Electric arc furnace (EAF) steelmaking is increasingly adopting sustainable carbon sources to improve slag foaming and reduce energy consumption. Among them, spent tire-derived carbon represents a viable alternative to coal, offering high volatile and carbon contents. However, its elevated sulfur level and modified slag chemistry can markedly affect foaming stability and desulfurization. This study elucidates the interactive effects of spent tire substitution (0-30 wt%) and slag basicity (CaO/SiO2 = 1.5-2.4) on foaming dynamics, bubble evolution, and sulfur behavior at 1,600 °C. Real-time imaging and quantitative analyses demonstrated that moderate substitution (10-20 wt%) enhanced initial foaming due to volatile-induced gas release, whereas excessive addition (30 wt%) caused unstable coalescence and premature collapse from sulfur-driven surface tension reduction. Lower basicity limited early foaming but improved long-term stability via increased viscosity, while higher basicity promoted rapid collapse and reduced sulfur retention. The optimal condition (CaO/SiO2 = 2.0) maintained stable foaming for over 40 min, achieving superior sulfur capture (about 24 %) and minimal refractory attack. Overall, these findings reveal the mechanistic coupling between carbon source, basicity, and interfacial properties, offering practical guidance for sustainable slag design and efficient sulfur control in EAF operations employing waste-derived carbonaceous materials.

PURPOSES: This paper, presents the results of a laboratory study aimed to verify the suitability of a particular type of Electric Arc Furnace (EAF) steel slag to be recycled in the lithic skeleton of both dense graded and porous asphalt mixtures for flexible pavements. METHODS : Cyclic creep and stiffness modulus tests were performed to evaluate the mechanical performance of three different asphalt mixtures (dense graded, porous asphalt, and stone mastic) prepared with two types of EAF steel slag. For comparison purposes, the same three mixtures were also designed with conventional aggregates (basalt and limestone). RESULTS : All the asphalt mixtures prepared with EAF steel slag satisfied the current requirements of the European standards, which support EAF steel slag as a suitable material for flexible pavement construction. CONCLUSIONS : Based on the experimental work, the use of waste material obtained from steel production (e.g. EAF steel slag) as an alternative in the lithic skeleton of asphalt mixtures can be a satisfactory and reasonable choice that fulfills the “Zero Waste”objective that many iron and steel industries have pursued in the past decades.