Water reduction mechanism of polycarboxylic ether based superplasticizers
Today'' s concrete superplasticizers are generally prepared by intensifying numerous products such as polycarboxylate water-reducing mom liquor as well as polycarboxylate slump-preserving mommy liquor plus retarders, air-entraining agents, as well as defoaming agents. Amongst them, the function of water-reducing mommy remedy in superplasticizer is irreplaceable. Possibly the amount of mom option will transform as a result of the adjustment of concrete product, but I have never listened to that water-reducing mother remedy is not included in superplasticizer since the sand is too excellent.
The water-reducing mother fluid is used as the outright major material in the water-reducing representative, and also its function is to decrease the concrete water-cement ratio (indirectly raise the toughness of the concrete), and at the same time guarantee the fluidness and also workability of the concrete mix, and also guarantee the stamina of the concrete. At the same time, it likewise facilitates the job of the building and construction device.
We know that along with cement and water in concrete, the effect of the staying products on the superplasticizer admixture particles is primarily adsorption (waste), so the water decreasing representative is primarily targeted at cement. So first, let’& rsquo; s learn about the hydration procedure of concrete.
The hydration procedure of general rose city cement is separated right into three phases:
( 1) Dissolution stage: When the cement is in contact with water, the surface of the fragments begins to moisturize, as well as a percentage of hydration products are generated, which are right away dissolved in water. The subjected brand-new surface permits hydration to proceed until a saturated solution of hydration products is developed.
( 2) Gelation phase: As a result of the saturation of the solution, the product that remains to be moistened can no more be dissolved, but is straight precipitated as colloidal bits. With the rise of hydration products, the hydration aggregates, as well as the cement slurry gradually sheds its plasticity, resulting in a coagulation sensation.
( 3) Crystallization phase: The colloid composed of microscopic crystals is not secure, and can gradually recrystallize to create macroscopic crystals, to make sure that the mechanical stamina of the solidified body of the concrete slurry is constantly enhanced, and finally it becomes a concrete rock with a specific mechanical toughness.
In the concrete slurry, the dispersion system of polycarboxylic ether based superplasticizers is typically considered to be the main duty of steric obstacle and the secondary function of electrostatic repulsion. On top of that, the complexation of calcium ions as well as the lubrication of hydration film likewise play a role. crucial duty.
1. Steric hindrance:
The hydration procedure of cement will make the concrete molecules bring in each other, leading to a flocculation framework.
During the development of the flocculation framework, the concrete particles will certainly envelop a part of the water particles, and also the encapsulated water represent about 10% -30% of the overall mixing water (this might be the reason why the water decreasing representative has a water decreasing price restriction). Since it is wrapped by concrete particles, it can not join the totally free circulation as well as lubrication between concrete particles, hence affecting the fluidness of concrete mixtures. When the polycarboxylate concrete admixture particles first come into call with the cement particles, the negatively billed main chain in the polycarboxylate concrete admixture molecules can be adsorbed externally of the positively charged concrete fragments, that is, an "anchoring" sensation happens, while the polycarboxylate superplasticizer The long side chain in the molecule is prolonged in the fluid phase of the cement slurry to form an adsorption layer with a particular thickness, and can form a three-dimensional as well as crossed lengthy side chain with other polycarboxylic acid superplasticizer particles expanding in the fluid phase of the concrete slurry at the very same time. Conformation. When the concrete fragments move toward each various other, the adsorption layer overlaps, and also the bigger the overlapping array, the better the repulsion between the cement particles, therefore enhancing the dispersibility of the cement fragments. Damage the flocculation framework in between cement particles. The launch of the water trapped by cement flocculation can additionally be understood as the water reducing representative molecules boost the lubricating utilization rate of the water molecules to the cement particles, as well as do not boost the water or minimize the variety of water molecules out of slim air.
2. The concept of electrostatic repulsion:
Polycarboxylic acid superplasticizer particles have anionic groups (COO2-), and also in the very early hydration process of concrete, the surface area of concrete fragments consists of positive fees (Ca2+), as a result, anionic Polycarboxylic acid superplasticizer molecules adsorb to favorably charged concrete bits surface area. Make the cement particles into a "hedgehog" with negative charge. Due to the fact that the cement fragments with the exact same negative charge drive away each other (electrostatic repulsion), the dispersibility between the concrete fragments is boosted. At the very same time, the adversely charged carboxyl teams and also positively charged calcium ions in the cement paste type unpredictable complexes. After the calcium ions liquified in the concrete system are caught, the calcium ion concentration lowers significantly, lowering the calcium ions in the system. It can minimize the formation of gel particles and also thus reduce the hydration rate of cement, hinder the hydration of concrete, and improve the diffusion performance of cement fragments. The greater the content of carboxylate ions in the Polycarboxylic acid superplasticizer, that is, the better the anion charge density, the higher the diffusion efficiency of cement particles (acid-ether ratio). The decline of calcium ion concentration can prevent the initial hydration of cement. With the continuous progress of hydration, the complex will break down on its own, so Polycarboxylic acid superplasticizer has a specific retarding effect without impacting the strength of concrete.
The branched chain of the polycarboxylic acid superplasticizer molecule has hydrophilic teams. These groups form a water movie externally of the concrete fragments by integrating with water particles, which lowers the surface area power of the cement fragments. Slides quickly. The mixed effect of the above results in splitting up between the cement fragments. The macroscopic efficiency is that the concrete mix has better fluidness.
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