It is used as an ingredient in cement in which it retards (to make slow, to delay) the setting of the mixture and improves its density and texture.
Plasticizers - Water-reducing admixture : ( The commonly used admixtures are Ligno-sulphonates and hydrocarbolic acid salts. )
To achieve a higher strength by decreasing the water-cement ratio at the same workability as an admixture free mix.
Water reduction of more than 5% but less than 12%
Plasticizers are usually based on lignosulphonate, which is a natural polymer, derived from wood processing in the paper industry.
lignosulphonate works as lubricator in concrete as it works as surface active agents which alter the physic-chemical forces at the interface. They are adsorbed on the cement particles, giving them a Negative Charge which leads to repulsion between the particles. Electrostatic forces are developed causing disintegration and the free water become available for workability, thus they lubricate the mix reducing the friction and increasing the workability.
lignosulphonate works as a retarder by forming a thin layer over the cement particles protecting them from hydration and increasing the setting time. Most normal plasticizers give some retardation, 30–90 minutes
Increased fluidity, Flowing, Self-leveling, Self-compacting concrete, Penetration and compaction round dense reinforcement, Reduced W/C ratio.
Also resulting
Very high early strength, >200% at 24 hours or earlier
Very high later age strengths, >100 MPa or 15000 psi.
Reduced shrinkage, especially if combined with reduced cement content.
Improved durability by removing water to reduce permeability and diffusion.
Most Common superplasticizers -
1.
2. SMF gives 16–25%+ water reduction in cement admixture.
3. Sulphonated Melamine Formaldehyde condensates (SMF) very effective at low temperatures especially where early strength is most critical. However, at higher temperatures, they lose workability relatively quickly.
Sulphonated Naphthalene formaldehyde condensates (SNF)
3. SNF improve cohesion.
4. SNF
Polycarboxylate ether superplasticizers (PCE)
3. PCE
After addition of
2. Uses of Retarder helps to allow later vibration of the concrete to prevent the formation of cold joints between layers of concrete placed with a significant delay between them. And retarder gives workability retention for
3. Retarder
4. The commonly known retards are Calcium Ligno-sulphonates and Carbohydrates derivatives ( SUGAR ) used
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