Optimizing the mixing procedure of warm asphalt rubber with wax-based additives through mechanism investigation and performance characterization

•The effects of different mixing procedures to produce WAR were evaluated.•Rheological and chemical characterizations were conducted on the liquid phase of warm asphalt rubber.•Direct mixing causes worse workability of WAR compared with conventional procedure.•Direct mixing leads to less wax content in liquid phase of WAR. Wax-based additives can be used as flow improvers to enhance the workability of asphalt rubber (AR). Conventionally, warm asphalt rubber (WAR) is produced by preparing AR first and then blending it with warm mix asphalt (WMA) additive. However, directly mixing WMA additive, base asphalt and crumb rubber together may save more energy since the early incorporation of WMA additive also helps decrease the production temperature of AR. To assess the feasibility of incorporating wax-based additives at an earlier stage, this study investigates the influence of the mixing procedure on WAR prepared by two wax-based additives, i.e., commercial Sasobit and conventional paraffin wax. Rheological tests on WAR revealed no significant difference between WARs prepared by different procedures. However, the direct mixing method led to worse WAR workability compared to the traditional mixing procedure. Chemical analysis on the liquid phase of WARs (crumb rubber removed) indicated that independent of the type of wax-based additive, there is less wax in the liquid phase of WARs when the additive is added earlier, which may be caused by the absorption of wax by crumb rubber during the interacting process. Thus, it is not recommended to replace the traditional mixing procedure with the direct mixing method.