3D Printing Geopolymers: Process, Porosity, and Performance

3D concrete printing is an innovative additive manufacturing technology that has revolutionized the construction industry by enhancing productivity and enabling the creation of complex components with novel functionalities. Ordinary Portland cement (OPC), as the main binder, poses environmental challenges since its production has a high CO₂ footprint. Geopolymers, as a green alternative, not only have a lower carbon footprint than OPC but also help promote a circular economy by using waste materials such as fly ash. This PhD dissertation aims to develop both dense and porous geopolymers for use in 3D printing applications and provides more insight into the adaptation of 3D printing through process optimization and evaluation of performance in terms of mechanical and insulation properties.

To this end, since the common practice for the printing process is a trial-and-error approach, this research first delves into the optimization of the printing process using machine learning. An experimental approach was conducted to assess the impact of each printing parameter and their interconnections. The experimental dataset was utilised to develop machine learning models aimed at predicting and optimizing the printing process of geopolymers.

Afterwards, the optimized process parameters were used for the creation of highly porous geopolymers with cellular structures, and the mechanical and fracture properties were evaluated. The objective was to utilise 3D printing to enhance the strength-density relationship and fracture characteristics of geopolymers. In this context, various high-resolution patterns with distinct pitch angles and infill densities were produced. Low pitch angles were found to enhance flexural strength, work of fracture, and the strength-density relationship.

Finally, to add multifunctionality to the 3D printed structures, stabilized foam geopolymers with varying densities and pore sizes were developed. The stabilized foam was used as an infilling material in a small-scale printed wall, and it demonstrated notable thermal performance due to its low thermal conductivity. The foam geopolymers were also printed with varying densities and showed enhanced thermal and sound absorption properties, highlighting the potential applications of 3D printed foam geopolymers in future construction projects.