It is well known that retarder can help retard cement to a certain extent. As a professional, you must know what kind of theory it is?
The theory of retarder's retarding effect on cement can be It can be summarized into the following four viewpoints.
(1) Adsorption theory:
Since the surface of cement particles has strong adsorption energy, after the retarder is adsorbed, a layer is formed on the surface of the cement particles to inhibit mud hydration. The retarder film acts on the cement hydration process and hinders the cement hydration process.
(2) Complex salt theory:
Certain retarder is a complex forming agent, which can form a complex salt with Ca2+ in the liquid phase to form a complex salt on the surface of cement particles. A thick and amorphous complex film, which delays cement hydration. As the alkalinity in the liquid phase increases, the complexed U film will be destroyed and hydration will continue normally.
(3) Precipitation theory:
This theory 4 is that organic or inorganic substances form a film of insoluble substances on the surface of cement particles, preventing further contact between cement particles and ice. , thus the hydration reaction process of cement is delayed. First, it inhibits the water velocity of the aluminate component, and also inhibits the hydration of the silicate component, slowing down the formation process of C-S-H and Ca(OH)2.
(4) Nucleation inhibition theory:
It is believed that the retarder is adsorbed on the nucleus of Ca(OH)2, inhibiting its continued growth and precipitation of crystals. When it reaches a certain Before supersaturation is reached, the growth of Ca(OH)2 will cease.
What are the main functions of adding retarder to concrete?
Retarder affects the initial setting time of concrete but does not affect the strength of concrete. The retarding time of concrete in some underwater operations can even reach more than 60 hours. At this time, it is difficult for common retarder to meet this requirement. Drawing on advanced foreign experience, Zouping County Delin New Materials Technology Co., Ltd. has launched a variety of retardant additives compounded with polyvalent organic phosphonic acids (salts) and polyhydroxy organic acid salts, which can effectively solve some problems. The products have mud resistance and slump protection. Performance is better than common additives.
There are many types of retarder, and most of them have the same mechanism. For example, citric acid is a typical retarder. When the retarder is added to fresh concrete, the retarder can effectively slow down the cement. The speed at which the four active mineral components (tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium aluminoferrite) react with water can achieve the purpose of low-heat retarding of concrete.
In addition, the concrete specifications stipulate that early strength agents and retarders can only improve the early strength and heat of hydration of concrete but cannot affect the final strength. Therefore, the retarder will not affect the later strength</p
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