1.1.2 Chemical composition
CaO = C,
SiO2 = S,
Al2O3 = A; Fe2O3 =F,
H2O = H,
SO3 = S (sulphur trioxide)
Ca(OH)2 = CH,
Thus we can write 3 CaO = C3 and 2 CaOoSiO2 = C2S.
Since the primary constituents of Portland cement are calcium silicate, we can define Portland cement as a
material which combine CaO SiO2 in such a proportion that the resulting calcium silicate will react with
water at room temperature and under normal pressure.
Minor components of Portland cement
The most important minor components are gypsum, MgO, and alkali sulphates.
Gypsum (2CaSO4o2H2O) is an important component added to avoid flash set.
Alkalies (MgO, Na2O, K2O) can increase pH value up to 13.5 which is good for reinforcing steel protection.
However, for some aggregates, such a high alkaline environment can cause alkali aggregate reaction