Influence of steel slag incorporation on internal skeletal contact characteristics within asphalt mixture

Abstract

• Shape features of steel slag and limestone were calculated. • Meso-parameters of skeleton such as contact points and length were analyzed. • Gradations dominate the contact performance of steel slag in asphalt mixtures. • Potential interaction exists between gradation and slag content on skeleton contact. • Contact indicators of skeleton are remarkably influenced by aggregate angularity. This study employed X-ray computed tomography (CT) and image processing technology to characterize and quantify the internal skeleton composition within asphalt mixtures incorporating steel slag. The shape indices of steel slag and limestone including form and angularity features were calculated and meso-parameters of skeleton such as contact points, coordination number, and contact length were analysed, aiming to establish the relationship between aggregate shape and skeleton. The effect of gradations and slag contents were considered as well. Results denote gradations dominate the contact performance, the beneficial angularity of steel slag allows the promotion of contact originated by 4.75 mm-16.0 mm particles with surrounding ones in stone matrix asphalt (SMA-13), while encourages the contact from 2.36 mm to 4.75 mm particles in dense-graded asphalt concrete (AC-13). Instead of the common short contact lines in AC-13, the introduction of steel slag assures that SMA mixture creates plentiful longer contact lines among aggregates. Significance analysis indicates there is potential interaction between gradation and slag content on the skeleton contact. The skeleton of SMA mixture is more susceptible with slag content rather than AC one. Among overall meso-parameters, the average coordination number of 4.75 mm-9.5 mm particles and the sum of contact length are closely related to rut depth, and are remarkably influenced by the angularity of aggregate. These findings contribute to optimizing the skeleton design of steel slag asphalt mixture from the perspective of aggregate shape and possess enormous potential to reduce the dual environmental impacts of steel slag accumulation as well as resource mining.