Superplasticizer or high range water reducers

Or dispersants are chemical admixtures that are added to concrete mix’s to improve workability and reduce water content. Unless the mix is hungry for water, the strength of concrete is inversely proportionate to the amount of water added to the mix or water to cement (w/c) ratio. In order to produce stronger concrete, less water is needed, which makes the concrete mixture less workable and difficult to mix, creating the need for plasticizers, water reducers, superplasticizer or dispersants.

Superplasticizer is also often used when pozzolanic ash is added to concrete to improve strength. This method of mix proportioning is especially popular when producing high-strength concrete and fiber-reinforced concrete.

Adding 1-2% superplasticizer per unit weight of cement is usually sufficient. However, note that most commercially available superplasticizers come dissolved in water, so the extra water added has to be accounted for in mix proportioning. Adding an excessive amount of superplasticizer will result in excessive segregation of concrete and is not advisable. Some studies also show that too much superplasticizer will result in a retarding effect.

Plasticizers are commonly manufactured from lignosulfonates, a by-product from the paper industry. High Range Superplasticizer have generally been manufactured from sulfonated naphthalene condensate or sulfonated melamine formaldehyde, although new-generation products based on polycarboxylic ethers are now available. Traditional lignosulfonate-based plasticisers, naphthalene and melamine sulfonate-based superplasticisers disperse the flocculated cement particles through a mechanism of electrostatic repulsion (see colloid). In normal plasticisers, the active substances are adsorbed on to the cement particles, giving them a negative charge, which leads to repulsion between particles. Lignin, naphthalene and melamine sulfonate superplasticisers are organic polymers. The long molecules wrap themselves around the cement particles, giving them a highly negative charge so that they repel each other.

Superplasticizer Technology

Polycarboxylate ethers (PCE) or just polycarboxylate (PC), the new generation of superplasticisers, are not only chemically different from the older sulfonated melamine and naphthalene-based products, but their action mechanism is also different, giving cement dispersion by steric stabilisation, instead of electrostatic repulsion. This form of dispersion is more powerful in its effect and gives improved workability retention to the cementitious mix. Furthermore, the chemical structure of PCE allows for a greater degree of chemical modification than the older-generation products, offering a range of performance that can be tailored to meet specific needs.

In ancient times, the Romans used animal fat, milk and blood as a superplasticizer for their concrete mixes.

Superplasticizer can be obtained from a local concrete manufacturer.

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