Shaping and Characterization of Additively Manufactured Geopolymer Materials for Underwater Applications

Additive manufacturing brings many benefits to the building industry, one of them being automatization and the possibility to work in harsh environments, including underwater applications. In addition, this technology enables faster infrastructure repairs and adjustments to the scope of work to specific damage caused by, for example, biocorrosion processes. The main aim of this article is to investigate the development of geopolymers as a printable material for civil engineering, including underwater applications. For that purpose, the process of the material extrusion will be modified, and material properties will be improved. In the first step, the raw materials were investigated (SEM, EDS, XRF, particle size analysis) and the proper additives were selected based on literature analysis. Next, geopolymer paste was synthesized and fresh paste properties were investigated, including time for curing samples and workflow. The mixture composition was modified to obtain the required printable parameters through the application of different additives and the modification of the proportion of components, especially alkali solution. Finally, small-scale additive manufacturing trials were conducted in the air and with submerged containers. Additionally, samples were prepared using the casting method to compare the mechanical properties and microstructure. The obtained results show that additives such as xanthan gum and superplasticizer improve the rheological properties of the paste efficiently. With the help of additive manufacturing, geopolymer samples with compressive strengths of up to 7.5 MPa and flexural strengths of up to 4.15 MPa after 28 respectively were achieved. Compared to the average of the cast samples, the compressive strength of the printed samples was at least 5% lower, while the flexural strength was at least 38% lower for printed samples. The 3D-printed samples showed strong anisotropy between the tested orientations of the flexural strength samples.