Experimental study of asphalt mixtures with recycled resources: Influence of electric arc furnace slag aggregate roughness and bitumen film thickness on fatigue performance

• The roughness of electric arc furnace slag increases stiffness in the mixtures. • Digital image analysis can determine the thickness of the bitumen film. • Electric arc furnace slag decreases film thickness due to its roughness and absorption. • Optimizing the bitumen film thickness in mixtures with EAFS improves fatigue performance. Electric arc furnace slag (EAFS) is a viable alternative in asphalt mixtures due to its favourable mechanical properties. This study examines the impact of EAFS content and bitumen film thickness ( TF ) on the fatigue performance of asphalt mixtures. Mixtures with varying levels of EAFS replacement were designed, and their mechanical properties were evaluated through indirect tensile strength and stiffness tests, followed by fatigue tests using the four-point bending method and EBADE (Strain Sweep Test). The results indicated that mixtures with EAFS exhibited increased stiffness, but fatigue performance decreased at high strain levels. At low strain levels, EAFS mixtures performed similarly or better than the control. HMA_GL had the highest TF (13.97 μm), followed by HMA_GS (13.60 μm), HMA_SL (12.66 μm), and HMA_SS (11.77 μm), showing that as the EAFS content increases, the TF decreases. This finding was verified through Digital Image Analysis. This decrease in TF is due to the high porosity and roughness of the EAFS, which in turn reduces the effective bitumen (P be ) in the mixture. HMA_SL*, with a TF equal to the control, demonstrated a 22 % improvement in fatigue performance compared to HMA_SL. In the EBADE tests, HMA_GL achieved 44.69 MJ/m 3 of dissipated energy, HMA_GS 31.55 MJ/m 3 , HMA_SL 34.45 MJ/m 3 , and HMA_SS 35.54 MJ/m 3 . The improved HMA_SL* recorded 42.15 MJ/m 3 , nearly matching the control. EBADE results confirmed that higher EAFS content increased initial stiffness, but the complex modulus (| E* |) decreased more rapidly as deformation increased. These results are consistent with the stiffness tests. These findings suggest that EAFS can successfully replace natural aggregates in asphalt mixtures, with a moderate increase in bitumen content recommended to improve fatigue performance.