Research Summary Report of A03

TU Munich, Chair of Concrete and Masonry Structures (mb)

Main Goal

With the near nozzle mixing (NNM) approach in A03, functionally graded 3D concrete printing (3DCP) has been established as a feasible process. Building on the concept of material gradation and the development of ‘Gradation-ready extrusion system (GRES)’, continues transitions from lightweight concrete to normal concrete have been successfully demonstrated.

Figure 1 shows the printing trial designed to study the performance transition within the functional gradient area, where material composition shifts from lightweight to normal concrete. On the basis of successful printing, the properties transition of the functional graded area is the primary focus of current investigation. Here, the variation is not merely treated as material parameter, but as a spatial variable applied within the structure.

The main goals at this stage are as follows: i) develop the GRES system to enhance transition efficiency; ii) explore a broader range of material variations, such as sustainable binders and coarse aggregate; iii) apply the concept of functional grading in concrete structure.

Following the RILEM TC 304-ADC study, we conducted a series of investigations on the properties of the transition area. Printing trials were carried out from lightweight to normal concrete, where mix designs and process setting were optimized to maintain consistent fresh state properties across the transition. Hardened state properties were then obtained through sampling and predetermined casting, which demonstrated the course of material transformation within the system, enabling a preliminary determination of the transition area length.

For finite element (FE) modeling of the transition area, the printed layers are represented individually, with each layer assigned specific material parameters. This approach enables analysis of how the gradient affects the overall structural response and stress distribution in the elastic stage and thus verifies the rationality of the transition design.

In parallel, attempts are being made to apply the GRES system to fiber reinforced 3D printing. Different types of glass fibers have been evaluated, and preliminary mix design trials have been conducted. Four-point bending tests were also performed to assess the residual stress behavior of glass fiber reinforced concrete (GFRC).