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.
It acts as the primary material of water-reducing agent. The concrete water-cement mixture is reduced, thus increasing its 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 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 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 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 results in a “coagulation phenomenon”.
(3) Crystallization stage. A colloid made of microscopic crystallines is unstable. It can slowly recrystallize and form macro-crystals. So, the mechanical strength is continually improved and it eventually becomes a cementstone with an optimum mechanical strength.
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.
The flocculation structure will form when the cement molecules encapsulate some of the water molecules. It accounts for approximately 10%-30% (which may explain why the water reducer has a maximum water reducing 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 into contact, the main chain in polycarboxylate concrete is negatively charged.
The surface of negatively charged cement particles can attract molecules, causing an “anchoring,” phenomenon. Meanwhile, the polycarboxylate Superplasticizer’s long side chain is extended in cement slurry to make an adsorption layers with a particular thickness. These layers can then be formed by the long side chain of the molecule and cross it with the other 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 cement particle 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, 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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