Micro-ice-lens formation in porous solid

The micro-ice-lens model is outlined. It is based on the stability criteria for the triple-phase condition of unfrozen water, ice, and vapor in porous solids far below the bulk freezing point as described in Ref. (1). Due to these stability criteria a negative pressure is generated in the unfrozen gel-water, increasing with falling temperature. The temperature change acts like a piston, squeezing water out of the not infinitely rigid gel-matrix during cooling: frost shrinkage. The water is trapped at the macroscopically behaving micro-ice-lenses. They act as a valve since they hinder the trapped water from flowing back to the expanding gel during heating. If external water is available it is sucked in. A cyclic freeze thaw attack works like a pump-called therefore the micro-ice-lens pump-increasing the degree of saturation with every cycle far above isothermal saturation level. Only if a critical degree of saturation is reached by this pumping does damage set in due to the expansion of ice. The model is supported by the results of frost testing, like the CDF/CIF test. Frost-heaving phenomena are based on the same triple-phase conditions and transport. (C) 2001 Academic Press.