Water reduction mechanism of polycarboxylic ether based superplasticizers
Today'' s concrete superplasticizers are essentially prepared by compounding numerous products such as polycarboxylate water-reducing mother liquor and also polycarboxylate slump-preserving mother liquor plus retarders, air-entraining agents, as well as defoaming representatives. Among them, the duty of water-reducing mother remedy in superplasticizer is irreplaceable. Maybe the amount of mommy option will certainly alter because of the modification of concrete material, however I have never heard that water-reducing mom solution is not added to superplasticizer because the sand is as well great.
The water-reducing mother liquid is used as the absolute primary product in the water-reducing representative, and also its function is to minimize the concrete water-cement proportion (indirectly raise the strength of the concrete), and also at the same time ensure the fluidity and also workability of the concrete mixture, and guarantee the toughness of the concrete. At the same time, it also helps with the work of the building system.
We understand that in addition to seal and also water in concrete, the impact of the remaining products on the superplasticizer admixture molecules is essentially adsorption (waste), so the water lowering agent is generally targeted at cement. So initially, allow’& rsquo; s learn more about the hydration procedure of cement.
The hydration process of basic rose city concrete is divided into three stages:
( 1) Dissolution stage: When the cement is in contact with water, the surface area of the bits starts to hydrate, and also a small amount of hydration items are generated, which are instantly liquified in water. The exposed new surface allows hydration to continue up until a saturated remedy of hydration products is created.
( 2) Gelation phase: Due to the saturation of the solution, the item that continues to be hydrated can no more be dissolved, but is directly precipitated as colloidal particles. With the increase of hydration items, the hydration accumulations, and the cement slurry slowly loses its plasticity, causing a coagulation phenomenon.
( 3) Formation phase: The colloid composed of microscopic crystals is not steady, and can slowly recrystallize to develop macroscopic crystals, to ensure that the mechanical toughness of the hardened body of the cement slurry is continuously boosted, and also ultimately it becomes a concrete rock with a specific mechanical strength.
In the cement slurry, the dispersion device of polycarboxylic ether based superplasticizers is usually taken into consideration to be the primary role of steric hindrance and also the second role of electrostatic repulsion. In addition, the complexation of calcium ions as well as the lubrication of hydration movie additionally play a role. crucial function.
1. Steric barrier:
The hydration procedure of concrete will make the concrete molecules bring in each various other, resulting in a flocculation structure.
During the development of the flocculation structure, the cement molecules will certainly encapsulate a component of the water molecules, as well as the encapsulated water represent about 10% -30% of the complete mixing water (this might be the reason that the water reducing agent has a water reducing price limit). Since it is wrapped by cement molecules, it can not join the complimentary circulation and also lubrication in between cement molecules, hence affecting the fluidity of concrete blends. When the polycarboxylate concrete admixture particles very first come into call with the concrete particles, the adversely charged primary chain in the polycarboxylate concrete admixture particles can be adsorbed externally of the positively billed cement particles, that is, an "anchoring" sensation occurs, while the polycarboxylate superplasticizer The lengthy side chain in the particle is expanded in the fluid phase of the concrete slurry to create an adsorption layer with a particular density, as well as can develop a three-dimensional and went across lengthy side chain with other polycarboxylic acid superplasticizer particles extending in the liquid phase of the concrete slurry at the exact same time. Conformation. When the concrete bits approach each other, the adsorption layer overlaps, and the bigger the overlapping range, the better the repulsion in between the concrete bits, thereby enhancing the dispersibility of the concrete particles. Ruin the flocculation structure in between cement molecules. The release of the water caught by concrete flocculation can also be recognized as the water lowering agent particles improve the lubricating application price of the water molecules to the cement particles, and do not increase the water or lower the variety of water molecules out of thin air.
2. The theory of electrostatic repulsion:
Polycarboxylic acid superplasticizer molecules contain anionic groups (COO2-), and in the early hydration process of concrete, the surface of concrete bits contains favorable charges (Ca2+), therefore, anionic Polycarboxylic acid superplasticizer molecules adsorb to positively charged concrete bits surface. Make the cement particles into a "hedgehog" with adverse charge. Since the cement fragments with the exact same unfavorable charge drive away each other (electrostatic repulsion), the dispersibility between the concrete fragments is improved. At the very same time, the negatively billed carboxyl teams and also favorably billed calcium ions in the cement paste type unsteady complexes. After the calcium ions liquified in the concrete system are captured, the calcium ion concentration decreases significantly, reducing the calcium ions in the system. It can decrease the development of gel bits and thus reduce the hydration rate of cement, hinder the hydration of cement, as well as improve the dispersion efficiency of cement particles. The higher the material of carboxylate ions in the Polycarboxylic acid superplasticizer, that is, the better the anion fee density, the better the dispersion efficiency of concrete fragments (acid-ether proportion). The decline of calcium ion concentration can inhibit the initial hydration of concrete. With the continual development of hydration, the complicated will certainly disintegrate on its own, so Polycarboxylic acid superplasticizer has a specific retarding effect without impacting the stamina of concrete.
The branched chain of the polycarboxylic acid superplasticizer particle has hydrophilic groups. These groups develop a water film externally of the cement particles by integrating with water molecules, which lowers the surface energy of the concrete bits. Slides quickly. The mixed impact of the above results in separation in between the cement fragments. The macroscopic performance is that the concrete combination has far better fluidness.
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