Hydration kinetics and structural characterization of MgO-based eco-sustainable cements

Cement formulations based on reactive periclase (MgO) constitute one of the most promising emerging technologies for the reduction of CO2 emissions in the cement production.1 In the presence of water, MgO/silicate mixtures hydrate and form a binder phase, M-S-H (magnesium silicate hydrate), a colloidal gel analogue to calcium silicate hydrate, C-S-H, that is present in traditional cements. M-S-H based formulations have compressive strengths compatible with many potential applications2, but systematic studies defining the relationship among composition, structure and properties of these binders are still lacking. This knowledge is essential to optimize the properties of building materials, allowing a predictive approach of the final properties starting from the initial composition. In this work the hydration kinetics of MgO/silicate mixtures were investigated by means of differential scanning calorimetry. The most significant kinetic parameters (induction time, diffusion time, kinetic constants of nucleation and growth of hydrated phases) were accessed and correlated to the initial composition. Concurrently, pastes were characterized starting from the molecular level up to the micro/macroscopic scale. In particular SS NMR was used to probe the local Si environment and the polymerization degree of M-S-H; small angle x-ray scattering measurements were used to achieve information on the shape and size of the structural gel unit and on the fractality of the phase. Finally the composition and the morphology were characterized by combining XRD, FTIR, SEM/EDX measurements. 1.Vandeperre L.J. et al, Microstructures of reactive magnesia cement blends. Cem. Concr. Comp. 30, 706-714 (2008). 2.Zang T. et al., Development of low pH cement systems forming magnesium silicate hydrate (M-S-H). Cen. Concr. Res. 41, 439-442 (2011)