Mechanical and Microstructural Evaluation of Utilizing Nickel Slag as Sustainable Aggregate in Asphalt Mixtures

Abstract

The use of industrial waste materials in asphalt mixes boosts sustainability in road building. This research examines the mechanical properties and microstructure of Nickel Slag (NS) in Stone Matrix Asphalt (SMA) mixes. NS replaces the coarse aggregates in asphalt. SMA test samples were prepared with different NS levels (0%, 50%, and 100%) at asphalt contents of 6%, 6.25%, 6.5%, 6.75%, and 7%. Mechanical testing employed the Marshall method to assess volumetric properties, stability, and flow. The highest stability scores for each mix occurred at an asphalt content of 6.5%, with values of 1031 kg, 919 kg, and 809 kg for SMA NS 100, SMA NS 50, and SMA Crush Stone (CS), respectively, surpassing the minimum requirement of 600 kg. The Voids in the Mix (VIM) values ranged from 3.078% to 4.95%, aligning with the standard of 3%–5%. The Voids in Mineral Aggregate (VMA) values ranged from 17.73% to 21.68%, all above the minimum of 17%. The flow values increased as the NS content grew, all meeting the 2 mm–4.5 mm requirement; however, SMA NS 100 at 6.75% and 7% asphalt exceeded this limit (4.66 mm and 5.00 mm). The Scanning Electron Microscope (SEM) analysis of the microstructure revealed a rough NS surface, which helped improve the asphalt-aggregate bonding. The XRD testing of the NS elements showed dominant components like O (20.96%), Si (19.97%), Ni (16.65%), Al (8.74%), and Fe (5.83%), present as silica (SiO₂), nickel oxide (NiO), aluminum oxide (Al₂O₃), and iron oxide (Fe₂O₃), potentially increasing mixture stability. This study demonstrates that NS can be a viable alternative material for road pavement asphalt.

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