Performance of a Dynamic Dew Point Method for Moisture Isotherms of Clays

Laboratory tests were conducted to assess the performance of a dynamic equilibrium method for rapidly measuring water vapor sorption isotherms of clays and clayey soils. Emphasis was placed on quantifying temperature stability, measurement reproducibility, establishing a recommended testing protocol, and comparing dynamically generated isotherms with those obtained using a conventional equilibrium method. Adsorption-desorption loops for water activity (aw) or relative humidity ranging from 0.03 to 0.95 and containing as many as 140 discrete measurements were obtained using the dynamic method in 12–24 h. Far less intensive sorption isotherms using the equilibrium method required ∼600 h (25 days). Measurement reproducibility was within 6 % of the full-scale range. Water contents measured using the dynamic method at aw less than 0.60 compared excellently with values measured using the equilibrium system and are within 10 to 15 % of the full-scale range at higher activity. Comparisons between total suction characteristic curves obtained using the dynamic system and the equilibrium system suggest a practical total suction measurement range from about 100 000 to 400 000 kPa for a wide range of clay types.