🔥 Heat of Hydration Test of Cement

📘 Aim

To determine the Heat of Hydration (HoH) of cement using a calorimeter as per IS 4031 (Part 9):1988.

🔍 Purpose

The heat of hydration is the amount of heat released when cement reacts with water during hydration. This reaction is exothermic and plays a crucial role in the strength development and temperature control of concrete, especially in mass concrete works such as dams and foundations.

⚙️ Apparatus Required

• Calorimeter (Vicat or Langavant type)
• Weighing balance (accuracy ±0.1 g)
• Thermometer (range up to 100°C)
• Dewar Flask or Insulated Container
• Water bath (to maintain temperature)
• Stopwatch

🧱 Material

• Cement sample (freshly prepared)
• Distilled water

🧪 Principle

When water is added to cement, chemical reactions occur between cement compounds (C₃S, C₂S, C₃A, C₄AF), producing heat. This released heat increases the temperature of the surroundings. By measuring this temperature rise using a calorimeter, we can calculate the total heat of hydration in calories or joules per gram of cement.

🧾 Chemical Reaction

The simplified reactions producing heat are:

• 2C₃S + 6H → C₃S₂H₃ + 3Ca(OH)₂ + Heat
• 2C₂S + 4H → C₃S₂H₃ + Ca(OH)₂ + Heat

🧪 Procedure

1. Weigh about 60 g of cement accurately.
2. Prepare a paste with water-cement ratio = 0.40.
3. Immediately place the paste in the calorimeter.
4. Seal the calorimeter tightly to avoid heat loss.
5. Immerse the calorimeter in a constant temperature water bath.
6. Record the temperature rise at fixed intervals (e.g., every 30 minutes) for up to 24 hours.
7. Note the maximum temperature rise and calculate the heat of hydration using the formula.

🧮 Formula

Heat of Hydration (H) = (W × C × ΔT) / M

Where:

• H = Heat of hydration (cal/g or J/g)
• W = Weight of water + calorimeter parts (g)
• C = Specific heat of water (1 cal/g°C)
• ΔT = Rise in temperature (°C)
• M = Weight of cement (g)

Conversion:

1 cal/g = 4.186 J/g

📊 Observation Table

Example Calculation:

Given:

• W = 300 g
• ΔT = 9.2°C
• M = 60 g

H = (300 × 1 × 9.2) / 60 = 46 cal/g = 192.6 J/g

✅ Result

The heat of hydration of the given cement sample is 192.6 J/g.

📋 Typical Values

• Ordinary Portland Cement (OPC): 75 – 100 cal/g (315 – 420 J/g)
• Low Heat Cement: 50 – 60 cal/g (210 – 250 J/g)

📖 Significance

• High heat of hydration may cause thermal cracking in mass concrete.
• Low heat cement is preferred for large structures such as dams and retaining walls.
• Used to control the temperature rise in concrete curing.

⚠️ Precautions

• Ensure the calorimeter is properly sealed to prevent heat loss.
• Conduct the test in a controlled environment (27 ± 2°C).
• Use freshly mixed cement paste for accurate results.
• Record temperature readings precisely at fixed intervals.

📘 Conclusion

The Heat of Hydration Test determines the heat released during the hydration of cement. The measured value of 192.6 J/g indicates normal hydration characteristics suitable for use in reinforced and mass concrete structures. Controlling heat of hydration helps in preventing thermal stresses and cracks in concrete.