Composition of cement

Cement is used as a binding material in construction activity, which is being manufacture artificially by intergrinding calcareous and argillaceous compound. 

Calcareous compound- Calcium Carbonate is predominant.

Example- Lime, chalk, Marine Shells, Cement Rock, etc.

Argillaceous compound- Clay is predominant.

Example- Clay, Marl, etc.

Cement used as a Binding Material

Constituents Present in OPC

Lime [62-67]% [CaO]
Silica [17-25]% [SiO2]
Alumina [3-8]% [Al2O3]
Calcium sulphate [3-4]% [CaSO4]
Iron oxides [3-4]% [Fe2O3]
Magnesia [1-3]% [Mgo]
Sulphur [1-3]% [S]
Alkalies [0.2-1]% [Na2O,K2O]

 Functions of cement ingredients-

1-Lime- It impart strength & soundness to the cement , if it is in excess , it makes the cement unsound & causes it to expand & disintegrate & if it is in deficiency strength of the cement is decreased & it causes the cement to set quickly.

2- Silica- It also impart strength to the cement. If it is in excess strength of the cement increased, but it also increases the setting time of the cement. 

3-Alumina- It imparts quick setting property to the cement. It helps in reducing the clinkering temp. If it is in excess, it weaker the cement. The temperature At which clinkers of cement forms is known as clinkering temp. 

4-Calcium sulphate- It is generally present in the form of Gypsum. It helps in increasing the initial setting time of the cement. 

5-Iron oxide- It imparts strength, Hardness, & color [Reddish brown] to the cement. 

6-Magnesia- It also impart strength, Hardness, & color [yellowish ting] to the cement. If it is in excess, it makes the cement unsound. 

7-Sulphur- sulphur in cement is responsible for volume changes, hence it also leads to unsoundness in cement. 

8-Alkalies- it is responsible for staining [white or Gray spots on structure where cement is used] & efflorescence of the structure in which it is used for construction. When these ingredients of the cement are intergrinding & burnt they fuse with each other, leading to the formation of complex chemical compound which are not formed simultaneously & are referred as bogues compound.

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