A novel approach for rational determination of warm mix asphalt production temperatures

Warm Mix Asphalt (WMA) has been developed to minimise environmental impact of asphalt by reducing production temperatures of this material. This study provides a new approach to design WMA production temperatures by two methods. First, aggregate coating was quantified at different mixing temperatures and mixing times using image processing principles. This task was accomplished by taking an image at specific times during the mixing process, then the collected images were processed using Matlab software to quantify aggregate coating as a function of mixing time. Second, performance of WMA concerning stiffness (ITSM) and strength (ITS) was correlated with mixing temperature and compared with performance of control asphalt. Two additives namely a wax additive (SWMA) and a chemical (CWMA) were used in this study. Aggregate coating results demonstrated that this method can successfully be implemented to design WMA mixing temperatures. The results also indicated that reducing mixing temperature of asphalt requires additional mixing time to entirely coat the aggregate regardless of whether WMA additives were used or not. But in the case of using additives, the additional mixing time was significantly less than the case of mixing asphalt without additives. Analysis of results indicated that for SWMA there is a significant correlation between performance and mixing temperatures: the higher the mixing temperature the greater the ITSM and ITS. However, CWMA performance was independent of mixing temperature. Combining aggregate coating with performance results can be utilised to design the mixing temperature of WMA which can be selected as the lowest temperature that satisfies both requirements. Furthermore, compactability of WMA was assessed by the effort of a roller compactor to achieve the design density. The compactability results indicated that WMA additives can significantly enhance asphalt workability and reduce compaction temperature by about 30 °C.