Anisotropic properties of additively manufactured lightweight concrete elements
Marco Lindner*, Ralf Gliniorz, Henrik Funke, Sandra Gelbrich
E-mail: marco.lindner@mb.tu-chemnitz.de
Keywords: Robotic 3D printing, additive manufacturing, extrusion with concrete, anisotropic properties,
Robotic concrete extrusion is a novel additive manufacturing process (3D concrete printing) and is part of a continuously digitally controlled value chain. According to the state of the art, concrete is considered to be an isotropic material due to the manufacturing process. However, for the additive manufacturing process, the isotropic approach hast to be reconsidered due to the layered structure. It can be assumed that due to the layered structure, the material properties vary depending on the deposition direction and the geometry of the layers. The aim of the work was to record the material-technical characteristics of extruded elements manufactured according to standards in comparison with concrete recipes. Process-related influences on the mechanical parameters of additively manufactured concrete elements were examined and evaluated in more detail. Based on the findings obtained, the dimensioning, design and measurement of components can be carried out and thus guidelines for components can be derived. With these derived guidelines, the material utilization and economic efficiency can be improved.
1. Introduction
Rapidity, precision, economics and resource saving are the most important requirements of the construction industry of the future. Modern lightweight construction technologies can implement these requirements and add the aspects of design freedom, efficiency, and sustainability. Therefore, the development of new manufacturing technologies for highly stressable, durable and free-forming prefabricated concrete components with low material and energy input is the focus of the research group “Lightweight Constructions in Civil Engineering” (LBW) at the Chemnitz University of Technology. In general, the well-known building material concrete is considered isotropic due to the material properties and classical processing methods (casting, laminating e.g.). In contrast, the application of additive manufacturing processes result in anisotropic material properties because of the layered structure of the concrete elements by means of extrusion.
The aim of the work was to determine and compare the material properties of test specimens produced by casting (in accordance with standards DIN EN 12390) and by means of extrusion technology to be able to draw conclusions about anisotropic material behavior because of the extrusion process.
In addition, numerical investigations were conducted to reproduce the results of the mechanical tests. As a part of the investigation, process-related influences on the mechanical parameters of additively manufactured concrete elements were examined and evaluated in more detail. Based on the findings obtained, design and dimensioning of components can be conducted and thus guidelines for components can be achieved. With these derived guidelines, material utilization and economic efficiency can be improved and the lightweight construction principles can be implemented.
2. Material and methods
2.1. Experimental procedure
Additive manufacturing with mineral materials, in particular robot-assisted concrete extrusion, is a new manufacturing technology in construction and offers architects and civil engineers a variety of options for implementing lightweight construction concepts. At the same time, it requires great care in selecting the correct manufacturing parameters and material composition. The development was executed at the research facility “LBW RoboArena” (Table 1 .) at Chemnitz University of Technology [1, 2, 3, 4, 5, and 6].
Table 1. Research facility “LBW RoboArena” at research group LBW