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Calcium Aluminate Cement provides sufficient demolding strength for castables in a short time through hydration behavior when encountering water and is a commonly used hydrating bonding agent for refractory castables.
The chemical composition of calcium aluminate cement mainly consists of alumina(Al2O3) and calcium oxide (CaO). The main minerals in calcium aluminate cement include calcium aluminate (CA), calcium aluminoferrite (CA2), and dodecacalcium hepta-aluminate (C12A7), and it often also contains gehlenite (C2AS).
Calcium Aluminate Cement hydration directly affects the workability of the castables, such as flowability, working time, and demolding strength. The hydration of calcium aluminate cement mainly includes three stages: dissolution, nucleation, and precipitation. Initially, the cement dissolves in water, hydrolyzing the particle surfaces and releasing Ca2+ and Al(OH)4- ions. When the solution reaches a certain concentration, a small amount of hydration product forms. The hydration products nucleate, gaining crystal size and quantity. After nucleation ends, the hydration products precipitate out of the solution.
The hydration speed of calcium aluminate cement is very fast because the hydration of calcium aluminate cement and the dissolution of CA occur simultaneously. The hydrating minerals do not form a tight structure on the surface of the unhydrated minerals, which would hinder further hydration reactions. The hydration of calcium aluminate cement and the crystallization status of the hydration products mainly depend oncalcium aluminate cement's primary phases (CA, CA2, and C12A7). The types of hydration products generated depend on temperature and time.
By studying the cement activity of calcium aluminate cement with different particle size distributions, it was found that the precipitation period of the hydration of finer calcium aluminate cement particles is delayed. The study also shows that the phases of calcium aluminate cement do not hydrate completely.
By researching the hydration behavior ofcalcium aluminate cement of different particle sizes under different curing temperatures, the results show that at 10°C and 20°C, as the particle size of calcium aluminate cement decreases, the amount of hydration product CAH10 generated decreases, and the degree of hydration lowers.
Moreover, the dense structure of hydration products CAH10 generated by smaller particles hinders the penetration of free water, delaying the hydration of calcium aluminate cement. At 30°C and 40°C, as the particle size ofcalcium aluminate cement decreases, the main hydration products formed are C2AH8 and C3AH6; the larger porosity in the structure of the hydration products generated by finer particles facilitates the penetration of free water, accelerating the hydration of calcium aluminate cement.
Calcium Aluminate Cement is known for its early strength, high refractoriness, and resistance to erosion and abrasion. It has become an essential high-performance bonding agent for refractory castables needed in fields such as defense, metallurgy, chemicals, and building materials. Initially used mainly for military engineering, calcium aluminate cement is now widely applied in general industries.
For example, in leak-proof treatments in construction engineering, adding an appropriate amount of gypsum to calcium aluminate cement can produce calcium aluminate expansion agents and gypsum expansion cement. In coal mine roadway support, sealing, and blocking,calcium aluminate cement can be made into quick-setting, high-water-content filling materials.
Additionally,calcium aluminate cement also has special uses such as emergency repairs, sulfate corrosion resistance, and construction under cold conditions. It can be used to formulate unshaped refractory materials, heat-resistant concrete, expansive cement, and prefabricated concrete products.
