Soil water content–water activity relations of structured kaolinitic specimens from GAB equation

Abstract

The GAB (Guggenheim–Anderson–de Boer) equation is explored to describe the relation between equilibrium soil water content (wequil) and water activity (relative humidity) of structured kaolinitic soils along the drying path. The equation is chosen as it has the advantage of a theoretical basis and can describe sorption behaviour of soils over a wide range of water activities. The GAB parameters evaluated from desorption experiments with de-structured specimens were successful in predicting the equilibrium water contents of structured kaolinitic specimens along the drying path. Insight into the influence of water activity on moisture desorption from structured soil specimens is obtained from energy requirements to desorb water molecules and by estimating the relative affinity (distribution constant) of water molecules for retention in soil pores or to undergo desorption.