Determination of Heat of Hydration

Operation

The determination is done by placing fresh concrete in the Heat-Box and afterwards registers the rise and decay of the temperature.

The procedure should take place in a room where the temperature is not changing more than ±5 °C (±9 °F). All sudden changes should be avoided.

If the initial temperature of the concrete is lower than the room temperature, then the heat development will be slightly overestimated. If, for example, the initial temperature of the concrete is 10 °C (18 °F) lower than the room temperature, temperatures are overestimated in subsequent simulations by up to approx. 0.2 °C (0.36 °F).

These conditions should be considered when deciding where to place the Heat-Box.

For acclimatization, the Heat-Box should be placed in the room 8 hours before operation, with the lid open.

1. Initialize the datalogger as described here.

2. Disconnect the datalogger from the PC.

3. Connect the thermocouple with long cord to terminal 1 and the other one to terminal 2, on the datalogger.

4. Attach the data logger on the front plate using the pre-mounted Velcro fastener. 

5. Lead the blue cord to the void at the front panel. Fix the cord to avoid squeezing, by means of the tapes.

6. Place the thermocouple inside a brass spear, with its soldering at the closed end.

7. Use a can of the same type as used for calibration.

8. Place the fresh concrete in the can and mount the closed end of the brass spear app. at the centre of the can.

9. After the brass spear has been placed ensure by vibration that the compression of the sample is good.

10. The total weight should be determined (concrete and can).

ATTENTION!

Try to perform the next 3 steps as quickly as possible.

It is important to use the start button instead of just using a data logger which already is running. This ensures that the initial time and temperature is correct.

11. Place the can in the Heat-Box by means of the lifting belt.

12. Press the “Go”-button on the datalogger until the display shows “Record” after app. 3 seconds.

13. Close the lit of the Heat-Box. Do not squeeze the cord or the lifting belt.

14. The display of the datalogger is showing the temperature of the concrete.

15. When the display is showing that the temperature after reaching maximum has dropped to approx. 5 °C (9°F) above the ambient temperature, you can perform the measurement analysis as described below. Do not finish the measurement yet.

16. If the result of the analysis shows that the hydration process has reached its end, you can finish the measurement. Otherwise, the measurement must continue for a while, then repeat the analysis.

Analysis of measurement in relation to determination of heat of hydration

Launch the Heat-Box software from Start-All Programs-Heat-Box Heat-Box.bat.

Select the id-number of the Heat-Box you want to work with.

Then the window in figure 7 will appear. Some of the buttons could be dimmed (inactive) until the first calibration/determination has been performed.

Figure 7

Click on the Calculate Heat of Hydration button and the window in figure 8 will appear:

Figure 8

Measuring data from the datalogger must be placed on the clipboard as described here.

In order to load measuring data, go to this.

When measuring data has been loaded, Figure 9:

,

Figure 9 Observed temperatures in sample and in the surroundings

When measuring data has been loaded:

1. Fill in the Material Properties and the weight.
2. Press the Calculate Q button
3. The calculation will last some minutes. During the calculation is shown how the calculation model is fitting to the measured data. In addition, the progress of the Heat of Hydration is shown continuously. See figure 10.
4. When the calculation is ended and you find the compliance between measured and calculated temperatures being alright, you can save the result. It is possible to present the Heat of Hydration curve with a linear or logarithmic maturity axis.

ATTENTION!

If the hydration process has reached its end, the Heat of Hydration (Fig. 10 curve at right) has stopped developing. This is most easily determined by selecting the linear Maturity-axis. If the Heat of Hydration has not stopped developing, the measurement must continue for a while, then repeat this analysis.

5. After saving the result, you will get the opportunity to save the data describing the Heat of Hydration in a text-file. The datafile is meant to be used as input for thermal simulation of concrete structures. Alternatively, you can approximate the data with a model by means of a Regression Analysis.

Note: The result is Heat development (energy) per weight-unit of cement or powder content per volume-unit of concrete, as defined in Material Properties.

6. Finally, you can print sheets for your archive.

Figure 10 Based on the determined Heat of Hydration (as a function of maturity) in the right figure, is in the left figure shown that the calculated and the observed temperatures are coincident.