Open AccessArticle

Towards Environmentally Friendly Buildings: An Assessment of the Mechanical Properties of Soil Mixtures with Graphene

Federico Iorio Esposito

Paola Gallo Stampino

Letizia Ceccarelli

¹,

Marco Caruso

Giovanni Dotelli

^1,*

and

Sergio Sabbadini

Department of Chemistry, Materials and Chemical Engineering “G. Natta”, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milan, Italy

Materials Testing Laboratory, Politecnico di Milano, Via Celoria 3, 20133 Milan, Italy

Disstudio, Via Piolti de Bianchi 48, 20129 Milan, Italy

Author to whom correspondence should be addressed.

C 2025, 11(1), 16; https://doi.org/10.3390/c11010016

Submission received: 17 December 2024 / Revised: 11 February 2025 / Accepted: 17 February 2025 / Published: 19 February 2025

(This article belongs to the Topic Application of Graphene-Based Materials, 2nd Edition)

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Figure 1
Additive used: (a) GUP ADMIXTURE (GUP); (b) Graphene paste (GSL). "> Figure 2
Experimental setup for Proctor compaction test. (a) Proctor machine; (b) The mold positioned on the machine; (c) The rammer compacting the soil inside the mold; (d) The sample is leveled inside the mold; (e) Extraction of the sample; (f) The final sample extracted from the mold. "> Figure 3
Experimental setup for unconfined compressive strength (UCS) test. (a) TRITECH Load Frame for UCS test; (b) Sample during the test; (c) Sample after failure. "> Figure 4
Samples preparation for unconfined compressive strength (UCS) test. (a) Proctor cylinder on hand-driven load frame; (b) Coring procedure; (c) UCS samples in the curing chamber. "> Figure 5
Verified water content (%) of ABS Mix and GSL series with respect to the reference optimum water content (OWC) of the ABS Mix (7.10%). Two distinct portions of the sample were tested for water content. The name of the sample consists of the soil name, followed by the percentage and the abbreviation of the additive (e.g., ABS 0.005% GSL). "> Figure 6
Proctor compaction test results for ABS mixtures. (a) ABS Mix; (b) ABS 0.001% GUP; (c) ABS 0.005% GUP; (d) ABS 0.01% GUP; (e) ABS 0.05% GUP; (f) ABS 0.1% GUP. The soil saturation curves (Sr) are reported, indicating different degrees of saturation from 0.5 to 1. "> Figure 7
Proctor compaction test results for T2 mixtures. (a) T2 Mix; (b) T2 0.01% GUP; (c) T2 0.05% GUP; (d) T2 0.1% GUP. The soil saturation curves (Sr) are reported, indicating different degrees of saturation from 0.5 to 1. "> Figure 8
Unconfined compressive strength (UCS) results. (a) ABS mixtures with GUP additive; (b) ABS mixtures with GSL additive; (c) T2 mixtures with GUP additive. The name of the sample consists of the soil name, followed by the percentage and the abbreviation of the additive (e.g., ABS 0.001% GUP). "> Figure 8 Cont.
Unconfined compressive strength (UCS) results. (a) ABS mixtures with GUP additive; (b) ABS mixtures with GSL additive; (c) T2 mixtures with GUP additive. The name of the sample consists of the soil name, followed by the percentage and the abbreviation of the additive (e.g., ABS 0.001% GUP). "> Figure 9
Results from the unconfined compressive strength (UCS) test. (a) Maximum stress, qu, with varying graphene concentration; (b) Stiffness modulus, E, with varying graphene concentration. "> Figure 9 Cont.
Results from the unconfined compressive strength (UCS) test. (a) Maximum stress, qu, with varying graphene concentration; (b) Stiffness modulus, E, with varying graphene concentration. "> Figure 10
Comparison between the two graphene-based additives of unconfined compressive strength results in ABS and T2. The name of the sample consists of the soil name, followed by the percentage and the abbreviation of the additive (e.g., ABS 0.001% GUP). ">

Versions Notes

Abstract

This study investigates the potential of graphene-based additives to improve the mechanical properties of compacted soil mixtures in rammed-earth construction, contributing to the development of environmentally friendly building materials. Two distinct soils were selected, combined with sand at optimized ratios, and treated with varying concentrations of a graphene liquid solution and a graphene-based paste (0.001, 0.005, 0.01, 0.05, and 0.1 wt.% relative to the soil-sand proportion). The effects of these additives were analyzed using the modified Proctor compaction and unconfined compressive strength (UCS) tests, focusing on parameters such as optimum water content (OWC), maximum dry density (MDD), maximum strength (q_u), and stiffness modulus (E). The results demonstrated that graphene’s influence on compaction behavior and mechanical performance depends strongly on the soil composition, with minimal variation between additive types. In finer soil mixtures, graphene disrupted particle packing, increased water demand, and reduced strength. In silt–sandy mixtures, graphene’s hydrophobicity and limited interaction with fines decreased water absorption and preserved density but likewise led to diminished strength. Conclusions from the experiments suggest a possible interaction between graphene, soil’s finer fraction, and potentially the swelling and non-swelling clay minerals, providing insights into the complex interplay between soil properties.

Keywords:

graphene; earthen materials; rammed earth; environmentally friendly buildings; Proctor compaction test; unconfined compressive strength test

1. Introduction

The construction industry remains a significant contributor to global greenhouse gas (GHG) emissions, accounting for approximately 37% of global emissions in 2022, with a substantial share arising from the production and use of cement and steel [1]. Indeed, the industrialization of construction in the mid-20th century shifted the preference toward concrete and steel, relegating traditional earthen materials to niche or legacy applications [2], even if historically, raw earth has been a cornerstone of vernacular architecture [3], prized for its low environmental impact, availability, and adaptability. Modern research, however, has reignited interest in raw earth, positioning it as a viable alternative in the pursuit of sustainable construction [4], thanks to the benefits of thermal regulation, moisture management, and acoustic insulation [5]. Additionally, plain earth can be easily recycled or disposed of when demolished [5]. Nevertheless, its broader adoption is hindered by technical challenges, particularly its susceptibility to water erosion, freeze–thaw cycles, and relatively low mechanical strength [5].

To address these challenges, soil stabilization typically involves the addition of natural fibers or mineral stabilizers, such as Portland cement and lime [6,7]. While natural fibers are more environmentally sustainable, they often result in significantly lower mechanical strength compared to soils stabilized with cement [8,9,10]. However, using cement-based stabilizers reintroduces the environmental drawbacks associated with cement production, such as high carbon emissions and resource consumption [11]. As an alternative, a “third approach” has emerged, focusing on the addition of small quantities of nanomaterials, including graphene. Graphene’s unique morphological and structural properties, such as its high surface area, exceptional mechanical strength, and electrical conductivity, make it highly desirable for applications ranging from gas and energy storage to optoelectronics [12,13,14,15]. Recently, these properties have also driven interest in the construction sector, where graphene and its derivatives show promise in enhancing the performance and durability of building materials.

Incorporating graphene into construction materials has demonstrated significant improvements, particularly in cement-based systems, where it mainly enhances mechanical, thermal, and electrical properties. For example, the addition of graphene oxide (GO) nanoplatelets has been shown to increase tensile strength by up to 48% in cement mortars, as reported by Babak et al. [16]. This improvement is primarily attributed to graphene’s role in accelerating C-S-H (calcium silicate hydrate) nucleation during hydration, promoting ion mobility, and fostering a denser cement matrix [16,17]. Beyond strength enhancement, graphene’s introduction enables the development of “smart materials” with electrical conductivity, allowing structures to monitor their strain state without external sensors, and thermal conductivity, which can be utilized in heating applications or to prevent ice formation on roads [18,19].

While studies on graphene’s integration into raw-earth materials are more limited, recent findings suggest its potential to address some of the weaknesses of earth-based structures. For instance, Ngo et al. demonstrated that adding graphene and graphene oxide to cement-stabilized earthen (CSE) mixtures resulted in notable improvements in compressive and tensile strengths by enhancing the nucleation of hydration products and reducing crack propagation [20]. Similarly, research by Li et al. showed that graphene oxide improved the compactability of soil–cement mixes by decreasing optimum moisture content and increasing dry density, along with better water resistance [21]. However, these findings contrast with observations in earthen plasters studied previously by Gallo Stampino et al., as their work revealed that graphene improved the cohesion of the plasters by possibly reducing the internal frictional angle but showed mixed results regarding water resistance at varying graphene concentrations when changing the soil type [22].

This study investigates the influence of two graphene-based additives on the mechanical properties of two distinct soils, focusing on their potential application in rammed-earth construction. By examining the interactions between these additives and compacted soil mixtures, the research aims to explore improvements in material performance for modern building practices.

2. Materials and Methods

2.1. Materials

2.1.1. Soils

Two distinct soils were selected as the basis for this work and served as reference materials. These soils, designated experimentally as ABS and T2, were combined with sand at earth-to-sand ratios determined through in situ testing to prevent crack formation during drying. For ABS, the ratio was 1:3, while for T2, it was 1:4. The resulting soil–sand mixtures were then tested with two graphene-based additives, a liquid solution (GUP) and a paste (GSL). Throughout this study, the untreated soils are referred to by their respective names (ABS and T2), while the soil–sand mixtures are identified as Mix (e.g., ABS Mix and T2 Mix). When a graphene-based additive was added to a mixture, it was denoted by the soil name followed by the corresponding additive concentration and type (e.g., ABS 0.1% GUP, ABS 0.01% GSL). Table 1 summarizes the investigated mixtures.

The ABS soil, supplied by Minerali Industriali S.r.l. (Novara, NO, Italy), was sourced from an Italian quarry located in Piedmont, near Lozzolo (VC). The T2 soil, kindly provided by Industrie Cotto Possagno (Possagno, TV, Italy), originated from a quarry in Morano (MO). The sand was supplied by Dal Zotto S.r.l. (Crocetta del Montello, TV, Italy) and was extracted from the Piave riverbed.

Gallo Stampino et al. previously conducted a geotechnical characterization encompassing particle size distribution, Atterberg limits, and specific gravity, along with chemical and mineralogical analysis through Attenuated Total Reflection—Fourier Transformed Infrared Spectroscopy (ATR-FTIR) and X-ray diffractometry (XRD) [22]. These analyses serve as reference data for this study [22]. Based on these findings, ABS and T2 can be classified according to ASTM D-2487 (the ASTM version of the Unified Soil Classification System) as inorganic silt (ML) and highly plastic inorganic clay, or fat clay (CH), respectively [23]. Table 2 summarizes the main geotechnical analysis results for the ABS and T2, while Table 3 reports the particle size distribution results for the ABS Mix and T2 Mix, which are considered highly relevant for this study.

2.1.2. Admixtures

The graphene-based additives (Figure 1) incorporated into the earth–sand mixtures are GUP ADMIXTURE (GUP) and a graphene paste, a semi-solid suspension of graphene (GSL), both supplied by GrapheneUP (Studeněves, Czech Republic). GUP ADMIXTURE is a water-based dispersion of certified 2-to-5-layer graphene, engineered to enhance cementitious materials’ physical, mechanical, and chemical properties. The graphene concentration is 1.5 wt.%. This admixture has shown compatibility across diverse applications, including cement, repair compounds, autoclaved aerated concrete, recycled concrete aggregate, and 3D printable mortars, offering ease of integration and flexibility in designing multifunctional materials [24]. On the other hand, the GSL slurry paste, a customized version of the commercial additive GUP DP Glycerol, with a higher graphene concentration of 3.0 wt.%, was developed to address some issues reported by clients using the GUP ADMIXTURE likely caused by the surfactants used for dispersing the graphene in the solution.

2.2. Methods

2.2.1. Modified Proctor Compaction Test

The Modified Proctor Test was used to determine the optimal moisture content and maximum dry density of the soil mixtures, simulating field compaction by pneumatic rammers in rammed-earth construction (Figure 2). Soil samples were compacted in a cylindrical mold with a diameter of 10.24 cm and a height of 12.30 cm. Compaction was performed in five layers, with each layer receiving 25 blows from a 4.54 kg ram falling from a calculated height to achieve a standard compaction energy of 2700 kN/m², following the procedure outlined in ASTM D1557 [25].

To prepare the samples, the soil and the sand were first allowed to air-dry indoors over an extended period to achieve a laboratory equilibrium in terms of water content. Once dried, the soil and sand were sieved to a particle size of 2 mm. The ABS and T2 were then mixed with the sand in soil-to-sand ratios of 1:3 and 1:4, respectively. For the samples containing GUP ADMIXTURE, the additive was incorporated at the concentrations reported in Table 1. Subsequently, the target amount of water corresponding to each point on the Proctor curve was added to the blend. For the GUP-based mixtures, the water content in the graphene-based solution was accounted for, and distilled water was added only as required to reach the target water content. A consistent interval of 2% water content was maintained between samples to ensure well-distributed points along the curve, but additional moisture contents were tested when the curves appeared unclear. At least five samples were prepared for each Proctor curve. The prepared mixtures were sealed in a plastic container and rested for 24 h to ensure uniform water diffusion. Afterward, the mixtures were compacted using the Proctor compaction device, following the procedure outlined in the Methods section. Finally, the resulting Proctor curves were generated from the compaction data.

2.2.2. Unconfined Compressive Strength Test (UCS)

The unconfined compressive strength (UCS) test was conducted using a 50 kN TRITECH load frame (CONTROLS S.p.A., Liscate, MI, Italy) equipped with steel plates on the top and bottom, leaving the lateral surfaces unconfined, as shown in Figure 3. The load was increased by moving the lower plate at a constant displacement rate of 0.5 mm/min, while a load cell on the upper plate recorded the force until failure. This displacement rate, chosen per the ASTM D2166 guidelines, ensured an axial strain rate between 0.5% and 2% per minute [26]. The test, which typically lasted about 5 min until failure, permitted a reasonable assumption that the water content of the samples remained constant throughout the process. The maximum stress from the stress–strain curve obtained is defined as q_u. The determination of the stiffness, E, in the mostly linear section of the curve is instead carried out following a procedure suggested by Rodrìguez-Mariscal et al., in which the stiffness modulus is identified by the slope of the chord passing through the (σ_1/3, ε_1/3) and (σ_2/3, ε_2/3) points, with respect to q_u [27].

The preparation of samples for the unconfined compressive strength (UCS) test involved the production of Proctor cylinders at the optimum water content determined during the previous compaction investigation. These Proctor cylinders were then cored using a hand-driven load frame and a sharpened sampler to obtain two smaller cylindrical specimens from each Proctor cylinder, as shown in Figure 4. Each specimen was prepared with a slenderness ratio of 2, as prescribed by ASTM D2166, resulting in a diameter of 38 mm and a height of 76 mm [26]. The remaining portion of each Proctor cylinder was oven-dried to verify that the actual water content matched the OWC targeted during preparation.

A minimum of four specimens were produced for each mixture. However, not all specimens appeared to have developed a properly shaped shear band at failure during UCS tests. Only those meeting the correct criteria were considered, resulting in 21 valid samples for the ABS Mix (11 for GUP testing and 10 for GSL testing), and 13 valid samples for the T2 Mix (all for GUP testing).

To ensure consistent water content across all the specimens, the samples were cured for approximately three months in a controlled environment. The relative humidity was maintained at approximately RH = 80% using a saturated sodium chloride solution (Figure 4). The samples were considered at equilibrium and ready for testing when their relative weight variation was less than 0.05% over three consecutive days, as Equation (1) reports.

\frac{{(m}_{n + 1} - m_{n})}{m_{n}} \times 100 < 0.05 %

(1)

3. Results

3.1. Proctor Compaction Test

The Proctor compaction test was conducted on both the ABS and T2 mixtures containing the graphene-based additive GUP. The objective was to determine the optimum water content (OWC) theoretically associated with maximum strength. For GSL-containing mixtures, however, compaction tests were not conducted. This decision was based on the assumption that the additive’s negligible water content would not significantly affect the OWC when added in small quantities. Consequently, the OWC for the GSL mixtures was approximated to align with the reference mixture, the ABS Mix, which had an OWC of 7.10%. This value, determined in this study, was compared with a similar result on the same soil reported by Losini et al. [10]. This hypothesis was validated by measuring the water content of the prepared GSL, which closely matched the target OWC, as shown in Figure 5. A notable distinction in the third mixture, compared to the first two, was the higher quantity of GSL used, approximately 45 g, compared to 4.5 g and 9.0 g in the first and second mixtures, respectively. While the additive’s minimal water content suggested a limited impact on the overall OWC, the higher quantity in the third mixture may have slightly influenced its overall water content, potentially leading to a different OWC. Nevertheless, this variation is unlikely to have significantly affected the sample’s mechanical resistance, as the OWC remained reasonably close to the reference value [28].

Figure 6 and Figure 7 show the compaction results for the ABS and T2 mixtures, with the OWC and maximum dry density (MDD) summarized in Table 4. The addition of GUP in the ABS Mix causes the OWC to increase, while the MDD gradually decreases. Conversely, the T2-based mixtures exhibited the opposite trend: OWC decreased with increasing graphene content, while MDD remained relatively stable.

The observed differences in OWC and MDD between the ABS and T2 mixtures could be attributed to the distinct granulometric and clay compositions of the two soil types. The ABS mixtures contain more fine particles (clay) than the T2 blends, while clay minerals comprised 14.41% in the ABS Mix compared to 17.19% in the T2 Mix (Table 5).

The higher fines content in the ABS mixtures, about 10%, likely increases water demand during compaction due to the higher surface area of fine particles and their water absorption capacity [29]. Instead, the lower fines content in the T2 mixtures, at just 4%, and the dominance of sand in T2 (79% sand, Table 3) reduces the water demand, as sand generally exhibits lower water absorption [29]. Furthermore, in the ABS mixtures, swelling clays (5.72%) are slightly less than those in the T2 mixtures (7.80%), as reported in Table 5. Swelling clays are critical for water retention and compaction behavior, as their ability to absorb water causes changes in particle spacing and overall soil structure [30]. The higher proportion of swelling clays in the T2 mixtures may explain the relatively low sensitivity of T2’s MDD to graphene content, as the sand-dominated structure remains stable despite graphene’s addition. Conversely, in the ABS mixtures, the higher fines content and a more significant proportion of non-swelling clays (8.69%) may interact with graphene additives to increase the OWC. Graphene could disrupt particle-to-particle contact, modifying the water retention properties of the mixture and increasing the water needed for compaction. The same conclusions can be drawn from the decrease in MDD, which suggests that the graphene particles might reduce particle-to-particle friction or interfere with the packing of soil particles, leading to a looser structure.

In contrast, in the T2 mixtures, the predominance of sand and the lower fines content likely limit the interaction between the graphene and finer particles. This led to a decrease in OWC, possibly due to graphene enhancing water dispersion or reducing water absorption by clay particles. The relatively stable MDD reflects the sand-dominated mixture’s resistance to significant structural changes.

3.2. Unconfined Compressive Strength (UCS) Results

Figure 8 shows all the unconfined compressive strength (UCS) test results, while Table 6 summarizes the average maximum compressive strength, q_u, and stiffness modulus, E, achieved by each mixture.

The results of the unconfined compressive strength (UCS) tests highlight different trends for the ABS and T2 mixtures with the addition of the two graphene-based additives (GUP and GSL), as illustrated in Figure 9. In the ABS mixtures, both maximum stress (q_u) and stiffness modulus (E) progressively decrease with increasing GUP content. Indeed, q_u drops from 2.51 MPa in the ABS Mix [10] to 1.16 MPa for ABS 0.1% GUP, while E decreases from 285 MPa to 110 MPa. These reductions align with the Proctor compaction results, suggesting that graphene disrupts particle-to-particle interactions, reducing compaction efficiency and creating a looser soil structure. In contrast, GSL showed better performance with respect to GUP in the ABS mixtures at the same concentrations. However, both q_u and E declined significantly at higher GSL dosages, likely due to the particles’ excessive interference with soil packing.

For the T2 mixtures, q_u and E were consistently lower due to the higher earth-to-sand ratio (1:4). The baseline q_u for the T2 Mix was 0.76 MPa, which decreased further with the GUP additions, reaching 0.25 MPa for T2 0.1% GUP. Similarly, E dropped from 93 MPa in the T2 Mix to 18 MPa at the highest GUP dosage. These declines can be attributed to the limited interaction between graphene and the sand-dominated structure, as evidenced by the Proctor compaction results. This suggests that graphene had minimal impact on the sand matrix and interfered with the clay component, further reducing strength and stiffness.

4. Discussion

The experimental results from the Proctor compaction test and the unconfined compressive strength test revealed a complex interplay between graphene-based additives (GUP and GSL) and soil properties, with distinct effects observed for the ABS and T2 mixtures. These differences are likely rooted in the soils’ geotechnical characteristics, mineralogy, and clay content, as well as a hypothesized mechanism of interaction induced by graphene.

In the ABS mixtures, the addition of a graphene-based solution (GUP) leads to an increase in optimum water content (OWC) and a corresponding decrease in maximum dry density (MDD). This behavior is attributed to the high fines content (10% clay) and the predominance of non-swelling clay minerals (8.69%) in the ABS mixtures. The graphene additive, due to its high surface area, likely acts onto soil particles, disrupting particle-to-particle interactions and altering the water retention properties of the soil. The results align with the concept that nanomaterials such as graphene, with their high surface area, can enhance cation exchange capacity at the nanoscale, potentially fostering active interactions with the soil’s mineral components [31]. This is similar to the behavior observed in concrete mixed with graphene, where C-S-H nucleation and growth are accelerated [17]. While this effect is beneficial in concrete, in soil it leads to modifications in the water retention properties, as graphene disrupts the typical packing of soil particles and alters their moisture behavior. This aligns with findings by Gallo Stampino et al. [22], who observed changes in the chemical environment of interstratified illite–smectite minerals through FTIR analysis. These findings suggest that graphene interacts with clay minerals, altering the spacing and packing efficiency of soil particles. The looser soil structure resulting from this interaction negatively impacts compaction efficiency, as evidenced by UCS results, which show progressive declines in both maximum compressive strength (q_u) and stiffness modulus (E) with increasing graphene content. These trends are true for both graphene-based additives, although the reduction in maximum compressive strength and stiffness modulus is less pronounced with the graphene paste. This difference is likely to be attributed to the better formulation of the graphene paste, which avoids using surfactants to produce a graphene solution.

In the T2 mixtures, the effects of graphene addition differ significantly. T2, characterized by a higher sand content (80%) and a lower fines fraction (4% clay), exhibits a decrease in OWC with increasing graphene dosage, while MDD remains relatively stable. The limited fines content and sand-dominated matrix reduce the interaction between graphene and soil particles, with the additive primarily influencing the limited clay fraction. The UCS results for the T2 mixtures show a significant reduction in q_u and E, likely due to graphene’s interference with the smaller particle fraction, as noted in Gallo Stampino et al. [22]. Additionally, the hydrophobic nature of graphene worsens water absorption along clay planes, especially in T2’s higher swelling clay content (7.80%), reducing both water erosion resistance and structural stability [22].

A potential lubricating effect of graphene could contribute to these observations. Graphene’s two-dimensional structure may reduce inter-particle friction within the soil matrix, promoting a looser particle arrangement during compaction. This phenomenon would explain the observed reduction in MDD and strength parameters, particularly in the ABS mixtures where graphene’s interaction with fines is more pronounced. Additionally, graphene’s hydrophobic properties amplify this effect by altering water distribution, reducing clay particle cohesion, and enhancing particle displacement within the soil matrix.

The challenges in achieving reproducibility when testing soil mixed with graphene additives are evident from the standard deviations shown in Figure 10. While some samples, such as the T2-based mixtures, exhibit relatively small deviations, likely due to the higher sand content ensuring more uniformity, others, particularly those treated with the graphene paste, show more significant deviations, highlighting pronounced variability. Such variability can be explained due to the heterogeneity of the soil matrix, mixed with graphene additives. These factors underscore how even minor adjustments in the experimental setup can significantly impact the mechanical properties of soil–graphene mixtures, further complicating standardization in an already challenging sector like soil-based construction.

5. Conclusions

This study assessed the impact of two graphene-based additives (a solution, GUP, and a paste, GSL) on the mechanical properties of compacted soil mixtures, focusing on their application in rammed-earth construction, in the light of their possible application in modern building practices. Through Proctor compaction and unconfined compressive strength (UCS) tests, distinct effects were observed for the two studied soils (ABS and T2), attributed to their differing geotechnical properties, granulometric composition, and clay content.

Graphene-based additives influenced soil properties based on composition. In finer mixtures (ABS mixtures), graphene disrupted particle packing, increasing water demand and reducing density and strength at higher concentrations. The GSL demonstrated better compatibility than the GUP with soils, mitigating these effects, which can be reasonably attributed to its surfactant-free formulation. In sand-rich mixtures (T2 mixtures), the sand-dominated matrix limited graphene’s interaction, leading to relatively stable compaction behavior but still causing reductions in mechanical strength, likely due to interference with the smaller clay fraction.

Overall, graphene-based additives show promising results for enhancing specific soil properties as well as improving the adhesion performance of clay plasters, as shown in previous studies. The application in rammed-earth construction should be carefully tailored to the soil composition and additive formulation. Future research in this field should investigate the reproducibility of the samples using a more standardized variety of soil types, particularly those with varied granulometric compositions and mineralogical properties, to better understand the compatibility and performance of graphene-based additives. Additionally, exploring alternative nanomaterials could provide insights into optimizing mechanical properties and addressing the drawbacks observed in this study.

Author Contributions

Conceptualization, F.I.E., P.G.S., L.C., M.C., G.D. and S.S.; methodology, F.I.E., L.C., M.C. and G.D.; investigation, F.I.E.; writing—original draft preparation, F.I.E.; writing—review and editing, F.I.E., P.G.S., G.D., L.C. and M.C.; supervision, P.G.S. and G.D. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The data that support the findings of this study are available from the authors upon reasonable request.

Acknowledgments

The authors are very grateful to Ing. Ivano Aglietto for providing the graphene-based additive GUP Admixture produced by GrapheneUP (Prague, Czech Republic). A special thanks to the Italian companies for supplying the soils goes to Minerali Industriali S.r.l. (Novara, Italy) for the ABS, to Industrie Cotto Possagno for the T2, and to Fornace Carena (Torino, Italy) in Cambiano for the TC. Dal Zotto S.r.l. (Treviso, Italy) kindly provided the sand. Finally, a special thanks to the bachelor’s degree students in Materials Engineering at Politecnico di Milano of “Gruppo 26” for carrying out some of the experimental parts.

Conflicts of Interest

The authors declare no conflicts of interest.

References

United Nations Environment Programme and Yale Center for Ecosystems + Architecture. Building Materials and the Climate: Constructing a New Future. Available online: https://wedocs.unep.org/20.500.11822/43293 (accessed on 5 December 2024).
Gallipoli, D.; Bruno, A.W.; Perlot, C.; Mendes, J. A geotechnical perspective of raw earth building. Acta Geotech. 2017, 12, 463–478. [Google Scholar] [CrossRef]
UNESCO. World Heritage List. Available online: https://whc.unesco.org/en/list/ (accessed on 19 November 2023).
Smithsonian Magazine. 40 Things You Need to Know About the Next 40 Year. Available online: https://www.smithsonianmag.com/issue/smithsonian/august-2010/ (accessed on 7 December 2024).
Gallipoli, D.; Bruno, A.W.; Perlot, C.; Salmon, N. Raw earth construction: Is there a role for unsaturated soil mechanics? In Unsaturated Soils: Research & Applications; Khalili, N., Russell, A., Khoshghalb, A., Eds.; CRC Press: Boca Raton, FL, USA, 2014. [Google Scholar] [CrossRef]
Al-Gharbawi, A.S.A.; Najemalden, A.M.; Fattah, M.Y. Expansive Soil Stabilization with Lime, Cement, and Silica Fume. Appl. Sci. 2022, 13, 436. [Google Scholar] [CrossRef]
Medina-Martinez, C.J.; Sandoval-Herazo, L.C.; Zamora-Castro, S.A.; Vivar-Ocampo, R.; Reyes-Gonzalez, D. Natural Fibers: An Alternative for the Reinforcement of Expansive Soils. Sustainability 2022, 14, 9275. [Google Scholar] [CrossRef]
Losini, A.E.; Lavrik, L.; Caruso, M.; Woloszyn, M.; Grillet, A.C.; Dotelli, G.; Stampino, P.G. Mechanical Properties of Rammed Earth Stabilized with Local Waste and Recycled Materials. In Proceedings of the 4th International Conference on Bio-Based Building Materials, Barcelona, Spain, 16–18 June 2021; pp. 113–123. [Google Scholar]
Losini, A.; Grillet, A.; Bellotto, M.; Woloszyn, M.; Dotelli, G. Natural additives and biopolymers for raw earth construction stabilization—A review. Constr. Build. Mater. 2021, 304, 124507. [Google Scholar] [CrossRef]
Losini, A.E.; Grillet, A.-C.; Woloszyn, M.; Lavrik, L.; Moletti, C.; Dotelli, G.; Caruso, M. Mechanical and Microstructural Characterization of Rammed Earth Stabilized with Five Biopolymers. Materials 2022, 15, 3136. [Google Scholar] [CrossRef] [PubMed]
Mustafayeva, A.; Moon, S.-W.; Satyanaga, A.; Kim, J. Enhancing Mechanical Properties of Expansive Soil Through BOF Slag Stabilization: A Sustainable Alternative to Conventional Methods. Minerals 2024, 14, 1145. [Google Scholar] [CrossRef]
Lee, X.J.; Hiew, B.Y.Z.; Lai, K.C.; Lee, L.Y.; Gan, S.; Thangalazhy-Gopakumar, S.; Rigby, S. Review on graphene and its derivatives: Synthesis methods and potential industrial implementation. J. Taiwan Inst. Chem. Eng. 2018, 98, 163–180. [Google Scholar] [CrossRef]
Qureshi, T.S.; Panesar, D.K. Nano reinforced cement paste composite with functionalized graphene and pristine graphene nanoplatelets. Compos. Part B Eng. 2020, 197, 108063. [Google Scholar] [CrossRef]
Bokobza, L.; Bruneel, J.-L.; Couzi, M. Raman Spectra of Carbon-Based Materials (from Graphite to Carbon Black) and of Some Silicone Composites. C J. Carbon Res. 2015, 1, 77–94. [Google Scholar] [CrossRef]
Farivar, F.; Yap, P.L.; Karunagaran, R.U.; Losic, D. Thermogravimetric Analysis (TGA) of Graphene Materials: Effect of Particle Size of Graphene, Graphene Oxide and Graphite on Thermal Parameters. C 2021, 7, 41. [Google Scholar] [CrossRef]
Babak, F.; Abolfazl, H.; Alimorad, R.; Parviz, G. Preparation and Mechanical Properties of Graphene Oxide: Cement Nanocomposites. Sci. World J. 2014, 2014, 276323. [Google Scholar] [CrossRef] [PubMed]
Meng, S.; Ouyang, X.; Fu, J.; Niu, Y.; Ma, Y. The role of graphene/graphene oxide in cement hydration. Nanotechnol. Rev. 2021, 10, 768–778. [Google Scholar] [CrossRef]
Schulte, J.; Jiang, Z.; Sevim, O.; Ozbulut, O.E. Chapter 4—Graphene-reinforced cement composites for smart infrastructure systems. In The Rise of Smart Cities [Internet]; Alavi, A.H., Feng, M.Q., Jiao, P., Sharif-Khodaei, Z., Eds.; Butterworth-Heinemann: Oxford, UK, 2022; pp. 79–114. [Google Scholar] [CrossRef]
Farcas, C.; Galao, O.; Navarro, R.; Zornoza, E.; Baeza, F.J.; DEL Moral, B.; Pla, R.; Garces, P. Heating and de-icing function in conductive concrete and cement paste with the hybrid addition of carbon nanotubes and graphite products. Smart Mater. Struct. 2021, 30, 045010. [Google Scholar] [CrossRef]
Ngo, T.P.; Bui, Q.B.; Nguyen, N.T.; Le, T.; Phan, V.T.-A. Application of nanotechnology for earth materials: An exploratory study with graphene-based nanosheets. Constr. Build. Mater. 2022, 324, 126677. [Google Scholar] [CrossRef]
Li, D.; Lei, P.; Zhang, H.; Liu, J.; Lu, W. Co-Effects of Graphene Oxide and Cement on Geotechnical Properties of Loess. Adv. Mater. Sci. Eng. 2021, 2021, 7429310. [Google Scholar] [CrossRef]
Stampino, P.G.; Ceccarelli, L.; Caruso, M.; Mascheretti, L.; Dotelli, G.; Sabbadini, S. Performance of Earth Plasters with Graphene-Based Additive. Materials 2024, 17, 2356. [Google Scholar] [CrossRef] [PubMed]
ASTM D2487-17; Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System). ASTM International: West Conshohocken, PA, USA, 2017. [CrossRef]
GrapheneUP. GUP® ADMIXTURE. Available online: https://www.grapheneup.com/shop/gup-admixture/ (accessed on 3 December 2024).
ASTM D1557-12; Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort. ASTM International: West Conshohocken, PA, USA, 2012. [CrossRef]
ASTM D2166-06; Standard Test Method for Unconfined Compressive Strength of Cohesive Soil. ASTM International: West Conshohocken, PA, USA, 2006. [CrossRef]
Rodríguez-Mariscal, J.; Solís, M.; Cifuentes, H. Methodological issues for the mechanical characterization of unfired earth bricks. Constr. Build. Mater. 2018, 175, 804–814. [Google Scholar] [CrossRef]
Bui, Q.-B.; Morel, J.-C.; Hans, S.; Walker, P. Effect of moisture content on the mechanical characteristics of rammed earth. Constr. Build. Mater. 2014, 54, 163–169. [Google Scholar] [CrossRef]
Davidson, D.T.; Pitre, G.L.; Mateos, M.; George, K.P. Moisture-Density, Moisture-Strength and Compaction Characteristics of Cement-Treated Soil Mixtures. In Proceedings of the 41st Annual Meeting of the Highway Research Board, Washington, DC, USA, 8–12 January 1962; Volume HR Board Bulletin, no. 353, pp. 42–63. [Google Scholar]
Zhang, X.; Liu, X.; Xu, Y.; Wang, G.; Wang, F. Swelling–shrinkage mechanisms of diatomaceous soil and its geohazard implication. Eng. Geol. 2023, 314, 107009. [Google Scholar] [CrossRef]
Majeed, Z.; Taha, M. A Review of Stabilization of Soils by using Nanomaterials. Aust. J. Basic. Appl. Sci. 2013, 7, 576–581. [Google Scholar]

Figure 1. Additive used: (a) GUP ADMIXTURE (GUP); (b) Graphene paste (GSL).

Figure 2. Experimental setup for Proctor compaction test. (a) Proctor machine; (b) The mold positioned on the machine; (c) The rammer compacting the soil inside the mold; (d) The sample is leveled inside the mold; (e) Extraction of the sample; (f) The final sample extracted from the mold.

Figure 3. Experimental setup for unconfined compressive strength (UCS) test. (a) TRITECH Load Frame for UCS test; (b) Sample during the test; (c) Sample after failure.

Figure 4. Samples preparation for unconfined compressive strength (UCS) test. (a) Proctor cylinder on hand-driven load frame; (b) Coring procedure; (c) UCS samples in the curing chamber.

Figure 5. Verified water content (%) of ABS Mix and GSL series with respect to the reference optimum water content (OWC) of the ABS Mix (7.10%). Two distinct portions of the sample were tested for water content. The name of the sample consists of the soil name, followed by the percentage and the abbreviation of the additive (e.g., ABS 0.005% GSL).

Figure 6. Proctor compaction test results for ABS mixtures. (a) ABS Mix; (b) ABS 0.001% GUP; (c) ABS 0.005% GUP; (d) ABS 0.01% GUP; (e) ABS 0.05% GUP; (f) ABS 0.1% GUP. The soil saturation curves (Sr) are reported, indicating different degrees of saturation from 0.5 to 1.

Figure 7. Proctor compaction test results for T2 mixtures. (a) T2 Mix; (b) T2 0.01% GUP; (c) T2 0.05% GUP; (d) T2 0.1% GUP. The soil saturation curves (Sr) are reported, indicating different degrees of saturation from 0.5 to 1.

Figure 8. Unconfined compressive strength (UCS) results. (a) ABS mixtures with GUP additive; (b) ABS mixtures with GSL additive; (c) T2 mixtures with GUP additive. The name of the sample consists of the soil name, followed by the percentage and the abbreviation of the additive (e.g., ABS 0.001% GUP).

Figure 9. Results from the unconfined compressive strength (UCS) test. (a) Maximum stress, q_u, with varying graphene concentration; (b) Stiffness modulus, E, with varying graphene concentration.

Figure 10. Comparison between the two graphene-based additives of unconfined compressive strength results in ABS and T2. The name of the sample consists of the soil name, followed by the percentage and the abbreviation of the additive (e.g., ABS 0.001% GUP).

Table 1. Overview of tested soil–sand mixtures with graphene additive. The name of the sample consists of the soil name, followed by the percentage and the abbreviation of the additive (e.g., ABS 0.001% GUP).

Soil	Ratio to Sand	Additive	Additive (wt.%)	Mixture Name
ABS	1:3	-	-	ABS Mix
		GUP	0.001	ABS 0.001% GUP
		GUP	0.005	ABS 0.005% GUP
		GUP	0.01	ABS 0.01% GUP
		GUP	0.05	ABS 0.05% GUP
		GUP	0.1	ABS 0.1% GUP
		GSL	0.005	ABS 0.005% GSL
		GSL	0.01	ABS 0.01% GSL
		GSL	0.05	ABS 0.05% GSL
T2	1:4	-	-	T2 Mix
		GUP	0.01	T2 0.01% GUP
		GUP	0.05	T2 0.05% GUP
		GUP	0.1	T2 0.1% GUP

Table 2. Geotechnical parameters of the investigated soils (¹ LL = Liquid Limit, ² PL = Plastic Limit, ³ PI = Plasticity Index) [22].

Soil	Specific Gravity	Granulometric Parameters			Atterberg Limits
Soil	Specific Gravity	Clay (%)	Silt (%)	Sand (%)	LL ¹ (%)	PL ² (%)	PI ³ (%)
ABS	2.78	36	44	20	45	30	15
T2	2.77	21	70	9	54	15	39

Table 3. Particle size distribution for ABS and T2 mixtures [22].

Mixture	Clay (%)	Silt (%)	Sand (%)
ABS Mix	10	11	79
T2 Mix	4	16	80

Table 4. Optimum water content (OWC) (%) and maximum dry density (MDD) (g/cm³) for the investigated mixtures.

Sample	ABS		T2
Sample	OWC (%)	MDD (g/cm³)	OWC (%)	MDD (g/cm³)
Mix	7.10	2.15	7.80	2.17
0.001% GUP	7.50	2.17	-	-
0.005% GUP	7.89	2.16	-	-
0.01% GUP	8.50	2.14	7.50	2.18
0.05% GUP	9.00	2.11	7.30	2.16
0.1% GUP	9.50	2.03	6.50	2.17

Table 5. Swelling and non-swelling clay amounts in ABS Mix and T2 Mix; data obtained from XRD [22].

	ABS Mix	T2 Mix
Swelling Clays (%)	5.72	7.80
Non-Swelling Clays (%)	8.69	9.39
Total (%)	14.41	17.19

Table 6. Unconfined compressive strength test results for the investigated mixtures and additives. The name of the sample consists of the soil name, followed by the percentage and the abbreviation of the additive (e.g., ABS 0.001% GUP).

Mixture	Dry Density (g/cm³)	Average Maximum Compressive Strength, q_u (MPa)	Average Stiffness Modulus, E (MPa)
ABS Mix [10]	2.08 ± 0.03	2.51 ± 0.17	285 ± 17
ABS 0.001% GUP	2.34 ± 0.04	2.26 ± 0.26	162 ± 68
ABS 0.005% GUP	2.32 ± 0.03	2.15 ± 0.34	128 ± 59
ABS 0.01% GUP	2.11 ± 0.02	2.08 ± 0.02	166 ± 25
ABS 0.05% GUP	2.08 ± 0.05	1.48 ± 0.41	111 ± 36
ABS 0.1% GUP	2.02 ± 0.01	1.16 ± 0.17	110 ± 19
ABS 0.005% GSL	2.25 ± 0.03	2.27 ± 0.34	145 ± 86
ABS 0.01% GSL	2.27 ± 0.03	2.31 ± 0.48	161 ± 80
ABS 0.05% GSL	2.33 ± 0.05	2.08 ± 0.34	88 ± 17
T2 Mix	2.08 ± 0.03	0.76 ± 0.03	93 ± 49
T2 0.01% GUP	2.03 ± 0.04	0.46 ± 0.02	23 ± 9
T2 0.05% GUP	2.05 ± 0.02	0.32 ± 0.04	25 ± 7
T2 0.1% GUP	2.06 ± 0.06	0.25 ± 0.01	18 ± 4

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MDPI and ACS Style

Iorio Esposito, F.; Gallo Stampino, P.; Ceccarelli, L.; Caruso, M.; Dotelli, G.; Sabbadini, S. Towards Environmentally Friendly Buildings: An Assessment of the Mechanical Properties of Soil Mixtures with Graphene. C 2025, 11, 16. https://doi.org/10.3390/c11010016

AMA Style

Iorio Esposito F, Gallo Stampino P, Ceccarelli L, Caruso M, Dotelli G, Sabbadini S. Towards Environmentally Friendly Buildings: An Assessment of the Mechanical Properties of Soil Mixtures with Graphene. C. 2025; 11(1):16. https://doi.org/10.3390/c11010016

Chicago/Turabian Style

Iorio Esposito, Federico, Paola Gallo Stampino, Letizia Ceccarelli, Marco Caruso, Giovanni Dotelli, and Sergio Sabbadini. 2025. "Towards Environmentally Friendly Buildings: An Assessment of the Mechanical Properties of Soil Mixtures with Graphene" C 11, no. 1: 16. https://doi.org/10.3390/c11010016

APA Style

Iorio Esposito, F., Gallo Stampino, P., Ceccarelli, L., Caruso, M., Dotelli, G., & Sabbadini, S. (2025). Towards Environmentally Friendly Buildings: An Assessment of the Mechanical Properties of Soil Mixtures with Graphene. C, 11(1), 16. https://doi.org/10.3390/c11010016

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