Plasticisers and Superplasticisers

Summary

Plasticisers and Superplasticisers - are chemicals which can be added to a concrete mix to increase its workability, without affecting the water / cement ratio.

Technical Information

Plasticisers and superplasticisers can be applied when:

A high strength concrete is required to flow with ease, but the water cement ratio can’t be affected.
There is congested reinforcement.
To save labour when constructing thin concrete floor slabs with a very large surface area due to their ability to improve the fresh concrete’s ability to flow.
Concreting in cold weather due to the fact that they can increase the early strength of the concrete.

For the same level of workability, plasticisers can reduce the required water content of the concrete mix by around 5-10% and superplasticisers can reduce it by 12-30%. Therefore, with a plasticiser a workable concrete is achieved, but also a lower water / cement ratio can be kept to provide a high strength concrete.

Plasticisers are an expensive concrete additive and superplasticisers can be multiple times more expensive than regular plasticisers (per kg of concrete).

Adding 1-2% plasticiser per unit weight of concrete is usually enough to achieve the desired effect whereas this value can be a lot lower for superplasticiser.

Some superplasticisers can entrain unwanted air in a concrete mixture; therefore it is important to be careful when using them in conjunction with an air-entraining agent or in a floor which is to be power trowelled. F