Which admixture actively modifies the viscosity of concrete?

Viscosity-modifying admixtures are specifically designed to modify the flow characteristics or viscosity of concrete. Unlike other types of admixtures that primarily focus on controlling setting times or reducing water content, viscosity-modifying admixtures target the workability of the concrete mix by increasing its viscosity. This can lead to improved stability of the mix, reduced segregation, and enhanced performance in applications like self-consolidating concrete.

These admixtures work by affecting the interaction between the cement particles and the water, creating a more cohesive and stable mixture. This is particularly beneficial in situations where a denser concrete is required, or where the concrete is being pumped or poured in complex forms where maintaining flow without segregation is crucial.

In contrast, set retarding admixtures are used to delay the setting time of the concrete, while water-reducing admixtures focus on decreasing the water content for the same workability. Set accelerating admixtures are employed to speed up the setting process. Each of these serves a distinct purpose that does not involve actively modifying the viscosity of the concrete. Viscosity-modifying admixtures, therefore, are uniquely positioned to enhance the flow behavior and manage the rheological properties of concrete.