Water reduction mechanism of polycarboxylic ether based superplasticizers
Today'' s concrete superplasticizers are basically prepared by compounding different materials such as polycarboxylate water-reducing mommy liquor and polycarboxylate slump-preserving mommy alcohol plus retarders, air-entraining representatives, and also defoaming representatives. Among them, the role of water-reducing mom remedy in superplasticizer is irreplaceable. Perhaps the quantity of mom option will certainly alter due to the modification of concrete product, however I have never ever heard that water-reducing mother service is not included in superplasticizer because the sand is also good.
The water-reducing mommy fluid is utilized as the outright major product in the water-reducing representative, and its function is to lower the concrete water-cement ratio (indirectly enhance the stamina of the concrete), and also at the very same time guarantee the fluidness and also workability of the concrete blend, and also guarantee the stamina of the concrete. At the same time, it additionally facilitates the job of the building and construction unit.
We know that in addition to cement and also water in concrete, the impact of the remaining products on the superplasticizer admixture particles is generally adsorption (waste), so the water reducing representative is generally targeted at cement. So initially, let’& rsquo; s learn about the hydration procedure of cement.
The hydration procedure of general portland concrete is divided into 3 stages:
( 1) Dissolution stage: When the cement is in contact with water, the surface of the fragments begins to moisten, and a small amount of hydration items are produced, which are immediately liquified in water. The revealed new surface area enables hydration to proceed up until a saturated remedy of hydration products is developed.
( 2) Gelation stage: Because of the saturation of the solution, the product that continues to be moisturized can no more be dissolved, but is straight sped up as colloidal bits. With the boost of hydration products, the hydration aggregates, as well as the concrete slurry gradually loses its plasticity, resulting in a coagulation sensation.
( 3) Condensation stage: The colloid made up of microscopic crystals is not steady, and can slowly recrystallize to develop macroscopic crystals, to ensure that the mechanical toughness of the hardened body of the cement slurry is constantly enhanced, and also finally it becomes a cement stone with a particular mechanical strength.
In the concrete slurry, the diffusion device of polycarboxylic ether based superplasticizers is usually taken into consideration to be the major role of steric barrier and the secondary duty of electrostatic repulsion. Furthermore, the complexation of calcium ions as well as the lubrication of hydration movie likewise play a role. essential role.
1. Steric limitation:
The hydration process of cement will certainly make the concrete molecules bring in each various other, leading to a flocculation structure.
Throughout the development of the flocculation framework, the concrete particles will certainly envelop a component of the water molecules, and the encapsulated water represent around 10% -30% of the complete mixing water (this may be the reason why the water minimizing agent has a water minimizing price limit). Because it is wrapped by concrete particles, it can not join the totally free flow as well as lubrication in between cement molecules, thus impacting the fluidness of concrete combinations. When the polycarboxylate concrete admixture molecules very first come into contact with the concrete fragments, the adversely charged primary chain in the polycarboxylate concrete admixture molecules can be adsorbed externally of the favorably charged concrete fragments, that is, an "anchoring" phenomenon occurs, while the polycarboxylate superplasticizer The lengthy side chain in the molecule is extended in the liquid stage of the concrete slurry to develop an adsorption layer with a specific thickness, as well as can form a three-dimensional and also went across lengthy side chain with various other polycarboxylic acid superplasticizer particles expanding in the liquid stage of the cement slurry at the exact same time. Conformation. When the concrete bits move toward each various other, the adsorption layer overlaps, and the bigger the overlapping variety, the greater the repulsion in between the cement bits, thus improving the dispersibility of the concrete fragments. Damage the flocculation framework between concrete molecules. The release of the water caught by cement flocculation can also be comprehended as the water lowering representative molecules boost the lubricating utilization rate of the water particles to the concrete molecules, and do not enhance the water or reduce the variety of water molecules out of thin air.
2. The concept of electrostatic repulsion:
Polycarboxylic acid superplasticizer molecules contain anionic teams (COO2-), as well as in the early hydration procedure of cement, the surface of concrete bits consists of favorable costs (Ca2+), for that reason, anionic Polycarboxylic acid superplasticizer particles adsorb to favorably billed concrete bits surface. Make the concrete fragments right into a "hedgehog" with unfavorable charge. Because the concrete fragments with the very same unfavorable charge push back each various other (electrostatic repulsion), the dispersibility in between the cement bits is enhanced. At the exact same time, the adversely billed carboxyl groups and positively charged calcium ions in the cement paste kind unsteady facilities. After the calcium ions liquified in the concrete system are captured, the calcium ion concentration lowers dramatically, lowering the calcium ions in the system. It can minimize the development of gel bits and also therefore decrease the hydration price of concrete, hinder the hydration of concrete, and also enhance the diffusion efficiency of cement bits. The higher the content of carboxylate ions in the Polycarboxylic acid superplasticizer, that is, the greater the anion charge thickness, the better the dispersion performance of cement particles (acid-ether ratio). The decline of calcium ion concentration can inhibit the preliminary hydration of concrete. With the continuous development of hydration, the facility will disintegrate on its own, so Polycarboxylic acid superplasticizer has a specific retarding impact without affecting the stamina 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 bits by combining with water particles, which minimizes the surface power of the cement fragments. Slides quickly. The consolidated result of the above results in separation in between the cement bits. The macroscopic efficiency is that the concrete mix has better fluidity.
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