Extrusion of Near-Nozzle Mixed Concrete –Individually Graded in Density and in Rate of 3D Fibre Reinforcement

Additive manufacturing in the construction industry represents one of the biggest changes in the last 50 years. On the one hand, the focus is on increasing efficiency in terms of required production time, as well as increasing resource efficiency. In contrast to filled concrete formwork castings, 3D concrete printing enables the possibility of using material specifically where it is needed. In addition, the use of continuous systems makes it possible to produce different types of concrete by adjusting the mixing ratios. This makes it possible to control not only the amount of material but also the properties of the concrete at specific points.

In most concrete extrusion processes used today, the concrete is premixed and transported to the nozzle in relatively long hoses by a pump. The complicated cleaning is a problem when using such hoses, as steel fibres that may have been used can get stuck in the hose. In addition, the friction occurring in the hose has a negative effect on the concrete properties. Thus, the already high demands on the concrete can partly not be reached. Such requirements include slow curing during the pumping process, which is in contrast to relatively fast curing after the deposition. Since there is only one concrete mix in the pump and the system is discontinuous, the possibilities of graded concrete strands are difficult or impossible to realize.

After the initial development of the 1st prototype, it is now being optimized for the use of “real concretes” (grading curve ≥ 8mm). Furthermore, the focus is on the dosing of the individual concrete components and the mechanical integration of the multi-component dosing system in order to ensure the accuracy and feasibility of different concrete recipes. Sensors and an “inline quality measuring device” are being installed and developed to further improve system intelligence. These components will provide real-time feedback on the properties of the extruded concrete and enable proactive adjustments to be made during the process to maintain consistency and quality.
Together with researchers from the Centre for Building Materials and Materials Testing (cbm) and the Chair of Concrete and Masonry Structures, formulations for this novel process are being developed and validated, and components manufactured using this process are being analyzed.