Air entraining water-reducing admixtures

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 presence of a water-reducing admixture can alter the air content of concrete, either as a deliberate measure (the air-entraining water-reducing admixtures) or as a side effect of the material in lowering the surface tension of the aqueous phase. 

Air-entraining water-reducing admixtures require special consideration the presence of entrained air leads to a reduction in compressive strength, whilst the water reduction results in a compensatory increase in strength. The effect can be quantified, however, by considering the amount of entrained air in terms of an equivalent volume of water to calculate the (air and water)-cement ratio. This new factor can be used to estimate the expected strength from Fig. 1.37. 

Concrete containing No admixture Neutralized wood resin Air-entraining water-reducing agent... 

HRB. 1971. Admixtures in Concrete Accelerators, Air Entrainers, Water Reducers, Retarders, Pozzolans. Special Report 119. Washington, DC Highway Research Board. 

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. 

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

Series Mix Air- entraining agent Water-reducing admixture Cement content (kg m - ) Water- cement ratio 28-day compressive strength (N mm-2) Air content (%) Slump (mm) Durability factor ASTM C290 1967... 

Water-reducing admixture Air-entraining admixture Slump (mm) Air content (%) Sand-aggregate ratio ml cm of surface % total mix water... 

When concrete is to be placed in cold weather, it is preferable that accelerators or antifreezers be used in combination with air-entraining agents and water-reducing admixtures. These combinations not only reduce the amount of freezable water in the mix but also generally reduce the quantity of antifreezers and accelerators needed to obtain desired effects compared to the amounts that have to be used when these are used separately. In addition these combinations may be useful in increasing the resistance of concrete to frost action and to corrosive agents. 

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... 

HRWRA = high range water-reducing admixture (superplasticizer). WRA = water-reducing admixture. AEA = Air-entraining Admixture. ... 

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