The various constituents combine in burning and form cement clinker. The compounds formed in the burning process have the properties of setting and hardening in the presence of water. They are known as Bogue compounds after the name of Bogue who identified them. These compounds are as follows: Alite (Tricalcium silicate or C3S), Belite (Dicalcium silicate or C2S), Celite (Tricalcium aluminate or C3A) and Felite (Tetracalciumalumino ferrite or C4AF) let’s know and know more about Composition of Cement Clinker.
It is supposed to be the best cementing material and is well-burnt cement. It is about 25-50% (normally about 40 percent) of cement. It renders the clinker easier to grind, increases resistance to freezing and thawing, hydrates rapidly generating high heat and develops early hardness and strength. However, raising of C3S content beyond the specified limits increases the heat of hydration and solubility of cement in water. The hydrolysis of C3S is mainly responsible for 7-day strength and hardness. The rate of hydrolysis of C3S and the character of gel developed are the main causes of the hardness and early strength of cement paste. The heat of hydration is 500 J/g.
It constitutes about 25-40% (normally about 32 percent) of cement. It hydrates and hardens slowly and takes a long time to add to the strength (after a year or more). It imparts resistance to chemical attack. Rising of C2S content renders clinker harder to grind, reduces early strength, decreases resistance to freezing and thawing at early ages and decreases the heat of hydration. The hydrolysis of C2S proceeds slowly. At early ages, less than a month, C 2S has little influence on strength and hardness. While after one year, its contribution to the strength and hardness is proportionately almost equal to C3S. The heat of hydration is 260 J/g.
It is about 5-11% (normally about 10.5 percent) of cement. It rapidly reacts with water and is responsible for a flash set of finely grounded clinker. The rapidity of action is regulated by the addition of 2-3% of gypsum at the time of grinding cement. Tricalcium aluminate is responsible for the initial set, high heat of hydration and has a greater tendency to volume changes causing cracking. Raising the C3A content reduces the setting time, weakens resistance to sulphate attack and lowers the ultimate strength, heat of hydration and contraction during air hardening. The heat of hydration of 865 J/g.
It constitutes about 8–14% (normally about 9 percent) of cement. It is responsible for the flash set but generates less heat. It has a poorest cementing value. Raising theC4AF content reduces strength slightly. The heat of hydration is 420 J/g.