Water Reducing Admixtures Plasticizers

The lignosulphorrates, byproducts, from the paper industry, were used first, about 1930. Their role of slurry thirmers in Portland cement chrrker production by wet method was well known. 

These plasticizers can be used as air enttairring admixtures because they ate ad-sotbed on the air bubbles, on the air-liquid phase interface in paste. The authors 

Adequate classification of plasticizers is diffienlt because of their diversity. The following, traditional classification is generally aeeepted [98, 360]  

Anionic surfactants are the most commonly used they dissociate in water to form the surface active anion, composed of hydrocarbon radical and hydrophilic group and inactive cation. The substances from this group can be classified further as follows [98]  

The water redncer from the first sub-gronp introdnce usually low quantity of air (on the level 2-3 % by mass of cement) and are retarders those from the second sub-group have no air entraining effect but they retard setting too. The retarding action increases markedly when the addition of plasticizer is too high and attains for example 0.6% by mass of cement [362]. 

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In order to understand more fully the effect that water-reducing admixtures have on the plastic properties of fresh concrete, and to gain an insight into the mechanism of action of this category of materials, it is useful to study the effect on the water-cement system. The topic can be considered from the... 

The initial plastic state of the fresh concrete subsequent to the mixing process, where properties such as the air content, density and workability are normally measured by relevant standard tests, and utilized as a means of control of production. The magnitude of these properties is affected by the addition of water-reducing admixtures, either intentionally or as a side effect, which could result not only in a change in the characteristics in the plastic state, but could also be reflected in changed properties in the hardened state. 

The durability of concrete is the ability of the material to maintain its structural integrity, protective capacity, and aesthetic qualities over a prolonged period of time. It is important that the benefits conferred to concrete in the plastic and early hardened state by water-reducing admixtures are not negated by any adverse effect on the long term durability. 

Although there are some anomalies in the literature, it is generally agreed that both types of volume deformation are a function of the same fundamental mechanism and that the influence of other factors such as admixtures will affect both shrinkage and creep in a similar manner. As outlined earlier, water-reducing admixtures can be used to obtain different effects on the plastic/hardened concrete and it is this factor, together with the admixture type, that is important in determining the effect on the volume deformations of concrete. 

Dampproofing admixtures are formulated to affect the properties of the hardened concrete, and not those of concrete in its plastic state. In the case of materials based solely on calcium and aluminum stearates, stearic acid in solid or emulsion form, bitumens and hydrocarbon resins, there will be no effect on the properties of the plastic concrete with regard to air content, workability, mix design parameters, etc. When water-reducing admixtures or accelerators are included in the formulation, the effect on the concrete will be a function of the particular type of material used (see relevant section). The wax emulsions do appear to have an effect on the properties of the plastic concrete because of the lubrication effect of the very small... 

In order to understand more fully the effect that water-reducing admixtures have on the plastic properties of fresh concrete, and to gain an insight into the... 

The effects of water-reducing admixtures on the properties of plastic concrete... 

Water-reducing admixtures are water soluble organic materials which reduce the amount of water needed to achieve a given workability in plastic concrete without significantly affecting the air content or setting characteristics of the concrete. This effect can be utilized in three ways ... 

In the mix composition of advanced cement-based materials a few admixtures for improving their special properties in fresh and in hardened states are normally included (cf. Section 4.3). In particular, different water reducers and plasticizers are used in a large majority of concrete production. This trend will intensify in the future, based on the results of investigations. 

Compatibility with other admixtures due to the inherent surfactant properties exhibited by most of the materials in classes A, B and C, their use with other admixtures such as water reducers should be evaluated in terms of the side effects on the plastic and hardened concrete, viz. severe set retardation and excessive air entrainment. The molecules of materials with fewer surfactant properties compete with the superplasticizer for adsorption sites on the cement particle. This will result in a higher dosage of the superplasticizer. 

Desired property Water reducer Accelerator Retarder Super- plasticizer AEA Other special admixtures... 

For special high strength appHcations, ie, up to 69 MPa (10,000 psi), special formulations of Pordand cement concretes have been developed. These ate based on the use of chemical and mineral admixtures. The typical mineral admixtures ate fumed siUca and other po22olanics. The chemical admixtures ate generally chemicals termed supetplastici2ets that allow very low water to cement ratios, ie, between 0.4 and 0.25, and reduce the amount of water needed to provide plasticity or dow to the concrete. PubHc works appHcations take just under 32% of the total Pordand cement market streets and highways represent 68% of this usage, and water and waste account for 23%. 

Addition of admixture to obtain higher strengths In this situation the small amount of reported work indicates that where the water-cement ratio is reduced, the shrinkage and creep of the concrete is also reduced. Figure 1.50 shows the effect of a hydroxycarboxylic acid plasticizer on the creep of the concrete where the material has been used to effect a reduction in the water- cement ratio without any other changes in the mix design. Thus it seems that the reduction of the water-cement ratio will compensate for the increases in creep observed in the data above. 

The pivotal role that superplasticizers play in the formulation of self-leveling mortars is due to the dramatic effects they produce on flow behavior. Such effects are believed to be derived by the adsorption of the admixture on the surfaces of cement grains, thereby providing surfaces of a similar or zero charge which are mutually repulsive. They thus fully disperse cement particles, freeing more water for lubrication and reducing interparticle attraction. Both yield stress and plastic viscosity are decreased and the decrease is greater for yield stress it may be completely eliminated if sufficient admixture is added so that Newtonian behavior is observed (Fig. 7.25) [75, 76]. 

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