Workability water-reducing agents

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

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. 

The effect produced by the incorporation of a lignosulfonate-based water-reducing agent is shown in Table 7.6. The results were obtained from a series of mixes over an 8-month period by a ready-mix plant used in the production of concrete piles. Since the standard deviation of this particular plant was 5.0 MPa for mixes produced without the use of admixtures, it is evident that the use of the admixture resulted in reduced variability. These results indicate that in high workability mixes with cement contents in the median range, the admixture may cause an increase in the standard deviation. Thus in redesigning the mix to have a lower cement content in this class of concrete, adequate consideration should be given to this difference in standard deviation. Increased uniformity can be attained in this instance... 

Water-reducing agents, also called plasticizers, allow a given degree of workability to be achieved at a lower w/c ratio. Conventional water reducers allow w/c to be decreased by 5-15%. To achieve greater decreases, they would have to be used at concentrations that would also cause excessive retardation, excessive air entrainment or flash setting. More powerful water reducers, called superplasticizers, allow w/c to be decreased by up to about 30 /o these are considered in Section 11.4.2. 

A more significant improvement in workability may be obtained by combining the accelerator with a water-reducing agent. 

Two types of high-range water-reducing agents, Sika ViscoCrete-10 and Sika ViscoCrete-premium, were used in the project to increase the workability of the paste and... 

Water-Reducing Agents These compounds reduce the amount of water required to produce a workable cement-water paste and concrete, respectively. Hence,... 

Admixtures are substances that are added during the mixing process in small quantities related to the mass of cement, in order to improve the properties of fresh or hardened concrete [7,8]. The most utilised admixtures are water reducers and superplasticizers that may be added to improve the workability of concrete or reduce the amount of mix water accelerators that are used to increase the rate of development of early strength of concrete set-retarders that reduce the setting time of concrete air-entraining agents that increase the freeze-thaw resistance of concrete (Section 3.1). Recently, corrosion inhibitors have been developed in order to increase the corrosion protection of embedded steel these will be treated in Chapter 13. 

Water reducers and superplasticizers. Admixtures aimed at increasing the workability of concrete are chemical substances that improve the mobihty of the particles in the fresh concrete mix by increasing the effectiveness of the mixing water. They contain surface-active agents that are adsorbed on the surface of solid particles and modify their electrical surface charge, so that they do not tend to flocculate, and thus are more dispersed, and the water can better lubricate the mix. 

Plasticizers or dispersion agents are additives which are incorporated into concrete to inqtrove its workability, reduce its water content needs, and enhance its strength development. Unfortunately, these properties are mutually... 

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