1 Basic principle and key points of ICC 1.1 Basic Principle The test method is designed to measure the heat of hydration of cement when mixed with water. The measurement takes place at essentially constant temperature, if the instrument and the measurement are well designed, therefore it is assumed to be the "isothermal heat of hydration of cement". An isothermal heat conduction calorimeter (here called calorimeter) consists of a thermostatic heat sink upon which two heat flow sensors are placed. The sample is placed in an ampoule that is placed in an ampoule holder that is in contact with one of the heat flow sensors, and an inert reference is placed in contact with the other. The sample ampoule and the reference ampoule are thermally connected by heat flow sensors to a thermostatic heat sink. The output from the calorimeter is the difference between the outputs from the sample heat flow sensor and the reference heat flow sensor. A general scheme of a heat conduction calorimeter is given in Figure 1. However the actual design of an individual instrument, whether commercial or home-built, may vary. (...) Most part of the calorimeters can measure the heat of hydration of samples mixed outside from the instrument therefore the heat produced during the mixing is not measured. It is not easy to solve this problem designing a calorimeter provided with an internally mixing device having the proper efficacy. 1.2 Key points of ICC When performing ICC measurements on cement samples some key points have to be considered and correctly managed: - Constant value of the temperature of the thermostat; - Stability of the temperature of the thermostat all over the test duration; - Control of the maximum difference between sample temperature and thermostat temperature (isothermal conditions); - The baseline of the instrument (measured with an inert sample of similar thermal properties of test sample) should be both repeatable and stable; - Calibration of the calorime ...