Amorphous Inorganic Material Contents and Changes in Plasticity Indexes by Air Drying

Drying greatly reduces the plasticity index of high-allophane Dystrandepts. This study sought to confirm a hypothesis that a decrease in plasticity index on drying will also occur in soils containing large amounts of other amorphous inorganic materials. Five soils, including a Dystrandept, containing various amounts of amorphous inorganic materials were used. In those that were not Dystrandepts the amorphous inorganic materials did not contain allophane. The liquid and plastic limits for fresh and air-dried samples of two soils that contained <10% amorphous inorganic materials showed a little change by air drying. A soil containing 22% amorphous inorganic material had a negligible change in plastic limit due to air drying, but the decrease in the liquid limit was about one half of the freshsoil plasticity index. Upon air drying, the liquid limits of two soils with >40% amorphous inorganic material were reduced to lower water contents than their fresh-soil plastic limits.