Effect of Steel Slag and Air-Cooled Blast Furnace Slag Aggregates on the Performance of Warm-Mix Asphalt Concrete Produced with Foamed Bitumen

Reducing asphalt mixture production temperatures and partially replacing virgin aggregates with industrially derived materials are potential pathways toward more sustainable pavement technologies. This study evaluated the effects of steel slag (SS) aggregate and air-cooled blast furnace slag (ACBFS) aggregate on the properties of asphalt concrete for pavement binder courses produced as warm-mix asphalt (WMA) using water-foamed bitumen. The reference hot-mix asphalt (HMA) and WMA mixtures were compared with WMA variants in which 20% or 40% of the virgin aggregate was replaced by SS or ACBFS. The slag aggregates were characterized by physical and mechanical properties, surface morphology, and local elemental composition. Mixture performance was evaluated based on air voids content, indirect tensile strength, water and freeze–thaw resistance, dynamic modulus, and rutting resistance, followed by statistical analysis. Slag type and replacement level affected the properties differently. Increasing slag content increased air voids content, whereas slag-containing mixtures showed a lower relative loss of tensile strength after conditioning than the reference mixtures. Compared with SS, ACBFS resulted in lower dynamic modulus and poorer rutting resistance. The mixture containing 20% SS satisfied all adopted technical requirements. The results support the use of SS at this replacement level, whereas ACBFS mixtures require further optimization.