Cement & Different Constituents of OPC

It is artificial building material used for imparting binding property in the construction work. Cement developed by JOSEPH ASPEON in 1824-25. Cement broadly consist of following:

1. Calcareous compound (Having calcium and Magnesium)
2. Argillaceous Compound (Silica, Alumina, & Oxide)

Example of calcareous compound : Chalk, Limestone, Cemented Rock, Marl, Alkali Waste, Marine Shell.

Argillaceous Compound : Clay, Shale, Slate, Ash

Different Constituents of OPC:

1. Lime : It imparts strength to the cement and is responsible for its soundness (Resistant against volume change). It can be represented in the CaO and it is in percentage 63-67%. If it is in excess it makes cement unsound causes it expands and finally integrate. If it is in deficiency it reduces strength of cement & causes it to set quickly.
   • CaO + H₂O ————-> Ca(OH)₂
     • Volume of Ca(OH)₂ is greater than CaO.
2. Silica (SiO₂) (17-25%):- It is also imparts strength to the cement. If it is in excess, it increases the strength of cement along with its setting time.
   • Quick setting cement is required in grouting work (to fill cracks), Structure made under the ground
3. Alumina (Al₂O₂) (3-8%) :- It imparts quick setting property to the cement. It acts as flux & helps in reducing clintering temperature.
   • Clintering temperature : Temperature at cement manufacture.
   • Flux : Help/aid.
4. Calcium Sulphate (CaSo₄) (3-4%):- It is generally added in the form of gypsum (CaSO₄ . 2H₂0). It helps to increase initial setting time of cement.
5. Iron Oxide (Fe₂O₃) (3-4%) :- It imparts hardness, strength & color to the cement.
   • In excess, over burning of cement.
   • Hardness : Resistance against wear & tear)
   • Colour : Reddis brown (Resultant : Gray)
6. Magnesia (MgO)(1-3%):- It also imparts strength, Hardness and colour (Yellow) to the cement. It is responsible for unsoundness of cement.
7. Sulphur (S) (1-3%):- It is responsible for unsoundness of cement.
8. Alkali (Na₂O, K₂O)(0.2-1%):- Presence of alkali in cement leads to efflorescence & expensive reaction with aggregates. (It is termed as cancer of cement )
   • we don’t want alkali but it presence in every building material.
   • efflorescence= Patches