Water reduction mechanism of polycarboxylic ether based superplasticizers
Today'' s concrete superplasticizers are primarily prepared by worsening different materials such as polycarboxylate water-reducing mom liquor and also polycarboxylate slump-preserving mommy liquor plus retarders, air-entraining agents, and also defoaming agents. Amongst them, the role of water-reducing mom option in superplasticizer is irreplaceable. Possibly the amount of mother option will certainly transform because of the change of concrete material, yet I have never listened to that water-reducing mommy solution is not included in superplasticizer because the sand is too great.
The water-reducing mommy liquid is made use of as the outright primary product in the water-reducing representative, and also its function is to lower the concrete water-cement proportion (indirectly boost the toughness of the concrete), and at the same time guarantee the fluidity as well as workability of the concrete combination, as well as guarantee the toughness of the concrete. At the very same time, it likewise facilitates the work of the building system.
We know that along with seal and also water in concrete, the impact of the remaining materials on the superplasticizer admixture molecules is primarily adsorption (waste), so the water decreasing representative is primarily focused on concrete. So first, let’& rsquo; s find out about the hydration procedure of concrete.
The hydration procedure of general portland cement is separated into 3 phases:
( 1) Dissolution phase: When the cement is in contact with water, the surface of the fragments begins to moisten, and a small amount of hydration items are generated, which are instantly liquified in water. The subjected brand-new surface area permits hydration to continue until a saturated service of hydration items is created.
( 2) Gelation phase: As a result of the saturation of the service, the product that continues to be moistened can no longer be liquified, but is directly sped up as colloidal bits. With the rise of hydration products, the hydration accumulations, and also the cement slurry progressively sheds its plasticity, resulting in a coagulation phenomenon.
( 3) Crystallization phase: The colloid made up of tiny crystals is not stable, and can progressively recrystallize to create macroscopic crystals, to ensure that the mechanical stamina of the solidified body of the cement slurry is constantly enhanced, and lastly it becomes a concrete rock with a particular mechanical toughness.
In the concrete slurry, the diffusion mechanism of polycarboxylic ether based superplasticizers is typically considered to be the main role of steric limitation and the additional function of electrostatic repulsion. On top of that, the complexation of calcium ions and also the lubrication of hydration movie likewise play a role. crucial function.
1. Steric obstacle:
The hydration procedure of cement will certainly make the cement molecules attract each various other, causing a flocculation framework.
During the development of the flocculation framework, the concrete molecules will envelop a component of the water molecules, as well as the encapsulated water represent around 10% -30% of the total mixing water (this may be the reason the water reducing agent has a water decreasing price limit). Since it is wrapped by concrete molecules, it can not participate in the totally free circulation and also lubrication in between cement molecules, therefore impacting the fluidness of concrete mixtures. When the polycarboxylate concrete admixture molecules very first entered call with the cement bits, the negatively billed major chain in the polycarboxylate concrete admixture particles can be adsorbed on the surface of the favorably charged cement bits, that is, an "anchoring" phenomenon happens, while the polycarboxylate superplasticizer The long side chain in the molecule is expanded in the fluid stage of the concrete slurry to develop an adsorption layer with a certain thickness, as well as can create a three-dimensional and went across lengthy side chain with various other polycarboxylic acid superplasticizer molecules prolonging in the fluid phase of the concrete slurry at the same time. Conformation. When the cement particles approach each various other, the adsorption layer overlaps, and also the bigger the overlapping array, the better the repulsion in between the cement particles, consequently boosting the dispersibility of the cement fragments. Destroy the flocculation framework between cement molecules. The release of the water entraped by cement flocculation can also be recognized as the water lowering representative particles enhance the lubricating usage rate of the water particles to the concrete particles, and do not increase the water or decrease the variety of water particles out of slim air.
2. The theory of electrostatic repulsion:
Polycarboxylic acid superplasticizer particles contain anionic teams (COO2-), and also in the very early hydration procedure of concrete, the surface of cement bits contains favorable costs (Ca2+), consequently, anionic Polycarboxylic acid superplasticizer molecules adsorb to positively billed cement bits surface. Make the concrete bits right into a "hedgehog" with negative fee. Due to the fact that the cement particles with the same negative cost repel each various other (electrostatic repulsion), the dispersibility in between the concrete bits is boosted. At the same time, the negatively billed carboxyl groups and also positively billed calcium ions in the cement paste form unsteady complicateds. After the calcium ions liquified in the concrete system are caught, the calcium ion concentration reduces substantially, lowering the calcium ions in the system. It can minimize the development of gel particles and also hence slow down the hydration rate of concrete, prevent the hydration of concrete, and also enhance the dispersion efficiency of concrete bits. The higher the content of carboxylate ions in the Polycarboxylic acid superplasticizer, that is, the higher the anion fee thickness, the higher the dispersion efficiency of cement bits (acid-ether proportion). The decline of calcium ion focus can prevent the first hydration of cement. With the constant development of hydration, the complicated will certainly decay on its own, so Polycarboxylic acid superplasticizer has a particular retarding result without influencing the toughness of concrete.
The branched chain of the polycarboxylic acid superplasticizer particle has hydrophilic groups. These groups form a water film externally of the cement fragments by combining with water molecules, which lowers the surface energy of the cement fragments. Slides easily. The mixed impact of the above lead to separation in between the concrete fragments. The macroscopic efficiency is that the concrete mix has better fluidity.
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