FROST ACTION IN CLAY SOILS .1. A TEMPERATURE-STEP AND EQUILIBRATE DIFFERENTIAL SCANNING CALORIMETER TECHNIQUE FOR UNFROZEN WATER-CONTENT DETERMINATIONS BELOW 0-DEGREES-C

A modified differential scanning calorimeter procedure was used to determine the relationship between temperature and unfrozen water content (UWC) in seven clays between 0°C and – 15°C to – 24°C. The procedure, which involved nucleation by a cooling followed by a rapid warming to – 0.l°C, avoided the difficulty of supercooling. Problems caused by temperature lag between the sample and its holder and by slowness of water movement within the sample, important even when cooling clay samples of about 17 mm3 at a rate of 0.31 K min−1, were overcome by cooling in a stepwise fashion which allowed time for equilibration between each temperature step. The clays studied included sodium and calcium Wyoming bentonites, < 1 μm and 1–2 pm fractions of St Austell kaolinite and three subsoil clays from England. After nucleation and as temperature fell below OT, water froze in two stages in most of the clays. UWCs at the minimum temperatures reached were up to 38% for the bentonites, between 9% and 20% for the subsoil clays and <4% for the kaolinites. Copyright © 1990, Wiley Blackwell. All rights reserved