Advancing Sustainable Construction: Insights into Clay-Based Additive Manufacturing for Architecture, Engineering, and Construction

Abstract

Additive manufacturing(AM) has evolved from rapid prototyping to a versatile technology in nano to large-scale fabrication, gaining traction in various sectors such as medicine, aeronautics, and pharmaceuticals. Its recent application in the architecture, engineering, and construction (AEC) industry marks a significant shift, especially in using traditional concrete and steel materials to innovative, sustainable options like clay. The increasing demand for ecofriendly construction materials propels this development. This chapter presents an overview of the latest developments in clay-based AM within the AEC sector. It discusses the challenges and opportunities of this technology, integrating design methods and material approaches. The chapter also examines the critical interplay of geometry, material properties, and process parameters in AM. Aimed at professionals in the field, it offers a comprehensive framework and practical guidelines for engineers, designers, and architects in this dynamic domain.

1. Introduction

The architecture, engineering, and construction (AEC) sector is a complex and large industry that contributes to nearly 5–7% of the global gross domestic product (GDP) [1, 2], playing a significant role in the global workforce, economic growth and development [3]. Despite the economic significance and impact of the construction industry, it accounts for a substantial portion of global energy and material consumption and emissions. Specifically, the AEC industry accounts for 30% of the final energy demand, covering space heating and cooling, water heating, lighting, cooking, and other uses. This percentage could increase to 34% when the energy used to produce construction materials is also considered. Moreover, it represents 37% of energy-related CO₂ emissions and 21% of total greenhouse gas emissions [4]. Growing global concerns over climate change, the depletion of raw materials, and the substantial carbon and water footprints associated with conventional materials have catalyzed a vigorous and ongoing quest for strategies and technologies to mitigate these challenges and enhance the AEC industry’s sustainability [5]. Consequently, there is a pronounced drive toward the adoption of innovative practices that not only reduce the environmental impact of construction activities but contribute to the resilience and sustainability of built environments. This encompasses exploring alternative materials, refining construction methodologies, and integrating eco-friendly technologies and designs to foster a more sustainable and environmentally responsible AEC industry.

Digital manufacturing and, furthermore, additive manufacturing (AM), commonly known as 3D printing in certain contexts, has been rapidly adopted by the AEC industry [6]. This technology spans a range of methodologies, each designed to enable the rapid, cost-effective, and efficient reproduction of components. The standards governing AM are encapsulated in ISO/ASTM 52900, which provides a comprehensive outline of the fundamental principles and terminologies associated with this domain. Thus, the AEC industry has widely adopted concrete-based additive manufacturing due to the attractive properties of the material, such as its mechanical performance, durability, availability, affordability, and workability, resulting in economic, technical, and scientific advantages [7, 8, 9], exploring concrete [10, 11, 12, 13], cementitious and geopolymers [14, 15, 16, 17, 18, 19, 20]. Despite these advantages, the environmental footprint of using such materials remains a topic of concern [5, 9]. Their production and use still entail substantial energy consumption and CO₂ emissions, underscoring the need for continued research and development to pursue more sustainable construction methodologies and materials that align with environmental conservation goals. Moreover, using low-carbon and energy-efficient materials is paramount in decarbonization strategies [4], and thus, currently, it still exhibits great challenges to be compatible with the sustainability and resilience necessary in cities [21].

Using low-carbon and energy-efficient materials is paramount in decarbonization strategies [4], which remains a great challenge for concrete. Even if it is used coupled with AM, it is believed that it can increase the sustainability of the AEC industry since structures could be shaped in forms that can efficiently weigh between mechanical performance and material use, increasing productivity. Most cases in which sustainability is addressed and increased for concrete relate to the use of additives such as recycled and waste-sourced materials [22, 23, 24], geopolymers [20, 25], clay, and similar [9], that could reduce the emissions, the energy and the material use [26]. This scenario has spurred heightened interest in exploring alternative materials to concrete for construction through AM.

Therefore, clay has recently emerged as a material of significant interest in the context of AM within the construction industry. Despite the complexity of categorizing clays due to their diverse compositions and properties, they are broadly recognized as natural, fine-grained mineral materials. Clays exhibit a distinct plastic behavior when moist, allowing them to be easily shaped and molded. Upon drying or firing, clay hardens, transforming into a durable material suitable for various construction applications [27, 28]. This transformation, coupled with their availability and expected lower environmental impact, positions clay as a promising candidate for sustainable construction practices, especially when coupled with AM. The Literature currently reveals promising results in using clay with AM to create clay-based complex structures [29, 30, 31, 32, 33, 34, 35], which can be coupled, for instance, with natural fibers to increase their mechanical performance [36], promoting, for instance, responsive structures [37].

This chapter explores the use of clay as a construction material within the additive manufacturing AM context, an emerging focus in the AEC industry. It begins with a thorough review of significant advancements and case studies demonstrating clay’s application in construction via AM technologies, underscoring its innovative potential in modern building practices. The chapter then delves into the crucial findings on how process parameters, material, and geometric parameters affect the performance and sustainability of clay-based construction. Drawing from recent research, it assesses the impact on structural integrity, thermal properties, and environmental impact. Finally, the chapter offers guidance and consolidates lessons learned from various projects, providing a framework for designers, architects, and engineers looking to use clay in sustainable construction through AM. This synthesis aims to deepen the understanding of clay’s potential and promote its informed use in future projects.

2. Recent advances in clay-based additive manufacturing for the AEC industry

Since ancient times, humanity has used earth-based materials for construction, aiming to develop shelters and structures. These materials rank among the oldest used in construction due to their widespread availability, cost-effectiveness, environmental adaptability, and the extensive knowledge surrounding their use. Earth-based construction remains prevalent today, underscoring its enduring relevance and practicality. Recently, there has been a growing interest in integrating earth-based materials with AM technologies across various scales as a construction technique for civil and building elements within the AEC industry.

2.1 Clay-based AM houses

Among the most notable initiatives, the Institute for Advanced Architecture of Catalonia (IAAC) leads in large-scale additive manufacturing with clay. Their first project, Pylos, focused on refining techniques and testing mechanical properties via robotics. Additionally, IAAC’s Digital Adobe wall, Terraperforma, and recent projects like TOVA and VOLTA prioritize sustainability, using local materials to achieve zero waste and minimal carbon emissions, showcasing the potential for sustainable construction practices within the AEC industry [38].

Wasp S.r.l developed some other well-known large-scale projects. For instance, they developed the Eremo project [39], which used a large-format Delta printer to develop a circular refuge model constructed from local materials, aiming for near-zero impact, and Gaia [40], the first circular-shaped, earth-based house made through additive manufacturing, that took just a couple of weeks to construct and requires no heating or air conditioning. The building material consisted of 25% local soil (30% clay, 40% silt, and 30% sand), 40% straw chopped rice, 25% rice husk, and 10% hydraulic lime. More recently, they also developed projects such as TECLA [41] using multiple crane-type Wasp 3D printers and collaboration with Dior to construct two circular modules installed in Dubai [42].

Another project developed during the COVID-19 pandemic was Casa Covida, a cohabitation concept in the San Luis Valley of the Colorado desert. This project integrated additive manufacturing with indigenous and traditional materials, differentiating itself from previous initiatives that used robotic and crane technologies. It employed a three-axis SCARA system, augmented with continuous flow and a stator-driven mortar pump, ensuring precise and efficient delivery of adobe material to the printing nozzle. This project also used natural-based and locally sourced building practices.

2.2 Envelopes and facades

An early study developed by Shi et al. [43] explored the potential of clay for additive manufacturing by introducing an interlocking screen system to develop a building envelope. Using parametric design techniques via Grasshopper, the team built each module with a Potterbot SCARA, using a commercial clay mix of 50:50 talc to ball clay. This modular approach was subsequently applied in the Hive project at Waterloo University, which featured a privacy wall consisting of 175 interlocking clay bricks [44].

Modulo Continuo, developed by Jiun Gan et al. [45], consisted of customized evaporative cooling façade modules. These modules were fabricated using a robotic arm with low-fire terracotta clay as the material. The authors tackled the intricacies of curved geometries by managing the convex deformation and curvature of the clay printings during the drying phase. The modules were printed by experimenting with various infill patterns and extruder pressures. By customizing each module’s visual porosity and surface area, the authors suggested the potential for a highly tunable wall or façade, indicating a novel approach to architectural design that integrates functional esthetics with environmental needs.

More recently, Sanga et al. [46] applied biomimicry in designing additively manufactured clay bricks, drawing inspiration from termite mounds. Termites use their saliva as a binder to build underground shelters, breaking down consumed cellulose into glucose, polysaccharides, and oligosaccharides. Mirroring this process, the authors used cassava flour as a substitute to emulate the termite’s construction behavior. Their findings showed that a 1.5% concentration of cassava flour in the mix yielded a compressive strength of 4.28 MPa, surpassing that of traditional burned clay bricks.

Furthermore, Taher et al. [47] delved into the design and fabrication of multi-functional building components, focusing on an approach to integrate air distribution duct networks directly into façade walls. They proposed a detailed workflow that employed parametric design and design for additive manufacturing (DfAM) principles to create a clay-based prototype. The study encountered several challenges related to geometric parameters, including the infill density and the complexity of intersection nodes along the toolpath. Despite these challenges, Taher et al. underscored the significant potential of clay for large-scale additive manufacturing within the AEC industry, highlighting its utility in developing innovative, functional building solutions.

2.3 Clay bricks

One of the most extended uses of clay in the AEC industry is bricks due to their easy-to-obtain load-bearing capacity as a structure. Economically, they are particularly appealing due to the low cost and widespread availability of raw materials, combined with the simplicity of the firing process used in their manufacture [48]. Despite a decline in their use since the 1980s in favor of concrete bricks, two-thirds of the global population is estimated to reside in buildings composed of clay materials [29, 48, 49]. The advent of digital fabrication technologies, particularly AM, has sparked renewed interest in clay bricks. This interest stems from AM’s potential to enhance sustainability within the AEC industry. Early experiments in integrating AM with clay bricks were showcased during the Dutch Design Week through the Building Bytes project. This initiative featured a desktop 3D printer modified to produce clay bricks to create diverse architectural structures [50], demonstrating the evolving intersection between traditional materials and modern manufacturing techniques.

The first formal investigation into clay bricks 3D printing was conducted by Cruz et al., laying the groundwork for subsequent innovations in this field. Among these advancements, Abdallah and Estévez [29] introduced an innovative approach centered on physiological optimization for material deposition. This method is tailored to the properties of clay and employs a biodigital design methodology. Using Grasshopper, the authors devised a reaction-diffusion system that leverages the hydrophilic characteristics of clay. This approach aims to boost sustainability by reducing the material consumption and the energy required during brick fabrication through the development of an optimization algorithm that identifies the shortest path between two points during the construction process, ensuring a more efficient distribution of loads across the brick structure, thereby enhancing its resistance to cracking.

Building upon these foundations, Sangiorgio et al. [34] delved into parametric modeling, exploiting minimal surface and periodic minimal surface geometries with Grasshopper. This approach aims to design, simulate, and prototype complex bricks that leverage the exceptional mechanical properties of minimal surfaces. Their findings indicated that bricks structured around a diamond-type minimal surface yielded the most promising results. However, configurations such as the Scherk tower, gyroid, and Schwarz P also demonstrated favorable printability, illustrating the potential of parametric modeling in pushing the boundaries of clay brick manufacturing toward more intricate and mechanically robust designs.

2.4 Material approaches

While some efforts have successfully created complex structures, most have focused on developing the manufacturing technique and material performance. For instance, some research has focused on process parameters. An early investigation by Kontovourkis and Tryfonos aimed at developing an algorithm for robotic toolpath planning, focusing on parameters such as infill, overhang control, toolpath planning, robotic and nozzle control, and printing time using parametric design tools Rhino and Grasshopper [51, 52]. Pitayachaval and Baothong [53] developed a clay printing machine using a screw-based extrusion method to layer clay models through a circular nozzle. They focused on key process parameters such as nozzle diameter, screw extruder velocity, and screw pitch and introduced a mathematical model to correlate these variables, assessing their impact on the extrusion process. Their analysis showed that screw extruder velocity had a minimal effect on the performance across different nozzle diameters, providing insights into the interactions of these variables during the clay printing process.

Regarding the material key parameters, Bajpayee et al. [54] explored them using naturally harvested burlewash clay with a pH of 4.94, aiming to develop a load-bearing structure by crosslinking the clay through forming a siloxane framework to assess the feasibility of local sourcing. They crafted a mixture with a 1:1 weight ratio of sodium silicate and ground burlewash clay, enhanced with alkaline water and a cellulosic admixture to improve extrudability. Using Grasshopper and RobotStudio for robotic toolpath planning, they achieved a structure with a yield stress of 34 Pa and a kinematic viscosity of 26.4 Pa s at a shear rate of 1.4 s⁻¹, demonstrating the sustainable potential of this material in construction practices.

Sauter et al. [55] developed a cost-effective, mobile 3D-printing platform with omnidirectional wheels for unrestricted movement along x- and y-axes, designed primarily for fine arts rather than the AEC industry. Their study provided a statistical experimental analysis of process and material parameters, such as layer height, width, printing speed, and material composition, which included the ratio of dry material to wetting agent. They noted that the platform’s mobility could introduce printing errors, particularly with larger objects, due to the lack of reference location. Similarly, Dielmans et al. [56] created a mobile robotic system for in-situ additive manufacturing (AM), testing its ability to produce accurate clay formworks for constructing reinforced, lightweight concrete columns.

Further research has focused on enhancing clay properties for AM. Sahoo and Gupta [57] integrated earth materials with alkali-activated slag-fly ash concrete, examining the rheological properties, extrudability, and buildability of mixtures containing 48–50% clay, predominantly Kaolinite with traces of Montmorillonite—with alkali-activated slag-fly ash concrete. While higher clay content presented structural strength challenges, their mixtures still met the IS1725 standards for soil-based block construction.

Research efforts have also been directed toward developing natural-based fibers to enhance clay-based mixtures for construction applications. Akemah and Ben-Alon [58] to identify suitable natural fibers for extrusion, aiming to optimize the mixtures for high static yield stress and minimal buckling, informed by research from Tay et al. [59]. They hypothesized that the effectiveness of a clay-based mixture as a construction material hinges on the cohesive interaction between the clay binder and the natural fiber reinforcement. Their experiments showed that adding fibers like wheat straw and hemp significantly improved the properties of clay. Evaluations confirmed that these fiber-enhanced clay mixtures are compatible with advanced additive manufacturing technologies such as direct and delta screw extrusion, demonstrating the potential of natural fibers to improve clay-based construction materials.

In another case, Jacquet and Perrot [60] explored the potential of enhancing clay by adding vegetable waxes, specifically coconut, soy, and rapeseed, focusing on soy wax. They discovered that a small addition of wax notably improved the water resistance of the clay materials, increasing their versatility. Furthermore, the wax’s thermal properties facilitated a smoother manufacturing process by reducing the clay’s stickiness and introducing a thermal setting aspect during printing. The study highlighted that these enhancements could benefit the AEC industry by providing innovative solutions for housing construction and reducing urban heat island effects. It also pointed out that the chemical composition of the materials influences the effectiveness of natural admixtures like wax and that the typical sticky and viscous nature of clay can be mitigated by adjusting the mixture composition or printing temperature.

3. Role of process, geometry, and material parameters

Earthenware and stoneware are the most common clay types used for architectural applications. The former consists of large particles and low-fire clay bodies, while the latter fires at high temperatures [61, 62]. Clay may differ from other materials commonly used for extrusion-based additive manufacturing in its unstable nature, mostly around its rheology and other properties, and the influence of the pumping pressure on the quality of the printed objects [63].

Even though the use of clay in additive manufacturing has been increasing recently, there remains a notable deficiency in systematic information, standardization, and testing to evaluate process, material, and geometry parameters. Directly applying standards common to traditional clay use could be challenging and may result in inaccurate assessments [5, 64]. Although the research addressing these parameters is not extensive, several key effects have been documented across various studies. This section provides a reference framework, summarizing significant findings and establishing a foundation for future research. This summary aims to consolidate knowledge and identify critical areas where further investigation could enhance understanding and improve practices in the relevant disciplines.

3.1 Permeability

Permeability is a crucial parameter often used to characterize soils, including clays. The permeability of clay is influenced by several factors, such as its particle structure, shape, pore size, uniformity and distribution, high specific surface area, the strong attraction of water to clay particle surfaces, and its plasticity [65, 66, 67]. Due to its cohesive nature, clay is generally considered to have low permeability. Various empirical and theoretical relationships, such as the Atterberg limits, have been established to determine clay permeability. These limits are used for the identification, description, and classification of clays and to evaluate their mechanical properties [65, 68]. One can also mention the extensively used Kozeny-Carman equation, an empirical approach widely used to determine the specific surface area of cohesive soils by predicting the hydraulic conductivity of soils [69].

The permeability of clays contributes to their hygric capacity, which can be leveraged to regulate indoor temperature and humidity levels, offering potential benefits in the AEC industry [58]. In the case of concrete, permeability in 3DCP can be assessed through typical experiments such as mercury intrusion porosimetry (MIP), water absorption, and sorptivity. However, the Literature has not extensively explored the effects of permeability on clay during and after the 3D printing process.

A recent study by Carr et al. [66] investigated the impact of 3D printing on the physical characteristics of clay, covering aspects like Atterberg limits, particle size gradation, and specific gravity. This study is among the few that have explored the effects of permeability in clay 3D printing, establishing a valuable framework for future research in this area. In their experiments, cylindrical clay-based specimens with a diameter of 35.5 mm and height of 50.8 mm, weighing 50 g each, were fabricated using Kaolinite clay with a void ratio of $e=1.0$. To enhance the flowability of the powder, it was dried for 10 hours at 200°C to minimize water content during the AM process. After printing, these specimens were sintered at 1093°C. For comparative analysis, control specimens were prepared using the dry pluviation technique with stoneware clay powder, achieving a void ratio of 𝑒=1.0, then remolded to facilitate direct comparison with the 3D printed specimens.

The authors addressed the impact of 3D printing on soil properties, focusing on clay permeability and shear strength. Sieve analysis was conducted on pulverized 3D-printed specimens to assess their particle size distribution, identifying the clay as low-plasticity. Analysis revealed particle fusion during sintering, and despite efforts to meet Atterberg limits through 24-hour hydration with de-aired water, these were not achieved. This suggested that the stoneware clay powder did not maintain cohesiveness post-printing. Further insights were obtained using scanning electron microscopy (SEM), which showed significant changes in the particle structures post-printing, notably smoother surface textures. This textural change, likely due to the addition of fire-resistant materials, was hypothesized to enhance specimen permeability by increasing porosity and reducing shrinkage during sintering, potentially improving the clay’s permeability. Nonetheless, permeability variability was minor and less influenced by confining pressure. The analysis also indicated increased strength in the printed specimens.

3.2 Plasticity and extrudability

The plasticity of clay-based materials is significantly influenced by their water content, a factor critical to their extrudability, especially in 3D printing applications [70]. Kaolin clay, for instance, features a crystalline platelet-like structure comprised of small particles and water of formation. In this context, water functions similarly to a lubricant, allowing particles to glide over each other under shear forces rather than breaking apart. This mechanism enables kaolin clay to exhibit plastic shear-thinning behavior, known as thixotropy, where the surface tension between water and clay particles helps maintain the object’s shape. However, water content also impacts the flowability of the clay. If the water content surpasses the minimum needed to sustain surface tension, the clay becomes overly fluid, consequently losing its ability to hold a defined shape [71]. Balancing water content and plasticity is crucial for successful 3D printing with clay, where maintaining the right consistency is critical to achieving the desired structural integrity and shape.

3.3 Buildability

Buildability is one of the most common criteria for testing the performance of an additively manufactured part, especially for cement-based and clay-based materials [57, 58, 64, 72]. This property can be evaluated both qualitatively and quantitatively, focusing on factors such as the build rate and the stability of the printed layers. Critical aspects that influence buildability include the maximum load that the initial layer can support, the material’s early strength development, and the printed part’s geometry. These factors are crucial in determining how effectively the structure can withstand the successive layering process without undergoing deformation or collapse, thereby ensuring that the additive manufacturing process yields durable and structurally sound components. Despite its importance, standardization in buildability testing remains underdeveloped. However, several tests are referenced in the Literature, such as the cylinder and single-direction wall tests, commonly used to assess the structural integrity and layer cohesion of 3D-printed objects. Additionally, stability settlement tests are also mentioned, which evaluate the plastic collapse of a structure under the maximum load that the first layer can bear.

3.4 Flow rate

Flow rate measurements are critical in optimizing the extrusion process in additive manufacturing. For instance, Fleck et al. [33] examined how the flow rate of material exiting the nozzles correlates with the temperature at the nozzle tips. In their study, temperature increases were induced by vibration, which, in turn, exponentially increased the flow rate. The authors employed the Andrade equation to model this behavior, which connects viscosity with temperature under the assumption of Bingham plastic behavior. This equation was paired with the relationship of laminar flow rate to viscosity, suggesting that the increased flow rates resulted from reduced viscosity due to the rise in temperature and vibrations at the nozzle tip.

The flow rate of extrusion also significantly influences other printing parameters. Wi et al. [35] noted that if the extrusion flow rate is too slow or too fast relative to the set printing speed, it can adversely affect the printability and buildability of the object. Inappropriate flow rates may cause the object to tilt, slump, or collapse over time, leading to severe distortion or poor printing quality.

Moreover, some studies have approached numerically the prediction of flow rates during additive manufacturing of cementitious and ceramic materials, but there is still a lack of studies on clay additive manufacturing.

3.5 Surface roughness

The surface roughness of 3D printed clay parts is a critical aspect often assessed by non-destructive methods such as direct visual inspection through images [53, 73] and a light scanning system [35]. These methods provide valuable insights into the effects of printing parameters, geometry, and material characteristics on the final product. Surface roughness is a significant parameter in manufacturing industries because it is closely related to product quality and precision, impacting critical factors such as friction, contact deformation, heat and electric current conduction, the tightness of contact joints, and positional accuracy [74]. Pitayachaval and Baothong [53] noted that higher screw pitches tend to result in smoother surfaces, although their assessments were purely qualitative without further quantitative measurements. Conversely, Wi et al. [35] introduced a 3D Light Scanning System (3D-SLSS) that operates akin to human stereo vision but uses a projector to emit multiple phase-shift patterns sequentially while a camera captures the surface images of the object. This setup allows for non-contact, non-destructive testing of various visual and surface parameters, including surface roughness. For this study, surface roughness was quantified using metrics such as the arithmetic average height (Ra), root mean square roughness (Rq), and 10-point height (Rz), finding that roughness increased with the extrusion flow rate and printing speed.

Additionally, Afriat et al. [73] explored the quality of external surfaces on printed elements using vibration-assisted printing (VAP), which allows the use of smaller nozzle diameters. This approach resulted in improved surface quality and sharper corner angles. The surface quality was evaluated using GOM Inspect (now ZEISS INSPECT Optical 3D), enhancing the assessment of the printed elements’ external characteristics. These methodologies highlight the importance of precise control over printing parameters to optimize surface quality in 3D-printed clay products.

3.6 Layer thickness

Layer thickness is a critical parameter directly impacting the printed part’s surface roughness and overall quality. Smaller extruder diameters are advantageous as they tend to produce thinner layers, resulting in smoother surface finishes. Some results in the Literature have shown an interesting relationship where the higher the printing speed, the less viscous the fluid becomes [71]. This observation aligns with the behavior of supersaturated clay suspensions, which are known to exhibit shear-thinning properties. This thixotropic, non-Newtonian behavior of clay makes it particularly suitable for processes where control over viscosity and flow rate is essential for achieving high-quality prints.

Besides, the first layer is fundamental for the printing process. Among the various factors influencing the first layer in printing, nozzle parameters, printing speed, bed temperature, surface adhesion, bed leveling, and the Z-offset calibration of the printer are crucial [33, 71]. Boyer et al. [71] investigated the impact of three different substrate types on the printing process: aluminum, paper, and polishing paper. They found that the material tended to slide over the surface of aluminum, which could compromise print quality. Although initial adhesion was adequate with paper substrates, the quality deteriorated over time, likely due to the paper’s water absorbance. In contrast, polishing paper, characterized by lower permeability and higher surface roughness, provided better adhesion and overall results than the other substrates tested. This study highlights the importance of selecting the appropriate substrate to ensure optimal first-layer quality and overall printing success.

3.7 Nozzle geometry

The nozzle is a critical component of material extrusion-based additive manufacturing technologies, serving as the conduit through which the material is extruded. Its design and geometry must be meticulously tailored to align with the specific properties of the material used, including its composition and consistency. Key factors such as viscosity, the presence of aggregates, and fiber lengths must be considered to ensure that the nozzle can effectively and efficiently handle the material without clogging or causing irregular extrusion. For cement-based and clay-based materials, the nozzle shape usually follows two types of sections: rounded or elliptical and rectangular or squared [75, 76], which are associated with the printing quality [5], including factors such as the presence of air pockets, cold joints, adherence between layers, among others [77].

The nozzle diameter is a key parameter in additive manufacturing, requiring careful selection to meet specific requirements. According to Chan et al. [32], the choice of nozzle significantly affects the printed parts’ quality, speed, material consumption, and precision. It is feasible to use larger nozzles provided they are paired with suitable combinations of printing pressures and speeds once the minimum nozzle size is exceeded. Furthermore, the design and architecture of the nozzle itself are crucial for the quality of the manufactured part.

Jauk et al. [78] introduced customized nozzles for the Delta WASP 40100 Clay model printer, designed to enhance the printing of filament-reinforced clay objects. These nozzles feature a filament-guiding mechanism that centers the filament within the extrusion channel, ensuring consistent application. The nozzle design includes a threaded base for secure attachment to the extruder, a smaller inner nozzle to guide the filament, and a larger outer nozzle that shapes the extruded clay. This adaptation is specifically tailored to incorporate fiber reinforcement directly into the clay matrix during printing, potentially increasing the tensile strength of the final product by approximately 15%, irrespective of the fiber type used. This innovation exemplifies how adjustments to nozzle design can significantly enhance the functional properties of 3D-printed objects.

The printer nozzle plays a crucial role in determining the resolution and detail of printed parts, with smaller nozzles allowing for thinner layers and greater accuracy in rendering fine details. According to the results shown by Chan et al. [32], a decrease in pressure and velocity is observed as the nozzle size increases. Conversely, increasing the storage space while maintaining the same printing speed and nozzle size needs higher pressure for effective printing. If the nozzle diameter is large, it results in higher material consumption per layer, which can significantly impact production costs. Conversely, smaller nozzle sizes enhance material efficiency, minimizing waste. Fleck et al. [33] delve into the critical parameters of extrusion additive manufacturing that are essential for maintaining control over material geometry, especially when printing at high viscosities and variable speeds, which can lead to over-extrusion.

Additionally, their rheology analysis showed that the printing was unsuccessful for diameters lower than approximately 0.26–0.30 mm. This suggests that the viscosity of the material is a limiting factor in achieving successful printing under certain conditions. Furthermore, larger nozzle diameters can facilitate higher printing speeds, allowing more material to be extruded quickly. This capability is particularly advantageous for the rapid production of parts. Afriat et al. [73] highlight an additional benefit when employing vibration-assisted printing (VAP), which can achieve printing speeds ranging from 5000 to 6000 mm/min. This significant increase in printing speed substantially reduces the time required to print highly viscous materials and enables the extrusion of even more viscous substances. The interplay between nozzle size, material viscosity, and printing parameters like pressure and speed are critical to optimizing 3D printing outcomes.

3.8 Tensile behavior

In the case of Fleck et al. [33], the authors assessed the mechanical properties of 3D-printed dogbones, adhering to ASTM D638 standards, and compared them with those manufactured conventionally. The findings indicated that the 3D-printed parts generally displayed poorer mechanical performance. Notably, parts printed at 0° orientation exhibited the highest elastic modulus, recorded at 6.10 ± 0.68, while the greatest ultimate strength was observed in parts printed at 90°, achieving 1.29 ± 0.07. The unexpected strength increase in 3D-printed parts at a 90° orientation was surprising, as this alignment is typically weaker due to its perpendicular orientation to the pulling direction, akin to composite laminates. However, the authors suggest that overfilling during printing may have inadvertently increased the interface’s contact pressure, thus enhancing the ultimate strength. This finding suggests that the interaction between material deposition and mechanical stresses during printing significantly impacts the final properties of 3D-printed objects, indicating a need for further research to optimize printing strategies for improved mechanical outcomes. Additionally, it highlighted that corner-turning in print geometry could cause overfilling, leading to reduced geometric accuracy due to the firmware’s requirement for zero-velocity changes based on Marlin’s trapezoidal velocity profiles [79]. To mitigate this, adjustments in the g-code are necessary to manage the flow and accommodate temperature-induced material behavior.

3.9 Printing quality and costs

Print speed is a crucial factor that significantly impacts operating costs in additive manufacturing. Faster printing speeds can reduce energy and material consumption, offering economic benefits. According to Kim et al. [80], the screw-type extrusion method is versatile, capable of handling various material types, including very thick ones, and can complete numerous tasks quickly. However, this method faces challenges in achieving precision, particularly with complex shapes. Increasing the printing speed initially may reduce the production time but at the cost of the quality of the output. High printing speeds are often associated with imperfections in the final part, such as layer errors or reduced resolution. Sauter et al. [55] delve into this issue by investigating the optimal printing parameters that minimize errors. Their study provides a detailed analysis of various parameter pairings such as layer width and concentration, layer height and concentration, layer width and printing speed, layer height and printing speed, and printing speed and concentration.

4. Lessons, challenges, and opportunities

One significant barrier to the broader adoption of clay in AM is the lack of clear guidelines, largely due to limited research on essential parameters like geometry, material, and process. Although many researchers and companies have demonstrated its technical feasibility for various applications such as facades, these studies often emphasize broad viability over detailed operational specifics.

This chapter addresses the need for more targeted research to understand how these key parameters impact outcomes in AM processes using clay. The AEC industry can harness AM with clay more effectively to enhance sustainability by developing a deeper understanding of these interactions. This could lead to more robust guidelines and standards that facilitate the integration of clay-based AM into mainstream construction practices, improving efficiency, cost-effectiveness, and environmental impact. Different approaches are essential to maximize the potential of AM, particularly when tailored to specific applications. Like traditional manufacturing, AM performance is influenced by various factors, focusing on technical, economic, and sustainability aspects to determine the most suitable method for the intended application. One strategy for leveraging AM’s full potential that considers the design of parts and products within the constraints of their capabilities is design for additive manufacturing (DfAM) [81].

DfAM is part of the broader DfX (design for X) family of methods, which aims to ensure that the engineering design process aligns effectively with AM capabilities. This approach helps to harness techno-economic benefits such as the ability to produce low-volume, high-complexity parts efficiently. DfAM involves using advanced tools that cater specifically to AM design challenges. DfAM must address the various technologies encompassed within AM and attempt to integrate them into a cohesive process chain. This integration allows all manufacturing process components to interact effectively, leading to efficient production outcomes [82]. By focusing on these aspects, DfAM optimizes the manufacturing process and enhances the functionality and customization of the products, making it a pivotal approach in the evolution of additive manufacturing.

The use of DfAM typically involves establishing a reference framework that facilitates the exploration, design, optimization, and manufacturing of parts or products [83, 84, 85, 86, 87]. For this chapter, the application of DfAM focused primarily on developing process parameters, geometry, and material approaches. In this context, the analysis deliberately excludes broader environmental, economic, and social factors, concentrating solely on the technical aspects that directly influence the various stages of design and manufacturing within AM. This focused approach allows for a deeper understanding and refinement of the technical factors critical to optimizing additive manufacturing processes. By narrowing the scope of investigation, this chapter aims to provide clear, actionable insights that enhance the effectiveness and efficiency of DfAM in addressing complex technical challenges within the AM field.

Based on a holistic analysis of data available in the literature and from manufacturers, the process parameters, geometry, and materials discussed in the previous sections were used to define a tailored framework for DfAM. This framework, inspired by the methodology outlined by Trovato and Cicconi [88], is designed to cater specifically to the unique challenges and opportunities presented in this particular case. The details of this adapted framework are visually represented and can be thoroughly examined in Figure 1. This figure illustrates how the conceptual framework integrates various elements of DfAM to effectively address the practical aspects of additive manufacturing, ensuring that the design process is optimized for the specific materials and technologies involved.

Figure 1.

Proposed DfAM reference framework for manufacturing clay-based non-structural blocks, adapted from the methodologies proposed by Trovato and Cicconi [88].

Furthermore, Table 1 shows some insights into the Literature related to the process, material, and geometry parameters that can serve as a troubleshooting table based on previous experiences.

Issue	Possible cause and proposed solutions	References
Lines and marks in the direction of extrusion	Cause: issues with the nozzle (adhered particles, damage, and others) or inadequate processing conditions.; Proposal: clean the nozzle. Check for any damage.	[73]; [31]; [32]
Non-uniform thickness in the transverse direction	Cause: nozzle calibration; Proposal: calibrate the nozzle to ensure it is centered.	[33]; [89]; [80]
Non-uniform thickness in the longitudinal direction	Cause: flow fluctuations. Proposal: check for the absence of pressure or motor power oscillations. Verify the extruder temperature. Ensure the temperature controllers, resistors, and fans are functioning properly.	[32]; [33]; [89]; [80]
Presence of impurities	Cause: adhesion in the nozzle, head, filters, or even extruder. Inadequate processing conditions.; Proposal: check the condition of filters. Clean the head, nozzle, or extruder. Purge with another material. Check for potential sources of contamination. Validate and adjust processing conditions if necessary.	[31]; [53]

Table 1.

Common problems and explored solutions reported in the literature.

5. Conclusions

Recent advances in clay-based additive manufacturing for the AEC industry have demonstrated remarkable progress, reflecting a growing trend of integrating traditional materials with modern technological approaches to enhance sustainability and efficiency. The use of earth-based materials, notably clay, in construction dates back millennia and continues to be significant due to its abundance, cost-effectiveness, and versatile properties suitable for various environmental conditions. Several pioneering projects have set benchmarks in the field, such as those spearheaded by the Institute for Advanced Architecture of Catalonia (IAAC). These projects have used large-scale additive manufacturing techniques with clay, enhancing traditional construction methods with modern precision and sustainability considerations. However, the application of this technology extends beyond the construction of large structures like houses to include envelopes and facades, as well as more traditional uses in brick manufacturing.

Research in this field is rapidly increasing, with studies exploring different properties of clay in additive manufacturing settings that can provide a deeper understanding of how clay behaves under different manufacturing conditions and how these properties can be optimized to improve product quality and structural integrity. The field of clay-based additive manufacturing is poised to expand further, exploring new material combinations, improving printing technologies’ precision, and enhancing construction practices’ sustainability. Collaborative efforts between academic institutions, industry leaders, and architectural firms are crucial in driving innovation and adoption of these technologies in mainstream construction projects. By bridging the gap between traditional materials and advanced manufacturing techniques, the AEC industry can better address the growing demands for sustainable development and environmentally adaptive construction solutions.

Acknowledgments

The authors sincerely thank the Design, Materials, and Manufacturing Research Group (DM+M) at the Faculty of Mechanical Engineering, Universidad Tecnológica de Panamá (UTP), for their invaluable collaboration. This work was partially supported by projects FIED22-13 and APY-NI-2022-24, both funded by the Panamanian Secretaría Nacional de Ciencia, Tecnología e Innovación (SENACYT), and by the Sistema Nacional de Investigación (SNI).

Conflict of interest

The authors declare no conflict of interest.