Freeze durability

FREEZE DURABILITY AND REQUIREMENTS IN THE CASE OF BOTH SIDES OF A FROZEN FISH FILET. 

Patterson T, O Neill, J and Perry, M (2007), Final Technical Report 2006, PEM Fuel Cell Freeze Durability and Cold Start Project, DE-FG36-06GO86042. 

Perry, M., Patterson, T., and O Neill, J. (2007) PEM fuel ceU freeze durability and cold start project, U.S. DOE Annual Hydrogen Program Review, Arlington VA, USA. 

Building durability, by preventing decay of wood-based materials, corrosion of metals, and spalling of masonry and concrete caused by freeze-thaw cycles... 

Figure 7. Configuration of the materials durability test system 1, Zymark robot arm 2, Mettler balance 3, blotting station 4, capping station 5, specimen rack 6, water bath 7, block oven 8, vacuum oven 9, freezing chamber 10, NDT station 11, automated micrometer, and 12, washing station. O, specimen holder.

The surface of concrete may be subjected to cycles of wetting and drying during normal service life. This process is a durability concern as harmful ions such as chlorides or sulfates can easily penetrate with the adsorbed water and there is the potential for saturation prior to freezing. Measuring the rate of water penetration into a dry concrete surface is thus important to the quality control of concrete mixes - hopefully yielding a durable product. 

Improved durability on exposure to freeze-thaw cycling, especially synthetic fibers. 

C. Lee and W. Merida. Gas diffusion layer durability under steady-state and freezing conditions. Journal of Power Sources 164 (2007) 141-153. 

Air-entraining water-reducing admixtures containing lignosulfonates can be based on impure lignosulfonate raw materials, as stated earlier, where only 2-3% additional air is required. However, this air may not be of the amount, type, and stability required, therefore additions of surfactants are made. Several different types can be used but in the majority of cases they are based on alkyl-aryl sulfonates (e. g. sodium dodecyl benzene sulfonate) or fatty-acid soaps (e.g. the sodium salt of tail-oil fatty acids). Additions of these types will allow incorporation of sufficient stable air of the correct bubble size to meet durability requirements under freeze-thaw conditions. 

The recorded data on lignosulfonate water-reducing agents indicate that, as far as freeze-thaw durability is concerned, because of the low water-cement ratios possible, an enhancement to the durability will invariably be obtained. When the admixtures are used to effect a reduction in the cement content, there are strong indications that a considerable enhancement of durability is obtained, presumably due to a reduction in the cement matrix which is the part of the concrete susceptible to frost damage. The higher aggregate content would therefore allow easier dissipation of stresses. 

There is little information on the effect of this class of material on the freeze-thaw durability of concrete into which the admixture is incorporated. However, one set of data is shown in Table 1.24 [101]. 

Water-reducing admixture Dosage Air-entraining agent type Water-cement ratio Freeze-thaw data Durability factor (%) Weight loss (%)... 

It can be concluded from the assessment of the data in this section that inclusion into a concrete mix of a water-reducing admixture of the lignosulfonate, hydroxycarboxylic acid and air-entraining type should not lead to any deterioration in the durability of that concrete to freeze-thaw cycling. Indeed there are strong indications that, when used either as a means of reducing the water-cement ratio or, alternatively, of reducing the cement content, more durable concrete may result. 

The alkyl-aryl sulfonates find application in both the production of lightweight concrete and for enhancing the freeze-thaw durability of normal concrete. The usual raw material is orthododecylbenzene sulfonate, which is a basic surfactant used in a variety of industrial and domestic detergents. The formula is shown in Fig. 3.3. 

Table 3.23 The effect of spacing factor on freeze-thaw durability...

Air-entraining admixture % air by volume Average spacing factor (mm) Durability to freeze-thaw cycling ... 

Air-entraining admixtures, therefore, produce concrete which is more durable to conditions of freezing and thawing, particularly in the presence of de-icing salts, more resistance to sulphate attack, provides better protection to embedded reinforcement and is more tolerant of poor curing conditions. There appears to be no... 

The presence of even small amounts of dampproofer improve the freeze-thaw durability of the concrete [16]. This is further indicated by... 

The reduction in porosity, decreased water content, and air entrainment that results when latexes are used in mortar and concrete mixes make them much more resistant to freezing and thawing conditions than conventional mortar and concrete. Figure 6.17 presents the freeze-thaw durability in water (-18 to 4°C) of combined water-and dry-cured SBR-, PAE- and EVA-modified mortars [98], The frost resistance of mortars made with these latexes is markedly improved even at polymer-cement ratios of 5%. However, an increase in the polymer-cement ratio does not necessarily produce further improvement in freeze-thaw resistance. EMM and EMC, when exposed to outdoor conditions involving freeze-thaw, UV radiation and carbonation show better weatherability when compared with conventional mortar and concrete. 

Durability most proprietary accelerating admixtures adversely affect the concrete s resistance to freezing and thawing [114, 118]. More recently, the widespread use of silica fume has enabled the use of considerably low dosages of accelerators and also contributed to the improvement of porosity values, thereby dramatically improving durability of such concretes. 

The use of superplasticizers in air-entrained concrete has caused much debate. Two main problems are associated with superplasticized air-entrained concrete (1) a decrease in air content by 1-3% when slump is increased from 75 mm to 220 mm after the addition of the superpiasticizer to create flowing concrete, and (2) a change in the air void system to less desirable values. However, most investigators [10-11, 12] have shown that, although the air-void spacing factor required for adequate frost resistance is altered, the change did not necessarily affect the freeze-thaw durability of... 

---