A comparison of conduction calorimeter and heat of solution methods for measurement of the heat of hydration of cement

Synopsis Factors governing the accuracy and precision of the heat of hydration of cement measured by isothermal conduction calorimetry are discussed and results are presented comparing the values with those obtained by the heat of solution method (BS 4550: Part 3: Section 3·8). Comparison of the two methods is also made on the basis of a review of the published data. The conduction calorimeters used, which are of the Wexham Developments type, have the capability of measuring heat evolution rates between 10 μW and 200 mW for sample weights in the range 0·1 to 50 g over periods from a few hours up to several weeks. Tests have shown that rates can be measured with an error of less than 1%. The error in the measurement of total heat evolved was less than 1% from 1 J to 10 kJ. The calorimeters have been used successfully between 5 and 60°C. Excellent agreement has been obtained with the heat of solution method but with standard deviations 3 to 5 times lower. It is shown that conduction calorimetry can provide a viable alternative to the heat of solution method for measuring the heat of hydration of hydraulic cements. It is less laborious, more precise and measurements can be continued up to 7 days, and in many cases up to 28 days. It can also provide valuable data on heat evolution rates at early ages.