Research Summary Report of A02

[24.03.2023]

Straßer, Alexander, TP editor, alexander.strasser@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

Main goal

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 WAAM-induced temperature loads on the SPI-made concrete is analyzed and whether potential issues can be solved by various cooling strategies.

Summary

Various investigations were carried out. These included investigating the effect of external temperature loads in the fresh state on the strength properties (see report from 22.07.2022), but also investigations with regard to particle coatings as passive cooling strategy on strength properties and alternative reinforcement strategies in collaboration with A05.

Current state of research

In the previous report, it was mentioned that a test series was planned to investigate the impact of external temperature loads in the fresh concrete on its compressive and flexural strength properties. The initial results indicate that a significantly decrease in both compressive and flexural concrete strength occurs at temperatures above 80°C.

In collaboration with iPAT, a 2^nd test series was performed to evaluate the efficiency of passive cooling by functionally coating the aggregates with dry water. Using the SPI process, test specimen were produced with coated aggregates, which were then compared to SPI produced specimen without aggregate coating in terms of compressive and flexural strength performance. The findings revealed that the dry water coating caused a decrease in strength, but an increased heat storage capacity.

In addition, investigations for alternative reinforcement strategies in the SPI process were initiated in cooperation with A05. A05 provided various types of reinforcement for the test specimens, which were fabricated by inserting them while printing with the SPI method. Also specimens without reinforcement as reference were produced. A big thank you to A05 for their support. The test results are yet to be evaluated.