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The amount of early ettringite crystallization is known to influence the rheology of cementitious materials. It is dependent on various factors, e.g., the reaction temperature, the chemical composition of the cement and the amount of PCE. In this study, we investigate the rheology and reactivity of synthetic model cements with different contents of C3S, C3A and β‐hemihydrate (β‐HH). Their reactivity is studied using in‐situ calorimetry and their rheology is studied using a rotational rheometer. Our results demonstrate that higher C3A contents in the clinker increase the early heat release of the cements which is associated with an increased formation of ettringite. Increased C3A contents from 2.5 wt.% to 12.5 wt.% enhance the early heat by four orders of magnitude. The static yield stress of the different cement pastes was determined with an oscillation based rheometry method 17 minutes after contact with water. Interestingly, the static yield stress increases exponentially with the heat of hydration. These findings have implications for the understanding of OPC hydration, as well as for chemical optimization and the design of OPC‐based materials. [ABSTRACT FROM AUTHOR]