"Water reduction" mechanism of polycarboxylic ether based superplasticizers
These are 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 water cement ratio and, at the same, ensures fluidity and the workability of concrete mixture, while also ensuring 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 mainly directed towards 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 surface to hydrate. A small quantity of hydration product are produced, which can be immediately dissolved in the 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 to become macroscopic crystals.
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 formation and maintenance of the flocculation structure. The encapsulated water makes up about 10-15% to 30% of the total mix water. Since it is enclosed by cement molecules it can't participate in free flow or lubrication of cement molecules. It will affect concrete mix fluidity. Once the concrete particles come in contact with the polycarboxylate concrete cement admixture molecules, the main chain is negatively charged.
The surface of negatively charged cement particles can attract molecules, causing an "anchoring" phenomenon. While the polycarboxylate Superplasticizer is extending the side chain of the molecule in the cement cement slurry, it can create an adsorption layers with a particular thickness. Also, the long side chain can cross with the other polycarboxylic acids superplasticizer molecules in the cement liquid phase. 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 cement particle dispersibility. The cement particles must be destroyed from their flocculation. You can understand how cement flocculation causes water to escape. The water reducing molecules increase the lubricating utilization of the water molecules in cement molecules. However, they do not reduce or increase the quantity 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 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 concrete strength.
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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