Freezing-thawing resistance

Moisture pickup and freeze—thaw resistance of various insulations and the effect of moisture on the thermal performance of these insulations has been reported (207). In protected membrane roofing appHcations the order of preference for minimizing moisture pickup is... 

Freeze-thaw resistance + Pure polymer cements absorb essentially no water [82]... 

For concrete used in dam construction, the results shown in Table 1.23 [99] have been obtained. From these results, it will be seen that a reduction in the water-cement ratios was obtained and in the large majority of cases (80% of the specimens) an improvement in freeze-thaw resistance was obtained. In fact, the average resistance of admixture-containing concrete was 39% greater than the control specimens. The ability of the lignosulfonates to... 

Fig. 1.41 The relationship between water-cement ratio and freeze-thaw resistance. 

Table 1.23 Freeze-thaw resistance of concretes used in dam construction...

Fig. 1.42 The freeze-thaw resistance of concrete containing lignosulfonates (sulfite liquor) under saline conditions.

Fig. 1.43 The freeze-thaw resistance of concretes of different cement contents in the presence of lignosulfonates (Hewlett).

Table 1.24 Freeze-thaw resistance of concretes containing a hydroxycarboxylic acid water-reducing agent...

Table 1.25 Freeze-thaw resistance of air-trained concrete containing water-reducing admixtures...

Table 1.26 Freeze-thaw resistance of concrete containing an air-training water-reducing...

Table 1.27 Freeze-thaw resistance of corresponding mixes containing water-reducing admixtures and air-entraining agents (after Mielenz)...

Table 2.4 Freeze-thaw resistance of superplasticized concrete (Rixom)...

Despite the fact that the minimum spacing factor is exceeded, the concrete freeze-thaw resistance of the concrete does not appear to be adversely affected [71]. Table 2.7 clearly shows how the presence of an SNF superplasticizer increases the spacing factor of the air void system at each of the three water-cement levels evaluated [71]. 

The degree of protection afforded is a function of the characteristics of the air void system entrained, and the significance of the variables involved requires an understanding of the mechanism of freeze-thaw resistance operating. 

Table 3.18 Air entrainment improves the freeze-thaw resistance of concrete in the presence of de-icing salts...

Freeze-thaw resistance (number of cycles to cause 7.5 42.5... 

Table 3.22 Freeze-thaw resistance of concrete air-entrained by different chemical types of admixture...

Air-entraining admixtures Air content (%) Relative classification of freeze-thaw resistance ... 

Fig. 4.7The freeze-thaw resistance of plain concrete and concrete dampproofed with a wax emsulsion type of admixture. 

The dampproofmg admixtures will, therefore, improve the aesthetic qualities of concrete in terms of maintenance of a clean appearance over a prolonged period of time without adverse effects on other properties, and in the areas of freeze-thaw resistance, shrinkage under wet-dry cycling and reinforcement protection, may contribute beneficially. 

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. 

It has sometimes been argued that concrete is seldom damaged by frost action if low water-cement ratio mixes are used. However, the paramount effect of air entrainment in improving freeze-thaw resistance was clearly demonstrated in a study of the freeze-thaw resistance of both air-entrained and non-air-entrained superplasticized concrete with low water-cement... 

Mixes in both low- and high-cement-content classes are more prone to problems than the medium range. In low-cement-content mixes, poor cohesion results in segregation and in high-cement-content mixes thixotropy causes pipeline friction. Admixtures will modify the flow characteristics of the paste, helping to achieve and maintain optimum flow characteristics. Because pumped concrete must not only meet specified job performance criteria (e. g. strength, freeze-thaw resistance) but should also remain stable under a variety of job conditions, particularly in hot and cold weather, it is common to find that concrete to be pumped often contains two or more types of admixtures. 

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