The hydration heat of the slag cements was measured at 20 °C with a TAM Air isothermal micro-calorimeter from TA Instruments. A total mass of 5.0 g of cement paste was weighed in the mix-ampoules immediately after mixing. The mix-ampoules were placed in the calorimeter at the same time as a reference composed of a precise mass of ultrapure water to have a calorific capacity similar to that of the cement samples. The resulting heat flows were normalized by the slag mass.