Silica , lime and alumina are the three basuc raw materials of cement . Iron oxide , sulphur trioxide , and other alkalies are alsomaterials are intimately mixed and then burnt at a clinkering temperature of about 1400 C .
Clinkers are lastly gound to a fine powser toi get cement . Following are the chief chemical ingredient and their proportions in an ordinary portland cement :
Lime 60-67 percent '
Sikica 17 to 25 percent 'Alumina 3 to 8 percent
Magnesia 0.1 to 4 percent
Sulphur trioxide 1 to 3 perent
Iron oxide 0.5 to 6 percent
Soda and potash alkalies 0.5 to 1 percent
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