Water reduction mechanism of polycarboxylic ether based superplasticizers
Today'' s concrete superplasticizers are essentially prepared by intensifying various products such as polycarboxylate water-reducing mommy alcohol as well as polycarboxylate slump-preserving mom liquor plus retarders, air-entraining agents, and defoaming representatives. Among them, the duty of water-reducing mommy service in superplasticizer is irreplaceable. Maybe the quantity of mommy service will change because of the change of concrete material, but I have actually never heard that water-reducing mother remedy is not contributed to superplasticizer since the sand is too great.
The water-reducing mommy liquid is made use of as the absolute main material in the water-reducing agent, and also its feature is to reduce the concrete water-cement proportion (indirectly raise the strength of the concrete), and also at the exact same time ensure the fluidity and workability of the concrete blend, as well as make certain the toughness of the concrete. At the exact same time, it also facilitates the work of the building system.
We understand that in addition to seal and also water in concrete, the result of the remaining materials on the superplasticizer admixture molecules is generally adsorption (waste), so the water reducing agent is mostly targeted at concrete. So first, let’& rsquo; s discover the hydration process of concrete.
The hydration procedure of basic portland concrete is split right into 3 phases:
( 1) Dissolution stage: When the cement is in contact with water, the surface of the bits starts to moisturize, and also a percentage of hydration products are produced, which are promptly liquified in water. The revealed new surface permits hydration to continue until a saturated option of hydration products is developed.
( 2) Gelation phase: Because of the saturation of the remedy, the item that continues to be moistened can no more be dissolved, however is directly sped up as colloidal particles. With the increase of hydration products, the hydration accumulations, and also the concrete slurry gradually loses its plasticity, causing a coagulation phenomenon.
( 3) Crystallization phase: The colloid made up of tiny crystals is not steady, and also can slowly recrystallize to form macroscopic crystals, so that the mechanical stamina of the hardened body of the concrete slurry is continuously boosted, as well as lastly it comes to be a concrete stone with a particular mechanical toughness.
In the cement slurry, the dispersion device of polycarboxylic ether based superplasticizers is usually taken into consideration to be the primary function of steric barrier as well as the second role of electrostatic repulsion. On top of that, the complexation of calcium ions and also the lubrication of hydration movie likewise play a role. crucial role.
1. Steric hindrance:
The hydration procedure of concrete will make the concrete molecules bring in each other, resulting in a flocculation structure.
Throughout the formation of the flocculation framework, the concrete molecules will certainly encapsulate a part of the water particles, and also the encapsulated water make up about 10% -30% of the total mixing water (this may be the reason the water reducing representative has a water lowering price limit). Since it is wrapped by concrete particles, it can not participate in the complimentary circulation as well as lubrication between cement particles, therefore impacting the fluidity of concrete mixes. When the polycarboxylate concrete admixture particles very first come into contact with the concrete bits, the adversely billed main chain in the polycarboxylate concrete admixture molecules can be adsorbed on the surface of the positively charged concrete particles, that is, an "anchoring" phenomenon happens, while the polycarboxylate superplasticizer The lengthy side chain in the particle is expanded in the fluid stage of the concrete slurry to develop an adsorption layer with a certain density, as well as can form a three-dimensional and went across lengthy side chain with other polycarboxylic acid superplasticizer molecules expanding in the liquid stage of the cement slurry at the very same time. Conformation. When the concrete bits move toward each other, the adsorption layer overlaps, as well as the larger the overlapping array, the greater the repulsion between the cement fragments, therefore improving the dispersibility of the concrete bits. Ruin the flocculation framework between cement molecules. The launch of the water trapped by concrete flocculation can also be recognized as the water lowering representative molecules boost the lubricating utilization rate of the water molecules to the concrete particles, and also do not boost the water or decrease the variety of water molecules out of slim air.
2. The theory of electrostatic repulsion:
Polycarboxylic acid superplasticizer particles have anionic groups (COO2-), and also in the very early hydration process of concrete, the surface of concrete particles has favorable fees (Ca2+), for that reason, anionic Polycarboxylic acid superplasticizer particles adsorb to favorably billed concrete particles surface area. Make the cement fragments right into a "hedgehog" with negative charge. Since the cement particles with the same negative charge ward off each various other (electrostatic repulsion), the dispersibility between the concrete fragments is improved. At the exact same time, the negatively billed carboxyl teams and also positively charged calcium ions in the cement paste type unpredictable complexes. After the calcium ions dissolved in the concrete system are captured, the calcium ion focus lowers considerably, reducing the calcium ions in the system. It can minimize the development of gel fragments and also hence decrease the hydration rate of cement, hinder the hydration of concrete, and boost the diffusion efficiency of concrete bits. The higher the material of carboxylate ions in the Polycarboxylic acid superplasticizer, that is, the greater the anion charge density, the greater the dispersion efficiency of concrete bits (acid-ether ratio). The decrease of calcium ion focus can prevent the first hydration of cement. With the continual progress of hydration, the facility will certainly disintegrate on its own, so Polycarboxylic acid superplasticizer has a specific retarding result without influencing the toughness of concrete.
The branched chain of the polycarboxylic acid superplasticizer molecule has hydrophilic groups. These groups develop a water movie on the surface of the concrete particles by incorporating with water particles, which lowers the surface energy of the cement fragments. Slips quickly. The consolidated effect of the above lead to splitting up between the concrete particles. The macroscopic efficiency is that the concrete blend has better fluidity.
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