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Why we could not use the Polycarboxylate superplasticizer and Sodium naphthalene formaldehyde together, Maybe this is the cause!

The adsorption morphology of PCE and SNF is different, so the mechanism of water reducing is different. The PCE is a comb like polymer, and the water reducing mechanism is steric hindrance. The main chain with polar anionic active groups adsorbed on the strong polar surface of cement particles, branched hydrophilic can extend into the formation of liquid phase polymer thicker adsorption layer, when the cement particle close, adsorption layer began to overlap, which produce steric effect between particles in cement, dispersed cement particles.

The SNF is an anionic surfactant, and the water reducing mechanism is electrostatic repulsive force. The -SO3 in the water reducing agent is adsorbed on the cement particles under the action of the positive charge Ca2+ of the cement particles, the formation of diffuse double layer (Zeta potential) of the ion distribution, make cement particles dispersed in the electrostatic repulsion, The irreducible water in the space grid structure formed during the hydration of cement is released to improve the dispersion of concrete.

The fluidity of concrete is worse if used PCE and SNF together, because of different water reducing mechanism of PCE and SNF, There is a competitive adsorption phenomenon between the anionic group -COO and -SO3 in the composite application. The group of the first adsorbed on the surface of cement particles will play a leading role in the dispersion of cement particles. Compared with the -COO anion groups of PCE, the -SO3 of SNF adsorption rate faster, so as to prevent the adsorption of poly carboxylic acid molecules on the cement particles, The plasticizing effect of PCE can not be brought into full play, so the water reducing effect is often affected by the combined use of PCE and SNF.
































































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