Which of the following Bogue's compounds of cement liberates maximum heat of hydration?
🔥 Heat of Hydration: The Cement's Exothermic Reaction
When cement is mixed with water, it undergoes a chemical reaction called hydration. This reaction is exothermic, meaning it releases heat. The amount and rate of heat released are critical properties of cement. Too much heat generated too quickly can cause thermal cracking, especially in large concrete structures (mass concrete).
Each of the four Bogue's compounds contributes to the total heat of hydration, but they do so at different rates and in different amounts.
📝 Detailed Analysis of the Options
(b) C₂S (Dicalcium Silicate)
This compound hydrates very slowly and is responsible for long-term strength. Because its reaction is slow, it liberates the least amount of heat (approx. 260 J/g).
(c) C₃S (Tricalcium Silicate)
This compound hydrates rapidly and is responsible for early strength. It liberates a significant amount of heat (approx. 500 J/g), but not the most.
(d) C₄AF (Tetracalcium Aluminoferrite)
This compound's reaction is moderately fast, but its contribution to heat is also moderate (approx. 420 J/g). It generates more heat than C₂S but less than C₃S.
(a) C₃A (Tricalcium Aluminate)
This is the correct answer. Tricalcium aluminate is the most reactive compound and hydrates almost instantly. This extremely rapid reaction liberates the maximum amount of heat in the shortest period (approx. 865 J/g). This is why C₃A is the primary cause of the initial high temperature rise in concrete and why its content is limited in Low Heat Cement.
📊 Heat of Hydration of Bogue's Compounds
| Compound | Heat of Hydration (Approx. J/g) | Order of Heat Liberation |
|---|---|---|
| C₃A (Tricalcium Aluminate) | 865 | 1st (Highest) |
| C₃S (Tricalcium Silicate) | 500 | 2nd |
| C₄AF (Tetracalcium Aluminoferrite) | 420 | 3rd |
| C₂S (Dicalcium Silicate) | 260 | 4th (Lowest) |
💡 Study Tips
- Remember the Order: C₃A > C₃S > C₄AF > C₂S. This sequence for heat of hydration is one of the most important facts to memorize about cement chemistry.
- A for Aluminate, A for Arsonist: Think of C₃A as the "arsonist" of the group. It starts the fire (initial set) and creates the most heat.
- Fast Reaction = High Heat: There is a direct correlation between the speed of reaction and the heat generated. The fastest reacting compound (C₃A) produces the most heat, and the slowest (C₂S) produces the least.