• Plaschnick, Paul
• Butler, Marko
• Taubert, Markus
• Storch, Florian
• Will, Frank
• Mechtcherine, Viktor

Abstract

Currently, most research work in the field of concrete 3D printing is focused on the use of fine-grained mortar. These building materials are only suitable to a limited extent for large-format, monolithic printing of building structures because they do not comply with existing concrete standards, require a higher binder content, and generally have significant disadvantages in terms of economic and ecological assessments compared to standard-conforming ready-mixed concrete. The article reports on the results of a research project in which concrete mixtures with a maximum grain size of 16 mm, largely complying with current regulations, corresponding test methods, and adapted machinery equipment were developed for extrusion-based printing. In addition to selecting a suitable concrete mix design, there are a number of challenges regarding the machinery technology when processing concrete with a maximum grain size of 16 mm. This includes limiting wear on the extruder by selecting a suitable material for the stator, developing a shaping unit for printing variable layer geometries, and geometrically checking the printed filaments cross-sections during the printing process as a basis for controlling the adequate discharge rate. To ensure a continuous and segregation-free material flow throughout the entire print head, which consists of the reservoir, extruder, and shaping unit, the introduction of vibration energy is an option. The available test results are presented, and recommendations are derived based on this. Overall, the results demonstrate that although the automated printing of monolithic structures with standard-compliant ready-mixed concrete presents specific challenges, these can certainly be overcome with careful material selection, machine design, and process engineering.

Topics

• impedance spectroscopy
• grain
• grain size
• extrusion