15241 Superplasticizers

In modern concrete practice, it is almost impossible to make HPC with adequate workability in the field without superplasticizers. Unfortunately, different superplasticizers would behave quite differently with different cements (even cements of nominally the same type). This is due in part to the variability in the minor components of the cement (which are not generally specified), and in part to the fact that the acceptance standards for superplasticizers themselves are not very rigorous. Thus, some cements will simply be found to be incompatible with certain superplasticizers.

There are, basically, three common types of superplasticizer: (1) lignosulfonate based; (2) poly-condensale of formaldehyde and melamine sulfonate (often referred to simply as melamine sulfonate); and (3) polycondensate of formaldehyde and naphthalene sulfonate (often referred to as naphthalene sulfonate).

In addition, a variety of other molecules might be mixed in with these basic formulations. It may thus be very difficult to determine the precise chemical composition of most superplasticizers; certainly manufacturers try to keep their formulations as closely guarded secrets.

It should be noted that much of what we know about superplasticizers comes from tests carried out on normal strength concretes, at relatively low superplasticizer contents. This does not necessarily reflect their performance at very low w/c ratios and very high superplasticizer dosage.

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