Novel high-resistance clinkers with 1.10Â <Â CaO/SiO2Â <Â 1.25: production route and preliminary hydration characterization

New amorphous calcium silicate binders, hydraulically active, were produced by a process consisting in fully melting and rapid cooling of a mixture of typical raw materials (limestone, sand, fly-ash and electric furnace slag) with overall CaO/SiO2 molar ratios (C/S) comprised between 1.1 and 1.25. Pastes were produced from these materials by mixing them with water in a water/binder ratio of 0.375. Compressive strength was determined at the ages of 7, 28 and 90 days and the hydration of these pastes was followed during this period by XRD, FTIR and 29Si MAS-NMR. Tobermorite-like structures with low C/S and semi-crystalline character were observed to develop upon hydration of these new amorphous calcium silicate hydraulic binders. Moreover, no Portlandite was formed during hydration of these materials. The maximum compressive strength after 90 days is above 40 MPa. TGA was performed in order to determine the amount of structural water present in the pastes and their content related to the amount of hydrated products obtained. The relation between compressive strength and the amount of hydration products was investigated and some considerations about the mechanical properties of the hydration products and paste microstructure were inferred.