In situ measurements of porosities and permeabilities of alumina pastes

The compaction behaviour of various water-based pastes prepared from mixtures of different sized α-alumina powders was investigated by determining the paste porosity as a function of the applied total stress, and the results confirmed a logarithmic stress–porosity relationship for a given paste. The corresponding paste permeabilities were measured using a test cell in which the local solid stresses on the matrix and the liquid pore pressures within the paste were independently controlled. The data were interpreted using a Darcyʹs law approach commonly used in soil mechanics, and the generated permeability coefficients were shown to vary exponentially with the porosity of a specified paste. The experimental permeabilities were compared with those predicted from a Carman–Kozeny analysis, and the results suggest that entrapped air (unsaturation), as well as particle size, shape, size distribution and residual surface charging, are important factors that influence the permeability of a consolidated paste.