Reducing Volume Expansion of Steel Slag by Using a Surface Hydrophobic Waterproof Structure

Reducing volume expansion of steel slag is a key problem for steel slag to be applied in asphalt concrete pavement. It not only avoids environmental damage caused by natural stone mining but also provides a cheap and excellent alternative to traditional aggregates. In this study, a surface hydrophobic waterproof structure (SHWS) was proposed for immersion pretreatment of the surface of steel slag particles. The main properties of the modified steel slag were analyzed and compared with those of unmodified steel slag; the properties analyzed included hydrophobicity, water absorption, adhesion strength to asphalt, and volume expansion. The water stability of the modified asphalt mixtures was also studied by considering volume stability, immersion Marshall test, and freeze–thaw split test. The results showed that the surface water absorption of the modified steel slag was at least 23.6% lower than that of unmodified steel slag due to the hydrophobicity of the SHWS. The volume expansion inhibition effect of the SHWS increased with decreasing particle size of the modified steel slag. For steel slag with particle sizes between 4.75 and 9.5 mm, the final volume expansion rate of the modified steel slag was 46% lower than that of unmodified steel slag. Water stability of the modified steel slag asphalt mixtures was also improved due to the alkaline rough hydrophobic steel slag surface and high adhesion strength to asphalt. The proposed immersion pretreatment is expected to provide an efficient alternative solution for improving the application of steel slag in asphalt pavement.