Microstructure and mixture proportioning of non-structural foamed concrete with silica fume

Abstract

This paper presents the results of an experimental study conducted to investigate the microstructure and mixture proportioning of non-structural foamed concrete with silica fume (SF). For the purposes of this study, 20 mix designs were made, including four different proportions of SF to cementitious materials (SF/CM) (0%, 5%, 10% and 15%) and five different densities (450, 500, 600, 700 and 750 kg/m3). All the mix designs were prepared with a water-to-cementitious materials ratio (W/CM) of 0·6. Compressive strength was measured at curing ages of 7, 14, and 28 d. It was found that replacement of cement with SF resulted in higher compressive strengths for the given densities examined. Scanning electron microscopy and X-ray diffraction tests showed that SF in foamed concrete reacts with the free calcium hydroxide of hydrated cement and produces calcium–silicate–hydrate, which is stiffer and more durable than calcium hydroxide. In addition, ettringite content reduces when the SF/CM ratio increases. Therefore, SF decreases the risk of sulfate attack in foamed concrete. Finally, it is shown that the method proposed in this study can be successfully exploited to develop foamed concrete mix designs for any given density.