The Application of Nano-Structured Silica Based Admixture in Gypsum Binders
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The Application of Nano-Structured Silica Based Admixture in Gypsum Binders E.V. Voitovich1, A.V. Cherevatova1, I.V. Zhernovsky1, H.-B. Fisher2, and K. Sobolev3 The Belgorod State Technological University named after V.G. Shoukhov, Belgorod, Russia 2 University of Weimar Bauhaus, Weimar, Germany 3 Department of Civil Engineering and Mechanics, University of Wisconsin-Milwaukee, Milwaukee, USA
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ABSTRACT This article reports on a new composite gypsum binder (CGB) with nanostructured silicabased 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 nanocomponent 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. INTRODUCTION Commercial grade gypsum-based materials have a low water resistance, which limits their application [1]. The gypsum compositions with improved performance (e.g. gypsum-pozzolanic binders) have been proposed [1, 2]. The addition of mineral components in gypsum binders can affect the setting time, the flow properties and improve the strength. The main objective of this study is to investigate the feasibility of zero-cement composite gypsum binders with nanostructured silica component (NSS) [3]. EXPERIMENTAL PROGRAM The research program uses the hemihydrate gypsum as a binder and nanostructured silica (NSS) as silica component. NSS is an inorganic polydisperse mineral system with a high concentration of solid phase containing nanosized component in an amount of 5–10%. The NSS binder is obtained by wet milling of quartz sand in a ball mill [4, 5]. The NSS is manufactured as mineral slurry with a moisture content of 14–20%. The ARL X'tra (Thermo Scientifie) diffractometer with Co–radiation is used for XRD analysis. Quantitative full-profile XRD Rietveld analysis is performed usin
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