Shear rheology and microstructure of mining material-bitumen composites as filler replacement in asphalt mastics

Magnetite is a mineral that occurs in many types of igneous rock and can be found in large quantities in fluvial and marine environments. It can also be extracted by reprocessing of existing mine tailings. In this paper, magnetite supplied from two different mining sites was evaluated as a substitution of natural limestone filler in asphalt mix design. Magnetite and limestone fillers were added to the bitumen according to three filler/bitumen ratios to form composite asphalt mastics. Rheology of the mixes was analysed to study the effects of magnetite as potential filler in asphalt pavement applications and comparisons were made with natural limestone filler-based mastics. In addition, particle size analysis, scanning electron microscope, Cryo-SEM and energy dispersive X-ray spectroscopy, were conducted to comprehensively characterize the composite mixes. Results showed that the addition of magnetite-based ferromagnetic filler in asphalt mix design represents a suitable way to recycle this material, which is available in large quantities in many countries. In addition, ferromagnetic particles could also be exploited for induction or microwave healing of asphalt cracks as demonstrated by recent studies. Viscoelastic properties of the bituminous mastic are improved by reducing the mastic's temperature and loading time susceptibility; stiffness and elastic behaviour at high temperature was also improved hence potentially increasing resistance to permanent deformation.