Superplasticizers are chemical additives that plasticize concrete and plaster mixes. Their main function is to reduce the amount of mixing water.
These chemicals are added to the mix in order to improve its rheological properties, which directly translates into increased stability of the finished products. The fluidity of the mix (mortar, concrete, gypsum) using the superplasticizer causes both a reduction of batched water and maintaining the same consistency as well as prolonged workability as compared to the reference mix.
Superplasticizers are adsorbed on joint grains, thus increasing the dispersion in the entire volume. The chemical structure of the additive molecule determines the operational mechanism of superplasticizers.
Electrostatic mechanism – after adsorption of negatively charged additive particle on the cement grain, a charge is formed on its surface, which causes the repulsion of its particles. As a result of the electrostatic forces, cement agglomerates are broken down, which improves the consistency of the mix.
Lubrication mechanism – the adsorption of superplasticizer particle on the surface of the cement grain forms a lubricating film, which provides ‘sliding’ between the cement particles. This reduces internal friction of the mix and its liquefaction.
Steric mechanism – it concerns molecules of superplasticizers having the comb structure, which are deposited on the surface of cement particles, forming a steric hindrance. They prevent the formation of agglomerates, resulting in liquefaction of the mix.
SNF admixtures (i.e. Sulfonated Naphthalene Formaldehyde) are adsorbed on the grains providing them with an electrostatic charge, and operate in accordance with the lubricating mechanism. PCE (polymers of polycarboxylic ether)thanks to their unique chain structure provide the steric effect. If the structure of these polymers includes hydrophilic groups, then they also have an electrostatic charge.
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