Mechanical property of red mud-slag-fly ash based alkali-activated mortar with recycled waste glass aggregate

In this study, red mud was adopted as a partial replacement for the precursor, and recycled waste glass aggregate (RWGA) was employed as a substitute for natural river sand in slag-fly ash based alkali-activated mortar. Five mix proportions were designed (with red mud replacement ratios of 10% and 20%, and RWGA replacement ratios of 50% and 100%) to explore the effects of these replacements on the workability, mechanical strength, interfacial transition zone (ITZ), and reaction products of the mortar. Tests conducted included flowability measurement, setting time determination, compressive and flexural strength tests, along with microstructural characterisation using Scanning Electron Microscope (SEM) equipped with Energy Dispersive Spectrometer (EDS), X-ray diffraction (XRD), and Fourier Transform Infra-red spectroscopy (FTIR). The results indicated that although increasing the replacement ratios of red mud and RWGA led to a reduction in workability and mechanical properties, the developed alkali-activated mortar still exhibited satisfactory workability (minimum flow diameter of 212.5 mm) and mechanical strength (28-day compressive strength up to 62 MPa). The reduction in strength was primarily attributed to the dilution effect and inert filler role of red mud, and the formation of the loose gel structure.