7. Additive Manufacturing for the Circular Built Environment: Towards Circular Construction with Earth-Based Materials

With the surge in the availability of large-scale construction format AM machines such as BOD II (COBOD International A/S 2017) and Crane WASP (WASP Srl 2018), the building sector was able to investigate various materials on a construction scale, including plastics, metals, and plaster. Nevertheless, material durability, size restrictions, and a slow production rate have limited these material systems to smaller building components, which has led to cementitious materials being the material of choice for structural building elements. After all, concrete is one of the most widely used building materials with superior structural properties, availability, and affordability (Crow 2008). Even though concrete processing is being improved and more automated, conventional construction activities that use concrete still generate a lot of waste and have high energy consumption.

In this context, 3D concrete printing (3DCP) has been the first AM technology to enter the construction industry, with the promise of an effective, customisable, and waste-free form of construction. Rapid growth in using 3D printers for building has highlighted the need to develop new material control systems, especially those that allow precise control over the material’s hydration, rheology, and curation rate, which is critical for achieving volumetric buildup (Jones et al. 2018).

However, the consumption volume of concrete and the chemicals added to accelerate the mix to facilitate 3DP make the process less structurally capable while possibly being even more harmful to the environment per volume (Flatt and Wangler 2022), exposing the need for alternative sustainable materials for 3DP such as excavated earth and geopolymers. In particular, earth-based material offers a significant advantage in terms of transportation and sustainability, as it can be extracted and processed directly on site. It is known for allowing the construction of sustainable, healthy, and thermally efficient buildings (Minke 2013). It is also a material linked to old construction techniques requiring extensive skills and manual labour, issues that could be solved with 3D printing machines.

In addition to material control, the successful implementation of additive manufacturing (AM) operations at the building scale relies on the effective integration and accessibility of material processing machines and fabrication machine configurations. The choice of machine setups for AM in construction is contingent upon factors such as size formats and mobility. Consequently, various machine and robotic configurations have been employed in this context. Broadly, these configurations can be classified into two groups: off-site and on-site manufacturing setups.

Off-site manufacturing setups entail the construction of components within a controlled factory environment, followed by transporting prefabricated customised parts to the construction site for assembly, ultimately forming a complete building structure. Using off-site manufacturing facilities ensures regulated conditions that shield production machinery from ambient fluctuations such as temperature and humidity, thereby enabling the mass production of high-quality products. To achieve this, rigid frame Cartesian-type machines (Khoshnevis et al. 2006) are commonly employed, offering three or five degrees of freedom depending on the specific application requirements. When more intricate fabrication operations are necessary, setups incorporating a robotic arm mounted on a Cartesian gantry (Anton et al. 2020) are being implemented. This configuration allows for the gantry’s robust manipulation capabilities and the robotic arm’s dexterity and precision, thus accommodating large-scale construction while maintaining high-resolution detailing.

On-site manufacturing setups vary in configurations, ranging from fixed machines with predetermined footprints to autonomous setups capable of movement and localisation within the construction site. Agility and precision are crucial for these setups to respond and adapt to the dynamic site conditions. Besides large-scale Cartesian 3-axis machines, researchers are exploring using robots on mobile platforms like the In Situ Fabricator (Giftthaler et al. 2017) and digitally controlled construction machinery (Jud et al. 2021) for construction operations.

Such machines have demonstrated applicability ranging from component-based architectural structures to full-scale in situ structures. While off-site manufacturing setups require additional peripherals, it allows for the fabrication of building components in a controlled environment (Gomaa et al. 2023). Thus, it avoids delays due to dynamic site conditions and widens the potential of testing the application of novel construction materials. On the other hand, on-site machinery reduces transportation overheads and produces larger objects, often directly in situ (Dubor et al. 2018). The role of this on-site machinery includes material sourcing, material processing, and building procedures. Additional machines might be required to process materials sourced from the site and surface finishing operations.

The paradigm shifts in architectural design, in which architects use more digital tools, parametric modelling, scripting, etc., to produce geometries providing an approach in which design-generating parameters may be changed on the go using intelligent systems such as machine learning (Guo Liang and Yeong 2022). In AM processes, such a parametric computational design approach acts as a ‘middleware’ in the workflow between generated digital designs and the already manufactured sequence. This allows a control to adjust relevant process parameters. The role of computational design tools is critical since most AM processes are time sensitive and need application-specific information exchange between the parameters.

Like the approach of dfab, AM processes involve integrating design and manufacturing processes within a single digital environment to reduce the gap between design and fabrication. Such control over the process in AM on a building scale is beneficial when site conditions and material qualities vary. Because of the parametric control workflow, it is now possible to model and record previously unanticipated material and site conditions change to effectively adapt to construction errors. This allows for the emergence of novel, cost-effective, and fabrication-aware individualised design solutions.

AM has established a new construction domain that can be generated digitally and has also addressed the construction sector’s problems of low productivity and waste generation. Yet the materials presently used for AM have severe environmental impacts owing to the material’s high embodied carbon and one-time use (Faludi et al. 2015). The following section will address the inclusion of AM processes within a circular economy framework, highlighting the essential characteristics that render AM a feasible option for transitioning towards a circular built environment.

AM enables product innovation through design freedom of mass customised and cost-effective components. It further presents unique features to support circular economy initiatives, such as waste-free production and the opportunity to test novel sustainable material systems promoting product durability and reuse. Consequently, AM has been adopted by various sectors to reduce environmental impacts. The overview from the preceding section about the diverse application of AM highlights its status as a technology driving the transition to a circular production system, which results in the reconfiguration of the supply chain, laying the groundwork for attaining a circular economy. The advantages of employing AM within a circular economy include the following (Hettiarachchi et al. 2022):

Resource efficiency is a key factor in AM stepping up to a building scale in the built environment context. The article presented ‘An Emerging Framework for the Circular Digital Built Environment’ (Çetin et al. 2021) identifies four distinct resource strategies to achieve the CE concept in the built environment: narrowing the loop, slowing the loop, closing the loop, and regenerating the loop. Building on this framework in the context of a circular built environment, AM showcases an impactful building solution: AM process allows for optimised material use for manufacturing, thereby ‘narrowing the loop’ by using less material to construct and generate minimal waste. The durability of the products achieved by the computational design workflow using CAD software helps ‘slow the loop’ by efficiently using material through geometric optimisation and targeted component repair, instigating a longer life cycle. Additionally, the materials used contribute significantly to the efficiency of the circularity process by ‘closing the loop’ by allowing the use of reclaimed and recycled materials. The freedom of using naturally sourced, nonconventional materials helps in the ‘regenerating loop’ of the product cycle by facilitating the disposal of materials upon the completion of the cycle.

The circularity of a building in AM processes is considerably affected by activities related to both the machine configuration and the materials employed, as they are closely dependent on the environmental and economic impact linked to their sourcing, manufacturing, and transportation. These operations include transporting resources for off-site manufacturing of stock materials or equipment transportation for on-site manufacturing setup. While prefabricated parts are often preferred in the construction industry due to quicker construction times, enhanced quality control, product durability, increased safety, and decreased waste, on-site manufacturing offers several advantages, including low environmental impact and high levels of customisation in construction.

Consolidating science-based information on building components’ greenhouse gas emissions (GHG) and related activities across their full life cycle is an important feature of implementing climate mitigation methods. In the context of the built environment, it is particularly informative to look at the emissions resulting from processes preceding the occupancy of a building early into the sourcing of construction materials: ‘Quantitatively, the phases of material manufacturing, transportation, and on-site construction were responsible for 94.89%, 1.08%, and 4.03% of energy consumption, respectively, and 95.16%, 1.76%, and 3.08% of global warming potential’ (Hong et al. 2014). While both off-site and on-site systems rely on transporting material or equipment from another location, the use of a kilometre-zero (km-0) approach in construction would prove to be an effective instance of AM in a circular built environment, promoting social, environmental, and economic sustainability (Farias et al. 2017). The km-0 strategy first appeared in the slow food movement to promote the consumption of local ingredients, reducing the distance between producers and consumers (Souza Eduardo 2021). In the framework of a circular built environment, this would include construction using only locally available building resources and materials benefiting from natural and low-impact processing. The following section will focus on 3D printing with earth (3DPE) as an effective solution for AM in a circular built environment using excavated sustainable and recyclable material primarily consisting of raw earth.

3DPE methods use the layer-based AM approach, comparable to the Contour Crafting method using earth-based materials. In contrast to other additive manufacturing (AM) processes used in the construction industry, such as 3DCP, 3DPE stands out for its ability to avoid the use of environmentally harmful chemicals to speed up the material curing process. Instead, it combines water and aggregates to achieve the necessary level of malleability for 3D printing. In 3DPE, the walls of the construction components are connected using infill. This helps create a load-bearing volume with enough structural depth. These infills provide more practical structural features, such as incorporating electrical and plumbing services, a network of air cavities for natural ventilation, adding a filler material to augment heat lag, etc. (IAAC 2022). By adopting 3DPE, there is a significant reduction in operating energy and a more efficient resource consumption loop. This is achieved by closing the cycle, which minimises the energy consumption required to operate the building. As depicted in Fig. 7.1, a crucial feature of 3DPE is the seamless integration of on-site processes, starting from excavation to the final detailed finishes in the constructed building, utilising locally sourced materials.

A 3-D illustrated process flow of a construction scenario with phases of excavation, sieving, mixing, pumping, printing, and finishing. Recycle stages are between excavated material and sieving, sieving and mixing, mixing and pumping, pumping and printing, and printing and excavated material.

3DPE presents an alternative building method with a circular design-to-construction life cycle consideration of the built environment, which counteracts the tendency of excessive energy consumption in building operations. Additionally, the different aspects of a 3DPE construction process, plus the use of local labour and participation in local economies across its value chain and its accommodation of complex and innovative building models, showcase the circularity of 3DPE as a construction system that closes the loop of circularity in a building process. The following subsections present three case studies demonstrating large-scale implementation of 3DPE that indicate how the transition from an off-site to an on-site mode of a 3DPE building significantly affects the circularity of the building. In addition, the case studies also display the integration of wooden components with 3DPE in ways that add architectural functionality to the built structure.

The first case study presents Digital Adobe, developed during the OTF 2017–2018 course at IAAC and built in the Valldaura Campus of IAAC (IAAC 2018). It is a 2-metre-wide and 5-metre-high printed clay wall with a varying thickness (0.7 m at its bottom and 0.2 m at its top) with a wooden slab resting on the wall at 2.6 m to simulate a clay/wood building unit, where the connections between two materials and the vertical load from a horizontal slab can be tested. Digital Adobe serves as the first large-scale exploration of combining 3DPE and wood elements where the 3D printed earthen component takes the compression load of the structure, and the wooden spanning element works in tension (Fig. 7.2).

3 photographs of the Digital Adobe wall. A vertical rectangular wall made of rounded earthen components with a ladder and a wooden platform behind on which a person stands, a top view of the hollow wall with rounded biconvex earthen cavities, and a low-angle view of the wall with the sky above.

The primary focus of the case study was to explore the climatic and structural performances of 3DPE. With the long-established understanding of clay’s thermal properties to moderate heat transmission, the team has sought a design to enhance such properties. To limit temperature transfer from one side of the wall to the other and to improve the compressive strength of the wall, the infills were filled with unprocessed soil. A ventilated wall design reduced summer heat gain through convection between the openable top and bottom openings. It retained heat in the winter when both openings were closed.

The material mix consisted of conventional adobe mix, including clay, sand, silt, and aggregates. Vegetable enzymes are used to reach the grade of the fluidity of the material mixture needed to achieve the flow rate required to extrude the material for 3D printing. The prototype was partially built with recycled material from the preceding research of On-Site Robotics at IAAC in 2017. Around two tonnes of material from On-Site Robotics (Dubor et al. 2018) was recycled, making up almost half of the prototype’s total material source. To make the recycled material usable for 3DPE again, it was crushed and rehydrated using a much-reduced number of enzymes. Finally, ‘closing the loop’ in resource management was proven by the recycling and reusing process.

TECLA (WASP 2022) is an innovative circular house unit built in Massa Lombarda by WASP and Mario Cucinella Architects (MCA), integrating research on vernacular building techniques with natural and regional materials. TECLA was constructed using two synchronised printer arms concurrently, utilising industrial automation protocols to optimise mobility, avoid collisions, and ensure efficient operation. Each printer unit has a printing surface of 50 square metres, allowing for the rapid construction of house modules. TECLA has a floor size of 60 square metres; it comprises a living zone with a kitchen and a night zone with services. The structure is a composition of two continuous elements that, through a sinuous and uninterrupted sine curve, culminate in two circular skylights that produce zenithal lighting (Fig. 7.3).

3 photographs of TECLA model houses with tall cranes at the center. Aerial view of 2 oblate spheroidal houses with vertical striations that have a hole on top and an opening on the side, and close-up and aerial cross-sectional views of the hollow wall with sinusoidal layers of support within.

In addition, the composition of the earth mixture responds to local climatic conditions, and the filling of the envelope is parametrically optimised to balance thermal mass, insulation, and ventilation according to the climate needs. The materials used were local soil of 6 mm maximum aggregate size, sand, rice husk, and Mapesoil, a lime-based binder added at 5% by weight of the batch.

The proposal was centred on environmental variables, particularly solar analysis, which was the design driver behind the undulated surface and increased the total surface area of the outer facade. Using computational tools to create climate-responsive shapes to improve raw earth’s physical qualities ensures increased passive energy performance of built structures.

TOVA is a building prototype (IAAC 2022) demonstrating the potential of 3DP with sustainable materials in response to increasing climate challenges and related housing emergencies. It was built in the Valldaura Labs facility in Collserola Park, on the outskirts of Barcelona. The construction spans 7 weeks and uses a Crane WASP modular printer and km-0 materials. Using local materials sourced within a 50-metre radius reduces the environmental impact of transportation and waste generation during construction. TOVA can be studied as a near-zero emissions project: the design is tested via digital and physical simulations to reduce carbon footprint, considering the life cycle assessment of the building components. The circular design approach is aimed at designing an environmentally responsive building constructed from reusable biomaterials across the construction phases as follows: a geopolymer foundation, a framework made of local earth, mixed with additives and enzymes to ensure the structural integrity and material elasticity necessary for the optimised 3DP of the house, a locally sourced timber roof structure, and wooden carpentry. To improve the material’s longevity and weather resistance, a waterproof coating is added using raw extracted materials such as egg whites.

The building design of TOVA is based on a precise site condition of the Mediterranean: the volume is compact to protect from the cold in winter, yet expandable for the other three seasons. For this purpose, the wall section, composed of six earth surfaces and a network of cavities containing air or insulation, was calculated to prevent winter heat loss while protecting from summer solar radiation. The result is a climate-responsive building: the design considers digital and physical simulations to reduce construction footprints, monitor the reduction of greenhouse gas emissions, and consider the life cycle assessment of the building components. It also demonstrates the valuable knowledge of traditional material craftsmanship in informing a technology-driven association for establishing circular constructions in the built environment (Fig. 7.4).

3 photographs of the TOVA building. A lateral view of a rectangular building with earthen walls and a single sloping roof supported by wooden rafters and straps, a top view of a crane beside the hollow walls that have layers of biconvex earthen cavities, and a close-up view of the rafters.

The implementation of on-site printing techniques and the use of natural materials in 3DPE guarantee the circularity of the construction process. As no chemical modification is needed to recycle the structure at the end of its life, it effectively prevents residual waste and pollution. The printed earth layers are returned to the source of the material, completing a full loop of circularity in the construction cycle.