The identification of eco-compatible cement is a relevant issue in the field of building materials research.Cement formulations based on reactive periclase (MgO) constitute one of the most promising emerging technologies for the reduction of CO2 emissions involved in traditional CaO-based cement production.In the present study, pastes were prepared by mixing Portland cement and MgO/SiO2 blend.The aim was to investigate the effect of mixing CaO-and MgO-based binders on the hydration reaction and on the microstructure development of the pastes.The kinetics of hydration of these pastes were monitored by Differential Scanning Calorimetry, while the formation of hydrated phases were determined by Thermogravimetric Analysis and X-ray Diffraction.The structural properties of all samples were investigated by solid state 29Si-NMR.Finally, the morphology of the pastes has been studied by means of Scanning Electron Microscopy.The results showed that in the mixed sample the formation of portlandite is completely inhibited while little amounts of brucite are present.The experimental evidences showed that both calcium silicate hydrate and magnesium silicate hydrate gel phase formed.Interestingly, the kinetics of hydration in the mixed sample is dominated by the MgO/SiO2 hydration in the first period, while the diffusional stage is regulated by the presence of Portland cement.