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.
The main active constituent of calcium aluminate cements is monocalcium aluminate (CaAl2O4, CaO, Al2O3, or CA in the cement chemist notation). It usually contains other calcium aluminates as well as a number of less reactive phases deriving from impurities in the raw materials. Rather a wide range of compositions is encountered, depending on the application and the purity of aluminium source used. Constituents of some typical formulations include:
Advantages of High Alumina Cement
- The initial setting time of this cement is more than 3.5 hours. The final setting setting time is about 5 hours. It therefore allows more time for mixing and placing operations.
- It can stand high temperature.
- It evolves great heat during setting. It is therefore not affected by frost.
- It resists the action of acids in a better way.
- It sets quickly and attains higher ultimate strength in a short period. Its strength after 1 day is about 40 N/mm2 and that after 3 days is about 50 N/mm2.
- Its setting action mainly depends on the chemical reactions and hence it is not necessary to grind it to fine powder.
Disadvantages of High Alumina Cement
Following are the disadvantages of High Alumina cement:
- The extreme care is to be taken to see that it doesn’t come in contact with even traces of lime or ordinary cement.
- It cannot be used in mass construction as it evolves great heat as it sets soon.
- It is costly
Applications of High Alumina Cement
- HAC is also used in refractory concretes where it requires more strength at very high temperature.
- In construction concretes, where rapid strength development is required, even at low temperatures.
- As a protective liner against microbial corrosion such as in sewer infrastructure
- As a component in blended cement formulations, for various properties such as ultra-rapid strength development and controlled expansion are required.
- In sewer networks for their high resistance to biogenic sulfide corrosion.
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