strength. The latter is assumed to characterize the stress at break of the acrylic or PA6 matrix. The second section examines the mechanical properties of composites pultruded with carbon, glass, and basalt fibres in the longitudinal direction, in order to analyze the influence of the resin on strength in the fibre direction. The third section compares the influence of the resin on intralaminar properties for the same fibre, presenting off-axis results.

The final section summarizes all the mechanical properties and compares all material configurations using radar charts. Almost all the stress-strain curves are linear with brittle failure, they are of little interest so the authors chose to present them only in the supplementary materials.

#### 3.1. Transverse tensile and compressive test results

##### 3.1.1. Composites made with acrylic-based resin

Regarding the tensile tests in the transverse direction, the Young's modulus of C1 (carbon fibres) and C2 (glass fibres), as shown in Fig. 6, are lower than the theoretical modulus determined using the mixture law (11.0 GPa and 10.5 GPa, respectively). Conversely, for C3 (basalt fibres), the modulus obtained is higher than the theoretical value: 12.0 GPa versus 10.0 GPa. For C4 (flax fibres), the experimental modulus is significantly lower than the theoretical calculation (2.2 GPa vs. 9.2 GPa). As shown in Table 8, this configuration exhibits the greatest discrepancy between the theoretical and experimental values: -76.1 %.

However, when scatter is taken into account as shown in figure 6, the experimentally obtained values are found to be consistent with the theoretical values, except for the C4 configuration, C1 in traction and C3 in compression. The results are generally more dispersed in compression than in tension. The maximum stress at failure also varies from one configuration to another. With fracture occurring at 26 MPa, the C1 configuration achieves the highest tensile strength. For all configurations, the experimental results obtained are below the theoretical calculations (64 MPa for C1 and C2, 63 MPa for C3, and 61 MPa for C4).

The observed mechanical differences between the composite specimens may be influenced by variations in fiber-matrix interfacial adhesion. Recent studies on acrylic-based matrix composites have shown that glass fibers have better wettability and load transfer at the interface than carbon, basalt, or aramid fibers [57]. Although the present study does not quantify interfacial properties, these findings suggest that interface quality may contribute to the reported mechanical behavior, in conjunction with porosity.

Since the porosity rates are almost identical for configurations C1, C2 and C3 (configuration C4 has a rate twice as high), the disparity in results can be explained by the location of the porosities within the samples. This location is influenced by the pultrusion process or fibre impregnation [58,59]. As illustrated in Fig. 4 for configuration C2 (glass fibres), porosity lines running across the sample from one surface to another create an initial phase of brittleness, resulting in early tensile failure in the XZ plane.

Additionally, the fibre type affects the impregnation of the acrylic-based resin during the pultrusion process. As shown in Fig. 2 (supplementary materials), the presence of dry fibres in configurations C2 (glass fibres) and C4 (flax fibres) indicates poor impregnation and decreased mechanical properties. Issues with fiber impregnation and porosity location result in a significant discrepancy between the theoretical and experimental values of transverse tensile strength: -85.9 % for configuration C2 and -90.2 % for configuration C4, as shown in Table 8.

These experimental results show that glass and flax fibres have a negative impact on the transversal strength of the composite with acrylic resin. Furthermore, the mechanical and physical properties of natural fibres derived from plants (such as flax) can vary from one location and

<table><caption>**Table 7**
Orientation, properties, standard, dimensions and quantity of specimens for each configuration.</caption><thead><tr><th>Test</th><th>Orientation</th><th>Properties</th><th>Standard</th><th>Dimensions [mm]</th><th>Number of samples</th></tr></thead><tbody><tr><td>Tensile</td><td>longitudinal</td><td>σ<sub>1</sub><sup>l</sup>, E<sub>1</sub><sup>l</sup>, ν<sub>lt</sub></td><td>ISO 527-4</td><td>250 x 25</td><td>5</td></tr><tr><td>Tensile</td><td>transversal</td><td>σ<sub>1</sub><sup>t</sup>, E<sub>1</sub><sup>t</sup>, ν<sub>tz</sub></td><td>ISO 527-4</td><td>100 x 25</td><td>5</td></tr><tr><td>Tensile</td><td>Off-axis</td><td>G<sub>lt</sub>, τ<sub>lt</sub></td><td>ISO 527-4</td><td>250 x 25</td><td>5</td></tr><tr><td>Compression</td><td>longitudinal</td><td>σ<sub>1</sub><sup>l</sup>, E<sub>1</sub><sup>l</sup></td><td>ASTM 3410</td><td>110 x 10</td><td>5</td></tr><tr><td>Compression</td><td>transversal</td><td>σ<sub>1</sub><sup>t</sup>, E<sub>1</sub><sup>t</sup></td><td>ASTM 3410</td><td>100 x 25</td><td>5</td></tr></tbody></table>
<figure><img src="image_10.png" /><figcaption>Fig. 6. Young modulus and stress at failure of acrylic matrix composite materials in transverse direction.</figcaption></figure>

<table><caption>**Table 8**
Relative gap between theoretical and experimental stiffnesses and strength of acrylic matrix composite materials in transverse direction.</caption><thead><tr><th>Configurations</th><th>Theoretical Young Modulus E<sub>1</sub><sup>1</sup> [GPa]</th><th>Experimental Young Modulus E<sub>1</sub><sup>1</sup> [GPa]</th><th>Relative gap [%]</th><th>Theoretical strength σ<sub>1</sub><sup>1</sup> [MPa]</th><th>Experimental strength σ<sub>1</sub><sup>1</sup> [MPa]</th><th>Relative gap [%]</th></tr></thead><tbody><tr><td>C-1</td><td>11.0</td><td>7.8</td><td><span style="color:red;">-29.1</span></td><td>64</td><td>26.0</td><td><span style="color:red;">-59.4</span></td></tr><tr><td>C-2</td><td>10.5</td><td>8.5</td><td><span style="color:red;">-19.0</span></td><td>64</td><td>9.0</td><td><span style="color:red;">-85.9</span></td></tr><tr><td>C-3</td><td>10.0</td><td>12.0</td><td><span style="color:red;">+20.0</span></td><td>63</td><td>15.0</td><td><span style="color:red;">-76.2</span></td></tr><tr><td>C-4</td><td>9.2</td><td>2.2</td><td><span style="color:red;">-76.1</span></td><td>61</td><td>6.0</td><td><span style="color:red;">-90.2</span></td></tr></tbody></table>

harvest to another, which can lead to high variability in the results [60].

The same type of disparity can be observed between fibres in the compression test results, mainly with the C4 configuration (flax fibre) at the bottom of the ranking. However, these variations are less significant than in tension tests. This is because the application of stress results in the closure of the voids, thereby minimizing the effect on the ultimate stress. The strengths of C1 (carbon fibres), C2 (glass fibres) and C3 (basalt fibres) are virtually equivalent at 105 MPa. As illustrated in Fig. 3 (supplementary materials), the failure modes are acceptable according to standard: “through thickness at grip top” (HAT) for C1 (carbon fibres), C2 (glass fibres) and C3 (basalt fibres), and “brooming gage middle” (BGM) for C4 (flax fibres).

In conclusion, the nature of the fibre affects the results of transversal tensile and compression tests for configurations using acrylic resin. Fibre/resin impregnation and the presence of porosity directly impact the behaviour of the composite material in this direction. Configuration C4 with flax fibres achieves the lowest results in the series due to its high porosity and low strength. Configuration C2 (glass fibres) shows significant variability in results (±150 % for $E_1^c$ ±80 % for $\sigma_1^c$ and ±40 % for $E_1^t$) due to the specific localization of porosity throughout the samples. Compared to the others, configuration C3 with basalt fibres achieves modest tensile strength results (equivalent in compression except for C2 and +40 % and +60 % compared to C2 and C4 in traction), but greater stiffness. Finally, as expected, the configuration with carbon fibres achieves the best results in terms of tensile and compressive strength.

### 3.1.2. Composites made with PA6 resin

For the transverse tensile test, the Young's modulus for the C5 configuration (PA6 glass fibres) is consistent with the theoretical calculation (8.9 GPa). Fig. 7 shows that the stiffness obtained for the C6 configuration (carbon fibres) is lower than the Young's modulus obtained using the rule of mixtures: 6.25 GPa versus 11.20 GPa, but this is consistent with the literature [61]. Greater dispersion is also present under compression with PA6 resin (±12 % for C5 and ±19 % for C6), though this is less significant than with acrylic resin (up to ±40 % for C2). This can be explained by the slightly lower porosity of these configurations, as well as their location within the sample, as illustrated in Fig. 4. Conversely, this configuration achieves the best tensile and compressive strengths. The failure modes are acceptable according to the standard, as shown in Fig. 4 (supplementary materials). Compared to acrylic resin, PA6 resin achieves higher strength values. These results suggest that the pultrusion process for PA6 resin is less challenging, as it minimizes the occurrence of porosity.

## 3.2. Longitudinal tensile and compressive test results

### 3.2.1. Composites with carbon fibres

As can be seen from Fig. 8, the results show similar values for Young's modulus in tension and compression. The value obtained for C1 (acrylic resin) is consistent with the theoretical determination of 165.0 GPa, with low dispersion. For this configuration, the stiffness value in
<figure><img src="image_11.png" /><figcaption>Fig. 7. Young modulus and stress at break of PA6 matrix composite materials in transverse direction.</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>Fig. 8. Young modulus and stress at break for carbon fibres in longitudinal direction.</figcaption></figure>

compression is lower than that obtained in tension. The Young's modulus for C6 (PA6 resin) is significantly lower than the theoretical value of 168.5 GPa, with a high dispersion rate. This is probably due to slight slippage of the two test pieces in the jaws during the test. The obtained curves are linear, with brittle failure. Unlike C1, the stiffness value obtained under tension is lower than that obtained under compression.

Furthermore, there is a difference in tensile and compressive strength between these two configurations. We report a 50 % reduction in tensile strength for the acrylic resin configuration compared to PA6 resin. This strength is lower than that reported in the literature for C1 [62] and equivalent to that for C6 [61,63]. These results can be explained by a significantly higher level of porosity: almost twice as much as expected in configuration C1 (3.3 %) compared to configuration C6 (1.8 %). Additionally, as shown in Fig. 4, the acrylic resin

promotes the formation of pore lines either through the thickness of the material or parallel to the plane of the pultruded plates. In contrast, the porosity in the PA6 matrix is much more uniformly distributed across the entire cross-section and not only at mid-thickness. This difference could account for the earlier breakdown of the C1 configuration.

The rupture modes observed for these two configurations differ. As illustrated in Fig. 5 (supplementary materials), fibre failure was observed under a tensile test and kinking failure under a compressive test for C6 (PA6 resin). In contrast, failure in both the tensile and compressive tests appears to be initiated by shear or compression of the resin in configuration C1 (acrylic resin). The presence and location of porosity in this configuration could lead to this rupture mode. Improving the manufacturing process would reduce porosity and significantly enhance the material's mechanical properties. However, a porosity rate of less than 10 % should not have a significant impact on the
longitudinal tensile properties [64]. This mode of failure may therefore
be explained by potentials issues with specimen preparation.

3.2.2. Composites with glass fibres

As can be seen in Fig. 9, the Young's modulus obtained in tension and
compression is equivalent for both configurations. The tensile and
compressive strengths are higher for C2 acrylic/glass and are consistent
with those reported in the literature [65,66]. Except for the calculation
of compressive stiffness for configuration C5 (PA6 resin), these results
demonstrate minimal dispersion. As with configurations containing
carbon fibres, the configuration with acrylic resin exhibits greater ten-
sile stiffness than compressive stiffness, in contrast to the stiffness values
obtained for the configuration with PA6 resin. The obtained curves are
linear with brittle stress at break. In compression, configurations C2
(acrylic resin) and C5 (PA6 resin) exhibit an acceptable mode of failure
involving kinking and fibre crushing, as illustrated in Fig. 6
(supplementary materials). The failure mode for C2 (acrylic resin) in
traction demonstrates good tensile behaviour (Fig. 6(a) – supplemen-
tary materials). However, C5 (PA6 resin) exhibits a tensile failure mode
with minimal fibre breakage (Fig. 6(b) – supplementary materials). This
failure is likely to be matrix-controlled, which explains the 20 %
reduction in properties compared to C2 (acrylic resin).

3.2.3. Composites with basalt fibres

Fig. 10 shows the Young's modulus and tensile and compressive
strengths obtained for basalt fibres with acrylic (C3) and epoxy (C7)
resins. These properties are consistent with those reported in the liter-
ature [67,68]. Although they are slightly higher in compression than in
tension, these configurations have low dispersion levels. Unlike con-
figurations involving carbon and glass fibres, the Young's modulus in
tension is lower than in compression. However, the latter's dispersion is
much greater. The obtained curves are linear with brittle stress at break.
The failure modes shown in Fig. 7 (supplementary materials) are
acceptable according to the standard.

3.3. Off-axis tensile test results

3.3.1. Composites with carbon fibres

As with the longitudinal tensile test, Fig. 11 shows that C1 (acrylic
resin) has a lower shear stress at break than C6 (PA6 resin). The presence
of nearly twice the porosity in C1 explains this weakness. The failure

modes shown in Fig. 8 (supplementary materials) are similar for each
configuration and are acceptable.

3.3.2. Composites with glass fibres

In contrast to the results of the longitudinal tensile tests, configura-
tion C5 (PA6 resin) shows greater stress at break in Fig. 12. This can be
explained by the extreme weakness of the acrylic resin in configuration
C2 ($\sigma_t^f = 9$ MPa). Lines of porosity running through the sample signifi-
cantly weaken the material. There is significant dispersion in the results
for both configurations. This may be due to a high porosity rate of
around 4 % for both materials, as well as impregnation issues. Fig. 9
(supplementary materials) depicts the failure mode observed for glass
fibre composites under off-axis loading.

3.3.3. Composites with basalt fibres

As shown in Fig. 13, the configuration C7 (epoxy resin) which is
related to a thermoset matrix, achieves better shear properties. This
indicates that acrylic resin is weaker than epoxy resin, a finding
confirmed by the results from transverse tensile strength $\sigma_t^f$ results ob-
tained: 15 MPa and 42 MPa for C3 (acrylic resin) and C7 (epoxy resin). It
should be noted that there is greater dispersion for the stress at break for
configuration C3 (acrylic resin). This can be explained by the porosity
rate being twice that of configuration C7 (epoxy resin): 4.2 % vs. 2.4 %.
The identical failure mode is shown in Fig. 10 (supplementary materials)
for off-axis loading.

3.4. Summary of results

Table 9 provides a summary of the tensile and compressive stiff-
nesses and strengths for all the studied configurations.

To compare the mechanical properties of each configuration, Fig. 14
show radar charts with normalised stiffness and strength data for lon-
gitudinal, transverse and off-axis orientations in tensile and compressive
tests. For each test, the value obtained for each composite configuration
is divided by the highest value from the seven configurations.

In terms of stiffness, configurations with carbon fibres achieve the
highest values in longitudinal tensile and compressive tests. In this
respect, the results obtained with basalt and glass fibres are equivalent,
regardless of the resin used. In the transverse and off-axis directions, the
configuration with thermoset C7 (epoxy/basalt) resin definitely ach-
ieves the best results. This is closely followed by configuration C3

<figure><img src="image_13.png" /><figcaption>Fig. 9. Young modulus and stress at break for glass fibres in longitudinal direction.</figcaption></figure>
<figure><img src="image_14.png" /><figcaption>Fig. 10. Young modulus and stress at break for basalt fibres in longitudinal direction.</figcaption></figure>

<figure><img src="image_15.png" /><figcaption>Fig. 11. Shear stress at break and shear modulus for C1 and C6.</figcaption></figure>

(acrylic/basalt). The C4 configuration (acrylic/flax) achieves the lowest scores in every direction.

In terms of strength, configuration C7 (epoxy/basalt) achieves the best mechanical properties, except in the longitudinal tensile and off-axis tests, where configuration C6 (PA6/carbon) dominates. It appears that the strength of all configurations using acrylic resin in the longitudinal tensile test is consistent, regardless of the fibres used. This suggests that, for these configurations, the composite's stress at break is not indicative of the fibres' strength, but is instead driven by matrix failure. This is corroborated by the results of the transverse tensile test: although the strengths should be similar for all configurations using the same resin, they are in fact highly variable. As previously mentioned, these significant differences appear to be linked to the high porosity rate of the acrylic resin, which is promoted by the pultrusion process. Additionally, the interaction between the fibre and the resin appears to exacerbate high porosity rates in locations that are more or less favourable to the material's structural integrity. These effects are less pronounced in the

transverse compression test because porosity has a low impact on the results of this test. Finally, configuration C4 (acrylic/flax) achieves the lowest properties due to its high porosity rate and weaker fibre properties compared to glass and basalt.

With the aim of selecting pultruded composite materials for new, low-emission, lightweight railway tracks, and to put the previously discussed results into perspective, Fig. 15 (a) shows the carbon cost/performance ratio. Preliminary rail dimensioning calculations suggest that stress is low in the fibre direction. However, significant compressive stress is observed in the transverse direction. Consequently, the cost/performance ratio focuses on the transverse properties of the composites. For each configuration, the GWP value given in Table 6 is divided by the transverse tensile and compressive strength. The resulting value corresponds to the 'carbon cost' per 1 MPa of transverse strength for each configuration.

These results demonstrate an interesting ratio for configurations with basalt fibres (C3 and C7), with configuration C5 (PA6/glass) close
<figure><img src="image_16.png" /><figcaption>Fig. 12. Shear stress at break and shear modulus for C2 and C5.</figcaption></figure>

<figure><img src="image_17.png" /><figcaption>Fig. 13. Shear stress at break and shear modulus for C3 and C7.</figcaption></figure>

<table><caption>**Table 9**

Stiffnesses and strengths for all configuration.</caption><thead><tr><th></th><th></th><th>C1<br>Acrylic/carbon</th><th>C2<br>Acrylic/glass</th><th>C3<br>Acrylic/basalt</th><th>C4<br>Acrylic/flax</th><th>C5<br>PA6/glass</th><th>C6<br>PA6/carbon</th><th>C7<br>Epoxy/basalt</th></tr></thead><tbody><tr><td rowspan="3">Longitudinal tensile test</td><td>EI<sup>l</sup> (GPa)</td><td>154.0</td><td>57.0</td><td>56.2</td><td>25.0</td><td>49.3</td><td>126.3</td><td>56.0</td></tr><tr><td>σ<sub>f</sub><sup>l</sup> (MPa)</td><td>1 060</td><td>1 050</td><td>1 085</td><td>350</td><td>830</td><td>1 965</td><td>1 095</td></tr><tr><td>ν<sub>lt</sub></td><td>0,39</td><td>0,27</td><td>0,27</td><td>0,45</td><td>0,32</td><td>0,3</td><td>0,27</td></tr><tr><td rowspan="2">Longitudinal compression test</td><td>EI<sup>c</sup> (GPa)</td><td>142.0</td><td>54.5</td><td>57.5</td><td>17.8</td><td>54.8</td><td>138.7</td><td>49.4</td></tr><tr><td>σ<sub>f</sub><sup>c</sup> (MPa)</td><td>795</td><td>765</td><td>670</td><td>85</td><td>456</td><td>480</td><td>800</td></tr><tr><td rowspan="3">Transversal tensile test</td><td>EI<sup>t</sup> (GPa)</td><td>7.8</td><td>8.5</td><td>12.0</td><td>2.2</td><td>8.0</td><td>6.3</td><td>14.6</td></tr><tr><td>σ<sub>f</sub><sup>t</sup> (MPa)</td><td>26</td><td>9</td><td>15</td><td>6</td><td>32</td><td>43</td><td>42</td></tr><tr><td>ν<sub>tz</sub></td><td>0,38</td><td>0,39</td><td>0,42</td><td>0,46</td><td>0,64</td><td>0,58</td><td>0,40</td></tr><tr><td rowspan="2">Transversal compression test</td><td>EI<sup>c</sup> (GPa)</td><td>9.7</td><td>15.0</td><td>17.8</td><td>2.8</td><td>11.3</td><td>7.1</td><td>17.2</td></tr><tr><td>σ<sub>f</sub><sup>c</sup> (MPa)</td><td>115</td><td>110</td><td>98</td><td>34</td><td>107</td><td>123</td><td>137</td></tr><tr><td rowspan="2">Off-axis tensile test</td><td>G<sub>lt</sub> (GPa)</td><td>5.5</td><td>6.2</td><td>6.4</td><td>2.8</td><td>3.7</td><td>4.4</td><td>7.0</td></tr><tr><td>τ<sub>lt</sub> (MPa)</td><td>42</td><td>25</td><td>28</td><td>15</td><td>40</td><td>50</td><td>44</td></tr></tbody></table>

behind. Configurations with carbon fibres achieve good mechanical properties, but are not competitive in terms of the carbon cost/

performance ratio.

The same calculation was performed to determine the cost-
<figure><img src="image_18.png" /><figcaption>**Fig. 14.** Radar chart of normalized stiffnesses and strengths for all configurations.</figcaption></figure>

effectiveness ratio, which is presented in Fig. 15 (b). The C4 (acrylic/flax) configuration was deemed unsatisfactory due to its poor mechanical performance. The estimated price of acrylic resin, which is double that of PA6 resin, and the cost of carbon fibres puts the C1, C2, C3 and C6 configurations at a disadvantage. These results highlight the advantages of configurations C5 (PA6/glass) and C7 (Epoxy/Basalt).

## 4. Conclusions and perspectives

The mechanical properties of the composite materials manufactured by the pultrusion process were characterized in this work for further sizing in low-carbon cost railway applications. Carbon, glass and basalt fibres, as well as natural flax fibres, were benchmarked alongside acrylic and PA6 matrix, and a thermoset epoxy, for the sake of comparison.

Experimental results indicate that the nature of the fibres influences the mechanical properties of acrylic-based resin composites, particularly in the transverse direction. Post-test observations revealed partially dry fibres, suggesting incomplete impregnation of glass and flax fibres. The relatively high porosity levels and their distribution across the samples, especially in the acrylic/flax and acrylic/glass configurations, may partly explain the reduction in mechanical properties compared to

values reported in the literature and those predicted using the rule of mixtures.

The low-pressure conditions inherent to the pultrusion process are likely a major factor contributing to porosity formation in these composites. This is particularly relevant for the acrylic resin, whose monomer has a saturation temperature below the processing temperature and undergoes a volumetric shrinkage of approximately 20 % upon polymerization. While these mechanisms are consistent with the observed microstructures, the precise interplay between monomer evaporation, chemical shrinkage, and polymerization kinetics remains to be fully understood.

A better understanding of these coupled effects may allow strategies to reduce porosity levels in pultruded acrylic matrix composites and provide a more nuanced interpretation of the current results. These considerations highlight remaining challenges and open questions in the processing of reactive acrylic-based composites.

In addition, natural fibres are known to be more difficult to impregnate, which partly explains the problems encountered. The tensile and compressive strengths of PA6 resin are higher than those of the acrylic resin, regardless of the fibre used. Furthermore, PA6 resin appears to present fewer processing difficulties, thereby limiting the
<figure><img src="image_19.png" /><figcaption>Fig. 15. (a) GWP in [kg CO2 eq] for 1 MPa of each configuration for transversal tensile and compressive test (b) Price in [€] for 1 MPa of each configuration for transversal tensile and compressive test.</figcaption></figure>

occurrence of porosity.

Improving the manufacturing process to minimize porosity would enable the use of all fibre types with the PA6 and acrylic resins. A comparison of the acrylic/basalt and epoxy/basalt configurations shows that the thermoset resin has superior properties. The weakness of the acrylic-based matrix, caused by impregnation and porosity issues, reduces the compression and shear properties.

Regarding the fibres, carbon fibres showed the best properties, closely followed by basalt and glass fibres. The flax fibre configuration produced poor results in tension and compression in both the longitudinal and transverse directions. Additionally, the significant variability in properties depending on the material's origin complicates the selection of this type of natural fibre for industrial products.

Despite their superior mechanical properties, the GWP highlights the difficulty of achieving a competitive cost/performance ratio with carbon fibre configurations. However, basalt fibre has a significantly lower carbon cost than other fibres and enables the acrylic/basalt configuration to be highly competitive. The natural flax fibre configuration has an unfavorable cost/performance ratio due to its poor mechanical properties. The epoxy/basalt configuration achieves the best results in terms of performance, economic cost and carbon cost ratio in a cradle-to-gate analysis. However, a life cycle analysis is required to determine the most appropriate resin type.

Taking all these factors into account, basalt fibres appear to be the best candidate for eco-design, given their high mechanical properties and the low carbon cost of their production compared to traditional fibres. Thermoset epoxy resin would be an effective solution for overcoming the high compressive and shear stresses in the resin of the rail structure.

Finally, a complete life-cycle analysis and manufacturing cost calculation for the configurations studied, taking into account recyclability methods depending on the material used, should also be

considered when choosing materials for the new composite railway design.

### Funding sources

This research was conducted as part of the INFRAlight project funded by the French government as part of the France 2030 plan operated by ADEME (the French Environment and Energy Management Agency): https://librairie.ademe.fr/mobilite-et-transports/6078-infralight-infr structure-innovante-connectee-adaptee-aux-trains-tres-legers.html.

The authors gratefully acknowledge the support of all parties involved.

### CRediT authorship contribution statement

**L. Sudriès:** Writing – original draft, Investigation. **I. Diboune:** Investigation. **A. Cloos:** Writing – original draft, Investigation. **O. De Almeida:** Writing – review & editing, Supervision, Project administration, Funding acquisition. **J. Serra:** Writing – review & editing, Supervision, Methodology. **W. Azoti:** Writing – review & editing, Supervision, Methodology. **B. Castanié:** Writing – review & editing, Validation, Supervision, Methodology, 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.

### Acknowledgements

The authors would like to thank everyone involved in the INFRAlight project, especially Laura Gouffet (IRT M2P) and Frank Chauzu (CQFD Composites), who both provided pultruded samples, and Jean-Yves
Oliver and Sophie Bourcier (Eugenie), who provided guidance.

## Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.matdes.2025.115401.

## Data availability

Dtas are provided in the paper

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