Superplasticizer is a concrete admixture that can reduce the water-cement ratio (w/c) in concrete. They can also be used to improve the flow and workability of concrete or to retard its setting time.
Super plasticizers are soluble macromolecules, which are hundreds of times larger than water molecules. They break the agglomeration of cement particles by repulsion of the same charges and release entrapped water.
They are typically formulated for the particular requirements of the market, application or area. For example, for tunnel construction a concrete producer needs to guarantee a good plasticity of the concrete until it is casted, which may take up to several hours.
Unlike water reducers, retarders or polymers for increasing water resistance, the performance of superplasticizers is affected by their compatibility with the concrete and its cement particles. This requires a lot of experience and test formulations to obtain the optimal admixtures.
In the past, lignosulphonate based superplasticizers were developed; but the synthesis of new polycarboxylate-containing graft copolymers has revolutionized the technology. They offer high-performance w/c ratios and excellent deflocculating properties.
Some of these superplasticizers also have a good dispersing performance, particularly in the form of polymers with branched or polyhedral moiety structures. Hyperbranched and hexabranched polyglycerols are currently under investigation for their possible dispersing abilities in concrete (Plank and Winter, 2008; Plank et al., 2010a).
In the first stages of hydration, the surface mineralogical composition of cement particles can affect the interactions of the superplasticizer and the cement. This is why it is important to use a cement with the same surface mineralogical composition as the superplasticizer (Aitcin, 2016b).
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