The reaction heat during the hydration of C 3 A/quartz model systems in the presence of the sodium salts was measured on an eight-channel isothermal calorimeter (TAM Air, TA Instruments, USA) at 20 • C. Custom mixers (Bohr-O-Mir 4000, Technisch Zeichnen Grassl, Germany) equipped with three T-shape paddles in a planetary mixer configuration were used. allowing the addition of solutions and mixing of pastes in the calorimeter. The sample vials were composed of a plastic/graphite composite, and the mixers were driven by an electrical motor at 600 rpm. For each experiment, 3.0000(5) g of the C 3 A MS was weighed into the sample vials. The solutions were prepared according to the desired dosages and were weighed into the three syringes corresponding to a w/s of 0.8 and a precision of ±0.5 mg.