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1. Hardening mechanism of calcium aluminate cement

Calcium aluminate cement is the cement with calcium monoaluminate or calcium dialuminate as the main mineral component. It is made by mixing natural bauxite or industrial alumina and calcium carbonate (limestone) in a certain proportion and then calcining or electric melting. It is also made by melting iron bauxite and limestone.

The setting and hardening speed of calcium aluminate cement is also related to the curing temperature. As the curing temperature increases, the setting and hardening speed of CA2 minerals speeds up, while CA minerals are somewhat abnormal. Their speed of setting and hardening are faster at about 20°C, slower at 30°C, and faster at higher than 30°C. According to the phase change of calcium aluminate hydrate during heating, it is very important to choose proper curing conditions. Because the hydrate formed when calcium aluminate cement is hydrated varies with curing conditions.

In practical use, many calcium aluminate cement with different labels are often seen. The label is the strength that the cement reaches after curing for a certain period of time. For example, calcium aluminate cement with CA as the main mineral is generally labeled with the strength achieved after curing for 3 days. The calcium aluminate cement with CA2 as the main mineral is marked by the strength achieved after 7 days of curing.

2. What are the composition and functions of ordinary calcium aluminate cement castables?

The fire resistance of ordinary calcium aluminate cement can be divided into three categories. The mineral composition is A type cement castable with cement based on CA as the binder. The main mineral composition is CA2 (about 60%), and the rest is B-type cement castable with cement with CA and a small amount of C2AS as the binder. The C-type cement castable is mainly composed of CA2 and hardly contains cement with CA as a binder.

A mixture prepared with ordinary calcium aluminate cement as a binder and refractory aggregate and powder in a certain proportion can be used directly after adding water, stirring, vibrating casting, curing and baking. Ordinary calcium aluminate cement is divided into low-iron type and high-iron type. The low-iron type is made of natural low-silicon bauxite (with SiO2 content less than 8%) and limestone.

The castables combined with ordinary calcium aluminate cement have a wide range of applications. Different types of calcium aluminate cements can be selected as binders according to the use temperature and use conditions, and different refractory aggregates and powders can be added. It is usually used in various heat treatment furnaces, heating furnaces, soaking furnaces, tapping and tapping troughs, boilers, rotary kiln heads and tails in mentallurgical, petrochemical, machinary, building materials and other industrial sectors, petrochemical reactors and various kind of heat pipes and valve linings, etc.

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