Water reduction mechanism of polycarboxylic ether based superplasticizers
Today'' s concrete superplasticizers are essentially prepared by compounding different products such as polycarboxylate water-reducing mommy alcohol and polycarboxylate slump-preserving mommy liquor plus retarders, air-entraining agents, and defoaming agents. Amongst them, the duty of water-reducing mom remedy in superplasticizer is irreplaceable. Maybe the amount of mom service will certainly transform due to the modification of concrete product, but I have actually never heard that water-reducing mommy remedy is not added to superplasticizer because the sand is also excellent.
The water-reducing mommy fluid is used 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 toughness of the concrete), and also at the very same time guarantee the fluidity and workability of the concrete mix, and also make sure the strength of the concrete. At the exact same time, it likewise facilitates the job of the building and construction system.
We understand that in addition to seal and water in concrete, the effect of the remaining products on the superplasticizer admixture particles is essentially adsorption (waste), so the water reducing agent is generally aimed at concrete. So initially, let’& rsquo; s discover the hydration process of cement.
The hydration procedure of basic rose city cement is separated right into 3 phases:
( 1) Dissolution stage: When the concrete is in contact with water, the surface area of the fragments begins to moisten, as well as a small amount of hydration items are generated, which are quickly liquified in water. The revealed brand-new surface area enables hydration to proceed up until a saturated service of hydration products is created.
( 2) Gelation stage: Due to the saturation of the option, the item that remains to be hydrated can no longer be dissolved, yet is straight sped up as colloidal fragments. With the increase of hydration products, the hydration aggregates, as well as the cement slurry gradually sheds its plasticity, resulting in a coagulation phenomenon.
( 3) Crystallization stage: The colloid composed of microscopic crystals is not secure, as well as can progressively recrystallize to develop macroscopic crystals, to ensure that the mechanical strength of the hardened body of the concrete slurry is continuously improved, and also lastly it becomes a concrete stone with a certain mechanical strength.
In the cement slurry, the diffusion device of polycarboxylic ether based superplasticizers is generally considered to be the major duty of steric obstacle as well as the additional duty of electrostatic repulsion. Furthermore, the complexation of calcium ions and also the lubrication of hydration film also play a role. crucial role.
1. Steric limitation:
The hydration process of cement will certainly make the cement molecules draw in each various other, leading to a flocculation framework.
Throughout the development of the flocculation framework, the concrete particles will encapsulate a component of the water particles, as well as the encapsulated water make up about 10% -30% of the total mixing water (this might be the reason why the water minimizing agent has a water reducing price limitation). Since it is covered by cement molecules, it can not take part in the complimentary flow and also lubrication between cement molecules, hence affecting the fluidness of concrete mixes. When the polycarboxylate concrete admixture particles first come into call with the cement fragments, the negatively billed main chain in the polycarboxylate concrete admixture particles can be adsorbed on the surface of the positively billed cement bits, that is, an "anchoring" phenomenon occurs, while the polycarboxylate superplasticizer The long side chain in the molecule is expanded in the fluid phase of the cement slurry to create an adsorption layer with a certain thickness, and also can form a three-dimensional as well as went across long 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 fragments approach each various other, the adsorption layer overlaps, as well as the larger the overlapping variety, the greater the repulsion between the concrete fragments, consequently improving the dispersibility of the cement bits. Damage the flocculation framework between concrete particles. The launch of the water caught by concrete flocculation can additionally be recognized as the water decreasing representative molecules boost the lubricating use rate of the water particles to the concrete molecules, and do not enhance the water or lower the variety of water particles out of thin air.
2. The theory of electrostatic repulsion:
Polycarboxylic acid superplasticizer molecules include anionic teams (COO2-), and also in the early hydration procedure of concrete, the surface area of concrete particles contains positive costs (Ca2+), for that reason, anionic Polycarboxylic acid superplasticizer particles adsorb to favorably charged concrete bits surface. Make the concrete bits right into a "hedgehog" with unfavorable fee. Because the concrete fragments with the exact same negative cost drive away each other (electrostatic repulsion), the dispersibility between the cement fragments is improved. At the exact same time, the adversely charged carboxyl groups and favorably billed calcium ions in the cement paste form unsteady complicateds. After the calcium ions liquified in the concrete system are recorded, the calcium ion concentration lowers significantly, lowering the calcium ions in the system. It can lower the development of gel particles as well as thus reduce the hydration price of cement, hinder the hydration of concrete, and also improve the diffusion performance of cement particles. The higher the content of carboxylate ions in the Polycarboxylic acid superplasticizer, that is, the better the anion cost thickness, the better the diffusion efficiency of concrete particles (acid-ether ratio). The decline of calcium ion focus can inhibit the initial hydration of cement. With the constant progress of hydration, the complicated will certainly disintegrate by itself, so Polycarboxylic acid superplasticizer has a certain retarding result without impacting the toughness of concrete.
The branched chain of the polycarboxylic acid superplasticizer molecule has hydrophilic teams. These groups develop a water film externally of the concrete fragments by incorporating with water molecules, which minimizes the surface area power of the concrete particles. Slips quickly. The mixed result of the above lead to separation in between the cement fragments. The macroscopic efficiency is that the concrete blend has better fluidness.
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