Rheological Behavior of Steel-Fiber-Reinforced Concrete in the Context of Additive Manufacturing

With increasing number of 3D-printed concrete structures, the demand for adequate reinforcement concepts for this modern construction method has been also increasing. From a technical perspective, the new technology can only be successfully used if the 3D printable materials fulfill the high requirements in terms of their rheological properties in a fresh state and mechanical properties in a hardened state. In this context, the integration of reinforcement presents major challenges for both industry and research. One promising approach to reinforcement is the addition of steel fibers to the concrete. These fibers enhance the ductility, durability, and robustness of 3D-printed structures. While the addition of fibers offers some manufacturing advantages, it considerably complicates the adjustment of the concrete mix’s rheology and requires a deep understanding of its behavior in the fresh state. Thus, this article addresses the time-dependent development of the static yield stress and the structural build-up rate of several cement-based materials containing steel fibers. In the printable cement-based materials with a maximum grain size of 8 mm, 0.5% and 1.0% by volume of straight steel fibers are added, each fiber measuring 25 mm in length and 0.4 mm in diameter. The test methods applied include the observation of the spread flow over time and the uniaxial compression tests. The results obtained provide a basis for the future efficient use of steel fibers in the context of 3D printing with concrete.