Water reduction mechanism of polycarboxylic ether based superplasticizers
Today'' s concrete superplasticizers are basically prepared by intensifying different products such as polycarboxylate water-reducing mommy liquor as well as polycarboxylate slump-preserving mom alcohol plus retarders, air-entraining representatives, as well as defoaming representatives. Amongst them, the duty of water-reducing mommy option in superplasticizer is irreplaceable. Maybe the quantity of mom service will certainly transform due to the modification of concrete product, but I have never heard that water-reducing mom remedy is not contributed to superplasticizer because the sand is too great.
The water-reducing mother fluid is made use of as the absolute primary material in the water-reducing agent, as well as its function is to reduce the concrete water-cement ratio (indirectly enhance the stamina of the concrete), and at the same time make certain the fluidity and workability of the concrete blend, as well as guarantee the toughness of the concrete. At the same time, it also facilitates the job of the building and construction unit.
We understand that along with cement and water in concrete, the result of the continuing to be products on the superplasticizer admixture particles is basically adsorption (waste), so the water lowering agent is primarily aimed at concrete. So first, let’& rsquo; s learn about the hydration process of cement.
The hydration process of basic portland cement is separated into three phases:
( 1) Dissolution stage: When the concrete is in contact with water, the surface of the fragments begins to moisturize, as well as a small amount of hydration products are generated, which are immediately dissolved in water. The revealed new surface area allows hydration to proceed till a saturated service of hydration items is developed.
( 2) Gelation stage: As a result of the saturation of the solution, the item that continues to be hydrated can no longer be dissolved, however is directly precipitated as colloidal fragments. With the increase of hydration items, the hydration aggregates, and also the cement slurry progressively sheds its plasticity, causing a coagulation sensation.
( 3) Condensation phase: The colloid composed of microscopic crystals is not steady, and also can gradually recrystallize to create macroscopic crystals, to ensure that the mechanical toughness of the hardened body of the cement slurry is continually boosted, and ultimately it comes to be 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 function of steric limitation and also the additional duty of electrostatic repulsion. On top of that, the complexation of calcium ions and also the lubrication of hydration film additionally contribute. essential function.
1. Steric obstacle:
The hydration procedure of cement will certainly make the cement particles bring in each other, causing a flocculation structure.
During the development of the flocculation framework, the concrete particles will envelop a component of the water molecules, as well as the encapsulated water accounts for about 10% -30% of the complete mixing water (this may be the reason the water reducing representative has a water reducing price limitation). Because it is covered by cement molecules, it can not take part in the complimentary flow as well as lubrication in between concrete molecules, thus affecting the fluidity of concrete combinations. When the polycarboxylate concrete admixture particles initial come into call with the cement particles, the adversely charged main chain in the polycarboxylate concrete admixture molecules can be adsorbed on the surface of the favorably billed concrete fragments, that is, an "anchoring" sensation happens, while the polycarboxylate superplasticizer The long side chain in the molecule is expanded in the fluid stage of the concrete slurry to form an adsorption layer with a particular thickness, as well as can create a three-dimensional and also went across lengthy side chain with various other polycarboxylic acid superplasticizer particles expanding in the liquid stage of the concrete slurry at the same time. Conformation. When the cement fragments approach each various other, the adsorption layer overlaps, and also the larger the overlapping variety, the better the repulsion in between the concrete bits, thereby improving the dispersibility of the concrete particles. Destroy the flocculation framework between cement molecules. The release of the water entraped by cement flocculation can likewise be comprehended as the water reducing agent molecules enhance the lubricating utilization rate of the water particles to the cement molecules, and also do not boost the water or reduce the variety of water particles out of slim air.
2. The theory of electrostatic repulsion:
Polycarboxylic acid superplasticizer particles include anionic teams (COO2-), and also in the early hydration process of concrete, the surface area of cement fragments has positive charges (Ca2+), consequently, anionic Polycarboxylic acid superplasticizer particles adsorb to positively billed cement particles surface area. Make the concrete bits right into a "hedgehog" with negative charge. Due to the fact that the cement fragments with the same negative fee ward off each various other (electrostatic repulsion), the dispersibility in between the concrete fragments is improved. At the very same time, the negatively billed carboxyl teams and positively billed calcium ions in the concrete paste kind unsteady complexes. After the calcium ions dissolved in the concrete system are caught, the calcium ion focus decreases dramatically, reducing the calcium ions in the system. It can decrease the development of gel bits as well as therefore slow down the hydration rate of cement, inhibit the hydration of concrete, as well as boost the diffusion performance of concrete particles. The higher the material of carboxylate ions in the Polycarboxylic acid superplasticizer, that is, the greater the anion fee thickness, the higher the dispersion performance of concrete bits (acid-ether proportion). The decline of calcium ion concentration can inhibit the initial hydration of concrete. With the constant progress of hydration, the complicated will decompose on its own, so Polycarboxylic acid superplasticizer has a particular retarding impact without affecting the stamina of concrete.
The branched chain of the polycarboxylic acid superplasticizer molecule has hydrophilic teams. These groups form a water film on the surface of the concrete bits by integrating with water particles, which decreases the surface power of the concrete particles. Slips conveniently. The combined impact of the above cause separation in between the concrete particles. The macroscopic performance is that the concrete mixture has much better fluidness.
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