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Superplasticizer in Concrete

30 Jun 2021, Posted by F.A. in Concrete Facts
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Concrete production relies on a reaction that binds water and cement with fine aggregates (primarily sand) and coarse aggregates (like crushed stone or natural gravel). A relatively small amount of water is usually needed to facilitate this chemical reaction, known as hydration, and to transform the ingredients into concrete’s final form. But in some cases, additional water is required to make the mix workable enough to be poured and finished; yet the addition of too much extra water can decrease the strength of the finished concrete. Reduced durability may mean more repairs and replacements are needed and at earlier times. Superplasticizers are one way this can be prevented.

Whether you are in search of concrete products, plywood for sale, or general information, learning about superplasticizers can increase your efficiency and quality.

What Are Superplasticizers?

In order to address the challenge of creating the right mix, many modern concrete mixes contain water reducers that improve the workability of wet concrete while decreasing the amount of water needed in the mix. Superplasticizers are a form of water reducer known as “high range water reducers” and are a chemical additive that is quickly gaining popularity.

Superplasticizers are composed of more advanced, higher-value chemicals than standard and mid-range water reducers. They work by decreasing the water to cement ratio while providing a range of benefits, including:

  • Increased density
  • Improved bond strength
  • Greater volume stability
  • Reduced shrinkage cracking
  • Increased abrasion resistance
  • Decreased permeability
  • Reduced segregation and bleeding
  • Higher early and ultimate strength

Because of these benefits, superplasticizers are used increasingly with high-performance concrete and other technological advancements like self-consolidating concrete.

How to Use Superplasticizers

There are three main ways that superplasticizers can be used: to create flowing and self-leveling concrete without increasing water or cement and without sacrificing strength; to produce workable, high-strength concrete by reducing water and the water to cement ratio; or to save cement by reducing both the water and cement contents while maintaining the same water to cement ratio and the same workability.

While some lignosulfonate-based superplasticizers retard the setting time about an hour when used with some cement types, superplasticizers in general do not affect the setting time, at most causing 15 minutes of additional setting time.

However, finishing problems can occur. Because superplasticizer mixes have a proportionately large volume of mixed mortar, they tend to be sticky. The concrete can then pull or drag on the trowel, causing the surface to tear and the mix to move under the finisher’s weight. This can be addressed by using coarser fine aggregate or a higher proportion of coarse aggregate, which stiffens the mix and provides a less mortar intensive appearance. Another remedy is to simply delay finishing.

A superplasticizer is not a cure-all admixture and comes with its own problems that need to be taken into account. But still, a dramatic transformation of stiff concrete into flowing concrete can occur when a superplasticizer is used instead of water.

Types of Superplasticizer

There are four main types of superplasticizers that are commonly used.

  • Sulphonated Melamine- Formaldehyde Condensates (SME): These are often preferred in the pre-cast industry because they do not dim the cement setting.
  • Sulphonated Naphthalene- Formaldehyde Condensates (SNF): This is a high range water reducer.
  • Modified Lignosulphonates (MLS): Lignosulfonates or sulfonated lignins are water-soluble anionic polyelectrolyte polymers; these are byproducts of wood pulp using sulfite pulping.
  • Polycarboxylate Superplasticizer- Carboxylated Acrylic0Ester Co-Polymers (CAEC): Also known as high-grade water reducers, these are chemicals used when well-dispersed particle suspension is required.

Combinations of high dosages of water reducing and accelerating admixtures are also commonly used.

Should I Use a Superplasticizer?

Superplasticizers have a number of advantages that have led to them gaining popularity recently. Benefits include:

  • Reduce water content by 25-30% for given workability of water.
  • When water is scarce, can improve workability of concrete.
  • Avoids segregation of concrete.
  • Allows concrete to be used in concreting heavily reinforced elements.
  • Increased speed of concreting.
  • Act as retarders in hot weather or when long placing periods are required.
  • More workable concrete means less energy is needed to compact the concrete. In some cases, self-compacting concrete can be made using superplasticizers.
  • Provide finishing surface of better quality.

However, there are some disadvantages as well, including:

  • High cost, leading to higher material cost in construction.
  • When used in excess quantity, bleeding of concrete can occur.

It is ultimately up to you if a superplasticizer is right for your project. Just like choosing where to find plywood for sale and choosing the right formwork, this is an individual decision for each project.