Water reduction mechanism of polycarboxylic ether based superplasticizers
Today'' s concrete superplasticizers are essentially prepared by intensifying different products such as polycarboxylate water-reducing mom alcohol as well as polycarboxylate slump-preserving mother alcohol plus retarders, air-entraining agents, and defoaming representatives. Among them, the function of water-reducing mommy option in superplasticizer is irreplaceable. Maybe the amount of mother solution will alter as a result of the change of concrete product, however I have actually never ever listened to that water-reducing mother solution is not contributed to superplasticizer due to the fact that the sand is as well great.
The water-reducing mom fluid is utilized as the absolute main product in the water-reducing representative, and its function is to lower the concrete water-cement ratio (indirectly boost the strength of the concrete), and also at the exact same time make certain the fluidness as well as workability of the concrete mix, as well as guarantee the toughness of the concrete. At the very same time, it also helps with the work of the construction system.
We know that along with seal and water in concrete, the result of the continuing to be products on the superplasticizer admixture particles is generally adsorption (waste), so the water reducing agent is generally targeted at concrete. So initially, let’& rsquo; s find out about the hydration process of concrete.
The hydration process of basic portland concrete is separated right into three stages:
( 1) Dissolution stage: When the concrete touches with water, the surface area of the fragments starts to moisturize, as well as a small amount of hydration products are generated, which are quickly liquified in water. The exposed brand-new surface allows hydration to continue till a saturated solution of hydration items is formed.
( 2) Gelation stage: As a result of the saturation of the remedy, the product that remains to be moistened can no longer be liquified, but is directly precipitated as colloidal fragments. With the rise of hydration products, the hydration aggregates, as well as the concrete slurry slowly sheds its plasticity, leading to a coagulation phenomenon.
( 3) Formation stage: The colloid composed of microscopic crystals is not steady, as well as can progressively recrystallize to form macroscopic crystals, to make sure that the mechanical toughness of the solidified body of the concrete slurry is constantly boosted, as well as finally it ends up being a cement rock with a certain mechanical strength.
In the cement slurry, the diffusion system of polycarboxylic ether based superplasticizers is generally taken into consideration to be the major function of steric barrier as well as the additional function of electrostatic repulsion. On top of that, the complexation of calcium ions and the lubrication of hydration film also play a role. crucial duty.
1. Steric limitation:
The hydration procedure of concrete will make the cement molecules attract each various other, causing a flocculation framework.
During the formation of the flocculation framework, the concrete particles will certainly encapsulate a part of the water molecules, as well as the encapsulated water represent about 10% -30% of the overall mixing water (this may be the reason that the water decreasing agent has a water lowering price limitation). Because it is covered by concrete molecules, it can not join the complimentary circulation and lubrication between concrete molecules, hence affecting the fluidness of concrete mixtures. When the polycarboxylate concrete admixture particles initial entered contact with the cement particles, the negatively charged primary chain in the polycarboxylate concrete admixture particles can be adsorbed on the surface of the positively charged concrete particles, that is, an "anchoring" sensation occurs, while the polycarboxylate superplasticizer The lengthy side chain in the particle is extended in the liquid stage of the cement slurry to develop an adsorption layer with a particular thickness, and can create a three-dimensional and also crossed lengthy side chain with other polycarboxylic acid superplasticizer particles extending in the fluid stage of the concrete slurry at the exact same time. Conformation. When the cement bits approach each other, the adsorption layer overlaps, and the larger the overlapping range, the better the repulsion between the concrete particles, thereby boosting the dispersibility of the concrete bits. Destroy the flocculation framework in between cement molecules. The launch of the water entraped by cement flocculation can also be comprehended as the water decreasing representative particles improve the lubricating utilization price of the water particles to the cement molecules, and also do not increase the water or decrease the variety of water particles out of thin air.
2. The concept of electrostatic repulsion:
Polycarboxylic acid superplasticizer particles have anionic groups (COO2-), and in the early hydration process of concrete, the surface area of concrete fragments contains positive costs (Ca2+), consequently, anionic Polycarboxylic acid superplasticizer molecules adsorb to favorably billed cement particles surface area. Make the concrete particles right into a "hedgehog" with negative fee. Since the cement particles with the very same negative fee ward off each other (electrostatic repulsion), the dispersibility between the cement particles is enhanced. At the same time, the adversely billed carboxyl teams as well as favorably billed calcium ions in the cement paste form unstable facilities. After the calcium ions dissolved in the concrete system are captured, the calcium ion concentration decreases dramatically, decreasing the calcium ions in the system. It can lower the formation of gel fragments and thus decrease the hydration rate of cement, prevent the hydration of concrete, and enhance the diffusion performance of cement particles. The greater the material of carboxylate ions in the Polycarboxylic acid superplasticizer, that is, the greater the anion cost density, the greater the dispersion performance of cement bits (acid-ether proportion). The decrease of calcium ion focus can hinder the first hydration of concrete. With the constant progress of hydration, the complicated will certainly decay on its own, so Polycarboxylic acid superplasticizer has a specific retarding result without impacting the toughness of concrete.
The branched chain of the polycarboxylic acid superplasticizer particle has hydrophilic teams. These teams form a water film externally of the concrete fragments by integrating with water particles, which lowers the surface power of the cement particles. Slides conveniently. The combined result of the above cause separation in between the cement bits. The macroscopic performance is that the concrete mix has better fluidness.
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