Water reduction mechanism of polycarboxylic ether based superplasticizers
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Today'' s concrete superplasticizers are essentially prepared by compounding various products such as polycarboxylate water-reducing mommy liquor as well as polycarboxylate slump-preserving mommy alcohol plus retarders, air-entraining representatives, as well as defoaming agents. Among them, the role of water-reducing mother remedy in superplasticizer is irreplaceable. Perhaps the amount of mom solution will transform due to the adjustment of concrete product, yet I have never heard that water-reducing mother service is not included in superplasticizer due to the fact that the sand is also great.
The water-reducing mommy liquid is used as the outright major material in the water-reducing representative, as well as its function is to minimize the concrete water-cement ratio (indirectly boost the stamina of the concrete), and at the same time ensure the fluidity and workability of the concrete mix, and also ensure the stamina of the concrete. At the very same time, it likewise facilitates the job of the building and construction device.
We understand that along with seal and water in concrete, the effect of the remaining products on the superplasticizer admixture particles is essentially adsorption (waste), so the water decreasing representative is mostly targeted at cement. So initially, let’& rsquo; s learn about the hydration process of cement.
The hydration procedure of basic rose city concrete is separated right into 3 phases:
( 1) Dissolution phase: When the cement touches with water, the surface area of the fragments starts to hydrate, and also a percentage of hydration items are created, which are quickly liquified in water. The subjected new surface area allows hydration to proceed up until a saturated option of hydration items is created.
( 2) Gelation phase: Because of the saturation of the remedy, the product that remains to be hydrated can no more be liquified, yet is directly precipitated as colloidal bits. With the boost of hydration products, the hydration accumulations, as well as the cement slurry slowly loses its plasticity, resulting in a coagulation phenomenon.
( 3) Crystallization phase: The colloid made up of microscopic crystals is not steady, and can progressively recrystallize to form macroscopic crystals, to make sure that the mechanical strength of the hard body of the concrete slurry is constantly enhanced, and ultimately it becomes a concrete rock with a specific mechanical strength.
In the cement slurry, the dispersion mechanism of polycarboxylic ether based superplasticizers is generally considered to be the main duty of steric barrier as well as the second function of electrostatic repulsion. Additionally, the complexation of calcium ions and the lubrication of hydration movie additionally play a role. important duty.
1. Steric limitation:
The hydration process of concrete will make the concrete particles draw in each other, resulting in a flocculation structure.
Throughout the development of the flocculation structure, the cement particles will encapsulate a part of the water molecules, and the encapsulated water make up around 10% -30% of the overall mixing water (this may be the reason why the water lowering agent has a water reducing price restriction). Because it is covered by concrete particles, it can not join the totally free circulation and also lubrication in between concrete particles, thus influencing the fluidness of concrete mixtures. When the polycarboxylate concrete admixture molecules first entered contact with the cement fragments, the negatively charged primary chain in the polycarboxylate concrete admixture particles can be adsorbed externally of the favorably charged cement particles, that is, an "anchoring" phenomenon happens, while the polycarboxylate superplasticizer The long side chain in the molecule is prolonged in the fluid phase of the concrete slurry to develop an adsorption layer with a specific thickness, as well as can create a three-dimensional and also crossed long side chain with various other polycarboxylic acid superplasticizer molecules expanding in the liquid phase of the concrete slurry at the same time. Conformation. When the cement bits approach each other, the adsorption layer overlaps, and also the bigger the overlapping range, the higher the repulsion between the cement fragments, thereby boosting the dispersibility of the concrete particles. Ruin the flocculation framework in between concrete particles. The release of the water trapped by concrete flocculation can also be comprehended as the water decreasing agent molecules improve the lubricating application rate of the water molecules to the concrete molecules, as well as do not increase the water or minimize the variety of water particles out of slim air.
2. The concept of electrostatic repulsion:
Polycarboxylic acid superplasticizer molecules have anionic groups (COO2-), and in the early hydration procedure of cement, the surface area of concrete bits consists of positive fees (Ca2+), consequently, anionic Polycarboxylic acid superplasticizer particles adsorb to positively billed concrete bits surface area. Make the cement bits right into a "hedgehog" with unfavorable cost. Because the cement fragments with the exact same negative charge push back each other (electrostatic repulsion), the dispersibility in between the cement particles is enhanced. At the very same time, the adversely billed carboxyl teams as well as favorably billed calcium ions in the concrete paste kind unstable complicateds. After the calcium ions liquified in the concrete system are caught, the calcium ion focus decreases dramatically, minimizing the calcium ions in the system. It can decrease the development of gel bits and thus reduce the hydration rate of concrete, prevent the hydration of cement, and boost the diffusion efficiency of cement fragments. The better the material of carboxylate ions in the Polycarboxylic acid superplasticizer, that is, the better the anion charge thickness, the better the diffusion efficiency of concrete fragments (acid-ether ratio). The decline of calcium ion focus can hinder the initial hydration of cement. With the continuous progress of hydration, the facility will disintegrate by itself, so Polycarboxylic acid superplasticizer has a particular retarding result without affecting the toughness of concrete.
The branched chain of the polycarboxylic acid superplasticizer molecule has hydrophilic groups. These teams create a water movie on the surface of the concrete particles by integrating with water molecules, which decreases the surface area energy of the concrete fragments. Slips easily. The mixed impact of the above cause separation in between the concrete particles. The macroscopic efficiency is that the concrete combination has far better fluidness.
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