Water reduction mechanism of polycarboxylic ether based superplasticizers
Today'' s concrete superplasticizers are generally prepared by intensifying various products such as polycarboxylate water-reducing mommy liquor and polycarboxylate slump-preserving mother alcohol plus retarders, air-entraining agents, as well as defoaming agents. Among them, the duty of water-reducing mom service in superplasticizer is irreplaceable. Perhaps the amount of mother option will alter because of the adjustment of concrete material, however I have never heard that water-reducing mommy solution is not contributed to superplasticizer since the sand is too good.
The water-reducing mom liquid is utilized as the absolute primary material in the water-reducing representative, as well as its function is to minimize the concrete water-cement proportion (indirectly raise the stamina of the concrete), and also at the same time ensure the fluidness and also workability of the concrete mix, and also make certain the toughness of the concrete. At the very same time, it likewise promotes the job of the building and construction unit.
We know that in addition to cement and water in concrete, the result of the remaining products on the superplasticizer admixture particles is basically adsorption (waste), so the water minimizing representative is mainly targeted at cement. So initially, let’& rsquo; s discover the hydration procedure of concrete.
The hydration process of basic portland cement is divided right into three stages:
( 1) Dissolution stage: When the cement is in contact with water, the surface area of the particles starts to moisturize, as well as a percentage of hydration items are generated, which are quickly dissolved in water. The subjected new surface allows hydration to proceed up until a saturated service of hydration products is formed.
( 2) Gelation phase: Because of the saturation of the option, the item that continues to be moistened can no longer be dissolved, but is directly precipitated as colloidal particles. With the boost of hydration items, the hydration accumulations, and the concrete slurry progressively sheds its plasticity, leading to a coagulation sensation.
( 3) Crystallization phase: The colloid made up of tiny crystals is not stable, and can gradually recrystallize to form macroscopic crystals, to make sure that the mechanical stamina of the solidified body of the concrete slurry is constantly enhanced, and also ultimately it becomes a concrete rock with a particular mechanical toughness.
In the concrete slurry, the dispersion system of polycarboxylic ether based superplasticizers is generally taken into consideration to be the primary duty of steric limitation and also the secondary duty of electrostatic repulsion. In addition, the complexation of calcium ions and the lubrication of hydration movie also contribute. crucial duty.
1. Steric barrier:
The hydration procedure of concrete will make the cement particles attract each other, causing a flocculation structure.
During the development of the flocculation framework, the concrete molecules will encapsulate a component of the water particles, and also the encapsulated water represent about 10% -30% of the complete mixing water (this may be the reason why the water minimizing agent has a water minimizing price limit). Since it is covered by cement molecules, it can not take part in the free flow and also lubrication in between cement particles, hence influencing the fluidity of concrete mixes. When the polycarboxylate concrete admixture particles very first come into contact with the concrete particles, the negatively charged major chain in the polycarboxylate concrete admixture molecules can be adsorbed on the surface of the positively billed cement bits, that is, an "anchoring" phenomenon happens, while the polycarboxylate superplasticizer The long side chain in the particle is prolonged in the fluid phase of the concrete slurry to develop an adsorption layer with a certain density, and can form a three-dimensional and also went across long side chain with various other polycarboxylic acid superplasticizer molecules expanding in the fluid stage of the concrete slurry at the exact same time. Conformation. When the concrete bits move toward each other, the adsorption layer overlaps, as well as the larger the overlapping range, the greater the repulsion between the concrete fragments, thus enhancing the dispersibility of the concrete bits. Ruin the flocculation framework in between cement molecules. The release of the water entraped by concrete flocculation can additionally be understood as the water minimizing representative particles enhance the lubricating use rate of the water particles to the cement particles, and do not increase the water or lower the variety of water molecules out of slim air.
2. The theory of electrostatic repulsion:
Polycarboxylic acid superplasticizer molecules consist of anionic teams (COO2-), as well as in the very early hydration process of cement, the surface of cement particles contains favorable charges (Ca2+), as a result, anionic Polycarboxylic acid superplasticizer molecules adsorb to positively charged concrete fragments surface area. Make the concrete fragments right into a "hedgehog" with adverse cost. Due to the fact that the cement fragments with the very same adverse cost push back each other (electrostatic repulsion), the dispersibility between the concrete fragments is enhanced. At the exact same time, the negatively charged carboxyl teams as well as favorably billed calcium ions in the cement paste kind unsteady complicateds. After the calcium ions dissolved in the concrete system are captured, the calcium ion concentration reduces significantly, reducing the calcium ions in the system. It can decrease the development of gel particles and therefore decrease the hydration rate of concrete, inhibit the hydration of concrete, and also enhance the diffusion efficiency of concrete fragments. The greater the material of carboxylate ions in the Polycarboxylic acid superplasticizer, that is, the greater the anion charge thickness, the better the diffusion performance of concrete fragments (acid-ether ratio). The reduction of calcium ion concentration can hinder the first hydration of cement. With the continual development of hydration, the complex will certainly disintegrate by itself, so Polycarboxylic acid superplasticizer has a specific retarding result without impacting the strength of concrete.
The branched chain of the polycarboxylic acid superplasticizer molecule has hydrophilic teams. These teams create a water film on the surface of the concrete bits by combining with water particles, which lowers the surface energy of the concrete bits. Slides conveniently. The consolidated result of the above lead to separation between the concrete fragments. The macroscopic efficiency is that the concrete blend has better fluidness.
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