This article reports on a new composite gypsum binder (CGB) with nanostructured silica-based admixture (NSS). NSS is obtained by a wet ultrafine milling of quartz sand resulting in the formation of an inorganic polydisperse binding system, which has a high concentration of active nanoscale phase (about 10%). Developed CGB contains hemihydrate gypsum and nano-component based on quartz sand. It is observed that the addition of 15–20 % of NSS improves the rheological properties of gypsum systems through the formation of solvate shells hindering the access of water to gypsum particles; this process also retards the setting of binder.
The experimental program used infrared IR spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) to reveal the contribution of NSS. The porosity of CGB is analyzed by the kinetics of water adsorption and BET. The XRD and IR investigations determined the formation of a new sulfosilicate phase, hydroxyellestadite during the hydration of CGB. With the addition of NSS an overall reduction in pore volume, as well as the shifts in macro-, meso- and nano- porosity values are observed.
Analysis of CGB microstructure reveals that in the presence of the NSS the size and morphology of crystals are changed contributing to the formation of dense fine-grained structure. Experimental studies have demonstrated that the composite gypsum binders with NSS are characterized by reduced water absorption and increased density, as well as improved mechanical performance especially, higher compressive strength.