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.
Water-reducing mother liquid acts as an absolute main substance in the water-reducing solution. It reduces concrete water-cement (indirectly increases concrete strength), while ensuring fluidity and concrete 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 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 comes into 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 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. After this, the mechanical strength is continually improved and the cement stone is of a certain mechanical strength.
The main role for steric hindrance is played by the superplasticizers made of polycarboxylic alcohol ether. 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 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 in contact with the polycarboxylate concrete cement admixture molecules, the main chain is negatively charged.
There are two ways molecules can interact with positively charged cement particles. The first is “anchoring”, which is when the polycarboxylate Superplasticizer’s long sidechain is extended in cement slurry to form an adhesive layer. Second, the three-dimensional, cross-linked side chain can form with the other polycarboxylic acids superplasticizer molecules that extend in cement slurry simultaneously. 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 water molecules and reduce the amount of water molecules in thin air.
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 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 content. 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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