What Does Superplasticizer Do to Concrete?

what does superplasticizer do to concrete?

A superplasticizer is an admixture that reduces the water content of concrete without reducing strength. It is used to create flowing and self-leveling concrete, and to produce high strength concrete by reducing the water to cement ratio while maintaining the same workability and hardening characteristics of normal concrete.

The admixture works by dispersing the large irregular agglomerates of cement particles that predominate in the water suspension. The agglomerates, because they have been reduced in size, become less dense and easier to place by mechanical means.

Dosage is generally from 0.5 to 1 per cent by weight of the cementitious material. GlobMarbe recommends starting with 1% by weight and gradually decreasing the dosage as needed.

When using superplasticizer with VMA, the two admixtures can help each other to improve concrete flow and set time. However, too much of either admixture can also affect the setting, air content, bleeding and segregation of concrete.

Types and Concentration of Admixtures

There are several different types of admixtures that can be added to a concrete mix to improve it's flow and set time. These include viscosity modifying admixtures (VMAs), superplasticizers, and accelerated hydration admixtures.

Viscosity modifying admixtures are commonly based on modified polysaccharides such as hydroxyethyl cellulose, welan gums or synthetic copolymers. They provide a higher tolerance to slight changes in water content, and they also reduce bleeding and segregation when either superplasticizer is overdosed or the water content is too high.