The re-use of palm kernel shell and steel slag as partial replacement of coarse aggregate in asphaltic concrete

This study investigates the potential of using palm kernel shell (PKS) and steel slag (SS) as partial replacements for conventional coarse aggregates in asphaltic concrete to reduce construction costs and improve sustainability. Various percentages of PKS and SS (0% to 25%) were incorporated into asphaltic concrete mixtures, and their effects on stability, flow, bulk density, air voids, voids in mineral aggregates (VMA), and voids filled with bitumen (VFB) were evaluated using the Marshall Stability test. The results showed that a 5% replacement of PKS and SS (A2) yielded the highest stability value of 6.54 kN, which was higher than the conventional mixture. However, the flow value of 5.47 mm exceeded the recommended range of 2–4 mm, likely due to the angular shape of PKS and SS. The bulk density ranged from 1.82 g/cm³ to 2.22 g/cm³, with the highest value observed for the A2 mixture. The air voids, VMA, and VFB were within acceptable limits, indicating that PKS and SS can be used as partial replacements without compromising the volumetric properties of the mixture. The study concludes that PKS and SS are viable alternatives for low-traffic roads, offering environmental and economic benefits. Further research is recommended to optimize the mix design and evaluate long-term performance under different traffic conditions.