Lightweight Mixtures with a High Proportion of Recycled Fillers in Terms of 3D Printing Parameters (2025-11)¶

Concrete is one of the most widely used man-made materials by volume in the construction industry due to its excellent performance. However, it has detrimental effects on the ecosystem because it extracts nonrenewable species (aggregates). It is therefore essential to reduce dependence on natural resources and find alternative fillers. In particular recycled aggregates from demolition sites have great potential here. They are the focus of world research, with the trend being towards 'performancebased' approach to achieve the required functional properties for the specific application. In this paper, mixtures prepared with full (100%) and 50% dosage of recycled aggregate are presented, while the design of the mixtures as well as the tested properties were focused on the use in 3D printing. The tested fillers were recycled brick as well as the little studied recycled aerated concrete. For these mixtures, parameters in the fresh state, such as change in workability over time - open time, extrusion deformation, and parameters in the hardened state, i.e. flexural strength and compressive strength, are presented. The applicability of these types of alternative fillers at such high dosage for extrusion technology are discussed. The results show favorable parameters for both fresh and hardened mixtures, except for 100% recycled brick in its fresh state.