Research Summary Report A02

Particle-Bed 3D Printing by Selective Cement Paste Intrusion (SPI) – Particle Surface Functionalisation, Particle Synthesis and Integration of WAAM Reinforcement

Straßer, Alexander, TP editor, alexander.strasser@tum.de, TUM, Chair of Materials Science and Testing

Matthäus, Carla, TP editor, c.matthaeus.@tum.de, TUM, Chair of Materials Science and Testing

Kränkel, Thomas, TP editor, thomas.kraenkel@tum.de, TUM, Chair of Materials Science and Testing

Gehlen, Christoph, PL, gehlen@tum.de, TUM, Chair of Materials Science and Testing

The goal of A02 is to implement reinforcement by Wire and Arc Additive Manufacturing (WAAM) in concrete elements produced by Selective Paste Intrusion (SPI), see Figure 1. Since the cement paste is applied to the aggregates and must penetrate the cavities between the aggregates by gravity, consistent rheological properties of the cement paste are essential. The welding process with WAAM generates high temperatures ­­– approx. 1500 °C at the welding point. This temperature load may harm the SPI process. Therefore, the impact of temperature and whether potential issues can be solved by various cooling strategies are analyzed.

Summary

The problems with clogged nozzles and the offset between x+ and x- direction (see last research summary report dated 03.12.2021) could be solved. Further investigations have been started.

Current state of research

The cause of the clogged nozzles (see Figure 2) was the insufficient flowability of the cement paste. The flowability of the cement paste could be adjusted by modifying the w/c ratio and the superplasticizer content. The offset between x+ and x- direction was measured and corrected in the machine control software.

Further investigation on the influence of temperature loads on strength has been started. It is analyzed whether temperature loads, which are transferred to the particle-bed due to the WAAM process, influence the strength respectively at which temperature threshold the strength decreases. In addition, test specimens are produced at different distances between the particle-bed surface and the printing nozzle. The analyses are used for a passive cooling strategy. A threshold to the maximum distance is determined.