Abstract
The objective of this paper is to provide an insight into current basic research at ITE on the manufacturing process of resource-efficient components through the controlled, automated magnetic distribution and alignment of steel fibers in UHPFRC (Ultra-High Performance Fibre-Reinforced Concrete). The method for distributing and aligning steel fibers in UHPFRC is based on the physical phenomenon of magnetism. Since steel fibers are ferromagnetic, magnetic fields can selectively change their position in the fresh concrete and align them according to the force flow and the maxim "form follows force". The magnetic fiber alignment (MFA) process developed on this principle combines the capabilities of digital and automized component manufacturing with the potential of targeted fiber alignment to increase the material efficiency of UHPFRC. It is highlighted at four levels: UHPFRC
 At the material level, studies were conducted on the composite properties of different brand-new and recycled microsteel fibers (MSF), formwork designs suitable for the MFA process were developed, flux densities of different magnets were simulated with special software solutions and measured in practice, and an end effector was fabricated that was implemented on 3- and 6-axis kinematics. At the process level, the interaction of the main parameters of the MFA process was evaluated by visual analysis on transparent glucose syrup-based solutions, and series of specimens were analyzed by micro-CT scans. At the component level, centric tensile tests were performed on a wide variation of dog-bones to provide an assessment of the potential increase in tensile performance of UHPFRC by the MFA process. At an economic and environmental evaluation level, the results from the tensile tests were used to assess and quantify the potential savings from reducing the fiber content and using recycled steel fibers.
Highlights
Lightweight and thin concrete components made of UHPFRC require tight manufacturing tolerances and high material efficiency due to their low wall thickness and filigree nature
The analyses presented above demonstrate that, in addition to the selection of a suitable fiber-matrix combination, fine adjustment of the process parameters of the magnetic fiber alignment (MFA) process is necessary to achieve a significant increase in the performance of UHPFRC components
The aim of the research described is to create the basis for the production of resourceefficient components with the aid of the controlled, automated magnetic distribution and orientation of microsteel fibers (MSF) in UHPFRC
Summary
Lightweight and thin concrete components made of UHPFRC require tight manufacturing tolerances and high material efficiency due to their low wall thickness and filigree nature. This can be achieved in terms of the material quality of the concrete matrix and the fiber content. In terms of fiber distribution and orientation, the precision and efficiency is missing: In expectation of a uniform distribution of fiber contents in the component, the microsteel fibers (MSF) are added to the matrix during the mixing process and poured into the forms as a complete mixture. To ensure a certain concentration of effective fibers in UHPFRC components, the overall quantity of all fibers is increased, with the consequence of poorer workability of the fresh concrete. In the course of the development of UHPFRC, MSF with a tensile strength of at least 2000 MPa in particular have proven to be effective due Ledderose et al | Open Conf Proc 1 (2022) "Vision and Strategies for Reinforcing Additively Manufactured Concrete Structures"
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