Moisture Damage Characterization of Rubber-Modified Asphalt Mixture Containing Waste Steel Slag under Multiple Freeze-Thaw Cycles

Recycling waste materials has become popular in the pavement industry because of its potential for significant environmental benefits, conservation of natural resources, and sustainability. This study investigated the feasibility of simultaneously recycling waste steel slag and tire rubber in bituminous pavements and analyze the moisture susceptibility of asphalt mixtures made of these solid wastes. The physical and chemical characteristics of the aggregates and the adhesive behavior of the aggregate-bitumen system were explored to determine their impact on moisture sensitivity. Accordingly, two different methods, freeze-thaw splitting test and fracture energy tests, were employed to assess the moisture stability of mixes in a multiple freeze-thaw environment. The microstructure of the interface between the aggregate and bitumen was investigated, and the long-term moisture damage process of the mixes was clarified and verified. The results indicate that the natural hyperalkalinity and porous structure of the steel slag have a favorable effect on the adhesion performance. Cohesive failure was found to be the primary mode of failure of loose asphalt mixtures in a multiple freeze-thaw environment. We tentatively propose that the adhesion energy loss is a secondary failure mode of the loose asphalt mixtures. The addition of 100% steel slag and asphalt rubber had the greatest impact on improving the long-term moisture resistance of the asphalt mixtures. The present work is beneficial for the practical application of waste tire rubber and steel slag in highway engineering.