The hydration kinetics of the non-activated slag cement and the slag pastes activated with NaOH, Na2CO3, or Na2Si1.7O4.4 were followed by isothermal micro-calorimetry for 13 days. Samples were made with a water/slag weight ratio of 0.4 and with 4 wt% of Na2O per mass of slag. The results presented in Figure show very different behaviors depending on the sample. First, almost no heat was released when the slag paste was not activated (hydrated in pure water). Again, this was expected since slag requires alkaline activators to hydrate in a reasonable period.