Influence of wet foam incorporation on the pore structure and properties of metakaolin-based porous geopolymers

Lightweight geopolymers are well-suited for construction applications, including thermal and acoustic insulation panels and fire-resistant barriers. Their porous microstructure can be tailored by incorporating gas bubbles into the fresh ceramic mixture. Several factors—such as geopolymer composition, mixing and curing conditions, and the setting behavior of the paste—play a crucial role in bubble retention within the consolidated specimens. This study investigated the processing of porous metakaolin-based geopolymers prepared with the addition of 5, 7.5, and 10 wt.% of a preformed liquid foam stabilized with xanthan gum. The addition of 0.45 wt.% xanthan gum improved foam stability, ensuring uniform pore distribution and minimizing bubble collapse during processing. This approach enabled the fabrication of specimens with low densities (0.87–1.46 g/cm³) and high porosity (39.49%–64.78%), significant air permeability, and well-controlled microstructural characteristics, with average pore sizes varying from 99 to 137 µm. Based on the findings, the geopolymeric binder containing 7.5 wt.% foam demonstrated a balance of strength, low density, reduced water absorption, and engineered porosity, making it a promising candidate for sealing components or thermal insulation materials. The direct foaming method and processing conditions effectively enhanced the properties of porous geopolymers, highlighting their potential for advanced construction applications.