Abstract
It has been reported by the authors that the instantaneous unfrozen water closed in ice phase in porous materials is one of the causes of frost damages. The present paper deals with the effect of pore size distribution as well as cooling rate on the character of the instantaneous formation of the unfrozen water surrounded by ice phase during one dimensional cooling, determining electric capacity of water saturated specimens. The samples employed are a series of commercial diatomaceous earth insulating bricks having specifically different pore size distribution but having nearly same values of physical properties such as wet strength, porosity and water absorption. The results obtained are summarized as follows;
(1) Water in smaller pores is instantaneously left unfrozen being surrounded by ice phase in larger pores resulting from the depression of freezing temperature which is inversely proportional to pore radius.
(2) The broader is the range of pore size and the slower is the cooling rate, the greater is the volume fraction of the instantaneous unfrozen water causing susceptibility to frost damages.
(3) It is suggested that the lowest temperature of cooling as well as cooling rate are significant for testing frost resistivity by freezing and thawing method, particularly when materials contain such a fine pores as less than 0.1μm in which water would freeze at the temperature as low as nearly -17°C.
