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“Water reduction” mechanism of polycarboxylic ether based superplasticizers

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Today’s concrete superplasticizers These are created by the combination of various 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 water-reducing agent is water-reducing mom liquid. This is because it reduces concrete’s water-cement content (directly increases concrete strength), as well as ensure fluidity and concrete workability and concrete strength. The water-reducing mother liquid also makes it easier to work in the construction area.

As we know, cement has water content in concrete. This means that superplasticizer molecules can also be affected by other materials. Water reducing agents are primarily directed 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 is placed in direct contact with water it causes the particles to begin to hydrate. A small quantity of hydration product are produced, which can be immediately dissolved in the water. Hydration can continue on the exposed new 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 eventually forms a coagulation phenomenon.
(3) Crystallization stage. A colloid made of microscopic crystallines is unstable. It can slowly recrystallize and form macro-crystals. As a result, the mechanical strength is continually improved and the cement stone is given a certain mechanical property.

The main role for steric hindrance is played by the superplasticizers made of polycarboxylic alcohol based superplasticizers in the cement slurry. 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.
A portion of water molecules is encapsulated by cement molecules in the flocculation structure. The encapsulated water makes up about 10-15% to 30% of the total mixture water. 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 contact, the main chain in polycarboxylate concrete is negatively charged. concrete admixture Adsorption of molecules on positively charged cement particles can lead to an “anchoring” phenomenon. The long side chain of the molecule can also be extended in cement slurry to form an adhesive layer. A three-dimensional cross-linked side chain can form with polycarboxylic acids superplasticizer molecules. 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 COO2- is an anionic group in molecules. The cement particle’s surface contains positive charges (Ca2+) during early hydration. Anionic Polycarboxylic Acid superplasticizer molecules can adsorb these positively charged 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 positively charged calcium ions and the negatively charged carboxyl group are unstable. 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 cement particle dispersion performances improved. A higher level of Polycarboxylic acids superplasticizers with carboxylates ions, or more anion charges density, will lead to a better dispersion ratio (acid-ether). 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 concrete 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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