Sunday, June 7, 2020

What is Superplasticizer?

What is Superplasticizer?

Superplasticizers are also known as "High-range water reducers". They are are capable of reducing the water requirements by about 30% .They enables the optimization of water in water to cement ratio and workability.

Most Superplasticizers are based on 
  • Sulfonated melamine formaldehyde (SMF).
  • Sulfonated naphthalene formaldehyde (SNF) .
  • Modified lignosulfonates

Now we will see how Superplasticizer works with concrete 


These High-range water reducers attach themselves to the cement particles and acts as base showing steric effect (which prevents a chemical reaction from taking place) rather than electrostatic repulsion[which is seen in plasticizers in which negative ions react with cement particles making them repel].
The steric effect helps reducing the accumulation of heaps or cluster of the cement particles which permits water to flow and keep the mix hydrated leading to increase the workability of concrete.

Superplasticizer steric effect
Superplasticizer steric effect

Constituents of Superplasticizers

Constituents of Superplasticizers
Constituents of Superplasticizers

Now we will see the Technical Performance due to Superplasticizers

1) It produces flowing concrete

2) Produce concrete with very low w/c ratio

  • Water sustainability can be reduced with maintaining the workability of the concrete.
  • Minimum of 30-40% of water can be reduced easily and least of 0.25 w/c ratio can be achieved with the help of superplasticizers.
  • They are mostly preferred in high strength and durable concrete.

3) Produce high performing concrete (HPC)

  • High performance concrete are very strong composite material which consist of very dense and stable hydrated paste results and bonding with aggregate and reinforcement .
  • HPC are achieved by reducing water content and enhanching workability with the help of superplasticizers.
  • These concrete have better workability and low water content than normal concrete.

Problems associated at site improved by superplasticizer

1) Slump loss with time

Concrete looses its workability with time for which additional plasticizers are added to overcome the slump problem while placement. Retarders can be used in regular intervals, maintaining the temperature and keeping heath of hydration low.

2) Air content variation

To improve durability against freezing and thawing, Air voids of proper size and spacing have to be present. The air content of air-entrained concrete may reduce with addition of SNF [Sulfonated naphthalene formaldehyde] or SMF [Sulfonated melamine formaldehyde (SMF).] based admixtures and, increase with MLS [Modified lignosulfonates] base admixture.

3) Segregation and Bleeding

This may happen due to the over dosage of superplasticizers, cement mix becomes too fluid and no longer suspension by fine aggregate.

Advantages of Superplasticizers

  • Cement content can be reduced to a large extent keeping the same w/c ratio, thereby leading to economy.
  • Water-cement ratio can be reduced to a great extent while keeping same cement content and the workability of concrete, leading to gain in strength.
  • High workability at low water cement ratio can be used for casting heavy reinforcement.

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