This article introduces the advantages and disadvantages of high alumina bricks. Read this article to learn about the application areas and product features of high alumina brick. What's more, You can know more details about difference between High Alumina Cement and Ordinary Portland Cement.
High Alumina Cement (HAC), sometimes known as calcium aluminate cement (CAC) or aluminous cement, is composed of calcium aluminates, unlike Portland cement which is composed of calcium silicates. It is manufactured from limestone or chalk and bauxite (Special clay having extremely high alumina content).
High Alumina Cement including lime, they are ground into cement clinkers in a process called fusing or sintering. Its popularity rose when the properties of this cement such as rapid strength gain and easy to manufacture were found out and widely used for precast concreting. High alumina cement is mostly used to manufacture structural concrete such as pre-cast beams.
The process of manufacture of High Alumina Cement
The process of manufacture of High Alumina Cement is different compared to that of ordinary portland cement. Bauxite and lime are used as the raw material. The raw materials are mixed in the required proportion and grinded into small fragments of 100 mm. These lumps are fed in kiln and heated up-to their fusion point which is 1600°C. The molten material fall down on the steel plate and it is send to cool down in rotary kiln. These clinkers are then grounded finely in tube mills unto the fineness not less than 2250 cm2/gram is achieved.
High alumina cement is manufactured by sintering or fusing a mixture in suitable proportions, of alumina and calcareous materials and grinding the resultant product to a fine powder.
There are two main elements used to make high alumina cements limestone and bauxite. These two ingredients were charged into the furnace.
The furnace is fired with pulverized coal or oil with a hot air blast. The fusion process in the furnace generally takes place at a temperature of about 1550-1600°C.
The cement is maintained in a liquid state in the furnace. Then after the molten cement is filled in molds and cooled.
These castings are known as pigs. After cooking this molten cement it looks like a dark, fine gey compact rock resembling the structure and hardness of basalt rock. The pigs of fused cement, after cooling are crushed and then ground in tube mills to a fineness of about 3000 sq. cm/gm.
The complete process of High Alumina Cement production step by step:
At first, use the chemicals Bauxite and lime as raw materials and crush them both into small proportions. Each lump must be less than 100 mm in size.
1.Put these small fragments in a furnace
2.Now maintain the temperature of heat between 1500-to-1600-degree C.
3.The melted material fell on the steel plate
4.Wait for the molten material to little cool down
5.Place this molten material into vessel
6.This form of cement will now look like a rock after cooling down and turns into a light grey colour
7.We will now break this cement rock into small chunks
8.Every chunk must be crushed till it turn to a fined powder form of cement
9.In last we will go through separation or filtration process by the use of separating funnel and magnetic separators to separate metallic iron and other impurities from the cement
10.This refined powder or form of cement is High Alumina cement.
Advantages of High Alumina Cement
The advantages of High Alumina Cement are as follows,
1.Due to the more setting time, time for mixing and placing is more.
2.The resistance for the chemical action is good.
3.Can withstand high temperature.
4.Frost action is low as the heat evolved is more during setting.
5.High alumina cement is very reactive and has very high compressive strength.
6.High resistant to fire.
Disadvantages of High Alumina Cement
The disadvantages of high alumina cement are as follows,
1.As the heat required for the manufacture of this cement is more, the manufacturing cost of this cement is high.
2.As the fineness is kept not less than 2250 cm2/gram, which is very fine. Care to be taken that it doesn't come in contact with human eye or mouth.
3.As the heat evolution while setting is high, it cannot be used in mass concreting works.
High Alumina Cement Raw Materials
| Raw Material | Percentage |
| Bauxite | 40 % |
| Lime | 40 % |
| Iron oxide | 15 % |
| Ferric oxide, silica, magnesia | Little |
High Alumina Cement Applications:
1.It is frequently utilized in sewer infrastructure and maritime building because of its quick hardening and strength properties.
2.Refractory concretes that need higher strength at very high temperatures, also use this cement.
3.High alumina cement is also used in refractory concretes where it requires more strength at very high temperature.
4. In construction concretes, where rapid strength development is required, even at low temperatures.
5. As a protective liner against microbial corrosion such as in sewer infrastructure
6. As a component in blended cement formulations, for various properties such as ultra-rapid strength development and controlled expansion are required.
7. In sewer networks for their high resistance to biogenic sulfide corrosion.
Characteristics of High Alumina Cement:
1.This cement is excellent resistance to chemical attacks.
2.There is a pH problem.
3.It is used to construct water and sewage pipes, factory drains, coastal constructions, and manufacturing chimneys due to its strong resistance to chemical corrosion.
4.There is a high refractive index in the cement issue.
5.It is highly resistant to sulfuric acid.
6.This cement’s rapid cementing property.
7.Due to its ability to establish a ceramic bond at high temperatures, it serves as a bonding agent when added to refractory castable.
Hydration of High Alumina Cement:
The important reaction during the setting of the high alumina cement (HAC) is the formation of monocalcium aluminate decahydrate (CAH10), dicalcium aluminate octahydrate (C2AH8), and alumina gel (Ahn).
These aluminates provide high strength to HAC concrete but they are metastable and at normal temperature convert gradually to tricalcium alumina hexahydrate (C3AH6) and gibbsite which are more stable.
Difference between High Alumina Cement and Ordinary Portland Cement
As compared to ordinary portland cement, high alumina cement has the following differences:
| High Alumina Cement | Ordinary Portland Cement |
| High alumina content about 40 % | |
| Higher resistance to sulphate attack | OPC is not much resistant to sulphate attack |
| Calcium hydroxide is absent in the hydrated products of high alumina cement | Calcium hydroxide and CSH gel are the main hydration products of OPC |
| No free lime is produced after setting and hardening even at high temperatures | At high temperatures, Ca(OH)2 decomposes producing free lime |
| Absence of free lime does not make HAC unsound when exposed to moisture or water | Free lime makes OPC unsound when exposed to moisture |
| Used for making refractory lining in furnaces | Used for normal construction purposes |
More details about High Alumina Cement:
What is high alumina cement used for?
Generally, this refractory product is widely used in sewer infrastructure and marine construction. Besides, it is also used in refractory concretes for furnaces, boilers, kilns, and chimneys. This is due to its strength to withstand very high temperatures with proven durability.
Why is high alumina cement not allowed to be used structurally?
High alumina cement possesses properties like high early strength, rapid hardening even at low temperature, and durability to sulphate attack. But the conversion of HAC has made it unfit for structural use due to gradual strength loss.
Which raw material is used for high alumina cement?
High alumina cement is manufactured by fusing together a mixture of 40% bauxite , 40% lime and 15% iron oxide and ferric oxide, 5% silica, magnesia etc.
What is another name for high alumina cement?
aluminous cement
Calcium aluminate cements are cements consisting predominantly of hydraulic calcium aluminates. Alternative names are "aluminous cement", "high-alumina cement", and "Ciment fondu" in French. They are used in a number of small-scale, specialized applications.
How high alumina cement is made?
High Alumina Cement is manufactured by grinding the clinkers of alumina and calcareous material such as lime by fusing or sintering process. This cement is also known as calcium aluminum cement.
By reading this article, have In-depth understanding of the advantages and disadvantages of high alumina bricks. If you are interested in other refractory products or other furnace solutions, welcome to contact us anytime.
Article Source: How to manufacture high alumina cement
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