Superplasticizer is an admixture which improves the workability of concrete and reduces water requirement, making it stronger. The use of this admixture in cement mixtures makes the concrete flow easily and produces a homogeneous, cohesive, and non-prone to segregation and bleeding, cement based, ready-mixed concrete.
The use of a plasticizer in the preparation of a cement based, concrete mix can increase the early strength (50 – 75%); this effect is dependent upon the dosage and the type of base admixture used. The total air content of a flowing concrete can reduce with the addition of SNF- or SMF-based admixtures and increase with MLS-based admixture.
The loss of slump due to the presence of superplasticizer in a concrete mixture is due to the dispersing action of the admixture on the hydrates. The dispersing action mainly occurs by the sulphonic acid which gets adsorbed on the surface of the cement particles and forms negatively charged ion complexes with the hydration molecules in the hydrates.
The superplasticizer is injected into the concrete mixture through the slurry mixer at a rate of 1 to 3 litres per cubic meter of concrete. The exact dosage depends on the type of concrete and the water/cement ratio, and is determined by the Marsh Cone Test.