“Water reduction” mechanism of polycarboxylic ether based superplasticizers


concrete superplasticizers

These are basically made from a combination of various materials like polycarboxylate water–reducing mother liquor and/or polycarboxylate shrink-preserving mother liquor. 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 cement-water ratio and helps to ensure fluidity and concrete mix workability. 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 targeted at cement. First, we will discuss the cement hydration process.

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

(1) The Dissolution Stage: After cement has been in contact water for a while, its surface begins 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 flexibility.

(3) Crystallization stage. A colloid made of microscopic crystallines is not stable and can slowly recrystallize to become macroscopic crystals. This increases the cement slurry’s mechanical strength, which eventually results in a cement rock with an increased mechanical strength.

The main role for steric hindrance is played by the superplasticizer polycarboxylic-ether based dispersers in the cement slurry. This secondary role plays the role of electrostatic attraction. 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 approximately 10% 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 of polycarboxylate concrete cement admixture molecules is negatively charged.

concrete admixture

Molecules can be adsorbed to the surface of negatively charged cement particles. An “anchoring” phenomenon takes place while the polycarboxylate SUPERplasticizer is in action. The long side chain of the molecule can be extended in cement slurry to form an adhesive layer with a particular thickness. Also, it can cross a long side chain with the other polycarboxylic acids superplasticizer molecules that are also in cement slurry. 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 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 cement particle dispersion performances 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 (ancid-ether ratio). Inhibiting the cement’s initial hydrolysis can be caused by a decrease in the calcium ion content. 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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