Calcium lignosulfonate

Calcium lignosulfonate Phenol-formaldehyde resin modified with fiirfuryl alcohol [1352]... 

Type Spruce wood sulfite lye calcium lignosulfonate (%) [12] Sodium lignosulfonate (%)... 

The accelerating water-reducing admixtures are simple blends of either calcium chloride, nitrate, thiocyanate or formate with a lignosulfonate or a hydroxycarboxylic acid salt. In some cases it may not possible to obtain a completely sediment-free solution and agitation of store tanks may be necessary. Typically, a mixture of approximately 33% calcium chloride and 4% calcium lignosulfonate by weight in water would be used. 

Fig. 1.15 Adsorption isotherm of calcium lignosulfonate on ordinary Portland cement (Ernsberger).

Water-reducing admixtures are not adsorbed equally by the various anhydrous and hydrated cement constituents and in studies with calcium lignosulfonate, the approximate maximum adsorption figures shown in Table 1.5 have been obtained [38,39], In addition, adsorption isotherms have been studied at various ages of C3A hydration [36] and it has been shown that it is the initial hydration products (less... 

In the absence of knowledge of the surface area of cement hydrates available for adsorption at the time of addition, it is difficult to estimate how many layers of water-reducing admixture molecules are adsorbed, but attempts have been made [40] indicating that over 100 layers may be formed with calcium lignosulfonate and salicylic acid at normal levels of addition. However, these calculations were based on specific surface areas of 0.3-1.0 m g-l, whereas other studies [27, 38, 39] have indicated... 

Fig. 1.16 Effect of hydration time on the adsorption of calcium lignosulfonate on C3A hydrates (Rossington).

Table f. 7 Adsorption data for calcium lignosulfonate and sodium gluconate... 

The amount of calcium lignosulfonate adsorbed on to hydrating cement is almost independent of initial water-cement ratio within the range 0.4 to 1.5 [34]. 

Fig. 1.19 Adsorption-desorption isotherms of calcium lignosulfonate on C3A hydrate (hexagonal phase) (Ramachandran).

The addition of a water-reducing admixture to a cement suspension can be shown to disperse the agglomerates of cement particles into smaller particles [33,38, 47] and can be seen clearly in photomicrographs as shown in Fig. 1.21. Maximum dispersion occurs at a level of 0.3-0.5% by weight of calcium lignosulfonate [33, 34] which would indicate the presence at the surface of about 0.2-0.4% calcium lignosulfonate. The separation of particles results in an increase in the surface area of the system by 30-40% [33, 38], which may explain the more rapid rate of cement hydration after the initial retardation period. 

As far as the final hydration products of ordinary Portland cement are concerned, there is an indication from isothermal calorimetry [57] that there is very little difference in the presence or absence of a calcium lignosulfonate water-reducing admixture. In this work, the heat evolved per unit of water incorporated into the hydrate has been determined for two cements, with the results shown in Fig. 1.25. It can be seen that the relationship between the amount of heat evolved and the amount of water combined with the cement is maintained whether the admixture is present or not. This work also indicated that the retardation in the early stages is compensated for at later times by an acceleration. 

In the presence of calcium lignosulfonate [58], the calcium silicate hydrate gel from the C3S and C2S... 

Table 1.10 Effect of calcium lignosulfonate on C3A reaction (after Chatterji)... 

Fig. 1.25 The heat evolved from hydrating cement with and without the addition of calcium lignosulfonate as a function of combined water (Khalil).

Method of addition of retarder (0.225% calcium lignosulfonate by wt cement) Water-cement ratio Slump Water reduction (mm) (%)... 

In view of the differences in initial setting time, most calcium lignosulfonates and hydroxycarboxylic-acid-based materials would extend... 

Agents A ammonium lignosulfonate solution. D hydroxycarboxylic acid solution. G calcium lignosulfonate solution. L calcium lignosulfonate solution. 

Agents A ammonium lignosulfonate. B ammonium lignosulfonate. G calcium lignosulfonate. L calcium... 

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