Additive Digital Casting: From Lab to Industry

Abstract

Concrete construction harms our environment, making it urgent to develop new methods for building with less materials. Structurally efficient shapes are, however, often expensive to produce, because they require non-standard formworks, thus, standard structures, which use more material than is often needed, remain cheaper. Digital fabrication has the potential to change this paradigm. One method is Digital Casting Systems (DCS), where the hydration of self-compacting concrete is controlled on the fly during production, shortening the required setting time and reducing hydrostatic pressure on the formwork to a minimum. This enables a productivity increase for standard concrete production. More importantly, though, it enables a rethinking of formworks, as the process requires only cheap thin formworks, thus, unlocking the possibility to produce optimised structural members with less bulk material and lower environmental cost. While DCS has already proven effective in building structural members, this process faces the challenge of moving into industry. This paper covers the next steps in doing so. First, we present the benchmark and expectations set by the industry. Second, we consider how we comply with these requirements and convert our fast-setting self-compacting mortar mix into a coarser one. Third, we present the next generation of our digital processing system, which moves closer to the industrial requirements in terms of size and the control system. Finally, two prototypes demonstrate how DSC: (a) increases standard bulk production by 50% and (b) can be cast into ultra-thin formworks. We discuss the results and the short-term industrial concerns for efficiency and robustness, which must be addressed for such a system to be fully implemented in industry.

In-Crease: Less Concrete More Paper

“…This mix allows for demoulding after 1.5 hours, when the material has reached a strength of 15MPa. The second mix design, a fast setting self-compacting concrete, was developed to implement in Digital Casting for a Swiss industrial prefabrication plant [48]. It is the first digital casting mix with aggregate sizes up to 8 mm and contains polypropylene fibres for fire resistance.…”

“…Superplasticizer ACE30 and a 30% sucrose solution as retarder were also used (3.2% and 0.35% by weight of cement respectively). The hardening is accelerated using calcium aluminate cement (CAC) [49] and the mix reaches a strength of 15MPa (needed for demoulding) within 4 hours and 85MPa after 28 days [48]. The mix and process will be referred to as DC-industry-mix from hereon.…”

“…For both mixes, we prepare a retarded base mix and place it in a conveyer pump. The material is pumped into a mixer, into which precise dosages of admixtures are added in a continuous process as the mix is cast into the formwork [11,48]. A custom control software regulates the dosing of the accelerator and flow enhancer to match the flowrate of the retarded concrete.…”

“…In this case the inline mixing devise is mounted to a 6-axis robotic arm that moves in a specific trajectory above the paper formwork depositing the fast setting mortar [13]. In the experiment described in section 3.3 we used the processing and DC-industry-mix developed for the industry partner [48], mimicking the industrial casting process developed for a Swiss prefabrication plant, where a crane is used to hover the digital concrete casting hose above the concrete during the casting.…”

Digitally fabricated ribbed concrete floor slabs: a sustainable solution for construction

“…Beyond these applications, which will be presented in more detail in Section 4, several other DFC technologies using non-conventional formwork have been used or could potentially be applied to produce ribbed slabs: -Slipforming is a widespread extrusion process in conventional construction of slabs, used to produce horizontally prestressed hollow-core slabs or joists. The DFC technology Smart Dynamic Casting broadens the possibilities of slipforming with variable cross-sections by adapting the slipping formwork through a robotic process and using a fast-hardening self-compacting concrete whose hydration is controlled through a digital process (known as set-on-demand or digital casting) [23,25]. -Flexible formwork technologies hold great potential for bespoke concrete structures [26], but their use to produce slabs is still scarce.…”