Effects of pretreatment methods on stability and abrasion performance of steel slag asphalt mixture

Steel slag presents a promising alternative to natural aggregates in asphalt pavements; however, its high free calcium oxide (f-CaO) content leads to volume instability, which limits its large-scale application. This study systematically examines the effects of three pretreatment methods, including natural aging, water bath aging and carbonation treatment, on the volume stability of steel slag. Additionally, it evaluates the water stability and abrasion performance of asphalt mixtures that incorporate pretreated steel slag, with complete replacement of coarse aggregates larger than 4.75 mm. The results demonstrate that all pretreatment methods effectively reduce the f-CaO content in steel slag. Among these methods, carbonation treatment achieves the most significant reduction, lowering the f-CaO content to 1.07%, followed by water bath aging at 90 °C for 7 days and natural aging. Consequently, carbonation treatment minimizes the 10-day water immersion expansion rate of steel slag to 0.76%, compared to 1.15% for water bath aging and 1.52% for natural aging. In terms of asphalt mixtures, carbonation treatment yields the highest water stability, achieving a residual stability ratio of 92.07% and a tensile strength ratio (TSR) of 88.67%. Furthermore, it exhibits superior abrasion performance, with a Los Angeles abrasion value of 8.8% and a British Pendulum Number attenuation rate of 10.2%. These enhancements are attributed to the formation of a dense CaCO 3 layer that improves the structural integrity and angularity retention of the steel slag. This study provides technical guidance for the sustainable utilization of steel slag in high-performance asphalt pavements.