CEMENT & ITS COMPOSITION

 CEMENT 

 Cement in its broadest term means any substance which acts as a binding agent for materials natural cement (Roman Cement) is obtained by burning and crushing the stones containing clay, carbonates of lime and some amount of carbonate of magnesia. The clay content in such stones is about 20 to 40 percent. Natural cement resembles very closely eminent hydraulic lime. It is not strong as artificial cement, so it has limited use in practice.   Artificial cement is obtained by burning at very high temperature a mixture of calcareous and argillaceous materials in correct proportion. Calcined product is known as clinker. A small quantity of gypsum is added to clinker and it is then pulverized into very fine powder is known as cement. Cement was invented by a mason Joseph Aspdin of leeds in England in 1824. The common variety of artificial cement is known as normal setting cement or ordinary cement or Portland cement. 

 

 Ingradeints 

Ordinary Portland cement contains two basic ingredients, namely argillaceous and calcareous. In argillaceous materials, clay predominates and in calcareous materials, calcium carbonate predominates. Good ordinary cement contains following ingradients.  

1. Lime (cao)    ………. 62% 

2. silica (Sio2)   ………. 22%  

3. Aluminca(Al2 u3)   ………. 5%

 4. Calcium sulphate (CaSo4)  ……….  4%

 5. Iron Oxide (Fe2 O3)   ………. 3% 

 6. Magnescia (Mgo)   ………. 2% 

7. Sulphur   ………. 1%

 8. Alkalies   ………. 1% 

 

Functions of Ingradients: 

1. Lime:

 Lime is the important ingredient of cement and its proportion is to be maintained carefully. Lime in excess makes the cement unsound and causes the cement to expand and disintegrate. On the other hand, if lime is in deficiency the strength of the cement is decreased and it causes cement to set quickly 

 

2. Silica: 

This also an important ingredient of cement and it gives or imparts quick setting property to imparts strength to cement. 

 

3.Alumina: 

This ingredient imparts quick setting properly to cement. Express alumina weakens the cement.   

 

4. Calcium Sulphate: 

This ingredient is in the form of gypsum and its function is to increase the initial setting time of cement. 

 5. Magnesia: 

The small amount of this ingredient imparts hardness and colour to cement. 

 6. Sulphur: 

A very small amount of sulphur is useful in making sound cement. If it is in excess, it causes the cement to become unsound. 

 

7. Alkalies:

 Most of the alkalies present in raw material are carried away by the flue gases during heating and only small quantity will be left. If they are in excess in cement, efflorescence is caused.  

practice Qtns.

 The main types cements 

 i) Acid resistance cement

 ii) Blast furnace cement 

iii) Coloured cement 

iv) Expanding cement 

v) High alumina cement 

vi) Hydrophobic cement 

vii) Low heat cement 

viii) Pozzolona cement

 ix) Quick setting cement 

x) Rapid hardening cement

 xi) Sulphate resistance cement 

xii) White resistance cement 

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