Question
Download Solution PDFWhich of the following compounds is responsible for slow hardening, less heat of hydration, and greater resistance to the chemical attack in OPC Cement?
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFExplanation:
1. Tricalcium Silicate C3S – (25 – 50%) – Normally 40%
- It is considered as the best cementing material and is well-burnt cement.
- It hydrates rapidly generating high heat and develops an early hardness and strength.
- Raising of C3S content beyond the specified limits increases heat of hydration and solubility of cement in water.
- The heat of hydration is 500 J/g.
2. Dicalcium Silicate (C2S) - (25 – 40%) - (Normally 32%)
- It hydrates and hardens slowly and takes a long time to add to the strength (after a year or more) i.e. it is responsible for ultimate strength.
- It imparts resistance to chemical attack.
- Raising of C2S content renders clinkers harder to grind, reduces early strength, decreases resistance to freezing and thawing at an early age and decreases heat of hydration.
- At an early age, less than a month, C2S 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.
3. Tricalcium Aluminate (C3A) - (5 – 11%) -(Normally 10.5%).
- It rapidly reacts with water and is responsible for the flash set of finely grounded clinkers.
- The rapidity of action is regulated by the addition of 2-3% of gypsum at the time of grinding the cement.
- It is most responsible for the initial setting, the 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.
4. Tetracalcium Alumino Ferrite - (C4AF 8 – 14%) (Normally 9%)
- It is responsible for the flash set but generates less heat.
- It has the poorest cementing value. Raising C4AF content reduces the strength slightly.
- The heat of hydration 420 J/g.
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