INTERPRETATION OF NITROGEN SORPTION ISOTHERMS ON HYDRATED CEMENTS.

Nitrogen sorption data on hydrated cements given in Technical Report 520 have been supplemented bY work of other specimens; the whole group of nitrogen isotherms, 300 in all, are analysed in the present report in terms of the relationship between sample preparation and isotherm shape. The ' alpha //s' method of assessing pore structure has been adopted, use being made of a composite reference isotherm on autoclaved cement hydrate and silica TK 800. The data show that capillary condensation is absent during adsorption of nitrogen onto rapidly dried pastes, but it is present during adsorption onto slowly dried or autoclaved systems. It is deduced that slit-shaped pores are present in rapidly dried systems and that such systems are likely to be closest in structure to the undried cement pastes.