“Water reduction” mechanism of polycarboxylic ether based superplasticizers

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concrete superplasticizers

These are prepared by compounding different materials like polycarboxylate water–reducing mother liquor and/or polycarboxylate shrink-preserving mother liquor with retarders, air-entraining agent and defoaming substances. It is the most important role for water-reducing mothers in superplasticizer. Although it is possible that the quantity of the mother solution may change with the changes in concrete, I’ve never seen water-reducing mothers added to superplasticizer. Perhaps because the sand quality is too high.
The absolute main substance in the water-reducing liquid is the water-reducing mom liquid. This is because it reduces the concrete water cement ratio and, at the same, ensures fluidity and the workability of concrete mixture and increases concrete strength. The water-reducing mother liquid also makes it easier to work in the construction area.

As we know, cement is not only water-soluble in concrete; the other materials have a significant impact on superplasticizer molecules. Water reducing agents are therefore primarily focused at cement. First, we will discuss the cement hydration process.

Three stages are involved in the general portland cement hydration process:

(1) Dissolution stage. When cement comes into contact with water it causes the surface to hydrate. A small quantity of hydration product are produced, which can be immediately dissolved in water. Hydration can continue on the exposed surface until there is a saturated solution.

(2) Gelation stage. Because of the saturation of the solution the product can’t be dissolved and becomes colloidal particles. As the amount of hydration products increases, the cement slurry loses its plasticity and the hydration aggregates begin to lose their plasticity.

(3) Crystallization stage. A colloid made of microscopic crystallines is not stable and can slowly recrystallize into macroscopic crystals. This increases the mechanical properties of the cement body and eventually makes it a cement stone.

In cement slurry the dispersion mechanism with polycarboxylic-ether based superplasticizers plays the principal role in steric hindrance. The secondary role is electrostatic repulsion. Complexation of calcium ions, lubrication for hydration film play important roles. important role.

1. Steric hindrance:

Cement molecules are attracted to each other during cement’s hydration, which results in flocculation.

The flocculation structure will form when the cement molecules encapsulate some of the water molecules. It accounts for between 10% and 30% of total mixed water. (This may explain why water reducing agents have a limit on the water reducing rates). Since it is enclosed by cement molecules it can’t participate in free flow and lubrication of cement molecules. It will affect concrete mix fluidity. Once the concrete particles come into direct contact, the main chain of polycarboxylate concrete cement admixture molecules is negatively charged.

concrete admixture

While the negatively charged cement particles can attract molecules, this is known as an “anchoring” phenomenon. The long side chain of the molecule can be extended in cement slurry in order to form an adhesive layer with a particular thickness. Also, it can cross a long side chain with the other polycarboxylic acids superplasticizer molecules in the cement liquid phase at the same. Conformation. The cement particles moving towards each other will cause the adsorption layers to overlap. A larger overlapping area means that there is more repulsion among the cement particles. This improves the dispersibility. The cement particles must be destroyed from their flocculation. You can understand how cement flocculation causes water to escape. Water reducing molecules are able to increase the lubricating efficiency of the water molecules in cement molecules. However, they do not decrease the amount of water molecules.

2. Electrostatic repulsion theory:

The superplasticizer polycarboxylic acids

Anionic groups are found in molecules (COO2-). Cement particles’ surface has positive charges (Ca2+) during early hydration. Therefore, anionic Polycarboxylic Acid superplasticizer molecules will adsorb the positively charged cement particles. You can make the cement particles into a hedgehog with a negative charge. It is possible to improve the dispersibility among cement particles by having them have the same negative charge. In the cement paste, both the negatively charged carboxyl group and the positively charged calcium are responsible for the formation of unstable complexes. Once the calcium is dissolved in cement, it becomes more concentrated, which reduces calcium ions. The formation of gel particles can be slowed down, the cement hydration process is inhibited, and the dispersion of cement particles improved. A higher level of Polycarboxylic acids superplasticizers with carboxylates ions, that is, a greater anion charge density, will lead to a better dispersion performance (acid-ether) for cement particles. Inhibiting the cement’s initial hydrolysis can be caused by a decrease in calcium ion levels. As the cement hydrates, it becomes more complex. The superplasticizer Polycarboxylic Acid has an effect that slows down but does not affect the strength.

3. Lubrication

The hydrophilic group is found in the branched chains of polycarboxylic acid supraplasticizer molecule. They form a water film over the cement particles, by reacting with water molecules. This decreases their surface energy. The cement particles slip easily. Combining the two causes separation of cement particles. This concrete mixture is more fluid.

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