A pilot study is presented that investigates the potential of reusing redmud, an abundant industrial waste produced from alumina refining by the Bayer process, via geopolymerization reactions with another solid waste, fly ash, and sodium silicate. A variety of parameters involved in the synthesis, including red mud to fly ash ratio (RM/FA = 80/20, 50/50, and 20/80), presence of sand filler, curing duration (up to 28 days), and sodium silicate solution to solid mixture (consisting of red mud and fly ash) ratio,were examined to understand the extent and degree of geopolymerization. Unconfined compression testing was employed to assess the influence of these synthesis parameters on the mechanical properties of the end productsred mud-based geopolymers. The composition and microstructure were characterized by X-ray diffraction and scanning electron microscopy, respectively,which confirm the geopolymerization reactions. The mechanical properties, including strength, stiffness, and failure strain, were analyzed againstthe chemical compositions of the red mud geopolymers, such as Si/Al and Na/Si molar ratios. For the studied geopolymers, the unconfined compressive strength ranging from 7 to 13 MPa, comparable with some types of Portland cement, increases with Si/Al ratio. A higher Na/Si ratio appears to reduce the strength and stiffness, but enhance the ductility. The results indicate that red mud geopolymers are a viable cementitious material that canbe used in roadway constructions. The engineering implications are discussed in terms of waste recycling, environmental benefits, and energy consumption.
Samenvatting