Geopolymer foams are promising sustainable lightweight materials combining insulation efficiency with interesting mechanical and fire resistance properties. Controlling their pore size remains challenging because intrinsic foam aging processes act before hardening. We highlight a physical approach to counteracting aging processes in fresh geopolymer foams and to maintaining the pore morphology that has been set initially by mixing metakaolin suspension with precursor aqueous foam. More precisely, it is shown that arrest of foam aging can be achieved if solid particle concentration in the suspension is larger than a critical value which is proved to depend on both bubble size and gas volume fraction. This behavior is understood through the jamming transition occurring for the metakaolin suspension when confined in the foam network, providing significant solid elasticity against bubble motions. The general significance of the reported result makes it useful, as a complement to chemical formulation, for designing morphology-controlled geopolymer foams.

Fluid permeability of solid foams is a crucial parameter to control transport phenomena in numerous engineering applications, such as heat exchangers or filters for example. Open-cell foams with monodisperse pore diameter ranging from 200 to 1000 µm and solid volume fraction ranging from 0.1 to 0.38 are produced and Darcy permeability is measured. The permeability divided by the square of the pore size shows an exponential decay as a function of solid volume fraction. Surprisingly, existing models do not capture this exponential decay and actually they predict permeability values significantly larger than the measured values. The observed exponential decay is then successfully described by using models based on the viscous dissipation occurring through the apertures that connect the foam pores and by accounting for both the mean size of the apertures and the mean number of apertures per pore. Highlights Monodisperse solid foams have been produced with both controlled pore size and void fraction  The dimensionless permeability is shown to decrease exponentially over the full range of void fractions  The exponential behavior is successfully modelled from both the viscous dissipation occurring through pore connections and the mean number of apertures per pore