Digital fabrication material processing strategy for bespoke low clinker mass concrete components

Digital manufacturing techniques are seen to be very promising in concrete construction because of their potential for increasing productivity, as well as their potential to increase sustainability due to reduced material usage via nonstandard geometry. Concrete 3D printing via extrusion has received the most attention as a method, however the problem of implementing reinforcement remains unresolved; therefore, printed concrete typically serves as either a formwork or as unreinforced masonry. The recently developed technique of Digital Casting allows for digitally produced concrete components that implement standard reinforcement bars. The technique was developed especially for digitally produced, nonstandard formworks, and relies on controlled set acceleration of a self-compacting concrete to control formwork pressure during production. Digital fabrication techniques such as Digital Casting (and 3D Printing), however, have notoriously high cement contents due to processing requirements, and this may negate any sustainability benefit that can be realized through material savings in a bespoke concrete component. Research efforts to bring these cement contents closer to standard concretes have focused on: 1) reducing paste content through increased aggregate content and 2) reducing clinker content through substitutions, with most recent efforts focused on the latter. A recent project demonstrated, additionally, that elevated clinker contents negatively impact the casting of mass concrete elements due to high heat generation, which limits the applicability of digital fabrication for mass concrete applications. In this study, the use of a CEMIII (slag substituted cement) based mix design for this type of application was examined. The mix was successfully accelerated to control formwork pressure in a digital casting process of a thick (>1 m) bespoke element with overhang, and internal temperatures monitored. The reduced heat release generated temperatures of only half of those generated by a previous mix design with higher clinker content.