Hydration lignosulfonate

A modified saturated saltwater mud is prepared with bentonite clay by a special technique. First, bentonite is hydrated in freshwater, then treated with lignosulfonate and caustic soda. This premix is then mixed with saltwater (one-part premix to three-part saltwater). The mixture builds up a satisfactory viscosity and develops filtration control. Thinning of the mud is accomplished by saltwater dilutions additional premix is required for viscosity and water loss control. 

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).

The nature of the bond between the molecules of the water-reducing admixture and the surface of the cement constituent hydrates has been described as ionic group outwards in many references [33, 42,], mainly based on work [33, 43] showing migration of cement particles under the influence of an electric current when lignosulfonate molecules are adsorbed on the surface. Similar results have been reported for hydroxycarboxylic acids [44], Other relevant data are summarized below ... 

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... 

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

Modem concretes often incorporate a mixture of chemical and mineral admixtures, each of which may interact with the various constituents of cements and influence cement hydration reactions. The admixture-cement interactions may in fact be viewed as the reaction between two complex chemical systems - the multicomponent, multiphasic inorganic materials in the cement and the organic compounds of multicomponent admixture systems. For example, lignosulfonate water-reducers are intrinsically complex mixtures of chemical compounds derived from the chemical degradation of lignin, while synthetic admixtures such as superplasticizers contain species with a broad distribution of molecular weights, reaction products, or other chemicals added for a specific purpose [125]. The performance of an admixture in concrete is highly dependent on many... 

Studies of the action of pure lignosulfonate acting on pure C3A and C3S also show that large amounts of lignosulfonate with small amounts of C3A result in lengthy delay of hydration of the C3S [130]. At lower C3A contents, smaller amounts of the WRA are adsorbed, leaving larger amounts of the admixture to affect the C3S component. Alkalis may affect dissolution and... 

In the presence of calcium lignosulfonate [58], the calcium silicate hydrate gel from the C3S and C2S phases tends to have a greater proportion of the crumpled foil morphology type than the corresponding system without the admixture. This observation tends to be made only at high concentrations of... 

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