Water reduction mechanism of polycarboxylic ether based superplasticizers
Today'' s concrete superplasticizers are generally prepared by compounding numerous materials such as polycarboxylate water-reducing mommy liquor and also polycarboxylate slump-preserving mother liquor plus retarders, air-entraining agents, as well as defoaming agents. Among them, the function of water-reducing mom solution in superplasticizer is irreplaceable. Possibly the amount of mommy option will alter due to the change of concrete material, but I have never heard that water-reducing mother option is not added to superplasticizer since the sand is as well good.
The water-reducing mommy liquid is made use of as the outright main product in the water-reducing agent, and also its feature is to lower the concrete water-cement ratio (indirectly enhance the strength of the concrete), as well as at the exact same time make certain the fluidness as well as workability of the concrete mixture, and make certain the toughness of the concrete. At the very same time, it likewise assists in the work of the building and construction unit.
We understand that along with cement as well as water in concrete, the result of the remaining products on the superplasticizer admixture particles is primarily adsorption (waste), so the water minimizing agent is mainly focused on cement. So first, allow’& rsquo; s learn more about the hydration procedure of cement.
The hydration process of general rose city concrete is separated into 3 phases:
( 1) Dissolution stage: When the concrete is in contact with water, the surface of the particles begins to moisten, as well as a percentage of hydration products are generated, which are promptly liquified in water. The exposed brand-new surface area enables hydration to continue up until a saturated solution of hydration items is developed.
( 2) Gelation stage: Because of the saturation of the option, the product that remains to be hydrated can no longer be dissolved, however is straight precipitated as colloidal bits. With the boost of hydration products, the hydration accumulations, as well as the concrete slurry progressively loses its plasticity, causing a coagulation sensation.
( 3) Formation stage: The colloid composed of tiny crystals is not stable, and can gradually recrystallize to develop macroscopic crystals, to ensure that the mechanical stamina of the solidified body of the concrete slurry is continuously improved, as well as lastly it ends up being a cement rock with a specific mechanical toughness.
In the cement slurry, the diffusion system of polycarboxylic ether based superplasticizers is normally taken into consideration to be the primary role of steric hindrance as well as the second duty of electrostatic repulsion. Furthermore, the complexation of calcium ions and also the lubrication of hydration film additionally play a role. important duty.
1. Steric limitation:
The hydration procedure of concrete will make the cement particles attract each other, resulting in a flocculation structure.
During the formation of the flocculation framework, the cement particles will envelop a part of the water molecules, as well as the encapsulated water accounts for about 10% -30% of the total mixing water (this might be the reason the water minimizing representative has a water decreasing price limitation). Due to the fact that it is wrapped by concrete molecules, it can not take part in the totally free circulation and also lubrication in between concrete particles, therefore impacting the fluidness of concrete mixes. When the polycarboxylate concrete admixture molecules very first entered into contact with the cement bits, the negatively charged major chain in the polycarboxylate concrete admixture particles can be adsorbed externally of the favorably charged cement bits, that is, an "anchoring" phenomenon takes place, while the polycarboxylate superplasticizer The long side chain in the molecule is extended in the fluid phase of the concrete slurry to form an adsorption layer with a certain density, and can form a three-dimensional and went across lengthy side chain with other polycarboxylic acid superplasticizer molecules expanding in the liquid phase of the cement slurry at the very same time. Conformation. When the concrete particles approach each various other, the adsorption layer overlaps, as well as the larger the overlapping range, the higher the repulsion in between the cement fragments, consequently boosting the dispersibility of the cement bits. Ruin the flocculation framework between cement particles. The launch of the water trapped by cement flocculation can likewise be understood as the water reducing representative molecules improve the lubricating usage rate of the water particles to the concrete particles, as well as do not enhance the water or lower the variety of water molecules out of thin air.
2. The theory of electrostatic repulsion:
Polycarboxylic acid superplasticizer molecules consist of anionic teams (COO2-), and also in the very early hydration procedure of concrete, the surface of concrete fragments consists of favorable costs (Ca2+), as a result, anionic Polycarboxylic acid superplasticizer particles adsorb to positively charged concrete fragments surface area. Make the concrete fragments right into a "hedgehog" with unfavorable charge. Since the concrete fragments with the very same adverse charge ward off each various other (electrostatic repulsion), the dispersibility in between the cement particles is enhanced. At the very same time, the negatively billed carboxyl teams as well as positively charged calcium ions in the concrete paste kind unpredictable facilities. After the calcium ions liquified in the concrete system are caught, the calcium ion focus decreases significantly, decreasing the calcium ions in the system. It can lower the development of gel fragments and also thus slow down the hydration price of concrete, inhibit the hydration of concrete, and also enhance the diffusion performance of concrete bits. The greater the content of carboxylate ions in the Polycarboxylic acid superplasticizer, that is, the greater the anion fee thickness, the higher the dispersion performance of cement fragments (acid-ether proportion). The reduction of calcium ion concentration can prevent the preliminary hydration of cement. With the constant development of hydration, the complicated will disintegrate by itself, so Polycarboxylic acid superplasticizer has a particular retarding impact without impacting the strength of concrete.
The branched chain of the polycarboxylic acid superplasticizer molecule has hydrophilic teams. These groups develop a water movie externally of the cement bits by integrating with water particles, which reduces the surface area power of the cement particles. Slips conveniently. The combined result of the above lead to splitting up between the cement bits. The macroscopic performance is that the concrete mix has better fluidness.
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