Effect of w/c and temperature on the early-stage hydration heat development in Portland-limestone cement

The early-stage hydration heat characteristics of the blended binder containing 80% of Portland cement CEM I 42.5 R and 20% of limestone are studied in a dependence on w/c and temperature. The specific hydration heat power and the specific hydration heat are monitored over the time period of 72 h using an isothermal heat flow calorimeter. Experimental results show an active role of limestone in the hydration process. After 72 h its net contribution to the specific hydration heat of the blended binder, QL, is significant for all studied combinations of w/c and temperature. At 20 °C QL is more pronounced for w/c = 0.35 (51.8 J/g-binder) than w/c = 0.50 (41.8 J/g-binder), contrary to 35 °C where a dependence of QL on w/c is not evidenced (34.6 J/g-binder for w/c = 0.35 and 35.5 J/g-binder for w/c = 0.50). Unlike the reference Portland cement, the apparent activation energy of the analyzed Portland-limestone cement is found to depend on w/c; for w/c = 0.5 it is 35.7 kJ/mol while for w/c = 0.35 only 28.0 kJ/mol.