Incorporation of activated bauxite to enhance engineering properties and microstructure of volcanic ash geopolymer mortar composites

In this study, mechanical activation of bauxite was done using ball milling to alter the material's geopolymeric reactivity. Geopolymer mortar composites were then prepared by partially replacing the volcanic ash with 0–25 wt% activated bauxite. A mixture of sodium hydroxide and sodium silicate, was used as the alkali activator. Workability, compressive strength, pore volume and water absorption characteristics of the geopolymer mortar composites, were determined. Microstructural investigations were carried out using X-ray diffraction, Fourier transform infrared spectroscopy, electron and optical microscopy. It was found that bauxite of higher fineness gave greater geopolymeric reactivity and promoted the formation of a compact microstructure containing fewer and smaller pores. Incorporation of 15 wt% bauxite of 1000–1730 m2/kg Blaine fineness, gave optimal mechanical and physical properties. The volcanic ash geopolymer mortar composites synthesized in this study, gave relatively high compressive strengths and generally low water absorption characteristics, indicating the binder's potential for use in structural applications. •Mechanical activation enhances geopolymeric reactivity of bauxite.•Activated bauxite significantly improves physical and mechanical properties.•SiO2/Al2O3 ratio of 3.1–3.9 gives optimum physical and mechanical properties.•Incorporation of 15 wt% bauxite of 1730 m2/kg fineness gives optimal performance.•Poly (siliate-siloxo) and poly (ferro-silico-aluminate) are the main binder phases.