“Water reduction” mechanism of polycarboxylic ether based superplasticizers

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Today’s concrete superplasticizers These are created by compounding 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. Water-reducing mother liquid acts as an absolute main substance in the water-reducing solution. It reduces concrete’s water-cement content (indirectly increases concrete strength), while ensuring fluidity and concrete mix workability and preserving 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 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 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 to become macroscopic crystals.
In cement slurry the dispersion mechanism of superplasticizers made from polycarboxylic alcohol based superplasticizers and steric hindrance is usually considered the principal role. 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%-30% (this could explain why water reducers have a maximum water reduction rate). 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 in contact with the polycarboxylate concrete cement admixture molecules, the main chain is negatively charged. concrete admixture Certain molecules may be adsorbed to the surface of negatively charged cement particles. An “anchoring” phenomenon takes place while the polycarboxylate SUPERplasticizer is in action. The long sidechain in the molecule can be extended in cement slurry to make an adsorption layers 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. 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 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 dispersion between cement particles by having them repel one another (electrostatic attraction). 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 (acid-ether) for cement particles. Inhibiting the cement’s initial hydrolysis can be caused by a decrease in the calcium ion level. 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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