Enhancing adhesion and performance of reclaimed asphalt mixtures using combined modified steel slag

The use of industrial by products such as steel slag as aggregate substitutes is crucial for sustainable pavement rehabilitation. This study investigated the combined modification of steel slag using silica powder and silane coupling agents to enhance its surface properties. The innovative combined modification process overcomes the limitations of traditional silica powder solutions by forming a robust bond between the modified steel slag and asphalt. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that silica powder-modified steel slag formed a C-S-H gel network, while silane-modified steel slag exhibited a layered structure with polysiloxanes. Enhanced adhesion and freeze-thaw resistance were observed in the modified steel slag compared to its unmodified variant, while refined soaking tests confirmed the improved bond strength between the modified steel slag and asphalt. Performance evaluations indicated that when that RAP content is 30%, the optimal addition of modified steel slag is 10%, which improved pavement performance significantly. The combined modification method enhances not only recycled asphalt mixtures’ mechanical properties and durability, but also promotes sustainability and cost-efficiency in pavement construction.