Chemical and physical influences of various carbonated hydrated cements on the early hydration of a composite cement

Novel supplementary cementitious materials (SCMs) such as carbonated cement pastes (cCP) are needed to achieve the sustainability objectives of the cement industry. In this study, cCPs are produced by aqueous carbonation using various hydrated CEM I and fully characterized. The hydration of the different ordinary Portland cement–cCP mixes is then tracked using heat flow calorimetry, quantitative in-situ XRD and pore solution analysis in combination with thermodynamic modeling, Imeter measurements and small angle oscillatory shear experiments. Results show that it is not the initial CEM I chemistry, but rather the physicochemical properties of the cCP that are crucial for the early hydration behavior of the mixes. In the presence of cCP, the ettringite formation rate during the induction period is enhanced, thereby affecting the rheological properties of the cement paste. Before the start of the main silicate reaction, the increased ettringite formation rate in the cCP systems strongly promotes the build-up of a structural network of the cement paste.