Basic Things you should know about Cement
1. Cement is made from limestone and clay in a powder form, which in the addition of the requisite quantity of water is capable of hardening.
2. The main
ingredients in the manufacture of cement are lime, silica, alumina and
other oxides.
3. Lime is the
main constituent which contributes to the strength. Its proportion has to
be properly maintained so as to make the cement sound and strong.
4. Silica contributes
to the strength of cement due to the formation of dicalcium and tricalcium silicates.
5. The quick-setting
quality is imparted by alumina to the cement.
6. Iron oxide provides colour, hardness and strength to the cement.
7. Correct quantity of magnesium oxide imparts hardness and colour to the cement.
8. Sulphur
trioxide makes the cement sound when present in small quantities.
9. The fineness
of cement is a measure of the size of particles of cement. It is expressed
as the specific surface of the cement.
10. When water is
added to cement and mixed, it forms a paste, which gradually becomes less
plastic and finally forms a hard material. The time is taken for the entire process is called the setting time, which is divided into the initial setting time
and the final setting time.
11. Initial
setting time is regarded as the time when the cement paste losses its
plasticity.
12. Final setting
time is the time elapsed between the time of water added to the cement
to the time when the paste has completely lost its plasticity.
13. Cement that has less
Expensive qualities when mixed with water is termed soundness.
14. Strength of cement is generally assessed from compression tests on cement-mortar cubes
(1:3) with an area of 500 mm2.
15. Reaction of silicates
and aluminates of cement with water forms a binding medium that solidifies
into a hardened mass which is termed hydration.
16. Heat of
hydration is defined as the quantity of heat (in calories/gram of hydrated
cement) liberated on complete hydration at a particular temperature.
17. Specific
gravity of Ordinary Portland Cement is around 3.15.
18. Loss on ignition is the loss in weight due to the ignition of cement at a high temperature
. Loss in weight is a measure of the freshness of cement.
19. An inactive part of cement is called the insoluble residue.
20. Production of
cement is performed in three stages, viz., (i) Mixing of raw materials in
the correct proportion, (ii) Burning of the mixture and (iii) Grinding.
21. There are two
processes in the manufacture of cement, viz., the wet process and the dry
process, depending upon whether the mixing and grinding of raw materials are
done in wet or dry conditions.
22. Major complex compounds formed due to chemical compositions are: tricalcium
silicate, dicalcium silicate, tricalcium aluminate and tetra calcium aluminoferrite.
23. Grades of
Ordinary Portland Cement are 33-Grade, 43-Grade and 53-Grade.
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