Effect of temperature on the early-stage hydration characteristics of Portland cement: A large-volume calorimetric study

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 32.2 kJ/mol.