Alite-calcium sulfoaluminate (ACSA) cement is a low energy cement and contains about 50% of alite and 10% ofyeelimite as main phases.Like Portland cement, the clinker is blended with about 5% of calcium sulphate.In order to further reduce the ecological impact, supplementary cementitious materials (SCMs) can be used to partially substitute the clinker phases.In this work, blends containing 10% of limestone or calcined clay are investigated in terms of kinetics and phase assemblage formed during hydration.The two SCMs affect the hydration differently.Isothermal calorimetry shows that limestone accelerates the reaction slightly whereas the calcined clay accelerates it even more.The XRD results indicate that ettringite and portlandite are the main hydrates formed during early hydration.After the depletion of calcium sulfate, monosulfate forms in addition.In the limestone-containing system, hemicarbonate and monocarbonate instead of monosulfate are present.The blend with calcined clay contains more monosulfate and less portlandite due to the reaction of the calcined clay.Thermodynamic modeling predicts the same kind and similar amounts of hydrates as observed experimentally.