Cement and its various kinds

  Cement and its various kinds 

 Cement is the binding material produced by burning together in definite proportion, a mixture of Calcareous  (containing Silica) Argillacious (containing Aluminium) material at the temperature of about 1500°C by doing so a fused product is obtained called Clinker. The Clinker is cooled and then ground (grinding) to the required fineness and we get a substance called Cement.

Commonly used cement for normal construction work is known as Ordinary Portland Cement.

The approximate composition of raw materials used for manufacturing ordinary Portland cement are :-

Lime (62 to 67%)

Silica (17% to 25%)

Alumina (3% to 8%)

Ironoxide (1% to 6%)

Magnesia (1% to 4%)

Sulphur (1% to 2%)

Alkalis (0.5% to 1%)

 Following are the important compound formed during the setting action of cement :-

1) Tricalcium aluminate

2) Tetracalcium aluminoferrite

3) Tricalcium silicate

4) Dicalcium silicate

Types of cement

Pozzolana cement

 Pozzolana cement is produced either by grinding together cement clinker and Pozzolana or by intimately and uniformly blending Portland cement and fine Pozzolana.

Pozzolana cement produce less heat of hydration and offers greater resistance to attack of aggressive water or sulphate. 

This cement is particularly useful in marine works and also in mass concrete structure.

Ultimate strength of the cement is more than that of ordinary cement but initial and final setting time are the same.

Quick Setting cement

 It sets faster than ordinary Portland cement. Its initial setting time is 5 minutes and the final setting time  is 30 minutes. It is used for making concrete that is required to set early as for laying under water or in running water. 

Rapid Hardening cement 

This cement gains strength faster than ordinary cement. Its initial and final setting time are the same as those of  ordinary cement. It contains more of tricalcium silicate and is more finally ground. It gives out more heat while setting and is as such unsuitable for mass concrete work.

High Alumina cement  

 It is manufactured by fusing together a mixture of Bauxite and Lime stone in correct proportions and at high temperatures. It develop strength rapidly. It is black in colour and resist the attack of chemicals especially of sulphates and of sea water. Its ultimate strength is much higher than that of Ordinary cement. Its initial setting time is more than 2 hours and the final setting take place immediately thereafter.

It is used for such structure as are to be subjected to load early, for example repair of roads and bridges etc .

Low Heat cement

 Heat generated by cement while setting may cause the structure to crack in case of concrete. Heat generation is controlled by keeping the percentage of Tricalcium Aluminate and tricalcium silicate low. Its initial and final setting times are nearly the same as those for ordinary cement. It is not very suitable for use in ordinary structure as this will prolonged the shuttering and also prolonged curing will have to be done.

White cement

 It is a cement with pure white colour and having same properties as those of ordinary cement. Greyish colour of ordinary cement is due to ironoxide.  It is manufactured from white chalk and clay free from iron oxide. For burning this cement oil fuel should be used instead of coal. It is much more costly than ordinary cement.