Freezing behavior of unsaturated porous materials

Abstract

The freezing/thawing behavior and the frost-resistance of unsaturated porous materials are quite different from those in water saturated condition. Most previously studies have focused on the water saturated porous systems, however, the effect of moisture content on the freezing behavior of unsaturated porous materials is not well understood. Cement paste is a porous material whose pores ranging from nanometers to micrometers. Herein, low-temperature calorimeter (LTC) measurements on porous hardened cement paste of various saturation degrees SL are performed. It is found that the decrease of moisture content leads to multiple nucleation of ice crystals due to the discontinuity of liquid pores. At the lowest temperature, a large portion of water remains unfrozen because of the block effect of air pores where the propagation of ice crystals into unfrozen pores is cut off. The nucleation temperature decreases with the decreasing SL due to the small probability of finding appropriate nucleation sites. Ice formed in pores varies from the smallest pore size it can be frozen to a certain big size, and cryo-suction into air pores is limited. This study advances the fundamental knowledge of the influences of moisture content on the freezing nature of unsaturated porous materials.