Introduction of Cement

Introduction of Cement: Cement means 'any substance that acts as a binding agent for different materials '. Cement, in engineering field and especially in construction industry, is a material, which is produced by calcining at high temperature (1400°C) an intimate mixture of calcareous, siliceous and aluminous substances and crushing the resulting clinkers to a fine powder.

Function of Cement in Concrete

When cement is mixed with water, it forms a paste, which hardens and binds the aggregate (sand, gravel) together to form a hard durable mass called concrete. Thus, cement is one of the important ingredients of concrete.

Chemical Ingredients of Cement

The chemical Ingredients of cement are:

1. Lime (CaO),
2. Silica (SiO),
3. Alumina (Al2O3),
4. Iron oxide (Fe2O3)

Chemical Compounds of Cement 

The main chemical compounds of cement are:

1. Tri-calcium Silicate,
2. Di-calcium Silicate,
3. Tri-Calcium Aluminate,
4. Tetra-calcium Aluminium Ferrite,
5. Free Lime,
6. Gypsum 

Chemical Constituents of Ordinary Portland Cement (OPC)

• The raw materials used for manufacturer of cement consists mainly of Silica, Lime and Alumina, Iron oxide, Sulphur trioxide and other alkalies are also present but in very small proportions.
• These materials are intimately mixed and burnt at a temperature of about 1400°C in a klin to form clinkers which are complex chemical compounds.
• The relative proportions of these oxides are responsible for affecting the various properties of cement.
• The chief chemical ingredients and their proportions, in any ordinary portland cement, are given below.

Compounds                                         Percentage 

Lime                                                          60 to 67%

Silica                                                         17 to 25%

Iron oxide or Ferrous oxide                 0.5 to 0.6%

Alumina                                                   3 to 8%

Gypsum or Calcium sulphate              3 to 4%

Magnesium oxide                                   0.1 to 4%

Sulphur trioxide                                     1 to 3%

Alkalies such as Soda and Potash       0.1 to 1%

Compounds                                           Formula 

Lime                                                          CaO

Silica                                                          SiO2

Iron oxide or Ferrous oxide                 Fe3O3

Alumina                                                   Al2O3 

Gypsum or Calcium sulphate              CaSO4

Magnesium oxide                                  MgO

Sulphur trioxide                                     SO3

Alkalies such as Soda and Potash       Na2O, K2O

Bogue's Compounds

The raw materials, when subjected to high temperature, combine with each other to form complex compounds. The four compounds usually regarded as majour compounds. These compounds are in anhydrous state (i.e. without any water molecules in their chemical formula).

Compounds                                         Percentage 

Tri-calcium Silicate                                  21 to 46%

Di-calcium Silicate                                   25 to 50%

Tri-Calcium Aluminate                           5 to 11%

Tetra-calcium Aluminium Ferrite        9 to 14%

Other constituents and Gypsum           80%

Compounds                                            Formula 

Tri-calcium Silicate                           2(CaO) SiO2

Di-calcium Silicate                            3(CaO) SiO2

Tri-Calcium Aluminate                    3(CaO) Al2O3

Tetra-calcium                                     4(CaO)   

Aluminium Ferrite                            Al2O3 Fe2O3

Other constituents and Gypsum