Research on performance enhancement and microscopic mechanism of steel slag asphalt mixture modified with compound fibre

Steel slag is an industrial solid waste. However, water damage and cracking have limited its engineering application. In this research, lignin fibre (LF) and basalt fibre (BF) were combined to reinforce a steel slag asphalt mixture. Rutting, low-temperature bending, freeze‒thaw splitting, immersion expansion and indirect tensile tests were carried out. AFM and SEM were used to reveal the microscopic reinforcement mechanisms. BF was more effective at improving high-temperature stability and low-temperature crack resistance, whereas LF was more effective at improving volume stability. The mixture containing compound fibre showed better water stability and tensile performance. Radar-chart evaluation indicated that the compound‒fibre mixture exhibited a more balanced performance among the selected indicators, although it was not statistically superior in every individual property. BF interwove with asphalt to form a three-dimensional network structure, providing reinforcement and bridging effects, promoting stress dispersion and transfer and restraining sliding of aggregates. LF could adsorb structural asphalt, increase the thickness of the asphalt film and fill the pores of steel slag. Compound fibre formed a denser fibre network, thereby achieving synergistic improvement in multiple properties. These results provide a reference for the high-value utilisation of steel slag in asphalt pavement.