Digital fabrication has been termed the “third industrial revolution” in recent years, and promises to revolutionize the construction industry with the potential of freeform architecture, less material waste, reduced construction costs, and increased worker safety. Digital fabrication techniques and cementitious materials have only intersected in a significant way within recent years. In this letter, we review the methods of digital fabrication with concrete, including 3D printing, under the encompassing term “digital concrete”, identifying major challenges for concrete technology within this field. We additionally provide an analysis of layered extrusion, the most popular digital fabrication technique in concrete technology, identifying the importance of hydration control in its implementation.

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This paper describes the structural design, digital fabrication and construction of KnitCandela, a free-form, concrete waffle shell with KnitCrete, a falsework-less formwork approach using a custom prefabricated knitted textile as multi-functional, structural shuttering layer and a form-found cable net as the main load-bearing formwork. The digitally designed and fabricated textile provided integrated features for inserting and guiding elements such as cables and inflatables that helped shape the sophisticated mould. With a total weight of only 55kg, the 50m 2 formwork was easy and compact to transport. On site, the formwork was tensioned into a timber and steel rig, the pockets were inflated, and then coated with a thin layer of custom-developed, fast-setting cement paste. This paste served as a first stiffening layer for the textile, minimising the formwork's deformations during further concrete application. Fibre-reinforced concrete was manually applied onto the formwork to realise a 3cm-thick shell with 4cm-deep rib stiffeners. The novel approach, for the first time applied at architectural scale in this project, enables the building of bespoke, doubly-curved geometries in concrete, with a fast construction time and minimal waste, while also reducing the cost and labour of manufacturing complex parts.

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Digital fabrication with concrete has for more than a decade been of high interest in both research institutions and industries. A particular interest has been set on Contour Crafting, a type of layered extrusion with concrete, which in recent years has been used for the fabrication of single and multi-story buildings. However, these have been done with little proof of systematic integration of reinforcement, which until now still requires tedious post processing to obtain the structural capabilities required. Smart Dynamic Casting, a robotic fabrication process for standard and nonstandard vertical structures, has recently proven a systematic integration of reinforcement and is thereby the first digital fabrication process worldwide which has unified reinforcement and concreting in a single robotic fabrication process. This paper presents the latest developments and challenges of SDC and introduces the first architectural application in the form of structurally optimised façade mullions that are to be installed in the dfab House at the EMPA premises in Dübendorf, Switzerland.