Influence of direct foaming methods on the early performance and microstructure of metakaolin‐based foam geopolymers

This study aims to explore the influence of direct foaming methods on the early‐stage performance and microstructure of metakaolin‐based geopolymer foam. Metakaolin is utilized as the primary silica–aluminum raw material, with various foaming methods employed to produce metakaolin‐based foam geopolymers exhibiting different dry apparent density gradients. The investigation encompasses an assessment of hardening time, early‐stage compressive strength development, and water absorption behavior of the foam geopolymers. Employing scanning electron microscopy (SEM) for microscopic morphology analysis, mercury intrusion porosimetry (MIP), X‐ray diffraction (XRD), and hot disk transient plane source method for chemical structure analysis, the study delves into the underlying mechanisms. Results reveal that the early compressive strength development of metakaolin‐based foam geopolymer is notably rapid, with the hydrogen peroxide foaming method demonstrating the swiftest performance. Among foam geopolymers of equivalent density levels, those produced via physical foaming exhibit the highest compressive strength, while those utilizing silicon carbide foaming display the lowest. Across different foaming methods, the foam geopolymer consistently demonstrates specific trends in pore structure characteristics, with a predominance of macropores in the low‐density range and gel nanopores in the high‐density range.