Investigation of water to ice phase change in porous media by ultrasonic and dielectric measurements

Abstract : The main objective of this paper is to study the evolution of the ice content of porous media submitted to sub-zero temperatures by dielectric and ultrasonic measurements. Dielectric measurements are made by a capacitive sensor-based apparatus. The amount of ice formed within the tested sample is estimated from the global dielectric constants of the sample and of all the phases that form the tested composite material. On the other hand, ultrasonic measurements are based on the evolution of the ultrasonic wave velocity through the tested sample during a freezing-thawing cycle. These two methods lead to very close results and appear to be cheaper alternatives to low temperature calorimetry. The ice content curves are analyzed with the help of thermoporometry concepts in order to characterize the pore size distribution. Results appear to be complementary to mercury intrusion porosimetry ones. Moreover the commonly observed hysteresis of the ice content during a freezing-thawing cycle is investigated with respect to material microstructure.