Types of admixtures

Specimens and type of admixture Water-cement ratio Durability factor Ck 10 months 20 months 28 months... 

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

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

The different types of admixtures, known to reduce alkali-aggregate reactions, can be divided into two groups those that are effective in reducing the expansion due to the alkali-silica reaction, and those that lower expansions resulting from the alkali-carbonate reaction. For the alkali-silica reaction, reductions in the expansion of mortar specimens have been obtained with soluble salts of lithium, barium and sodium, proteinaceous air-entraining agents, aluminum powder, CUSO4, sodium silicofluoride, alkyl alkoxy silane,... 

Dam Type of admixture Coefficient of variation (%) of compressive strength at 3 months... 

Because of the essential role that air-entrained concrete has played in reducing freeze-thaw susceptibility, its use in North America has been predominantly associated with this property. Consequently, other favorable modifications have often been ignored. In Europe, Australia and Africa where freeze-thaw action seldom or rarely affects the concrete, the secondary modifications produced by air-entraining admixtures have been realized to their full potential, when used as a composite water-reducing and air-entraining admixture. The increased use of this type of admixture is due to the following reasons ... 

Type of admixture in 270 kg m Mean strength (N mm Standard deviation (N mm... 

In North America almost all air-entrained concrete contains a water-reducing admixture. There is some reluctance to use a composite type of admixture because of the concern that it reduces flexibility in use due to the variation in concrete materials and job site conditions. Therefore, the use of... 

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. 

The important features of this type of admixture is that such benefits are realized by addition of the admixture with the gauging water (like conventional admixtures and very unlike the SNF and SMF materials) thus eliminating some of the problems associated with the first- and second-generation superplasticizers. Table 7.15 [48] presents the effect of the time of... 

Type of admixture used, how it is furnished (powder or liquid), brand name, manufacturer and date of manufacture. 

In all three ways of use, this type of admixture can be regarded as a cement saver, as illustrated in Fig. 1.1. 

Type of admixture in Mean strength Standard deviation... 

Other types of admixtures used with calcium aluminate cements include water reducers and superplasticizers (Section 11.4), which also act as retarders, and thickening agents, such as carboxymethylcellulose. Complex formulations may be used for special purposes for example, a ready-mix mortar for high-performance road repair might contain 55% Ciment Fondu and 45% sand, with glass fibre, aluminium powder, Li2C03, sodium gluconate and methyl ethyl cellulose (M93). 

Admixtures are materials other than water, aggregate or hydraulic cement which are used as ingredients of concrete and which are added to the batch immediately before or during the mixing. Their function is to modify the properties of the concrete so as "to make it more suitable for the work at hand, or for economy, or for other purposes such as saving energy." The major types of admixtures can be summarized as follows ... 

Check the rate of administration, amount, and type of admixture solution. 

Table 4. Changes in the refractive index (for A = 677nm) at the glass surface depending on the type of admixture ions...

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