Freezing damage from

Air-Entrainment Agents. Materials that are used to improve the abiUty of concrete to resist damage from freezing are generally known as air-entrainment agents. These surfactant admixtures (see Surfactants) produce a foam which persists in the mixed concrete, and serves to entrain many small spherical air voids that measure from 10 to 250 p.m in diameter. The air voids alleviate internal stresses in the concrete that may occur when the pore solution freezes. In practice, up to 10% air by volume may be entrained in concrete placed in severe environments. 

As a crystallization modifier, it can prevent syrups from forming crystals of sugar. It is used to add body and viscosity to mixtures, and can protect against damage from freezing and drying. 

Towers that operate in freezing weather required special consideration to provide dependable service and to prevent damage from freezing and ice accumulation. The most prevalent winter operating problem of water cooling towers is the formation of ice on the louvers to the extent of seriously, or even totally, restricting the air flow. 

To understand the nature of freeze-tolerance, it is critical to look carefully at (i) the nature of the solid-state water that forms, (ii) where this solid-state water can be generated without lethal effects, and (iii) how the formation of true ice, which is but one of water s potential solid states, is regulated to minimize damage from freezing. As we would predict from the earlier analysis of the types of damage caused by formation of ice in biological fluids, each of these three variables is critical for the development of a successful ability to withstand freezing. 

Figure 12 Hypothetical model of cause of damage from intracellular freezing. See text for details. (From Ref. 21.)...

The difference in the recovery of cortical neurons in the presence of these additives might be a result of the cryopreservation process that is explained as follows DMSO is taken up into the cell and allows vitrification of the intracellular solution, leading to the stabilization of the cell membrane. However, in the case of trehalose, the molecules may be too large to permeate into the cell they may only contact the membrane extracellularly and protect the cell from freezing damage. To clarify the details of this cryoprotection mechanism, we need to study the process of cell freezing. 

The low temperature range affecting arthropods could perhaps be divided into three bands. From the minimum breeding temperature down to the chill coma, insects will be able to feed, but because of their low metabolic rate, be unable to repair accumulating damage. From the chill coma temperature down to the supercooling point, they will be unable to feed and therefore slowly starve. At and below their supercooling temperature, death will occur when the water in their body fluids crystallises (freezes). 

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