Historical development of cement - Overview of
2020-6-27 · The magnesia (magnesium oxide, MgO) content of raw materials must be low because the permissible limit in Portland cement is 4 to 5 percent. Other impurities in raw materials that must be strictly limited are fluorine compounds, phosphates, metal oxides and sulphides, and excessive alkalies. Another essential raw material is gypsum, some 5 ...
