Water reduction mechanism of polycarboxylic ether based superplasticizers
Today'' s concrete superplasticizers are basically prepared by worsening numerous products such as polycarboxylate water-reducing mommy alcohol as well as polycarboxylate slump-preserving mom alcohol plus retarders, air-entraining representatives, and also defoaming agents. Amongst them, the role of water-reducing mommy option in superplasticizer is irreplaceable. Maybe the quantity of mom option will certainly alter as a result of the adjustment of concrete product, but I have actually never heard that water-reducing mother solution is not included in superplasticizer since the sand is too good.
The water-reducing mother liquid is made use of as the absolute major material in the water-reducing agent, and its function is to reduce the concrete water-cement ratio (indirectly enhance the toughness of the concrete), as well as at the exact same time make sure the fluidness and workability of the concrete mix, and guarantee the toughness of the concrete. At the same time, it additionally assists in the job of the construction unit.
We understand that in addition to cement and also water in concrete, the result of the continuing to be products on the superplasticizer admixture molecules is essentially adsorption (waste), so the water reducing agent is generally aimed at concrete. So first, let’& rsquo; s learn about the hydration process of concrete.
The hydration process of basic rose city cement is divided right into three stages:
( 1) Dissolution phase: When the cement is in contact with water, the surface area of the fragments begins to moisturize, as well as a small amount of hydration items are produced, which are quickly dissolved in water. The revealed brand-new surface allows hydration to continue up until a saturated option of hydration items is created.
( 2) Gelation stage: Because of the saturation of the remedy, the item that continues to be moistened can no more be dissolved, yet is directly sped up as colloidal fragments. With the increase of hydration products, the hydration accumulations, as well as the concrete slurry progressively loses its plasticity, leading to a coagulation sensation.
( 3) Crystallization stage: The colloid composed of tiny crystals is not stable, and also can progressively recrystallize to create macroscopic crystals, so that the mechanical toughness of the solidified body of the cement slurry is continuously improved, as well as ultimately it becomes a cement rock with a certain mechanical strength.
In the concrete slurry, the diffusion mechanism of polycarboxylic ether based superplasticizers is usually thought about to be the main duty of steric barrier as well as the second duty of electrostatic repulsion. Furthermore, the complexation of calcium ions as well as the lubrication of hydration movie likewise play a role. crucial role.
1. Steric obstacle:
The hydration process of concrete will make the concrete particles draw in each other, resulting in a flocculation structure.
During the development of the flocculation structure, the cement molecules will certainly envelop a component of the water particles, and also the encapsulated water accounts for about 10% -30% of the total mixing water (this may be the reason why the water minimizing agent has a water minimizing rate limitation). Since it is covered by concrete molecules, it can not take part in the complimentary flow and also lubrication between concrete particles, therefore impacting the fluidness of concrete mixes. When the polycarboxylate concrete admixture particles first entered into call with the concrete particles, the negatively charged primary chain in the polycarboxylate concrete admixture molecules can be adsorbed on the surface of the favorably billed cement particles, that is, an "anchoring" phenomenon happens, while the polycarboxylate superplasticizer The long side chain in the molecule is prolonged in the fluid stage of the cement slurry to form an adsorption layer with a specific thickness, and can form a three-dimensional and went across long side chain with other polycarboxylic acid superplasticizer particles expanding in the liquid stage of the cement slurry at the same time. Conformation. When the cement bits approach each other, the adsorption layer overlaps, and also the bigger the overlapping variety, the better the repulsion between the concrete fragments, thus improving the dispersibility of the cement particles. Ruin the flocculation structure between cement molecules. The launch of the water caught by cement flocculation can additionally be understood as the water lowering agent molecules boost the lubricating utilization rate of the water molecules to the concrete molecules, and do not boost the water or reduce the variety of water particles out of slim air.
2. The concept of electrostatic repulsion:
Polycarboxylic acid superplasticizer particles include anionic groups (COO2-), and also in the early hydration procedure of concrete, the surface area of cement fragments has favorable fees (Ca2+), therefore, anionic Polycarboxylic acid superplasticizer molecules adsorb to positively billed cement fragments surface area. Make the cement bits into a "hedgehog" with unfavorable fee. Since the cement fragments with the same negative charge fend off each various other (electrostatic repulsion), the dispersibility in between the cement fragments is improved. At the exact same time, the adversely charged carboxyl teams and favorably billed calcium ions in the concrete paste form unsteady complexes. After the calcium ions dissolved in the concrete system are captured, the calcium ion focus lowers substantially, decreasing the calcium ions in the system. It can lower the formation of gel particles as well as hence decrease the hydration price of cement, hinder the hydration of concrete, as well as enhance the diffusion performance of concrete fragments. The higher the material of carboxylate ions in the Polycarboxylic acid superplasticizer, that is, the better the anion fee density, the higher the diffusion performance of concrete fragments (acid-ether proportion). The decline of calcium ion focus can prevent the initial hydration of concrete. With the continuous progression of hydration, the complicated will certainly decay by itself, so Polycarboxylic acid superplasticizer has a specific retarding result without affecting the strength of concrete.
The branched chain of the polycarboxylic acid superplasticizer molecule has hydrophilic groups. These groups create a water movie externally of the cement particles by incorporating with water molecules, which reduces the surface energy of the concrete fragments. Slips conveniently. The mixed result of the above results in splitting up in between the concrete fragments. The macroscopic performance is that the concrete mixture has better fluidness.
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