Abstract: Isothermal adsorption is quantitatively utilized to determine types and boundary line of bound water on clays. Results show that pure montmorillonite adsorption tendency assume the type “S” which is from single molecule layer adsorption to double layers adsorption, many layers adsorption and continuous adsorption along with relative vapor pressure p/p_s increasing (p/p_s=0～0.98). Isothermal adsorption curve have two clear turning points which are p/p_s =0.9 and V =0.98, standing for the special humidity of claywater system. The relative vapor pressure 0.9 is the boundary line between the strong bound water and the loose bound water (osmotic bound water) on clays, the relative vapor pressure 0.98 is the boundary line between the loose bound water and free water on clays. The experiment determines the bound water quantities on clays (mass, volume, density, thickness, average integral specific volume). The relationship between hydroclay datum face interval distance d₀₀₁and p/p_s has been obtained, and the two special humidity by isothermal adsorption and the boundary line of bound water on clays have been verified.

Key words: clay, isothermal adsorption, bound water mass, bound water boundary line, special humidity