Holistic Investigation of Robotically Assisted 3D Printed Cob Walls: From Fabrication to Environmental Impacts

Abstract

The rapid increase in the adoption rate of large-scale 3D printing into the construction industry has revealed a number of potential applications. This rapid implementation has also led to a higher degree of construction process optimisations and increased ability of mass customisation. Most existing applications of 3D printing technologies in construction are, however, heavily dependent on concrete and other cement-based materials, resulting in a pursuit to explore other building materials with lower environmental impact and higher adaptability to natural contexts. This pursuit has led to re-approaching earth materials and architecture to be applied in modern constructions. For centuries, earth architecture has offered potential solutions for several problems associated with buildings, such as high CO2 emissions, high embodied energy of the construction process, and depletion of natural resources. Yet this method of construction is possibly on the edge of extinction as its slow and very labourintensive process requires highly skilled craftsmen. Thanks to digital construction methods and technologies, earth materials can now become a key to promoting a new range of sustainable construction solutions that are adaptable to a local context. ‘Cob’ stands as one of many types of earth construction methods that has been utilised all over the world. Its mix consists of subsoil (earth), water, and fibrous material (typically straw), and its construction can comprise a variety of geometries and design goals without the need for formwork or any mechanical compaction method. The main aim of this research is to leverage the qualities of conventional cob construction as a groundwork for digital innovation through robotic-supported 3D printing (3DP) techniques. This aim has been approached through a comprehensive feasibility assessment of 3DP cob walls. The feasibility study included four main lines of exploration. First is the material fabrication and design process. In this line, the research systematically explored the relationship between the revised cob recipes and the geometrical and design characteristics offered by the new 3DP system. The findings of this exploration provide a new understanding about the opportunities and challenges of the current 3DP cob process, which becomes the basis to develop a novel 3DP system for earth-based materials. The second line examined the structural feasibility of using 3DP cob walls used in low-rise residential buildings. This investigation involved monotonic axial compression tests, in addition to a numerical modelling via Finite Element Analysis (FEA). The results proved the ability of 3DP cob load-bearing walls to support a two-storey residential house and meet building regulations. The test also established an optimised design chart, describing the relationship between building design and the loadbearing capacity of 3DP cob buildings. The third line of exploration involved investigating the thermal conductivity of 3DP cob walls. The assessment has revealed a lower thermal conductivity of 3D printed cob (as low as 0.32 W/mK) compared to its manually constructed cob counterparts, which means using 3DP cob for the building walls would potentially reduce heating and cooling energy use in the building. The fourth exploration focused on assessing the environmental impacts of 3DP cob walls using a Life Cycle Assessment (LCA) method, from cradle to site. The results showed a superior environmental performance of 3DP cob over the concrete-based construction methods while providing the same structural functionality in a onestory house. The results also indicate that the use of renewable energy resources can further boost the environmental potentials of 3DP cob for future construction. In summary, this research brings 3DP cob construction closer to full-scale applications. On a broader scale, the study contributes to the disciplines of architectural design and construction by providing a framework capable of bridging the knowledge gap between vernacular modes of architecture and contemporary digital practice. Moreover, this technology is not exclusive for new buildings as it can potentially be a useful strategy for conservation and repairing existing cob buildings. This is expected to benefit architects, designers and researchers currently looking into indigenous crafts as a source of material and design knowledge for a revisited digital-based architecture.