Effect of the geometrical and physical nature of filler on the rheological properties of mastics

This study investigates properties of mastics produced with 70/100 neat bitumen, three mineral fillers (granite, quartz-granite, and diorite), and a lime-based active filler at filler-to-bitumen (F/B) ratios of 40%, 50%, and 60%. The physical, geometrical, and mineralogical properties of the fillers were assessed. Their influence on mastics' behaviour was evaluated using conventional penetration and softening point tests, as well as frequency sweep tests at different temperatures with a dynamic shear rheometer (DSR). Although mineral components are not strongly correlated with mastic behaviour, differences in particle size distribution and rigid void (RV) properties explain the varying stiffening effects. Granite, with finer particles, had the least rut resistance, while diorite, with coarser particles, had the greatest resistance at F/B values of 40% and 60%. Quartz-granite exhibited the highest F/B ratio dependency and strongest interaction with bitumen at 50% F/B at lower temperatures, highlighting the importance of selecting the appropriate filler proportion over the filler type when the features are similar. The study underscores necessity of using DSR to assess mastics with diverse fillers across various conditions. Therefore, two equations to estimate the complex modulus |G*| from standardised softening point test and RV normalised with F/B ratio are proposed, which require further research.