Research Summary Report of A03

[07.04.2023]

Hechtl, Christian Maximilian, TP editor, m.hechtl@tum.de, TUM, Chair of Materials Science and Testing (cbm)

Dr.-Ing. Kränkel, Thomas, PL, thomas.kraenkel@tum.de, TUM, cbm

Prof. Dr.-Ing. Gehlen, Christoph, PL, gehlen@tum.de, TUM, cbm

Main goal

The goal of A03 is to establish a concrete extrusion process using a near-nozzle mixing (NNM) approach to enable a quick change of material properties during printing (gradation). This approach allows for the creation of multifunctional components, such as combined load-bearing and thermally insulating structures, by precisely altering material properties as required throughout the printing process.

Summary and current state of research

GRES V1 is a gradation-capable extrusion system that demonstrates the potential to extrude a homogeneous concrete mix with low property variations. However, the first prototype still showed potential for improvement. For instance, dead zones were found in the mixing chamber due to the component geometry, which led to material accumulation and consequently to an undesired structural build-up of the material in the mixing chamber. Also, some clogging occurred.

GRES V2 was developed to address these issues by redesigning the process and the system. It consists of a shortened mixing compartment supplied with aggregates, cement paste, and water or additives as required. This updated design prepares the cement paste beforehand, improving binder performance and reducing the required mixing time and energy in the print head. The gradation of material is achieved by altering the type of aggregates and the binder-to-aggregate ratio. An additional water supply is installed to accommodate the varying water demands of different aggregate types and to control the water-to-binder ratio during printing. Preliminary tests of GRES V2 show improved concrete homogeneity and a more robust, controllable transition between different material properties.