Eggshell: Ultra-Thin Three-Dimensional Printed Formwork for Concrete Structures

Abstract

Concrete is a material favored by architects and builders alike due to its high structural strength and its ability to take almost any form. However, to shape concrete structures, heavy-duty formwork is usually necessary to support the fresh concrete while curing. To expand geometrical freedom, three-dimensional (3D) printed concrete formwork has emerged as a field of research. This article presents one possible application, a novel fabrication process that combines large-scale robotic fused deposition modeling 3D printing with simultaneous casting of a fast-hardening, set-on-demand concrete. This fabrication process, known as ''Eggshell,'' enables the production of nonstandard concrete structures in a material-efficient process. By casting a fast-hardening concrete in a continuous process, lateral pressure exerted by the fresh concrete is kept to a minimum. In this way, a 1.5-mm-thin thermoplastic shell can be used as a formwork, without any additional support. Geometries of different scales are tested in this article to evaluate the feasibility of the Eggshell fabrication process in an architectural context. An array of printing materials are also tested, and several different reinforcement concepts are analyzed. The findings are used to produce a full-scale architectural demonstrator project. This article shows that a wide range of concrete geometries can be produced in a material-efficient fabrication process, paving the way toward mass customization and structural optimization within concrete architecture.

Opportunities and challenges for structural engineering of digitally fabricated concrete

“…In the Eggshell method, an ultra-thin 3D-printed formwork (Figure 4b, left) is digitally filled with set-on-demand concrete at a speed that is controlled to limit the build-up of hydrostatic pressure to values that the formwork can support [89,95]. This technology is similar to the smart dynamic casting process, but the use of an ultra-thin formwork allows for more complex geometries.…”

Design and Fabrication of a Non-standard, Structural Concrete Column Using Eggshell: Ultra-Thin, 3D Printed Formwork

“…Due to public access to the pavilion the structure had to ensure building code compliance. Therefore, despite the fact that several novel reinforcement concepts exist for the Eggshell process (active reinforcement, steel hooked fibres [15]) it was chosen to use conventional, passive reinforcement. A benefit of the Eggshell fabrication process is that it allows for the relatively easy integration of such reinforcement: a reinforcement cage can be prefabricated and installed inside the thin formwork.…”

“…In contrast to these approaches is the fabrication method Eggshell [15], the subject of this paper. Eggshell enables the use of FDM 3D printing of ultra-thin formworks with a high degree of complexity, good surface quality and no additional support.…”

Print Paths Key-framing

“…On the downside, with fast material deposition rates material retraction and interruptions of the print process become hard to achieve, making continuous spiral or zig-zag paths favorable for the realization of surfaces. Single-shell FDM parts can be used as final architectural products, as molds for concrete casting [Burger et al 2020;Jipa et al 2017], or as parts of a multi-material print [Kwon et al 2019a,b].…”

“…Our fabrication setup consists of a UR5 robot and a custom PLA extruder with nozzle diameter d n = 2 mm, which uses 2.75 mm standard PLA filament (figure 8). The extruder was developed for planar robotic printing as part of the project Eggshell [Burger et al 2020] and includes a fan for the cooling of the print. To achieve paths of variable thickness, we regulate the quantity of material that is extruded by printing with constant filament feed rate and variable robot tool center point (TCP) speed.…”