Experimental investigation and hygrothermal modelling of freeze-thaw process of saturated fired clay materials including supercooling phenomenon

Abstract

To investigate the supercooling phenomenon in fired clay materials, low-temperature differential scanning calorimetry (DSC) and a one-dimensional freeze-thaw (FT) experiment were performed on saturated specimens. The rate of increase in ice saturation during freezing was calculated from the DSC result. Rapid ice growth over a relatively narrow temperature range (within about 0.2 K) was observed at a cooling rate of 0.25 K/min. In the FT experiment, the temperature distribution of a specimen was measured with inserted thermocouples. According to the results of the FT experiment, a rapid temperature increase was observed at sub-zero temperatures accompanied by freezing of the supercooled water. When the supercooled water began to freeze, the released latent heat was found to strongly prevent the specimen temperature from dropping even during the cooling period. Finally, a hygrothermal model of freezing and thawing including a non-equilibrium supercooling process was developed. The freezing rate of the supercooled water was modelled based on the DSC result. The validity of the model was verified by comparing the results of the FT experiment and calculations. The model was found to be able to replicate the rapid temperature rise during the cooling period of the FT experiment.