Effect of mechanical activation of red mud on the strength of geopolymer binder

Abstract The growing interest in utilization of industrial waste and green construction has motivated the present work. Red mud is an industrial waste produced in the process of extraction of aluminum from bauxite by Bayer’s process. The paper presents the studies conducted to assess the influence of mechanical activation of red mud and curing methods on the strength of red mud-fly ash geopolymer paste. Red mud was used in both unprocessed and pulverised form and the alkali activated paste samples were cured thermally as well as in ambient condition. The percentage of red mud varied from 0 to 90% and alkalinity from 6 M to 12 M NaOH solution. X-ray diffraction (XRD) was carried out to identify the mineral phases in pulverised and unprocessed red mud. SAED (selective area diffraction diagram) test was done on the red mud, along with SEM (scanning electron microscopy), TEM (transmission electron microscopy) and HRTEM analysis (high resolution transmission electron microscopy) to study the effect of mechanical activation and validate the experimental findings. Mechanical activation increased the reactivity of silica and the hematite phase of red mud as reflected in the silica reactivity and Fourier transform infrared spectroscopy (FTIR) test results. Use of pulverised red mud enhanced the mechanical properties of ambient cured paste and the specimens possessed maximum 7 day compressive strength of 40 MPa at 6 M alkalinity with 30% mechanically activated red mud content.