The Na2Si1.7O4.4-activated slag paste reacted the fastest with a first heat peak with a flow maximum at only 2 h. This was followed by a period of low thermal activity for about 20 h before a second heat peak appeared around 50 h. When the slag was activated with Na2CO3, hydration also followed a two-step pathway with a first peak at 22 h and a second peak at 210 h (8.75 days). On the contrary, NaOH-activation led to only one relatively large heat release peak with a maximum at 11 h. The width and asymmetry of the peak suggested the overlay of two thermal events, which could correspond to the formation of two different reaction products or to different classes of slag particle size with differing reactivity. Moreover, even though the sample activated with Na2Si1.7O4.4 reacted first, it was quickly caught up by the NaOH-activated sample, which did not present an observable thermally dormant period (Figure ). Finally, hydration with Na2CO3 was the slowest and the total heat released after 13 days was only about half that released for the two other samples.