It is known as Belite. This compound is in the range of 20-45%. It hydrates slowly and imparts ultimate strength. The C2S has less heat of hydration therefore it is resistant to chemical attack. 3. Tri-calcium Aluminate (C3A) The formula is 3CaOAl2O3 and the symbol of Tri-calcium silicate is C3A. It is known as Celite.