Investigation of a hybrid binder system for large scale 3D printing

Large-scale additive manufacturing of reactive suspensions, such as concrete, is being developed to freely create objects without the constraints of a formwork. One challenge in printing suspensions is the precise spatio-temporal control over their rheological properties. For extrusion-based processes the material must be pumpable to the nozzle of the printer, while once it has passed the nozzle, it must maintain its shape under the increasing pressure of subsequent layers. Therefore, it is beneficial if the material exhibits an appropriately designed rheology change at the nozzle. The objective of this work is to develop a printing suspension which achieves a rheological step change at the nozzle. Therefore, we create a hybrid binder system comprising of a fast, reactive organic component, which can be activated by heat and a second inorganic binder components, in our system the carbonation of calcium hydroxide, which delivers the final strength. The temperature dependent stiffening of the model suspensions is studied by oscillatory rheology at temperatures between 20 °C to 80 °C. For mechanical testing purposes, cuboid shaped samples are obtained by microwave heating followed by carbonation under ambient conditions. For the given porosity, the material reaches a compressive strength of up to 0.39 MPa in 10 seconds or up to 1.94 MPa in 10 minutes depending on the heating program. Subsequent carbonation for 7 days under ambient conditions gives a strength of up to 4.76 MPa. © 2023 The Authors. Published by Ernst & Sohn GmbH.