Two-filament 3D printing with concrete and earth

3D printing is a popular term for computer-controlled additive manufacturing where a product is shaped by adding rather than subtracting the material. While the concept of additive manufacturing is not new, it is the development of computers which opens up new possibilities. Technological advances are paving the way for 3D printing also in construction where concrete is in the spotlight due to its properties and wide applicability. Concrete consumption constitutes ~80 % of total material consumption and therefore 3D concrete printing has the potential to digitalize and automate the construction industry. Furthermore, digital fabrication methods will also shift the design approach since topologically optimized structures are material-minimized but geometrically complex elements which can only be designed and fabricated by digital means. The most promising 3D printing method is an extrusion-based approach where concrete is pumped to the printhead and squeezed through a circular or square nozzle. The motion of the printhead is enabled by an articulated robotic arm or a gantry crane. The behaviour of the filament after the extrusion is governed by its rheological properties. While stiff concrete enables the deposition of a larger number of subsequent layers without collapse the bond between the layers is poor. Soft filaments, on the other hand, bond well but they are prone to collapse due to the weight of the subsequent layers. Extrusion-based 3D printing with concrete, therefore, relies on the manipulation of the rheological properties and the use of accelerators. Both requires expert knowledge and testing equipment not readily available in the construction industry. This project thus proposes printing with two filaments where the soft filament binds the layers of stiff filaments and where the latter provide the stability to the printed product. The mix design of such filaments is simple. The 3D-printed structural elements are often assessed by adopting the principles of masonry construction. The aptness of such an approach is even more evident in two-filament printing. Masonry structures are associated with bricks and brick forming is done by extrusion. This leads us to the idea of using two-filament printing to fabricate earth buildings. Building with earth, which contains a sufficient amount of clay, is an ancient construction technique which is on the rise in modern construction due to sustainability benefits and accessibility. However, to facilitate the implementation, it is of paramount importance to develop digital fabrication methods since a lack of technology is recognized as a technical barrier in earth construction. Project objectives are thus defined as: develop a double-nozzle printhead and build a small-size printer prototype for two-filament printing; determine the range of suitable rheological parameters for stiff and soft filaments for concrete and earth and establish a system of simple test methods to assess filament suitability; demonstrate the two-filament 3D printing technology by printing a small-scale structural element, test both elements and compare the results with structural analysis derived from masonry structures. The main results of the project are a printer prototype and a showcase of two-filament printing with concrete and earth which will be presented in a promotional video. The results in the public domain will also include the report on filament properties for concrete and earth as well as the structural analysis protocol. Confidential results will comprise the printer specifications and design plans for the fabrication of the printer and its components. It is expected that results in the public domain will be published in at least two scientific and at least two technical journals, while the printer itself will be presented at a public workshop or a fair. Confidential results are expected to be the subject of at least one patent application.