Pre-treatment of steel slag and its applicability in asphalt mixtures for sustainable pavements

Abstract

The secondary utilization of steel slag is significant for land occupation reduction, natural aggregate conservation, and environmental protection. This study aims to enhance the utilization of steel slag aggregate (SSA) in pavement engineering by providing guidance on selecting efficient and rapid pre-treatment methods. It compares the macroscopic morphological characteristics of basalt, SSA, and SSA prepared using various pre-treatment methods. The chemical composition and surface micromorphology of the samples were investigated by X-ray fluorescence spectrometry and scanning electron microscopy. The effects of the pre-treatment methods on the SSA and the performance of its asphalt mixture were comparatively evaluated based on laboratory tests. The carbon dioxide equivalent (CO2e) and cost associated with steel slag asphalt mixtures were quantified in this study. The findings revealed that the high angularity and roughness of the SSA make it an ideal candidate for use in pavement layer aggregates. Pre-treatment methods such as thermal water and acetic acid soaking expedited the hydration and oxidation reactions. Furthermore, applying a silane coupling agent resulted in the forming of a polymer membrane on the SSA surface, significantly enhancing its volume stability and adhesive properties. All these methods present compelling alternatives to natural aging. Compared with the original SSA, the performance of asphalt mixtures prepared using pretreated SSA was optimized, particularly concerning the volumetric stability and moisture damage resistance. In general, although the CO2e from using SSA for pavement construction increased compared to those using other substances, the CO2e was significantly lower than those from SSA lying idle, which positively impacts the alleviation of SSA accumulation and promotes sustainable development.