Chemically foamed geopolymers for 3D printing applications

Using chemically foamed geopolymers in 3D-printed building applications offers multifunctionality to the construction sector and enhances environmental sustainability; however, this topic remains virtually unexplored. To this end, the first part of this paper focuses on the fundamental stabilisation mechanism of chemically foamed geopolymers. In the second part, the most promising compositions were selected for applications in two potential areas: i) integration as an infilling material in 3D-printed sandwich envelopes, and ii) direct 3D printing of foam geopolymers. The findings indicated that to prevent instability mechanisms, various mix-design practices are necessary, including the use of an appropriate surfactant to inhibit coalescence, and the regulation of rheological properties to control drainage and coarsening. Implementing stabilised foam as infill in 3D-printed walls significantly enhances thermal performance due to its low thermal conductivity. Additionally, by adjusting Al dosage (up to 0.3%) and using SDS as a stabilising surfactant, the foams were successfully printed with densities and compressive strengths ranging from 0.58 to 1.1 g/cm 3 and 1.2 to 13.5 MPa, respectively. Moreover, 3D-printed foams demonstrated a thermal conductivity of 0.097 W/m·K and an impressive sound absorption coefficient (0.84 at 630 Hz) for the mix containing 0.3% Al. The results underscore the viability of 3D-printed chemically foamed geopolymers in future construction projects.