Many chemical industry practitioners have worked for several years without knowing what the concrete retarder formula is. According to senior personnel, the retarder forms an unstable complex between the alkaline medium of the cement hydration product and free Ca2+. It reduces the concentration of Ca2+ in the liquid phase in the early stage of hydration and delays the crystallization of CH. It can also be adsorbed on the surface of cement hydration particles and form hydrogen bonds with the oxygen ions in the "silicon-rich layer". A protective film is formed on the surface of the particles to inhibit the hydration reaction, thereby producing a retarding effect. As the hydration process proceeds, this unstable complex will decompose itself, and hydration will continue normally without affecting the later hydration of the cement. A large number of tests have proven that the addition of retarder can improve the dispersion of water reducing agent and prolong the setting time of concrete, so it is widely used in industry.
Concrete retarder formulas are not unique, including concrete super retarder, alkali slag concrete retarder, oil well cement retarder, cement concrete composite super retarder, etc. Now we provide you with several retarder formulas detected by microspectroscopy:
Concrete ultra-retarder formula:
Maltodextrin 73%
Citric acid 13%
Sodium pyrophosphate 14%
Oil well cement retarder formula:
20% multi-component copolymer solution 88%
50% hydroxyethylene diphosphonic acid solution 12%
The polycopolymer solution is composed of 2.5% itaconic acid, 4% acrylic acid, and 4% potassium persulfate A solution of 13.5% 2-acrylamido-2-methylpropanesulfonic acid and 76% deionized water.
Cement retarder formula:
Phosphogypsum: 55%
Fly ash: 40%
Calcium material: 4 %
Activator: 1%
Retarder is classified according to structure:
1. Sugars: calcium saccharide, gluconate, etc.
2. Citric acid, tartaric acid and their salts
3. Zinc salts, phosphates
4. Lignosulfonate
In commercial concrete The purpose of adding a retarder is to prolong the hydration and hardening time of cement so that fresh concrete can maintain its plasticity for a longer period of time, thus adjusting the setting time of fresh concrete.
Main properties of retarder
1. Retarder is a commonly used admixture used to extend the setting time of concrete. In summer construction, adding an appropriate amount of retarder can Make fresh concrete maintain good plasticity for a long time.
2. Retarder is a surfactant that only plays a physical adsorption and dispersion role in concrete, and does not directly participate in the cement hydration reaction to generate new substances. Therefore, it has a certain effect on concrete within a certain dosage range. The final strength has no direct impact, but because it delays the setting time of concrete, it affects the early strength of concrete to a certain extent. However, the later strength can generally catch up with or exceed the concrete without retarder.
Today, with the rapid development of commercial concrete, retarder plays a very important role. As people's understanding of concrete retarder continues to deepen, the application of retarder will become more and more extensive, especially when producing large-volume concrete that needs to reduce the instantaneous hydration heat of cement and delay the peak hydration peak of cement. Coagulant is indispensable.
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