The properties and varieties of concrete additives for refractories, especially refractory castables, ramming materials, plastics and other amorphous refractories are different. The role of an concrete additive is also different due to the difference of the amount of concrete additive, the type of binder used, the ingredients and so on. In the production process of amorphous refractories, the concrete additives mainly used can be divided into the following twelve categories according to their uses:
Accelerator can shorten the setting and hardening time of amorphous refractories. The action mechanism of coagulant accelerator is complicated, which varies with the properties of binder and accelerator used. Different binders should use different accelerators of different properties. The accelerators used in calcium aluminate cement binder are mostly basic compounds: NaOH, KOH, Ca (OH) 2, Na2CO3, Na2SiO3, etc.; phosphoric acid and aluminum dihydrogen phosphate binder are used together with activated aluminum hydroxide, talc, magnesium oxide, calcium aluminate cement, etc.; sodium fluorosilicate, aluminum phosphate, sodium phosphate, lime, dicalcium silicate, Glyoxal and so on.
Retarders can delay the setting and hardening time of amorphous refractories, and the action mechanism of retarders varies with the properties of binders and retarders used. Retarders are mainly used in amorphous refractories bonded with calcium aluminate cement containing fast hardening minerals. The commonly used retarders are low concentration of NaCl, citric acid, tartaric acid, ethylene glycol, glycerol, starch, phosphate, lignosulfonate and so on.
7. Delayed coagulant
The delayed accelerator can cause the binder contained in amorphous refractories to solidify and harden after a certain period of time. For the castable with ultra-fine silica powder as the main binder, calcium aluminate cement can be used as the delayed accelerator, because Al3+ and Ca2+ ions can be released slowly during the hydrolysis process of calcium aluminate cement. After adsorbed on the surface of silica particles, the particles will lose the electric property of coagulation, thus play the role of delayed coagulation.
8. Foaming agent, air entraining agent, and aerating agent
The foaming agent can reduce the surface tension of the liquid and produce a large number of uniform and stable foams. Foaming agents include rosin soap, resin saponin grease, aluminum petroleum sulfonate, hydrolyzed blood, etc., and air entraining agents include rosin heat polymer, Nonionic surfactant, alkylbenzene sulfonate and so on. In addition, there is a kind of aerating agent whose function is to produce bubbles by chemical and physical interaction between aerating agent and water after castable mixing and pouring. It is evenly distributed in the slurry. The commonly used aerating agent is aluminum powder. The aluminum powder is very active and will react with water to release hydrogen, and the escaped H2 gas forms bubbles in the castable. However, the addition of aluminum powder should be appropriate, otherwise the strength of amorphous refractories will be greatly reduced, or uneven connected pores will be caused. This kind of admixture can be used to prepare lightweight porous amorphous refractories.
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