Water reduction mechanism of polycarboxylic ether based superplasticizers
Today'' s concrete superplasticizers are basically prepared by worsening numerous products such as polycarboxylate water-reducing mom liquor as well as polycarboxylate slump-preserving mom liquor plus retarders, air-entraining representatives, and defoaming representatives. Among them, the role of water-reducing mommy option in superplasticizer is irreplaceable. Perhaps the amount of mother remedy will certainly change due to the adjustment of concrete material, but I have never ever listened to that water-reducing mother remedy is not added to superplasticizer because the sand is as well great.
The water-reducing mommy liquid is used as the outright primary product in the water-reducing agent, and also its feature is to minimize the concrete water-cement ratio (indirectly boost the strength of the concrete), and at the same time guarantee the fluidity and workability of the concrete combination, as well as make sure the stamina of the concrete. At the very same time, it additionally promotes the job of the building and construction system.
We know that in addition to 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 aimed at cement. So first, let’& rsquo; s find out about the hydration process of cement.
The hydration process of general rose city cement is separated into three stages:
( 1) Dissolution phase: When the concrete touches with water, the surface of the bits starts to moisturize, as well as a percentage of hydration items are produced, which are right away dissolved in water. The subjected new surface permits hydration to continue till a saturated solution of hydration products is formed.
( 2) Gelation stage: As a result of the saturation of the remedy, the item that continues to be moistened can no longer be liquified, but is directly sped up as colloidal bits. With the boost of hydration products, the hydration accumulations, and the concrete slurry gradually sheds its plasticity, resulting in a coagulation sensation.
( 3) Crystallization stage: The colloid composed of microscopic crystals is not steady, as well as can gradually recrystallize to create macroscopic crystals, so that the mechanical stamina of the solidified body of the concrete slurry is continuously enhanced, as well as lastly it comes to be a cement stone with a particular mechanical toughness.
In the concrete slurry, the diffusion mechanism of polycarboxylic ether based superplasticizers is normally thought about to be the major role of steric hindrance as well as the second function of electrostatic repulsion. On top of that, the complexation of calcium ions as well as the lubrication of hydration movie likewise contribute. vital role.
1. Steric hindrance:
The hydration procedure of concrete will certainly make the cement particles draw in each other, leading to a flocculation framework.
During the development of the flocculation framework, the cement molecules will certainly envelop a component of the water particles, and the encapsulated water accounts for around 10% -30% of the overall mixing water (this may be the reason the water minimizing agent has a water reducing rate limitation). Because it is covered by concrete molecules, it can not join the complimentary circulation and lubrication between cement particles, hence influencing the fluidity of concrete mixtures. When the polycarboxylate concrete admixture molecules very first entered into contact with the concrete fragments, the adversely charged major chain in the polycarboxylate concrete admixture molecules can be adsorbed on the surface of the positively billed cement fragments, that is, an "anchoring" sensation takes place, while the polycarboxylate superplasticizer The long side chain in the particle is extended in the liquid stage of the concrete slurry to create an adsorption layer with a specific thickness, and also can form a three-dimensional and also crossed long side chain with other polycarboxylic acid superplasticizer molecules prolonging in the liquid phase of the concrete slurry at the exact same time. Conformation. When the concrete particles approach each other, the adsorption layer overlaps, and also the larger the overlapping range, the higher the repulsion in between the cement fragments, thereby enhancing the dispersibility of the cement particles. Damage the flocculation framework in between concrete particles. The launch of the water entraped by concrete flocculation can also be recognized as the water decreasing representative particles enhance the lubricating use price of the water particles to the concrete molecules, and do not raise the water or decrease the number of water molecules out of slim air.
2. The concept of electrostatic repulsion:
Polycarboxylic acid superplasticizer molecules include anionic teams (COO2-), and in the early hydration process of cement, the surface area of cement fragments consists of positive costs (Ca2+), therefore, anionic Polycarboxylic acid superplasticizer molecules adsorb to favorably charged cement fragments surface. Make the cement particles into a "hedgehog" with negative fee. Since the cement fragments with the very same negative cost fend off each various other (electrostatic repulsion), the dispersibility between the cement bits is enhanced. At the same time, the negatively billed carboxyl teams as well as favorably billed calcium ions in the cement paste kind unpredictable complexes. After the calcium ions dissolved in the concrete system are caught, the calcium ion concentration lowers substantially, lowering the calcium ions in the system. It can minimize the formation of gel bits and thus slow down the hydration rate of cement, hinder the hydration of cement, and enhance the dispersion efficiency of concrete bits. The greater the web content of carboxylate ions in the Polycarboxylic acid superplasticizer, that is, the greater the anion cost density, the greater the dispersion efficiency of cement bits (acid-ether ratio). The decrease of calcium ion concentration can hinder the preliminary hydration of cement. With the continuous development of hydration, the facility will break down by itself, so Polycarboxylic acid superplasticizer has a specific retarding result without influencing the strength of concrete.
The branched chain of the polycarboxylic acid superplasticizer particle has hydrophilic groups. These groups develop a water movie on the surface of the concrete bits by incorporating with water particles, which lowers the surface area energy of the cement bits. Slides quickly. The mixed impact of the above cause splitting up in between the concrete bits. The macroscopic efficiency is that the concrete blend has better fluidness.
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