Relationship between Water Vapor Sorption Kinetics and Clay Surface Properties

Abstract

A complete understanding of soil–water interactions and the corresponding mechanical behavior of unsaturated soils requires differentiating adsorptive and capillary components of water retention and dominant water uptake mechanisms. Water vapor sorption (WVS) isotherms have historically been used to quantify the water uptake behavior of clayey soils and to determine related mineral surface properties, such as specific surface area and cation exchange capacity. This paper introduces the WVS kinetics curve as a new measure for gaining additional insights into the WVS behavior of clays. The sorption rate calculated from WVS kinetics curves scales with the cation heat of hydration at low relative humidity (RH<10%), indicating that cation hydration is the first mechanism for water uptake by dry clays. Sorption rates up to 25% RH are related to monolayer adsorption and specific surface area (SSA). A distinct relationship is proposed to relate SSA to the sorption rate normalized with predominant cation valence.