What are the characteristics of aluminate cement?

Aluminate-containing salts. The general formula of the aluminate ion is ALO2- or AL(OH)4-. Alkali metal aluminate is soluble in water, because aluminum acid is a weak acid, the aqueous solution of alkali metal aluminate is strongly alkaline.

Aluminate can be prepared by the reaction of aluminum hydroxide with alkali solution. The natural divalent metal anhydrous aluminate is called spinel [m(alo2)2]. For example, beryllium spinel [BE(alo2)2] is called chrysoberyl and is used as an ornament.

The aluminate of calcium is the main component of cement. Aluminate cement is a hydraulic cementitious material made of bauxite and limestone as raw materials, calcined with calcium aluminate as the main ingredient and alumina content of about 50%, and then ground into a hydraulic cementitious material. Aluminate cement is often yellow or brown in color, but also gray.

The main minerals of Portland cement are monocalcium aluminate (CAO·AL2O3, abbreviated CA) and other aluminates, as well as a small amount of dicalcium silicate (2CAO·SiO2). Aluminate cement can be used to formulate amorphous refractories; It can be made into heat-resistant concrete with refractory coarse and fine aggregates (such as chromite, etc.); It is used for urgent projects, such as national defense, road and special emergency repair projects; It can also be used for sulfate corrosion resistance and winter construction projects.

According to the provisions of the national standard (GB201-2000), the density and bulk density of aluminate cement are similar to those of ordinary Portland cement. Its fineness is 300 m2 kg of specific surface area or 20% of 45 m sieve remains.

Aluminate cement is divided into four types: Ca 50, Ca 60, Ca 70 and Ca 80, and the setting time and strength of each type of cement shall not be lower than the standard provisions. Portland cement includes three types of cement: calcium aluminate, barium aluminate, and barium zirconium aluminate. Among them, barium aluminate cement has the characteristics of fast hardening, high strength and high refractoriness.

1. Technical performance: compared with other varieties of cement, it has obvious characteristics of fast hardening and early strength, and has the advantages of low alkalinity, small expansion rate, fast stability, dry shrinkage without deformation, high retention rate of composite strength with glass fiber, long service life, and is a special cement for GRC products.

2. Scope of application: used for the production of various types of lightweight internal and external composite wall panels, beamless floors, exterior wall hanging boards, ventilation ducts, European-style reliefs, large scaffolding, grid panels and other small building accessories.

3. Storage: The cement storage period is three months, pay attention to moisture, and re-test it if it is found to be damp and hardened.

Fourth, precautions: cement before use, should be prepared, has been stirred before the initial setting must be used up, mortar or concrete lost fluidity after the second mixing use.

Cement products must be cured after the final setting, and the curing period shall not be less than seven days, in the process of use, if the setting time is not suitable, it can be adjusted appropriately with sulfur and aluminum special quick-setting agent or retarder, and the amount added needs to be tested.

Answer]: a, b, c, e

The characteristics of aluminate cement are: long-term strength has a tendency to decrease, and the decrease in strength may be caused by crystal transformation, therefore, high-alumina cement is not suitable for long-term load-bearing structures and projects in high temperature and high humidity environments. It should be prohibited in general concrete works.

The early strength grows rapidly, and the strength can reach more than 80% of the maximum strength in one day, so it is suitable for urgent repair projects and special projects that require high early strength. The heat of hydration is large, and the heat release speed is fast, 70% and 80% of the total heat of hydration can be released in one day, therefore, high-alumina cement is suitable for concrete projects constructed in winter, and is not suitable for large-volume concrete projects. The construction temperature shall generally not exceed 25, therefore, high-alumina Zheng cement is not suitable for construction in high temperature season, nor is it suitable for steam curing.

High heat resistance. It has strong resistance to sulfate erosion and good acid resistance, but the alkali resistance is very poor, and it should not be used in the project in contact with alkaline solution. The mixing of high-alumina cement with Portland cement or lime not only produces flashing, but also cracks and even destroys the concrete due to the formation of highly alkaline calcium aluminate hydrate.

Therefore, in addition to mixing with lime and Portland cement, it is also not allowed to be used in contact with Portland cement that has not yet hardened.

Aluminate cement is a commonly used building material that has many different features and advantages over Portland cement.

First of all, the strength of aluminate cement is higher than that of Portland cement. The main reason for this is that the calcium-aluminium minerals contained in aluminate cement have higher chemical reactivity, which allows for a faster hardening reaction, resulting in a stronger concrete structure. As a result, aluminate cement is often used in construction projects that require higher strength, such as high-rise buildings and bridges.

Secondly, the refractory properties of aluminate cement are also better. Due to the special structure of calcium and aluminum minerals, in a high-temperature environment, Portland cement can maintain stability and strength for a longer time, and is not prone to cracking and damage. Therefore, aluminate cement is an important raw material that is often used in the manufacture of refractory materials.

In addition, aluminate cement also has good chemical stability and corrosion resistance for correcting mills. It can maintain good stable ecallability in acidic and alkaline environments, and will not be brittle and damaged due to chemical reactions. At the same time, the corrosion resistance of aluminate cement is also better, and it can be used for a long time in wet and corrosive environments without problems such as corrosion and damage.

In conclusion, compared with Portland cement, aluminate cement has higher strength, better fire resistance and chemical stability, and better corrosion resistance. It has a wide range of uses in the application of building materials and is widely recognized as a high-performance building material.

1. Different compositions: Portland cement is a hydraulic cementitious material made of bauxite and limestone as raw materials, calcined with calcium aluminate as the main ingredient and alumina content of about 50%, and then grinded. Calcium aluminate cement is cement with calcium monoaluminate or calcium dialuminate as the main mineral component.

2. Different appearance: calcium aluminate cement is mostly yellow-brown. Aluminate cement is often yellow or brown in color, but also gray and white.

3. Different uses: Aluminate cement is mainly used for projects with urgent construction periods, such as national defense, roads and special emergency repair projects. Calcium acid cement is mainly used as a binding agent for refractory castables and refractory injection materials.

Salt cement is not suitable for long-term load-bearing structures and projects in high temperature and high humidity environments, it is only suitable for emergency military projects, road and bridge repair projects, temporary projects such as plugging leaks, and the configuration of heat-resistant coagulation and potato soil.

The mixture of aluminic acid imitation salt cement and silicic acid aluminous cement and lime not only produces flashing, but also cracks and even destroys the concrete due to the generation of highly alkaline calcium hydrated aluminate, because hail imitation shall not be mixed with lime or Portland cement during construction, nor shall it be used in contact with unhardened Portland cement.

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Answer]: False GB 175-2007 "General Portland Cement" stipulates that general Portland cement is divided into Portland cement, ordinary Portland cement, slag Portland cement, pontana Portland cement, fly ash silicate chazhi saltless cement, and composite Portland cement according to the variety and dosage of mixed materials.