Unusual water transport properties of some traditional Scottish shale bricks

Sorptivity, porosity and pore size distribution have been measured for five types of pressed fired-clay bricks recovered from a Second World War airfield in East Lothian, Scotland. It was found that the bricks, all manufactured locally from colliery shale, had similar porosities but significantly different compositions, leading to differences in pore structure and transport properties. Unusually high concentrations of organic carbon were found by analysis. In imbibition tests using water and n-decane, capillary absorption generally did not scale with time(1/2), indicating material non-uniformity in the flow direction. A sharp front n-layer model was used to estimate the variation of sorptivity and permeability in drilled cores taken through bed and stretcher faces. A surface skin of lower sorptivity was found in some materials. This is attributed to compression of the green clay in the brick mould during manufacture. Comparison of water and decane imbibition showed that water sorptivity is reduced throughout by partial wettability. This hydrophobicity of these shale bricks is tentatively related to their high organic carbon content, which is incompletely burned out during firing. We show how the partial wettability may be expressed in terms of a wetting index derived from imbibition data.