Water reducing agents

Water-Reducing Agents and Superplasticizers. Common admixtures that improve fluidity of concrete mixes are often used in high strength concrete. These admixtures make possible the incorporation of siUca fume while maintaining necessary workabiUty. Three principal types of... 

In academia too, workers have advanced our knowledge of how water-reducing agents and superplasticizers function and have made our earlier theories look simplistic and pedantic. 

A general update of references and developments in all chapters including a major new chapter on superplasticizers , or high-range water-reducing agents. 

Fig. 1.12 Shear-stress-shear-rate relationships for cement pastes containing various water-reducing agents.

The addition of a water-reducing agent to the aqueous phase is followed by a rapid reduction in the quantity of admixture in solution and an... 

Fig. 1.31 The loss of slump with time when straight addition of a water-reducing agent is made (Ravina).

Fig. 1.32 Changes in slump and VeBe values for concrete containing straight addition of a hydroxycarboxylic-acid-based water-reducing agent.

Fig. 1.33 Reductions in water-cement ratio as a function of aggregate-cement ratio for lignosulfonate and hydroxycarboxylic-acid-based water-reducing agents.

Table 1.12 Water reduction by water-reducing agents as a function of workability...

In the case of lignosulfonate water-reducing agents, the effectiveness in reducing the water-cement ratio diminishes with an increase in either the the C3A or alkali content. In a comparative experiment with three... 

Table 1.19 Elastic modulus of concrete containing a lignosulfonate-based water-reducing agent as a ratio of a plain mix (Tam)...

The graphs given in Fig. 1.38 show the logarithmic relationship between the water-cement ratio and the permeability coefficient of hardened cement paste. Thus concrete with a paste water-cement ratio of 0.4 will be almost impermeable. Water-reducing agents can be used to reduce the water- cement ratio, so ensuring that the permeability is kept to a minimum. 

Table 1.20 Elastic modulus of concretes containing a hydroxycarboxylic acid water-reducing agent (Brookes)...

Fig. 1.39 Initial surface absorption of oven-dried concretes containing lignosulfonate water-reducing agents (see Fig. 1.40 for key) (Hewlett).

Table 1.21 Sulfate resistance of concrete mixes containing water-reducing agents (no mix design changes other than addition of water-reducing admixture)...

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. 

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

Table 1.28 Effect of a lignosulfonate-based water-reducing agent on reinforcement bond under an appiied external voltage (after Kondo)...

F/g. 1.46 The increase in compressive strength of concretes containing various water-reducing agents. 

Fig. 1.50 The effect of a hydroxycarboxyiic acid water-reducing agent on the creep of concrete when used to lower the water-cement ratio (Rodrigues).

When materials other than a lignosulfonate water-reducing agent are used, in conditions where significant drying of concrete can take place, caution must be exercised where straight additions are used and where differential creep rates could be obtained in comparison to adjacent concrete containing no admixtures. 

The superplasticizers are a special category of water-reducing agents in that they are formulated from materials that allow much greater water reductions, or alternatively extreme workability of concrete in which they are incorporated. This is achieved without undesirable side effects such as excessive air entrainment or set retardation. 

This raw material was one of the first materials referred to in the literature as a water-reducing agent [16] yet only since 1970 has it found extensive application in admixture formulations. 

Earlier work [37] by one of the authors indicated that superplasticizers of the SNF and SMF type were less strongly adsorbed onto the hydrating cement than normal water-reducing agents and this was used to explain why there was less retardation by the superplasticizers. This... 

The literature describes the use of several materials of this type and these are shown in Table 3.2. These products are also compatible with many water-reducing agents to produce air-entraining water-reducing agents. 

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