Limestone
Its the major and main raw material for cement manufacture. Without this you cannot produce cement. For cement manufacture, you require quick lime (CaO) which is not directly available (the lime is quickly reactable,so it was called as quick lime).But it was obtained in the form of limestone which can be decomposed to quick lime at high temperature.
Chemical name: Calcium carbonate (CaCO3). (it contains lime)
Melting point : 825 deg celcius (since we are going to partially fuse the raw mix, hence melting point is important)
You can add this limestone from any source, but the only thing is that the material should have the required level of calcium carbonate to produce cement or else the cement lacks strength.
Usually high lime content is preferable for good cement.Some of the limestone sources/ grades:
Calspar or calcite (purest form of limestone), aragonite, marble , chalk, limestone, shale, sea shells, marlaceous limestone,clayey marl, marlaceous clay, clay, calcareous marl or marlstone, dolomite etc.,
The purest varieties of limestone will be white in colour.
Any limestone material having more than 95% of limestone content is called high grade limestone.
What to do if you have only low grade limestone?
If you have low grade limestone ,mix low grade limestone with a material with high grade limetone or any material which has high lime content(for example, paper sludge, a rejected material from paper industry which also contains lime can also be added to increase lime content) so that the resultant material will have required calcium carbonate content to make cement.
A material called calcareous marl which naturaly contains the chemical composition equal to portland cements chemical composition. So it was used to produce natural cement. But that kind of deposits are rarely found.
The following table shows you how to define a limstone based on its calcium carbonate content:
CaCo3 content
|
Limestone type
|
96 to 100 %
|
High grade limestone
|
90 to 96 %
|
Marlaceous limestone
|
75 to 90 %
|
Marlstone or calcareous marl
|
40 to 75 %
|
Marl
|
10 to 40 %
|
Clayey marl
|
4 to 10 %
|
Marlaceous clay
|
0 to 4 %
|
clay
|
