Microstructural and Mineralogical Characterization of Aksu Ferroalloy Slag for Use as Road Construction Aggregate

This study investigates the potential use of ferroalloy slag from the Aksu Ferroalloy Plant (Aksu, Pavlodar region, Kazakhstan) as a road construction aggregate. A bulk stockpile sample was characterized using Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). FTIR spectra and XRD patterns reveal a predominantly silicate matrix composed of feldspar-type aluminosilicates, clinopyroxenes (diopside), and minor quartz, with nanocrystalline phases embedded in a glassy background and no evidence of free CaO or periclase. SEM images show angular, blocky particles with rough, cracked surfaces and limited vesicular porosity, indicating a dense, rock-like texture favorable for mechanical interlock. EDS analysis confirms a silica-rich, aluminosilicate composition (≈60 wt.% SiO2, 13 wt.% Al2O3, 12 wt.% MgO, 5 wt.% CaO) with significant MnO and only ≈1 wt.% Cr2O3, corresponding to an acidic to weakly basic slag. Compared with the CaO-rich BOF steel slags and MgO- and Cr-rich ferrochrome slags widely reported in the literature, the Aksu slag is chemically more stable and less reactive, making it a promising candidate primarily as unbound or asphalt aggregate, subject to standard mechanical and environmental verification.