Zinc Slag as a Partial or Total Replacement for Mineral Filler in Warm Mix Asphalt and Its Effects on Self-Healing Capacity and Performance Characteristics

Utilizing the self-healing properties of asphalt materials is a way to improve the service life of asphalt pavements. Enhanced self-healing capabilities can be achieved through mixture modification. Using waste or by-product materials to modify asphalt mixtures can provide further environmental benefits. However, with a given mixture modification method, the resulting materials should be adequately vetted to ensure that enhanced self-healing capability is not attained at the expense of the mixture’s overall performance. This research aims to investigate the feasibility of using zinc slag filler to enhance the self-healing properties of warm mix asphalt (WMA) and evaluates the rutting susceptibility and moisture-resistance of the slag-modified mixtures. To this end, zinc slag filler was used to replace a portion of the mineral filler at different replacement rates in WMA mixtures. Self-healing capabilities of the resulting mixtures were studied under microwave induction heating. The influence of zinc slag modification on asphalt mixture’s characteristics and conventional performance indicators were evaluated by the Texas boiling test, the three-point bending test, and the Kim test (a deformation test). Also, the adhesion between bitumen and aggregate was evaluated using the broken sample from the three-point bending test and digital image analysis. The results of self-healing tests demonstrated that the heat generation capability of the specimens increased with filler replacement rate, such that the specimens with 100% of the mineral filler replaced with slag showed the highest heating performance. Zinc slag filler showed the potential to improve the moisture resistance of WMA by enhancing aggregate–bitumen adhesion and thus reducing stripping. The slag-modified WMA samples exhibited better tensile strength ratio (TSR) and deformation resistance than their non-modified equivalents.