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Freeze-Dried and Critical-Point-Dried Clay — A Comparison¹

ABSTRACT

The results of experiments conducted with an illitic soil, which has been freeze-dried and critical-point-dried, confirm that the freeze-drying process fails to preserve the structure of the swollen material. The pore structures, associated with clay "domains" (<10 nm), in samples freeze-dried from a wide range of soil-moisture potential, are improbably similar to that of an air-dried sample. In addition, the presence of large pores (about 1 µm), which should have drained at the equilibrium suctions, in the normal swelling range, which the samples experienced prior to freeze-drying, is inconsistent with the capillary rise equation. Furthermore, soil which has been freeze-dried from 10 kPa suction swells when placed at 5 MPa suction (p/p₀ = 0.96). During mercury intrusion, freeze-dried samples retain most of their total porosity while critical-point-dried samples collapse; this collapse is thought to be consistent with the metastable nature of a dry, but swollen, clay structure.

¹ Contribution from the Director's Research Unit, Waite Agric. Research Institute, The University of Adelaide, Glen Osmond, South Australia 5064.

² Professional Officer and Director, respectively.

Received for publication July 9, 1979. Accepted for publication December 5, 1979.