With the development of the concrete industry, the use of various raw materials, cement and other mixed products in different parts of the construction, structural components, and construction methods have become increasingly demanding. The results show that the setting time will prolong with the increase in the amount of retarder. At the same time, different types of additions have great differences in the impact on the setting time. As the temperature increases, the setting time will shorten significantly. The setting time of the admixture can be directly controlled. What are the functions of retarders that affect the progress of construction and other issues? As an industry professional, you must understand clearly. Ultra-early strength and ultra-retarded setting are both important research topics in concrete. Rapid determination of whether admixtures exceed the standard can better serve the industry and provide reference for industrial production.
The early hydration process of Portland cement is divided into four stages, namely: the initial reaction period. The hydration reaction occurs immediately after the cement is mixed with water. C3S generates hydrated calcium silicate and releases Ca. (OH)2;C3A mineral dissolves in water and reacts quickly with dissolved gypsum to precipitate ettringite, which adheres to the surface of cement particles to form a thin film coating; during the rest period, the thin film coating formed during the initial reaction period hinders the interaction between cement and With the further hydration of water, the plasticity of the cement slurry remains basically unchanged; during the setting period, about 6 to 8 hours after the cement is mixed with water, the cement will set.
When the film coating on the surface of the cement particles breaks, hydration continues, resulting in the setting period; the hardening period, after the setting period, enters the hardening period. At this time, the hydration rate of the cement is slow, but Still continuing, hydrates continue to fill the capillary pores, and the strength continues to increase.
What are the functions of coagulant? It is a small admixture that prolongs the setting time of concrete. In order to prevent the cement product from prematurely solidifying and losing its plasticity when the temperature is high or the transportation distance is long, which will affect the pouring quality, and to prevent quality accidents such as cold joints, it is often added. Commonly used organic retarder: wood sulfonates and their derivatives, hydroxycarboxylic acids and their salts, sugars and their derivatives, organic phosphoric acid and its salts, acrylic copolymers, etc.; inorganic include: phosphates , borax, zinc salt, etc.
When producing building gypsum products, chemicals such as citric acid, trisodium citrate, tartaric acid, boric acid, and phosphates can be directly used as retarder according to the needs of the production process. This kind of main function is better in retarding effect. When used, it can generally be pre-dissolved in water according to a certain proportion, and then the gypsum powder can be mixed with an aqueous solution containing a retarder. However, these will affect the strength of gypsum, and the amount should be reduced as much as possible when using it.
Admixtures that can introduce a large number of evenly distributed, stable and closed micro-bubbles during the mixing of concrete are called air-entraining agents. Air-entraining agents are more suitable for applications where the strength requirements are not too high and the water-cement ratio is large, such as hydraulic large-volume concrete; concrete with high durability requirements such as frost resistance also needs to be mixed with air-entraining agents
In summary Description: The function of a retarder is to delay the setting time of cement products. Qingdao Dingchang New Materials Co., Ltd. has developed a new type of retarder that can replace sodium gluconate in equal or excessive amounts. The price is favorable and it is much easier than sodium glucose. By adjusting the setting time of concrete, the dosage can be reasonably adjusted according to the ground material and temperature in each region. It can reduce the slump loss over time and adjust the workability. At the same time, it has a certain auxiliary water-reducing effect and is suitable for various types of water-reducing mother liquors.
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