Abstract
A large-volume isothermal heat flow calorimeter is applied for determination of the specific hydration heat power, N, and specific hydration heat, Q, of Portland cement CEM I 42.5 R as a function of time. The measurements are carried out for the cement paste with w/c=0.3, 0.35, and 0.4 in the temperature range of 5–30°C. Experimental results show that Q in the initial hydration phase (including C3A hydration and the dormant period up to the first local minimum on the N(t) curve) decreases two times when the temperature increases from 5°C to 30°C, and it is independent of w/c within the studied range. The second local maximum on the N(t) curve (corresponding to the C3S hydration phase) is four to five times higher for 30°C as compared with 5°C, and it decreases up to 20% with increasing w/c; the time of its appearance is three times lower for 30°C than 5°C, and it is also independent of w/c. The apparent activation energy of the CEM I 42.5 R hydration is found independent of w/c within the analyzed range, its average value being 32.2kJ/mol.
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