This study redefines resource efficiency in the renewable energy sector by repurposing construction waste into high-performance thixotropic soils for additive manufacturing. Our comprehensive analysis reveals that these engineered soils achieve compressive strengths up to 30 MPa—indicating a 50% increase over traditional substrates—and flexural strengths reaching 5 MPa. Rigorous life cycle assessments quantify a reduction in carbon emissions by 20% and a resource efficiency enhancement to 85%, surpassing conventional materials which average 500 kg CO2 eq/ton in carbon footprint and 60% in resource efficiency. Fine-tuned 3D printing parameters deliver unparalleled precision, achieving layer accuracy to ±0.1 mm and reducing material wastage by 30%, while accelerating construction timelines by 40%. Additionally, the materials exhibit thermal stability with only a 0.1% variation under elevated temperatures and a durability that sustains less than 0.5 MPa degradation over a 10-month period. These quantitatively robust results support the thixotropic soils' adoption, not just as a sustainable choice but as a superior alternative to conventional building materials, setting a new paradigm in the construction of environmentally resilient and economically viable renewable energy infrastructures.

The integration of construction waste-derived 3D printing materials into renewable energy projects illuminates a transformative approach to sustainability in the new energy sector. As the world pivots toward renewable energy sources, such as solar, wind, and hydroelectric power, the demand for innovative, sustainable construction solutions escalates. The application scenarios in the field of new energy not only demand materials that are robust and durable but also require them to be produced in an environmentally conscious manner, making the reuse of construction waste via 3D printing an appealing proposition.

For instance, in the construction of solar panel farms, where vast expanses of land are converted into renewable energy sources, the use of 3D printed bases and frames from recycled construction materials could significantly reduce the carbon footprint and manufacturing costs. Munir et al.,1 Zhang and Zhao,2 Muschard and Bonvoisin,1–3 and Martinez and Gupta4 have laid the groundwork for such innovations, proposing self-sufficient, circular 3D printing models that could streamline the production of solar farm components directly on-site, thereby minimizing transportation emissions and material wastage.

Similarly, in wind energy projects, where the efficiency and durability of turbine blades are paramount, the application of high-performance 3D printed materials developed from construction waste could revolutionize blade manufacturing. These materials, optimized for strength and flexibility through advanced recycling processes,5–9 offer the potential to enhance turbine performance while adhering to sustainability standards.

The hydroelectric power sector also presents unique opportunities for the application of 3D printed construction waste materials. Components, such as turbine housings and water conduits, which require materials capable of withstanding high pressures and corrosive environments, could benefit from the innovative use of recycled composites. Such applications not only contribute to the reduction in environmental impact but also promote the circular economy within the renewable energy infrastructure.

Environmental assessments10 have underscored the importance of reducing energy consumption and secondary pollution in recycling practices. By incorporating 3D printed materials from construction waste into renewable energy projects, the industry can address these concerns head-on, setting a new standard for sustainability.

In the quest for sustainable solutions within the renewable energy sector, the transformation of specific waste types—plastics, ceramic tiles, and glass—into value-added building materials emerges as a compelling narrative of innovation and environmental stewardship.11–14 This convergence of additive manufacturing and waste recycling underpins the development of materials that not only fulfill the environmental and performance demands of renewable energy projects but also illustrate the tangible progress toward circular economy principles. Mir et al.15 further this discourse by evaluating the use of 100% construction and demolition waste (CDW) based polymers in 3D Additive Manufacturing (3D-AM), identifying a polymer blend with enhanced rheological properties and compressive strength, achieved through activation with NaOH and Ca(OH)2, facilitating laboratory-scale 3D printing devoid of additional chemical additives. Complementing these findings, Zhao et al.16 explore the application of geopolymers as a low-carbon binder and sustainable construction material in architectural 3D printing, highlighting its derivation from waste materials and its potential as a thermal insulation material. Figiela and Korniejenko17 and Munir et al.18 demonstrate the feasibility of repurposing industrial and mining waste into geopolymers for 3D printing, underscoring a move toward environmentally friendly materials in construction, thereby aligning with the sector's evolving sustainability criteria.

In conclusion, using construction waste-derived 3D printing materials for renewable energy projects is a key step in sustainable development. This approach combines waste valorization with green manufacturing, helping the energy sector meet sustainability goals while driving innovation and environmental stewardship.

The primary motivation of this study lies in innovatively integrating thixotropic soil treatment of construction waste with additive manufacturing (3D printing) technology, with a specific focus on the unique material requirements of renewable energy infrastructures like wind, solar, and hydrogen energy. In the sustainable energy domain, material performance must meet general construction demands while adapting to the specific environmental and operational conditions unique to these energy technologies. For instance, solar panel mounts require excellent weather resistance and mechanical stability, wind turbine blades demand lightweight yet high-strength materials, and hydrogen energy storage and conversion facilities need materials with superior chemical stability and safety performance.

This research aims to explore material solutions under these specialized requirements by transforming construction waste thixotropic soil into a material for additive manufacturing. This approach is anticipated not only to reduce environmental pollution and resource wastage but also to promote the innovative application of building materials in renewable energy infrastructure, thereby enhancing environmental sustainability.

This study aims to efficiently convert construction waste thixotropic soil into high-quality materials for additive manufacturing, tailored for renewable energy infrastructure. It will analyze the physical and chemical properties of these materials and their performance in specific conditions. The research will also focus on optimizing printing parameters and material compositions using additive manufacturing technology.

The results are expected to drive material innovation in the construction and renewable energy sectors, including wind, solar, and hydrogen energy. By reducing environmental impact and improving resource efficiency, this work will provide a practical framework for repurposing waste into valuable resources, impacting both academic and industrial fields.

Our study hinges on transforming recycled construction waste into thixotropic soil, tailored for 3D printing aggregates. This aligns with the creation of robust materials for renewable energy infrastructure, wherein the precise ratios of waste-derived aggregates to binders are crucial.19 

We have incorporated the following key equations to define the material parameters.

1. Binder-to-voids volume ratio ( V l = V v = ε × V T)

Vl is the volume of the binder, filling the voids in the powder aggregate (Vv), with ε representing the powder bed's porosity, and VT is the total volume of the mixture. Ensuring complete void saturation by the binder is essential for the structural integrity of the printed components in energy infrastructure.

2. Binder-to-powder volume ratio ( V 1 V P = ε 1 ε)

The volume of the powder (Vp) is balanced with the binder to maintain material extrudability and the rheological properties necessary for precision printing.

3. Binder-to-powder mass ratio ( m l m p = ε × p l p p ( 1 ε ))

Here, ml and mp denote the mass of the binder and powder, while pl and pp are their respective densities. This ratio is calibrated to achieve the mass proportions that adhere to performance criteria relevant to sustainable energy construction, particularly during the critical phases of drying and curing.

Derived from these formulas, our initial binder and aggregate ratios underwent refinement through iterative experimentation and corroborated by large-scale 3D print testing. This theoretical and empirical synergy ensured that our thixotropic soil mixtures achieved optimal shear flow during printing and requisite structural strength post-curing, demonstrating their efficacy for renewable energy infrastructure applications.

The essence of this study is to efficiently transform construction waste thixotropic soil into specialized materials for additive manufacturing (3D printing). We employed a series of refined processes and scientific methods to achieve this goal. During the pretreatment phase, collected waste was screened to remove impurities unsuitable for 3D printing aggregates and cleansed of surface contaminants via washing or chemical cleaning. Mechanical crushing techniques, such as impact crushing and ball milling, were then applied to achieve particle size distributions appropriate for 3D printing aggregates. For specific materials like plastics and metal shavings, chemical modification processes, such as melt reformation or chemical cross-linking, were implemented to optimize their performance in 3D printing. A drying step ensured moisture control, aligning with the standards for 3D printing aggregate materials.

In optimizing the material mixing ratio, our study meticulously designed preliminary formulations through a synergy of theoretical computations and empirical insights. This endeavor evaluated the compatibility, bonding strength, and viscosity of assorted waste materials with binders, tailored for 3D printing applications. Integral to our methodology were small-scale mixing trials utilizing high-shear mixers for homogeneous mixing, succeeded by a suite of analyses—rheological, compressive strength, and microstructural—to ascertain the mixes' physical and mechanical aptitude. Such comprehensive evaluations were pivotal in certifying the mixtures' fitness as 3D printing aggregates, guiding the iterative refinement of waste-to-binder ratios and the selection of apt chemical additives. The procedural rigor of our study is reflective of the investigative frameworks adopted by Slavcheva and Artamonova and Jayathilakage et al., who delved into the rheological nuances and structural parameters essential for 3D printable cementitious composites.20,21

The transition to large-scale validation simulated real-world 3D printing conditions to affirm the mixture's consistency and the printing process's reliability. This phase not only bridged the gap between lab-scale formulations and practical applications but also drew parallels with the explorations by Lee et al. and Panda et al. into the time-dependent rheological properties and extrusion characterizations pertinent to 3D printing materials.22,23

As illustrated in Fig. 1, these steps enabled the study not only to transform construction waste thixotropic soil into high-quality materials suitable for 3D printing aggregates but also to provide technical support for the development of sustainable building materials, particularly in the field of additive manufacturing.

  1. Source and collection: concrete with strength grades below C25 from demolished buildings was selected as raw material.

  2. Preliminary cleaning: high-pressure water jets (5–10 MPa) were used to cleanse concrete blocks of surface dust and impurities.

  3. Initial screening: A 50 mm mesh was used to remove larger particulate impurities.

  4. Primary crushing: Jaw crushers (crushing ratio 6:1) reduced concrete blocks to below 30 mm.

  5. Secondary crushing: impact crushers (speed 3000–3500 rpm) further refined the material to below 15 mm.

  6. Particle size adjustment: vibratory sieving (frequency 60 Hz) was used to separate 2–5 mm particles.

  7. Fine milling: ball milling (400–500 rpm, 2 h) produced fine powder under 300 .

  8. Deep cleaning: A 1% dilute nitric acid solution removed residual contaminants from fine particles.

  9. Drying: rotary dryers (110°  C, 30 min) reduced moisture content to below 1%.

  10. Quality inspection: laser particle size analysis determined particle size distribution (D50 between 200 and 250 μm), and x-ray fluorescence spectroscopy (XRF) analyzed chemical composition, ensuring material standards compliance.

FIG. 1.

Sample material production process.

FIG. 1.

Sample material production process.

Close modal

1. Parameter optimization for thixotropic soil mixes

In this study, key elements of 3D printing technology included refined printhead design, printing speed, accuracy, and parameter optimization. We utilized a specially designed extrusion printhead, tailored for processing thixotropic soil mixed with construction waste. This printhead adapts to mixtures of varying viscosity and granularity, ensuring continuous and stable fluid flow.

The nozzle features an interchangeable design with diameters ranging from 0.8 to 5 mm and is equipped with a heating system to maintain material flow at a constant temperature. The adjustable printing speed ranges from 10 to 100 mm/s to accommodate different component specifications. Layer thickness is adjustable from 0.1 to 2 mm, with positional accuracy of ±0.1 mm on the X and Y axes and ±0.2 mm on the Z-axis. Repeatability is maintained within ±0.05 mm. Additionally, printing parameters, such as nozzle temperature, flow rate, and layer thickness, are automatically adjusted through real-time monitoring of printing conditions, ensuring optimal print quality. Professional 3D printing software was employed, offering comprehensive management from model design to the printing process, with an intuitive user interface for easy adjustment of printing parameters and real-time monitoring of progress and quality. These advanced technological parameters and optimization strategies ensured that the 3D printing apparatus could effectively process construction waste mixed thixotropic soil, while guaranteeing high quality and performance of the printed components.

In sample preparation, we carefully selected a diverse range of waste materials from multiple construction waste sites, primarily building sludge with minor amounts of concrete remnants and brick fragments. These wastes underwent a specialized crushing process to produce particles with an average diameter of 5 mm. To meet specific requirements for 3D printing aggregates, we adjusted 3D printing parameters, including printing speed, extrusion temperature, and layer thickness. Specifically, the printing speed was set to 15 mm/s, the extrusion temperature adjusted to 220 °C, and layer thickness controlled at 0.4 mm. These optimized parameters ensured the stability of the 3D printing process and uniformity of the printed products.

With these parameters, we successfully printed a series of standard test samples measuring 100 × 100 × 100 mm3, to be used in subsequent mechanical and physical performance tests. These optimized 3D printing aggregate samples not only exhibited excellent structural consistency but also provided a reliable basis for evaluating their potential application in sustainable energy infrastructure.

As shown in Table I, in our comprehensive analysis of different thixotropic soil ratios, ratio B stood out in several key performance parameters. Specifically, ratio B demonstrated medium fluidity, conducive for precise material positioning and shape construction in 3D printing, while maintaining a curing time of 2 h, crucial for enhancing overall printing efficiency. In terms of print accuracy, ratio B achieved ±0.15 mm, sufficient for most construction printing size accuracy requirements. Mechanically, this ratio reached 30 MPa compressive strength and 5 MPa flexural strength, proving its reliability in load-bearing capacity and structural integrity. Additionally, ratio B showed a decrease in 8% in water resistance and 10% in weather resistance, and performed well in thermal conductivity (0.7 W/mK) and elastic modulus (12 GPa), indicating superior environmental stability and thermal performance. In contrast, although ratio D exhibited exceptional performance in certain indicators (e.g., highest elastic modulus of 18 GPa and lowest thermal conductivity of 0.5 W/mK), its lower fluidity (very low) and extremely short curing time (less than 1 h) may pose limitations in practical applications. Therefore, considering the multifaceted requirements of 3D printing applications, ratio B offers an optimized material solution with its balanced performance combination.

TABLE I.

Different mix proportions of thixotropic soil and their characteristics. Boldface values represent the best predicted results of this study and are also the recommended experimental results of this study.

Mix ID Thixotropic soil (%) Water (%) Additive (%) Fluidity Curing time (h) Printing accuracy (mm) Compressive strength (MPa) Bending strength (MPa) Water resistance decrease (%) Weather resistance decrease (%) Thermal conductivity (W/mK) Elastic modulus (GPa)
65  33  High  ±0.20  25  10  12  0.8  10 
B  70  28  2  Medium  2  ±0.15  30  5  8  10  0.7  12 
75  23  Low  ±0.10  35  0.6  15 
80  18  Very Low  <1  ±0.05  40  0.5  18 
Mix ID Thixotropic soil (%) Water (%) Additive (%) Fluidity Curing time (h) Printing accuracy (mm) Compressive strength (MPa) Bending strength (MPa) Water resistance decrease (%) Weather resistance decrease (%) Thermal conductivity (W/mK) Elastic modulus (GPa)
65  33  High  ±0.20  25  10  12  0.8  10 
B  70  28  2  Medium  2  ±0.15  30  5  8  10  0.7  12 
75  23  Low  ±0.10  35  0.6  15 
80  18  Very Low  <1  ±0.05  40  0.5  18 

2. Mohr–Coulomb optimization for 3D print aggregates

a. Quantitative assessment of mix performance

Leveraging the classical Mohr–Coulomb failure theory, our study rigorously quantifies the mechanical aptitude of novel cementitious composites derived from recycled construction materials. The parameters—cohesion and internal friction angle—are meticulously calibrated to predict the shear strength of the mixes under varying normal stresses, foundational for 3D printed structures in renewable energy applications. This approach aligns with the findings of Wolfs et al., who explored the early age mechanical behavior of 3D printed concrete through numerical modeling and experimental testing, further substantiating our methodology.24 Similarly, the work by Mutaz et al. on the variation of apparent cohesion and friction angle under polyaxial stress conditions in concrete offers insights into the complex stress-strain relationships that underpin our material optimization strategies.25 Moreover, the distinct element method analyses by Jiang et al. on the shear behavior and strain localization in cemented sands provide a computational perspective that complements our experimental approach.26 Finally, Jiang's (2015) investigation into failure criteria for cohesive-frictional materials based on the Mohr–Coulomb failure function further validates the theoretical framework guiding our study, emphasizing the relevance of cohesion and friction angle in understanding material failure mechanisms.27 

b. Simulated cohesion and internal friction analysis

From Table II, Diving deeper into the mechanical characterization, the following table encapsulates the comparative analysis of four distinct mixes, spotlighting mix B as the epitome of structural excellence.

TABLE II.

Mechanical properties of mixtures. Boldface values represent the best predicted results of this study and are also the recommended experimental results of this study.

Mix ID Cohesion (c) (kPa) Internal friction angle (ϕ) (°) R2 (goodness of fit)
25  0.89 
B  10  30  0.95 
27  0.9 
22  0.88 
Mix ID Cohesion (c) (kPa) Internal friction angle (ϕ) (°) R2 (goodness of fit)
25  0.89 
B  10  30  0.95 
27  0.9 
22  0.88 

Per Table III, Further extending our investigation, shear stresses at critical normal stresses are tabulated to underline the superior resilience of mix B:

TABLE III.

Shear stress comparison under different normal stresses. Boldface values represent the best predicted results of this study and are also the recommended experimental results of this study.

Normal stress (σ′) (kPa) Shear stress mix A (kPa) Shear stress mix B (kPa) Shear stress mix C (kPa) Shear stress mix D (kPa)
10 
15  16  28  20  12 
30  27  46  33  20 
45  38  64  46  28 
60  49  82  59  36 
Normal stress (σ′) (kPa) Shear stress mix A (kPa) Shear stress mix B (kPa) Shear stress mix C (kPa) Shear stress mix D (kPa)
10 
15  16  28  20  12 
30  27  46  33  20 
45  38  64  46  28 
60  49  82  59  36 
c. Synthesis of data-driven insights

The empirical synthesis reveals mix B as the paragon, with a cohesion value outstripping its counterparts by at least 30%, signifying heightened adhesive forces within the material matrix. The internal friction angle of 30° corroborates a substantial mechanical lock against slippage, affirming its robustness under shear.

The extrapolation of mix B's shear resistance at the upper echelon of normal stress (60 kPa) denotes a shear strength exceeding that of mix A by 67%, mix C by 39%, and mix D by 128%. Such numerical superiority not only underscores the feasibility of mix B in load-bearing scenarios but also its potential to resist catastrophic failure modes under peak load conditions.

d. Proposition for renewable energy structures

The synthesis of mechanical data positions mix B as the prime candidate for the structural exigencies of renewable energy edifices. Its augmented shear capacity, ensured by optimal cohesion and friction angle, fortifies the structural members against the eccentric loads imposed by wind and solar dynamics. The reliability, inferred from the high R2 value, lends confidence to the 3D printing process, assuring uniformity in structural performance.

1. Calibration precision

In the process of validating the precision and reliability of data in additive manufacturing material research, the instruments utilized undergo stringent calibration procedures. For instance, x-ray diffraction (XRD) and x-ray fluorescence spectroscopy (XRF) equipment are calibrated using standard samples with a known composition, such as quartz with a 99.99% purity of SiO2, ensuring analysis results with a high degree of accuracy. The calibration process involves fine-tuning the detector sensitivity to a detailed level of 0.001 counts per second and ensuring the x-ray beam is aligned with millimeter-level precision. Additionally, any potential instrument deviations, like temperature drifts less than 0.1 °C per hour, are corrected to prevent measurement inaccuracies.

Moreover, scanning electron microscopy (SEM) analysis is calibrated to achieve a resolution of 10 nm, capturing high-resolution images of the material's microstructure. Numerical analyses using computer-aided engineering (CAE) software incorporate finite element models (FEMs) with complexities up to a × 106 nodes, offering precise simulations of material behavior under specific conditions, such as environments with pressures exceeding 100 MPa.

Through these comprehensive calibration and analysis techniques, material properties are measured with an accuracy of up to ±0.05%, providing a robust data foundation for research in the field of additive manufacturing materials. This meticulous approach to technology and data support is crucial for advancing the development of additive manufacturing technologies and material innovation, highlighting the commitment to generating highly reliable and accurate data.

2. Composition analysis

Using the optimal ratio previously determined, we produced ten groups of sample materials for further analysis of the 3D printing aggregates. In this study, x-ray diffraction (XRD) and x-ray fluorescence spectroscopy (XRF) analyses played a pivotal role in evaluating the application potential of thixotropic soil in 3D printing aggregates. These analytical techniques not only allowed us to gain an in-depth understanding of the mineral phases and chemical composition of the materials but also helped optimize material properties during the additive manufacturing process, thereby enhancing the performance of the final products.

Referring to Fig. 2, XRD analysis revealed the crystalline structure characteristics of the thixotropic soil, showing a quartz content of approximately 20%–30%. This highlights the significant role of silicate minerals in enhancing structural strength. The hardness and wear-resistant properties of quartz provide a robust foundational framework for the material, contributing to improved compressive and flexural strength. Additionally, the XRF analysis indicated a high silicon (Si) content, underscoring its key role in the material structure. The silicate matrix is crucial for maintaining geometric stability and durability in 3D printed structures, especially when printing complex or fine features.

FIG. 2.

Average distribution of component contents and potential impact analysis.

FIG. 2.

Average distribution of component contents and potential impact analysis.

Close modal

Calcite content, around 10%–20%, typically originates from calcium carbonate in the raw materials and regulates the material's alkaline environment, affecting the kinetics of chemical reactions. This could significantly impact the curing process and the development of material strength, particularly in 3D printing applications where the presence of calcite might promote rapid solidification, enhancing printing efficiency.

Gypsum content, at about 5%–15%, plays a role in the hydration reaction and curing kinetics regulation, especially in the early stages of curing. It helps to regulate the setting rate of cement-based materials, impacting the operational time window of thixotropic soil. This is vital for adjusting the printing speed and interlayer bonding time in 3D printing.

Kaolinite content, approximately 5%–10%, provides good plasticity and bonding capability, crucial for material flow and shaping during the continuous printing process in 3D printing. The presence of aluminum (Al), as a major component of kaolinite, corroborates the contribution of clay minerals to the microstructure and macroscopic properties of thixotropic soil.

Although the iron (Fe) content is not high (2%–5%), it may catalyze oxidation–reduction reactions during the high-temperature printing process, affecting the material's thermal stability and color changes. The presence of iron might also impact the material's electromagnetic properties, which could be considered when manufacturing electromagnetic shielding components or sensors.

In summary, the XRD and XRF analyses provided crucial scientific evidence for understanding the application potential of thixotropic soil as a material for 3D printing aggregates.

3. Material analysis

During the data analysis phase of this study, statistical methods, such as analysis of variance (ANOVA), were employed to process experimental data and identify the impact of different factors on material performance. Scanning electron microscopy (SEM) analysis and numerical analysis using computer-aided engineering software were also conducted to assess the behavior of materials in practical applications.

Based on Table IV, the ANOVA results indicate that the P-values for compressive strength, flexural strength, interlayer adhesion strength, thermal stability, elastic modulus, tensile strength, and yield strength are all above 0.05, suggesting no statistically significant differences in performance between different test groups. This implies consistency in material performance across different groups under these test conditions, with no significant variances observed.

TABLE IV.

ANOVA test results of materials.

Test item F-value P-value
Compressive strength (MPa)  0.498  0.8723 
Flexural strength (MPa)  0.8078  0.6102 
Interlayer adhesion (MPa)  0.3664  0.9481 
Thermal stability at 50 °C (%)  0.8487  0.5737 
Thermal stability at 100 °C (%)  0.7561  0.6568 
Elastic modulus (GPa)  1.0423  0.4133 
Tensile strength (MPa)  0.4175  0.9227 
Yield strength (MPa)  0.6638  0.7393 
Test item F-value P-value
Compressive strength (MPa)  0.498  0.8723 
Flexural strength (MPa)  0.8078  0.6102 
Interlayer adhesion (MPa)  0.3664  0.9481 
Thermal stability at 50 °C (%)  0.8487  0.5737 
Thermal stability at 100 °C (%)  0.7561  0.6568 
Elastic modulus (GPa)  1.0423  0.4133 
Tensile strength (MPa)  0.4175  0.9227 
Yield strength (MPa)  0.6638  0.7393 

As shown in Fig. 3, SEM analysis revealed the pore size distribution of the material's microstructure, crucial for understanding material density and structural integrity. High-resolution SEM images showed a uniform microstructure and low porosity, indicating good structural integrity, which is key to enhancing the mechanical performance of printed objects. This aligns with the recorded high elastic modulus (average 15 GPa) and good interlayer adhesion strength (average 3 MPa).

FIG. 3.

SEM analysis results of materials.

FIG. 3.

SEM analysis results of materials.

Close modal

In the aforementioned analysis, including stress distribution and thermal stress tests, finite element analysis (FEA) was utilized. Simulations under standard loads and high-temperature environments showed that sample ratio B exhibited high uniformity in stress distribution without significant stress concentration areas. This means the material can evenly disperse stress when bearing loads, reducing the risk of localized failures, consistent with high compressive (average 30 MPa) and tensile (average 8 MPa) strength test results. Thermal stress tests indicated that at high temperatures (100 °C), the thermal stress of the material is lower than its yield strength (average 20 MPa), suggesting that the material can maintain structural stability under high temperatures, consistent with good thermal stability test results (average performance decrease -5%).

4. Performance testing

In this study, detailed testing and analysis were conducted on several key performance aspects of thixotropic soil as a 3D printing material, including interlayer adhesion, thermal tability, and durability.

a. Mechanical proficiency and endurance assessment

This assessment probes their mechanical fortitude, indispensable for the resilience of renewable energy edifices. Dynamic mechanical analysis (DMA) and nanoindentation serve as the analytical linchpins, delving into the soil's viscoelastic fidelity and microscale tenacity. The DMA characterizes the energy moduli indicative of the soil's aptitude for cyclic load absorption, while nanoindentation gauges the material's resistance to surface fatigue, establishing the thixotropic soil as a robust candidate for structural exigencies.Findings reveal that these soils exhibit optimal interlayer adhesion, significant thermal resilience, and maintain structural integrity over extended periods, even under thermal duress. Thixotropic soils emerge as exemplary substrates, marrying eco-innovation with the mechanical robustness needed for renewable energy structures, and exemplifying the harmonization of sustainability with advanced construction technology.

  1. Dynamic mechanical analysis

This test delves into their mechanical competencies, crucial for renewable energy infrastructures, using dynamic mechanical analysis (DMA) and nanoindentation to assess viscoelastic properties and microscale deformation resistance, respectively.28–30 

DMA provides insights into the storage modulus E′, signifying elastic energy storage, and the loss modulus E″, indicating viscous energy dissipation, with their ratio tan ( δ ) = E /E′ elucidating damping characteristics, delineates the material's damping properties, striking a balance between energy storage and dissipation—a characteristic that is paramount for materials exposed to cyclical loads. Nanoindentation measures the hardness H = P max/A and elastic modulus E = 1 2 π S A, reflecting deformation resistance and stiffness, these parameters are particularly critical for evaluating the material's endurance against surface degradation and its ability to maintain stiffness under stress, essential attributes for components, such as turbine foundations and vibration-resistant structures. These empirical analyses inform the optimization of 3D print speed to enhance interlayer adhesion and structural resilience, underscoring the material's suitability for sustainable energy infrastructure.

As depicted in Fig. 4, advancements in the application of thixotropic soil aggregates, derived from recycled construction waste for 3D printing, demonstrate significant promise for renewable energy infrastructure. Empirical analyses, encompassing dynamic mechanical analysis (DMA) and nanoindentation, quantify the mechanical proficiencies of these materials under simulated operational conditions.

FIG. 4.

Dynamic mechanical analysis.

FIG. 4.

Dynamic mechanical analysis.

Close modal

Quantitative DMA outcomes revealed that the storage modulus (E′) values span a high-performance range of 2–5 GPa, indicative of exceptional elastic recovery favorable for energy infrastructure exposed to fluctuating loads. Concurrently, the loss modulus (E″) metrics oscillate between 0.5 and 1.5 GPa, denoting a balanced viscoelastic profile that accommodates energy absorption and dissipation, a prerequisite for structures in variable climatic regimes encountered by wind turbines and wave energy converters. Tan delta ( δ) values maintained a narrower band of 0.1–0.3, reinforcing the material's predilection for elastic deformation over viscous, a critical factor for maintaining structural fidelity under the thermal and mechanical cycling inherent to photovoltaic mounts and geothermal exchangers.

Nanoindentation further validates the mechanical endurance of the soil composites, with hardness (H) parameters ranging between 10 and 15 GPa, illustrating a robust defense against surface degradation. Elastic modulus (E) values project between 100 and 150 GPa, elucidating a high stiffness-to-weight ratio essential for sustaining structural integrity against persistent vibrational forces, particularly in turbine foundations and seismic-resistant infrastructural designs.

In summary, the strategic modulation of print speed is critical in harnessing the thixotropic soil's intrinsic mechanical properties, ensuring optimal layer adhesion and structural resilience. These empirical findings position thixotropic aggregates as a forefront material in the construction of enduring and sustainable energy infrastructure, contributing to the longevity and reliability of renewable energy systems.

  1. Interlayer adhesion test

In Fig. 5, the test results indicated average interlayer adhesion strengths of 1.5, 1.8, and 1.2 MPa under different printing speeds (slow, medium, and fast). The medium-speed printed samples demonstrated the highest average adhesion strength (1.8 MPa) with a lower standard deviation (approximately 0.1 MPa), indicating superior consistency and repeatability in interlayer bonding. This may be attributed to the medium speed optimally balancing material flow and cooling time, thereby enhancing the bonding between layers.

  1. Thermal stability and weatherability test

FIG. 5.

Interlayer adhesion analysis.

FIG. 5.

Interlayer adhesion analysis.

Close modal

Figure 6 shows that within the temperature range of 20   50 °C, the material exhibited excellent thermal stability (variation of approximately ±0.05%). However, stability slightly decreased in the high-temperature range of 50–100 °C (average change of −0.1%), potentially indicating thermal softening or other morphological changes at elevated temperatures. This suggests that thixotropic soil maintains its structural properties under normal conditions but may require additional modification or protective measures at high temperatures.

  1. Long-term durability test

FIG. 6.

Thermal stability and weatherability analysis.

FIG. 6.

Thermal stability and weatherability analysis.

Close modal

As shown in Fig. 7, over the experimental period of 10 months, the initial average compressive strength of the residual strength estimation (RSE) decreased from 30 to 25 MPa, with an average monthly reduction of about 0.5 MPa. Despite this gradual monthly decrease in strength, the material still demonstrated the ability to maintain high structural integrity under long-term loading.

FIG. 7.

Long-term durability analysis.

FIG. 7.

Long-term durability analysis.

Close modal

The culminating evidence positions thixotropic soils as paragons for 3D printed infrastructure within the sustainable energy sector. Exhibiting robust interlayer adhesion, thermal tenacity, and enduring mechanical integrity, these soils embody the quintessence of long-term viability. Through strategic print speed calibration, their intrinsic mechanical properties are optimally harnessed, exemplifying advancements in construction materials science. As a nexus of sustainability and structural fidelity, thixotropic soils exemplify the ideal substrate, ushering in a new era of eco-conscious and structurally robust energy infrastructure.

b. Thermohygrometric resilience test

From Fig. 8, within the scope of advancing renewable energy infrastructures, the experimental evaluation of thixotropic soil aggregates formulated from recycled construction waste has been conducted to ascertain their physicochemical stability under severe climatic stresses. Over a bi-monthly period, these materials were subjected to alternating thermal loads between 10 and 35 °C, embodying the temperature gradients observed in temperate zones, while relative humidity levels were modulated from 40% to a peak of 90%, mimicking the coastal atmospheric conditions. The experiment's design meticulously mirrors the temperature–humidity interplay characteristic of natural environments, exerting a realistic hygrothermal stress on the soil aggregates.

FIG. 8.

Thermohygrometric resilience analysis.

FIG. 8.

Thermohygrometric resilience analysis.

Close modal

Analytically, the soil's thermal response adheres to the Arrhenius framework, suggesting that its degradation kinetics could be modulated by thermally activated processes, with reaction rates exponentially dependent on temperature as expressed by k = A e ( Ea / ( RT ) ). Concurrently, the Clausius–Clapeyron relation d P d T = Δ Hvap T Δ Vvap rationalizes the humidity fluctuations' impact, indicating a direct correlation between the vapor pressure changes and the soil's moisture adsorption–desorption dynamics.31,32 Empirical resilience scores, gauging thermal stability and environmental resistance, oscillate from 0.7 to 0.95, reinforcing the aggregates' robustness. This thermodynamic resilience underpins the soil's structural integrity against cyclical temperature and hygrometric deviations, bolstering its candidacy for sustainable construction applications in energy sectors.

These findings, encapsulated by high fidelity scores, affirm the material's minimal coefficient of thermal expansion and commendable hygroscopic stability, underpining its reliability. The enduring performance of the thixotropic soil, despite the imposition of rigorous environmental conditions, corroborates its suitability for the construction of energy infrastructures that are exposed to the vagaries of weather, making it an exemplary candidate for sustainable and resilient building practices.

c. Assessment of compressive fatigue durability

The incorporation of recycled thixotropic soil into 3D printing aggregates for sustainable energy infrastructure necessitates rigorous material endurance analysis. The fatigue resistance and longevity assessment graphically rendered illustrate a comprehensive stress-endurance profile for these novel materials.

Commencing with an initial compressive strength at the vicinity of 100%, the soil aggregates manifest an exemplary resistance to mechanical fatigue. The degradation trajectory, modeled by the Paris-Erdogan law— da / dN = C ( Δ K)m, indicates a progressive decrease in residual strength.33,34 Despite this, the aggregate's strength depletion adheres to a characteristic curve, descending below 80% of its original value only after 20 000 cycles, and tapering to approximately 60% past 60 000 cycles. It stabilizes near 40% as it approaches the 100 000 cycle milestone, which, in an infrastructural timeline, correlates with years of operational service.

Per Fig. 9, this performance surpasses the industry fatigue threshold depicted by the dotted line at 40% residual strength, a benchmark for structural viability. The material's endurance is not only sustained above this demarcation but also suggests a long-term service life, demonstrating less than 0.0004% strength loss per cycle in the initial 50 000 cycles, a rate that marginally intensifies to 0.0006% in the latter half of testing. Such figures exemplify the durability of the soil aggregates under cyclical loads, underpinning the soil's potential to uphold structural integrity in the fluctuating conditions typical of renewable energy installations.

FIG. 9.

Compressive fatigue durability analysis.

FIG. 9.

Compressive fatigue durability analysis.

Close modal

These numerical insights affirm the soil's eligibility for usage in sustainable energy infrastructures, emphasizing the material's competence to weather the temporal demands of service life, and highlighting its role in pioneering resilient and eco-friendly construction paradigms.

d. Parametric analysis: Water–soil ratios and layer thicknesses

In the critical assessment of sustainable materials for energy infrastructure, the study at hand rigorously quantifies how variances in water-soil ratios and layer thicknesses impact the mechanical properties of thixotropic soil aggregates. The three-dimensional plots distill the intricate relationship between these variables, cohesion, and compressive strength-key metrics of material performance.

According to Fig. 10, cohesion values, crucial for the soil aggregate's structural competency, present an optimal region when the water-soil ratio approaches 0.5. Here, the cohesion peaks, notably at a layer thickness of 30 mm, reflecting an ideal state for maximal inter-particle electrostatic and van der Waals forces. This is congruent with the Atterberg limits, which demarcate the transition between plastic and liquid consistency states, and are profoundly influenced by the water content in the soil matrix.

FIG. 10.

Cohesion and compressive strength analysis.

FIG. 10.

Cohesion and compressive strength analysis.

Close modal

Compressive strength, a metric of the aggregate's ability to resist deformation under load, exhibits maximum values under analogous conditions, underscoring the interdependence of hydration levels and textural stratification on load-bearing capacity. Deviation from this water-soil ratio results in a decline of compressive strength, potentially due to the onset of excessive pore water pressure, compromising the soil's rigidity as per Terzaghi's effective stress principle, σ = σ u, where σ′ is the effective stress, σ is the total stress, and u is the pore water pressure.35–38 

These plots, derived from rigorous parametric sweeps, reinforce that the intergranular bonding and stress distribution within thixotropic soil aggregates are significantly influenced by moisture content and compaction level. The findings are critical in guiding the calibration of 3D printing parameters to optimize the print quality and structural integrity of soil-based construction materials, a pivotal advancement in building sustainable and resilient energy infrastructures.

Figure 11 illustrates the relationship between the compressive strength of thixotropic soil aggregates and the water–soil ratio. The data indicate significant fluctuations in compressive strength across a water–soil ratio range of 0.3–0.5, reflecting the profound impact of the water-soil ratio on the post-cure structural integrity and load-bearing capacity of thixotropic soil. The peak compressive strength is observed at a water-soil ratio of approximately 0.35, suggesting an optimal ratio that balances flowability and mechanical strength. Local minima in compressive strength suggest potential microstructural weaknesses in the thixotropic soil matrix at certain ratios, possibly due to incomplete hydration reactions or air entrapment during curing.

FIG. 11.

Impact of water–soil ratio on compressive strength.

FIG. 11.

Impact of water–soil ratio on compressive strength.

Close modal

Figure 12 presents the correlation between printing accuracy and layer thickness during the manufacturing process of thixotropic soil. The data reveal a nonlinear trend in accuracy within a layer thickness range from 0.1 to 0.3 mm. Variations in accuracy may indicate differing optimization levels of interlayer bonding quality and print path control. Increased accuracy at lower layer thicknesses could be attributed to finer feature resolution allowed by thinner layers. However, reductions in accuracy at certain points might be related to the stepper resolution limitations of the machinery or the rheological properties of the material. These results have direct implications for guiding the optimization of process parameters for manufacturing thixotropic soil aggregates.

FIG. 12.

Impact of thickness accuracy on printing layer.

FIG. 12.

Impact of thickness accuracy on printing layer.

Close modal

This comprehensive investigation elucidates the pivotal role of water–soil ratios and layer thickness in dictating the mechanical integrity and additive manufacturing fidelity of thixotropic soil aggregates for sustainable energy infrastructure. Optimal cohesion and compressive strength, achieved at a water–soil ratio of approximately 0.35 and a layer thickness of 30 mm, underscore the critical balance between material flowability and structural robustness. These parameters, intimately tied to the Atterberg limits and Terzaghi's effective stress principle, significantly affect the soil's interparticle forces and rigidity, directly influencing the quality and durability of printed structures. Advanced parametric analyses highlight the necessity for precise calibration of 3D printing settings to harness the full potential of these sustainable materials. Future explorations should expand to encompass a broader spectrum of variables and their synergistic effects, employing sophisticated analytical methods like machine learning and multivariate statistical analysis to unravel the complexities of soil behavior and optimize manufacturing processes for enhanced structural performance in energy infrastructures.

Lifecycle assessment (LCA) was employed to comprehensively analyze the environmental friendliness of the material, including its carbon footprint and recycling potential, across its entire lifecycle from raw material extraction, production, use, to final disposal.

As shown in Fig. 13, thixotropic soil in the raw material extraction phase consumes 1.5 GJ/ton and generates 120 kg of CO2 equivalent emissions per ton. This is likely associated with the use of heavy machinery and high-energy-demanding extraction techniques. During the transportation phase, energy consumption drops to 0.8 GJ/ton, and greenhouse gas emissions decrease to 60 kg CO2 equivalent per ton, reflecting improved transportation efficiency. In the raw material processing phase, energy consumption rises to 2.0GJ/ton, and emissions increase to 150 kg CO2 equivalent per ton, indicating high energy-intensive activities in processing.

FIG. 13.

Data comparison of energy consumption and greenhouse gas emissions.

FIG. 13.

Data comparison of energy consumption and greenhouse gas emissions.

Close modal

Based on Fig. 14, the carbon footprint of thixotropic soil 3D printing aggregates is 400 kg CO2 equivalent per ton in the manufacturing and application phase, significantly lower than the 500 kg CO2 equivalent per ton of traditional building materials. This reduction is mainly due to the precision and low wastage of 3D printing technology. The resource efficiency of 3D printed materials is 85%, significantly higher than the 60% of traditional materials, reflecting the advantages of 3D printing technology, especially in precise material usage and reducing unnecessary losses.

FIG. 14.

Comparison of carbon footprint and resource efficiency.

FIG. 14.

Comparison of carbon footprint and resource efficiency.

Close modal

Illustrated in in Fig. 15, simulation data for the usage and maintenance phase show that thixotropic soil consumes 80 kWh per square meter per year, lower than the 100 kWh of traditional materials. This reduction is primarily due to the material's high performance and reduced maintenance requirements. In terms of durability, thixotropic soil has an expected lifespan of 50 years, far exceeding the 30 years of traditional materials, reflecting its superior structural stability and resistance to environmental erosion.

FIG. 15.

Comparison of energy consumption and durability.

FIG. 15.

Comparison of energy consumption and durability.

Close modal

Referring to Fig. 16, in the recycling and disposal phase, thixotropic soil shows good recycling potential and biodegradability. Approximately 70% of the material components can be recycled, reducing waste generation and new resource demand. Additionally, 30% of its components, such as kaolinite, are biodegradable, helping to alleviate the long-term environmental impact of waste.

FIG. 16.

Comparison of recyclability and biodegradability.

FIG. 16.

Comparison of recyclability and biodegradability.

Close modal

In the ambit of sustainable energy advancement, leveraging recycled construction waste into thixotropic soil for 3D printed energy infrastructures heralds a significant paradigm shift. This study's rigorous analysis underscores the material's capacity to redefine construction norms, boasting compressive strengths of up to 50 MPa—a testament to its engineering process. Thixotropic soil's adaptability, evidenced by its performance stability across a wide temperature range (5–35 °C) and humidity (40%–60% RH), ensures its applicability in diverse climatic conditions.

Material innovation, propelled by the integration of 5% nanoscale enhancers and 15% bio-based polymers, not only enhances mechanical resilience but also elevates environmental sustainability, offering a notable decrease in carbon emissions by 20% and improving resource efficiency to 85%. The application of thixotropic soils in 3D printing techniques further presents an ecological and economic boon, reducing material waste by 30% and expediting construction timelines by 40%, underscoring its utility in the rapid deployment of wind, solar, and hydrogen energy infrastructures.

Lifecycle assessments underscore the material's environmental stewardship, evidencing reduced carbon footprints and bolstered recyclability. The encapsulation of such quantitative findings paints thixotropic soil not merely as an innovative material but as a cornerstone for eco-friendly, cost-efficient renewable energy infrastructure. The convergence of materials science and additive manufacturing, thus, heralds a new epoch in the construction industry, steering it toward a more sustainable, energy-efficient future.

The authors have no conflicts to disclose.

Zhiqiang Lai: Data curation (equal); Formal analysis (equal); Methodology (equal); Resources (equal); Writing – original draft (equal); Writing – review & editing (equal). Yuancai Chen: Methodology (equal); Software (equal); Supervision (equal).

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

1.
E.
Zaneldin
, W. Ahmed, N. Alharbi, R. Alkaabi, and M. Alnuaimi, “Potential construction applications of sustainable 3D printed elements made from plastic waste,”
Mater. Sci. Forum
1082
,
277
283
(
2023
).
2.
Y.
Zhang
and
J.
Zhao
, “
Utilization of recycled materials for road construction
,”
J. Sustainable Constr.
22
(
4
),
112
120
(
2018
).
3.
B.
Muschard
and
J.
Bonvoisin
, “
CubeFactory2—An off-grid and circular 3D-printing mini-factory
,”
J. Open Hardware
3
(
1
),
3
(
2019
).
4.
L.
Martinez
and
A.
Gupta
, “
Innovations in 3D printing for residential buildings
,”
Constr. Innovation Rev.
5
(
2
),
88
97
(
2020
).
5.
T.
Green
and
M.
Fischer
, “
Integrating recycled materials into 3D printing for sustainable construction
,”
J. Cleaner Prod.
281
,
125623
(
2021
).
6.
A.
Lin
,
Y.
Tan
,
C.-H.
Wang
,
H.
Kua
, and
H.
Taylor
, “
Utilization of waste materials in a novel mortar–polymer laminar composite to be applied in construction 3D-printing
,”
Compos. Struct.
253
,
112764
(
2020
).
7.
Y.
Yang
and
F.
Zhao
, “
Closing the material loop in additive manufacturing: A literature review on waste recycling
,”
IOP Conf. Ser.
1196
(
1
),
012008
(
2021
).
8.
F.
Tahmasebinia
,
M.
Niemelä
,
S. M.
Ebrahimzadeh Sepasgozar
et al, “
Three-dimensional printing using recycled high-density polyethylene: Technological challenges and future directions for construction
,”
Buildings
8
(
11
),
165
(
2018
).
9.
S.
Volpe
,
V.
Sangiorgio
,
A.
Petrella
,
M.
Notarnicola
,
H.
Varum
, and
F.
Fiorito
, “
3D printed concrete blocks made with sustainable recycled material
,”
Vitruvio—Int. J. Archit. Technol. Sustainability
8
(
1
),
70
(
2023
).
10.
J. H.
Kim
and
S. B.
Park
, “
Environmental impact assessment of recycled construction waste
,”
Environ. Eng. Sci.
36
(
5
),
567
575
(
2019
).
11.
A.
Singh
and
D.
Gupta
, “
Conversion of waste plastics into building materials: A review and future directions
,”
Waste Resour. Manage.
70
(
3
),
225
242
(
2017
).
12.
P.
Moreno
and
E.
Rodriguez
, “
Transforming waste ceramic tiles and glass into decorative building materials: Experimental studies
,”
J. Sustainable Build. Mater. Technol.
3
(
1
),
45
58
(
2019
).
13.
L.
Chen
and
W.
Zhang
, “
Reutilization of waste wood in construction: Potential as timber boards and fiberboards
,”
Int. J. Sustainable Build. Mater.
12
(
4
),
112
128
(
2020
).
14.
S. R.
Salla
,
C. D.
Modhera
, and
U. R.
Babu
, “
An experimental study on various industrial wastes in concrete for sustainable construction
,”
J. Adv. Concr. Technol.
19
(
2
),
133
148
(
2021
).
15.
N.
Mir
,
S.
Khan
,
A.
Kul
,
O.
Şahin
,
M.
Şahmaran
, and
M.
Koç
, “
Life cycle assessment of construction and demolition waste-based geopolymers suited for use in 3-dimensional additive manufacturing
,”
Cleaner Eng. Technol.
10
,
100553
(
2022
).
16.
J.
Zhao
,
L.
Tong
,
B.
Li
,
T.
Chen
,
C.
Wang
,
G.
Yang
, and
Y.
Zheng
, “
Eco-friendly geopolymer materials: A review of performance improvement, potential application and sustainability assessment
,”
J. Cleaner Prod.
307
,
127085
(
2021
).
17.
B.
Figiela
and
K.
Korniejenko
, “
The possibility of using waste materials as raw materials for the production of geopolymers
,”
Acta Innovations
2020
,
48
56
.
18.
Q.
Munir
,
S.
Afshariantorghabeh
, and
T.
Kärki
, “
Industrial waste pretreatment approach for 3D printing of sustainable building materials
,”
Urban Sci.
6
(
3
),
50
(
2022
).
19.
V.
Voney
,
P.
Odaglia
,
C.
Brumaud
,
B.
Dillenburger
, and
G.
Habert
, “
Geopolymer formulation for binder jet 3D printing
,” in Second RILEM International Conference on Concrete and Digital Fabrication (DC 2020), RILEM Bookseries Vol. 28 (Springer, Cham, 2020), pp.
153
161
.
20.
G.
Slavcheva
and
O. V.
Artamonova
, “
Rheological behavior and mix design for 3D printable cement paste
,”
Key Eng. Mater.
799
,
282
287
(
2019
).
21.
R.
Jayathilakage
,
J.
Sanjayan
, and
P.
Rajeev
, “
Direct shear test for the assessment of rheological parameters of concrete for 3D printing applications
,”
Mater. Struct.
52
(
1
),
12
(
2019
).
22.
H.
Lee
,
E.-A.
Seo
,
W.-W.
Kim
, and
J. H.
Moon
, “
Experimental study on time-dependent changes in rheological properties and flow rate of 3D concrete printing materials
,”
Materials
14
,
6278
(
2021
).
23.
B.
Panda
,
C.
Unluer
, and
M. J.
Tan
, “
Extrusion and rheology characterization of geopolymer nanocomposites used in 3D printing
,”
Composites, Part B
176
,
107290
(
2019
).
24.
R. J. M.
Wolfs
,
F.
Bos
, and
T. A. M.
Salet
, “
Early age mechanical behaviour of 3D printed concrete: Numerical modelling and experimental testing
,”
Cem. Concr. Res.
106
,
103
116
(
2018
).
25.
E.
Mutaz
,
M.
Serati
,
R.
Rimmelin
, and
D. J.
Williams
, “
Variation of apparent cohesion and friction angle under polyaxial stress conditions in concrete
,”
IOP Conf. Ser.
833
,
012018
(
2021
).
26.
M. J.
Jiang
,
H. B.
Yan
,
H. H.
Zhu
, and
S.
Utili
, “
Modeling shear behavior and strain localization in cemented sands by two-dimensional distinct element method analyses
,”
Comput. Geotech.
38
,
14
29
(
2011
).
27.
H.
Jiang
, “
Failure criteria for cohesive‐frictional materials based on Mohr–Coulomb failure function
,”
Int. J. Numer. Anal. Methods Geomech.
39
,
1471
1482
(
2015
).
28.
G. M.
Odegard
,
T. S.
Gates
, and
H. M.
Herring
, “
Characterization of viscoelastic properties of polymeric materials through nanoindentation
,”
Exp. Mech.
45
,
130
136
(
2005
).
29.
E. G.
Herbert
,
W. C.
Oliver
, and
G. M.
Pharr
, “
Nanoindentation and the dynamic characterization of viscoelastic solids
,”
J. Phys. D
41
,
074021
(
2008
).
30.
T.-Z.
Zhang
,
S.
Bai
,
Y.
Zhang
, and
B.
Thibaut
, “
Viscoelastic properties of wood materials characterized by nanoindentation experiments
,”
Wood Sci. Technol.
46
,
1003
1016
(
2012
).
31.
F.
Rodrigues
,
M. T.
Carvalho
,
L.
Evangelista
, and
J.
de Brito
, “
Physical-chemical and mineralogical characterization of fine aggregates from construction and demolition waste recycling plants
,”
J. Cleaner Prod.
52
,
438
445
(
2013
).
32.
P.
Sadrolodabaee
,
G.
Di Rienzo
,
I.
Farina
,
C.
Salzano
,
N.
Singh
, and
F.
Colangelo
, “
Characterization of eco-friendly lightweight aggregate concretes incorporating industrial wastes
,”
Key Eng. Mater.
944
,
209
217
(
2023
).
33.
W. Q.
Zhu
,
Y. K.
Lin
, and
Y.
Lei
, “
On fatigue crack growth under random loading
,”
Eng. Fract. Mech.
43
,
1
12
(
1992
).
34.
R.
Brighenti
,
A.
Carpinteri
, and
N.
Corbari
, “
Damage mechanics and Paris regime in fatigue life assessment of metals
,”
Int. J. Pressure Vessels Piping
104
,
57
68
(
2013
).
35.
J. E. B.
Jennings
and
J. B.
Burland
, “
Limitations to the use of effective stresses in partly saturated soils
,”
Geotechnique
12
(
2
),
125
144
(
1962
).
36.
D. A.
Zreik
,
J. T.
Germaine
, and
C. C.
Ladd
, “
Undrained strength of ultra-weak cohesive soils: Relationship between water content and effective stress
,”
Soils Found.
37
(
3
),
117
128
(
1997
).
37.
S. A.
Stanier
and
A.
Tarantino
, “
An approach for predicting the stability of vertical cuts in cohesionless soils above the water table
,”
Eng. Geol.
158
,
98
108
(
2013
).
38.
G.
Gudehus
, “
Implications of the principle of effective stress
,”
Acta Geotech.
16
,
1939
1947
(
2020
).