Interactive powder mixture concept for the preparation of geopolymers with fine porosity

A new concept of chemical foaming is proposed for the preparation of geopolymers with fine porosity. The use of an interactive powder mixture of gas releasing agent and carrier particles, potentially combines the benefits of small point sources of gas with easy homogenization in the fresh geopolymer. This concept was exploited here for the preparation of porous flyash-based geopolymers. The interactive powder mixture was a SiC powder containing reactive submicron FeSi/FeSi2 particles. Premature foaming was avoided due to prolonged induction period and slow reaction rate of the active phase. Samples were characterized using scanning electron microscopy, mercury porosimetry, tree-point bending tests and thermal conductivity measurements. In addition, total porosity was determined using measured apparent and real densities. It was found that fine pore structure (diameter 140 ± 80 μm) not normally obtained using chemical foaming, was achieved in a reproducible manner with this approach.